nmap(1) — Linux manual page


NMAP(1)                   Nmap Reference Guide                   NMAP(1)

NAME         top

       nmap - Network exploration tool and security / port scanner

SYNOPSIS         top

       nmap [Scan Type...] [Options] {target specification}

DESCRIPTION         top

       Nmap (“Network Mapper”) is an open source tool for network
       exploration and security auditing. It was designed to rapidly
       scan large networks, although it works fine against single hosts.
       Nmap uses raw IP packets in novel ways to determine what hosts
       are available on the network, what services (application name and
       version) those hosts are offering, what operating systems (and OS
       versions) they are running, what type of packet filters/firewalls
       are in use, and dozens of other characteristics. While Nmap is
       commonly used for security audits, many systems and network
       administrators find it useful for routine tasks such as network
       inventory, managing service upgrade schedules, and monitoring
       host or service uptime.

       The output from Nmap is a list of scanned targets, with
       supplemental information on each depending on the options used.
       Key among that information is the “interesting ports table”.
       That table lists the port number and protocol, service name, and
       state. The state is either open, filtered, closed, or unfiltered.
       Open means that an application on the target machine is listening
       for connections/packets on that port.  Filtered means that a
       firewall, filter, or other network obstacle is blocking the port
       so that Nmap cannot tell whether it is open or closed.  Closed
       ports have no application listening on them, though they could
       open up at any time. Ports are classified as unfiltered when they
       are responsive to Nmap's probes, but Nmap cannot determine
       whether they are open or closed. Nmap reports the state
       combinations open|filtered and closed|filtered when it cannot
       determine which of the two states describe a port. The port table
       may also include software version details when version detection
       has been requested. When an IP protocol scan is requested (-sO),
       Nmap provides information on supported IP protocols rather than
       listening ports.

       In addition to the interesting ports table, Nmap can provide
       further information on targets, including reverse DNS names,
       operating system guesses, device types, and MAC addresses.

       A typical Nmap scan is shown in Example 1. The only Nmap
       arguments used in this example are -A, to enable OS and version
       detection, script scanning, and traceroute; -T4 for faster
       execution; and then the hostname.

       Example 1. A representative Nmap scan

           # nmap -A -T4 scanme.nmap.org

           Nmap scan report for scanme.nmap.org (
           Host is up (0.029s latency).
           rDNS record for li86-221.members.linode.com
           Not shown: 995 closed ports
           PORT     STATE    SERVICE     VERSION
           22/tcp   open     ssh         OpenSSH 5.3p1 Debian 3ubuntu7 (protocol 2.0)
           | ssh-hostkey: 1024 8d:60:f1:7c:ca:b7:3d:0a:d6:67:54:9d:69:d9:b9:dd (DSA)
           |_2048 79:f8:09:ac:d4:e2:32:42:10:49:d3:bd:20:82:85:ec (RSA)
           80/tcp   open     http        Apache httpd 2.2.14 ((Ubuntu))
           |_http-title: Go ahead and ScanMe!
           646/tcp  filtered ldp
           1720/tcp filtered H.323/Q.931
           9929/tcp open     nping-echo  Nping echo
           Device type: general purpose
           Running: Linux 2.6.X
           OS CPE: cpe:/o:linux:linux_kernel:2.6.39
           OS details: Linux 2.6.39
           Network Distance: 11 hops
           Service Info: OS: Linux; CPE: cpe:/o:linux:kernel

           TRACEROUTE (using port 53/tcp)
           HOP RTT      ADDRESS
           [Cut first 10 hops for brevity]
           11  17.65 ms li86-221.members.linode.com (

           Nmap done: 1 IP address (1 host up) scanned in 14.40 seconds

       The newest version of Nmap can be obtained from https://nmap.org .
       The newest version of this man page is available at
       https://nmap.org/book/man.html .  It is also included as a chapter
       of Nmap Network Scanning: The Official Nmap Project Guide to
       Network Discovery and Security Scanning (see
       https://nmap.org/book/ ).


       This options summary is printed when Nmap is run with no
       arguments, and the latest version is always available at
       https://svn.nmap.org/nmap/docs/nmap.usage.txt . It helps people
       remember the most common options, but is no substitute for the
       in-depth documentation in the rest of this manual. Some obscure
       options aren't even included here.

           Nmap 7.94 ( https://nmap.org )
           Usage: nmap [Scan Type(s)] [Options] {target specification}
             Can pass hostnames, IP addresses, networks, etc.
             Ex: scanme.nmap.org, microsoft.com/24,; 10.0.0-255.1-254
             -iL <inputfilename>: Input from list of hosts/networks
             -iR <num hosts>: Choose random targets
             --exclude <host1[,host2][,host3],...>: Exclude hosts/networks
             --excludefile <exclude_file>: Exclude list from file
           HOST DISCOVERY:
             -sL: List Scan - simply list targets to scan
             -sn: Ping Scan - disable port scan
             -Pn: Treat all hosts as online -- skip host discovery
             -PS/PA/PU/PY[portlist]: TCP SYN/ACK, UDP or SCTP discovery to given ports
             -PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes
             -PO[protocol list]: IP Protocol Ping
             -n/-R: Never do DNS resolution/Always resolve [default: sometimes]
             --dns-servers <serv1[,serv2],...>: Specify custom DNS servers
             --system-dns: Use OS's DNS resolver
             --traceroute: Trace hop path to each host
             -sS/sT/sA/sW/sM: TCP SYN/Connect()/ACK/Window/Maimon scans
             -sU: UDP Scan
             -sN/sF/sX: TCP Null, FIN, and Xmas scans
             --scanflags <flags>: Customize TCP scan flags
             -sI <zombie host[:probeport]>: Idle scan
             -sY/sZ: SCTP INIT/COOKIE-ECHO scans
             -sO: IP protocol scan
             -b <FTP relay host>: FTP bounce scan
             -p <port ranges>: Only scan specified ports
               Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080,S:9
             --exclude-ports <port ranges>: Exclude the specified ports from scanning
             -F: Fast mode - Scan fewer ports than the default scan
             -r: Scan ports sequentially - don't randomize
             --top-ports <number>: Scan <number> most common ports
             --port-ratio <ratio>: Scan ports more common than <ratio>
             -sV: Probe open ports to determine service/version info
             --version-intensity <level>: Set from 0 (light) to 9 (try all probes)
             --version-light: Limit to most likely probes (intensity 2)
             --version-all: Try every single probe (intensity 9)
             --version-trace: Show detailed version scan activity (for debugging)
           SCRIPT SCAN:
             -sC: equivalent to --script=default
             --script=<Lua scripts>: <Lua scripts> is a comma separated list of
                      directories, script-files or script-categories
             --script-args=<n1=v1,[n2=v2,...]>: provide arguments to scripts
             --script-args-file=filename: provide NSE script args in a file
             --script-trace: Show all data sent and received
             --script-updatedb: Update the script database.
             --script-help=<Lua scripts>: Show help about scripts.
                      <Lua scripts> is a comma-separated list of script-files or
           OS DETECTION:
             -O: Enable OS detection
             --osscan-limit: Limit OS detection to promising targets
             --osscan-guess: Guess OS more aggressively
             Options which take <time> are in seconds, or append 'ms' (milliseconds),
             's' (seconds), 'm' (minutes), or 'h' (hours) to the value (e.g. 30m).
             -T<0-5>: Set timing template (higher is faster)
             --min-hostgroup/max-hostgroup <size>: Parallel host scan group sizes
             --min-parallelism/max-parallelism <numprobes>: Probe parallelization
             --min-rtt-timeout/max-rtt-timeout/initial-rtt-timeout <time>: Specifies
                 probe round trip time.
             --max-retries <tries>: Caps number of port scan probe retransmissions.
             --host-timeout <time>: Give up on target after this long
             --scan-delay/--max-scan-delay <time>: Adjust delay between probes
             --min-rate <number>: Send packets no slower than <number> per second
             --max-rate <number>: Send packets no faster than <number> per second
             -f; --mtu <val>: fragment packets (optionally w/given MTU)
             -D <decoy1,decoy2[,ME],...>: Cloak a scan with decoys
             -S <IP_Address>: Spoof source address
             -e <iface>: Use specified interface
             -g/--source-port <portnum>: Use given port number
             --proxies <url1,[url2],...>: Relay connections through HTTP/SOCKS4 proxies
             --data <hex string>: Append a custom payload to sent packets
             --data-string <string>: Append a custom ASCII string to sent packets
             --data-length <num>: Append random data to sent packets
             --ip-options <options>: Send packets with specified ip options
             --ttl <val>: Set IP time-to-live field
             --spoof-mac <mac address/prefix/vendor name>: Spoof your MAC address
             --badsum: Send packets with a bogus TCP/UDP/SCTP checksum
             -oN/-oX/-oS/-oG <file>: Output scan in normal, XML, s|<rIpt kIddi3,
                and Grepable format, respectively, to the given filename.
             -oA <basename>: Output in the three major formats at once
             -v: Increase verbosity level (use -vv or more for greater effect)
             -d: Increase debugging level (use -dd or more for greater effect)
             --reason: Display the reason a port is in a particular state
             --open: Only show open (or possibly open) ports
             --packet-trace: Show all packets sent and received
             --iflist: Print host interfaces and routes (for debugging)
             --append-output: Append to rather than clobber specified output files
             --resume <filename>: Resume an aborted scan
             --noninteractive: Disable runtime interactions via keyboard
             --stylesheet <path/URL>: XSL stylesheet to transform XML output to HTML
             --webxml: Reference stylesheet from Nmap.Org for more portable XML
             --no-stylesheet: Prevent associating of XSL stylesheet w/XML output
             -6: Enable IPv6 scanning
             -A: Enable OS detection, version detection, script scanning, and traceroute
             --datadir <dirname>: Specify custom Nmap data file location
             --send-eth/--send-ip: Send using raw ethernet frames or IP packets
             --privileged: Assume that the user is fully privileged
             --unprivileged: Assume the user lacks raw socket privileges
             -V: Print version number
             -h: Print this help summary page.
             nmap -v -A scanme.nmap.org
             nmap -v -sn
             nmap -v -iR 10000 -Pn -p 80
           SEE THE MAN PAGE (https://nmap.org/book/man.html) FOR MORE OPTIONS AND EXAMPLES


       Everything on the Nmap command-line that isn't an option (or
       option argument) is treated as a target host specification. The
       simplest case is to specify a target IP address or hostname for

       When a hostname is given as a target, it is resolved via the
       Domain Name System (DNS) to determine the IP address to scan. If
       the name resolves to more than one IP address, only the first one
       will be scanned. To make Nmap scan all the resolved addresses
       instead of only the first one, use the --resolve-all option.

       Sometimes you wish to scan a whole network of adjacent hosts. For
       this, Nmap supports CIDR-style addressing. You can append
       /numbits to an IP address or hostname and Nmap will scan every IP
       address for which the first numbits are the same as for the
       reference IP or hostname given. For example,
       would scan the 256 hosts between (binary: 11000000
       10101000 00001010 00000000) and (binary: 11000000
       10101000 00001010 11111111), inclusive. would
       scan exactly the same targets. Given that the host
       scanme.nmap.org is at the IP address, the
       specification scanme.nmap.org/16 would scan the 65,536 IP
       addresses between and The smallest
       allowed value is /0, which targets the whole Internet. The
       largest value for IPv4 is /32, which scans just the named host or
       IP address because all address bits are fixed. The largest value
       for IPv6 is /128, which does the same thing.

       CIDR notation is short but not always flexible enough. For
       example, you might want to scan but skip any IPs
       ending with .0 or .255 because they may be used as subnet network
       and broadcast addresses. Nmap supports this through octet range
       addressing. Rather than specify a normal IP address, you can
       specify a comma-separated list of numbers or ranges for each
       octet. For example, 192.168.0-255.1-254 will skip all addresses
       in the range that end in .0 or .255, and 192.168.3-5,7.1 will
       scan the four addresses,,,
       and Either side of a range may be omitted; the
       default values are 0 on the left and 255 on the right. Using - by
       itself is the same as 0-255, but remember to use 0- in the first
       octet so the target specification doesn't look like a
       command-line option. Ranges need not be limited to the final
       octets: the specifier 0-255.0-255.13.37 will perform an
       Internet-wide scan for all IP addresses ending in 13.37. This
       sort of broad sampling can be useful for Internet surveys and

       IPv6 addresses can be specified by their fully qualified IPv6
       address or hostname or with CIDR notation for subnets. Octet
       ranges aren't yet supported for IPv6.

       IPv6 addresses with non-global scope need to have a zone ID
       suffix. On Unix systems, this is a percent sign followed by an
       interface name; a complete address might be
       fe80::a8bb:ccff:fedd:eeff%eth0. On Windows, use an interface
       index number in place of an interface name:
       fe80::a8bb:ccff:fedd:eeff%1. You can see a list of interface
       indexes by running the command netsh.exe interface ipv6 show

       Nmap accepts multiple host specifications on the command line,
       and they don't need to be the same type. The command nmap
       scanme.nmap.org 10.0.0,1,3-7.- does what you would

       While targets are usually specified on the command lines, the
       following options are also available to control target selection:

       -iL inputfilename (Input from list)
           Reads target specifications from inputfilename. Passing a
           huge list of hosts is often awkward on the command line, yet
           it is a common desire. For example, your DHCP server might
           export a list of 10,000 current leases that you wish to scan.
           Or maybe you want to scan all IP addresses except for those
           to locate hosts using unauthorized static IP addresses.
           Simply generate the list of hosts to scan and pass that
           filename to Nmap as an argument to the -iL option. Entries
           can be in any of the formats accepted by Nmap on the command
           line (IP address, hostname, CIDR, IPv6, or octet ranges).
           Each entry must be separated by one or more spaces, tabs, or
           newlines. You can specify a hyphen (-) as the filename if you
           want Nmap to read hosts from standard input rather than an
           actual file.

           The input file may contain comments that start with # and
           extend to the end of the line.

       -iR num hosts (Choose random targets)
           For Internet-wide surveys and other research, you may want to
           choose targets at random. The num hosts argument tells Nmap
           how many IPs to generate. Undesirable IPs such as those in
           certain private, multicast, or unallocated address ranges are
           automatically skipped. The argument 0 can be specified for a
           never-ending scan. Keep in mind that some network
           administrators bristle at unauthorized scans of their
           networks and may complain. Use this option at your own risk!
           If you find yourself really bored one rainy afternoon, try
           the command nmap -Pn -sS -p 80 -iR 0 --open to locate random
           web servers for browsing.

       --exclude host1[,host2[,...]] (Exclude hosts/networks)
           Specifies a comma-separated list of targets to be excluded
           from the scan even if they are part of the overall network
           range you specify. The list you pass in uses normal Nmap
           syntax, so it can include hostnames, CIDR netblocks, octet
           ranges, etc. This can be useful when the network you wish to
           scan includes untouchable mission-critical servers, systems
           that are known to react adversely to port scans, or subnets
           administered by other people.

       --excludefile exclude_file (Exclude list from file)
           This offers the same functionality as the --exclude option,
           except that the excluded targets are provided in a newline-,
           space-, or tab-delimited exclude_file rather than on the
           command line.

           The exclude file may contain comments that start with # and
           extend to the end of the line.

       -n (No DNS resolution)

           Tells Nmap to never do reverse DNS resolution on the active
           IP addresses it finds. Since DNS can be slow even with Nmap's
           built-in parallel stub resolver, this option can slash
           scanning times.

       -R (DNS resolution for all targets)
           Tells Nmap to always do reverse DNS resolution on the target
           IP addresses. Normally reverse DNS is only performed against
           responsive (online) hosts.

       --resolve-all (Scan each resolved address)
           If a hostname target resolves to more than one address, scan
           all of them. The default behavior is to only scan the first
           resolved address. Regardless, only addresses in the
           appropriate address family will be scanned: IPv4 by default,
           IPv6 with -6.

       --unique (Scan each address only once)
           Scan each IP address only once. The default behavior is to
           scan each address as many times as it is specified in the
           target list, such as when network ranges overlap or different
           hostnames resolve to the same address.

       --system-dns (Use system DNS resolver)
           By default, Nmap reverse-resolves IP addresses by sending
           queries directly to the name servers configured on your host
           and then listening for responses. Many requests (often
           dozens) are performed in parallel to improve performance.
           Specify this option to use your system resolver instead (one
           IP at a time via the getnameinfo call). This is slower and
           rarely useful unless you find a bug in the Nmap parallel
           resolver (please let us know if you do). The system resolver
           is always used for forward lookups (getting an IP address
           from a hostname).

       --dns-servers server1[,server2[,...]]  (Servers to use for
       reverse DNS queries)
           By default, Nmap determines your DNS servers (for rDNS
           resolution) from your resolv.conf file (Unix) or the Registry
           (Win32). Alternatively, you may use this option to specify
           alternate servers. This option is not honored if you are
           using --system-dns. Using multiple DNS servers is often
           faster, especially if you choose authoritative servers for
           your target IP space. This option can also improve stealth,
           as your requests can be bounced off just about any recursive
           DNS server on the Internet.

           This option also comes in handy when scanning private
           networks. Sometimes only a few name servers provide proper
           rDNS information, and you may not even know where they are.
           You can scan the network for port 53 (perhaps with version
           detection), then try Nmap list scans (-sL) specifying each
           name server one at a time with --dns-servers until you find
           one which works.

           This option might not be honored if the DNS response exceeds
           the size of a UDP packet. In such a situation our DNS
           resolver will make the best effort to extract a response from
           the truncated packet, and if not successful it will fall back
           to using the system resolver. Also, responses that contain
           CNAME aliases will fall back to the system resolver.

HOST DISCOVERY         top

       One of the very first steps in any network reconnaissance mission
       is to reduce a (sometimes huge) set of IP ranges into a list of
       active or interesting hosts. Scanning every port of every single
       IP address is slow and usually unnecessary. Of course what makes
       a host interesting depends greatly on the scan purposes. Network
       administrators may only be interested in hosts running a certain
       service, while security auditors may care about every single
       device with an IP address. An administrator may be comfortable
       using just an ICMP ping to locate hosts on his internal network,
       while an external penetration tester may use a diverse set of
       dozens of probes in an attempt to evade firewall restrictions.

       Because host discovery needs are so diverse, Nmap offers a wide
       variety of options for customizing the techniques used. Host
       discovery is sometimes called ping scan, but it goes well beyond
       the simple ICMP echo request packets associated with the
       ubiquitous ping tool. Users can skip the discovery step entirely
       with a list scan (-sL) or by disabling host discovery (-Pn), or
       engage the network with arbitrary combinations of multi-port TCP
       SYN/ACK, UDP, SCTP INIT and ICMP probes. The goal of these probes
       is to solicit responses which demonstrate that an IP address is
       actually active (is being used by a host or network device). On
       many networks, only a small percentage of IP addresses are active
       at any given time. This is particularly common with private
       address space such as That network has 16 million
       IPs, but I have seen it used by companies with less than a
       thousand machines. Host discovery can find those machines in a
       sparsely allocated sea of IP addresses.

       If no host discovery options are given, Nmap sends an ICMP echo
       request, a TCP SYN packet to port 443, a TCP ACK packet to port
       80, and an ICMP timestamp request. (For IPv6, the ICMP timestamp
       request is omitted because it is not part of ICMPv6.) These
       defaults are equivalent to the -PE -PS443 -PA80 -PP options. The
       exceptions to this are the ARP (for IPv4) and Neighbor Discovery
       (for IPv6) scans which are used for any targets on a local
       ethernet network. For unprivileged Unix shell users, the default
       probes are a SYN packet to ports 80 and 443 using the connect
       system call.  This host discovery is often sufficient when
       scanning local networks, but a more comprehensive set of
       discovery probes is recommended for security auditing.

       The -P* options (which select ping types) can be combined. You
       can increase your odds of penetrating strict firewalls by sending
       many probe types using different TCP ports/flags and ICMP codes.
       Also note that ARP/Neighbor Discovery is done by default against
       targets on a local Ethernet network even if you specify other -P*
       options, because it is almost always faster and more effective.

       By default, Nmap does host discovery and then performs a port
       scan against each host it determines is online. This is true even
       if you specify non-default host discovery types such as UDP
       probes (-PU). Read about the -sn option to learn how to perform
       only host discovery, or use -Pn to skip host discovery and port
       scan all target addresses. The following options control host

       -sL (List Scan)
           The list scan is a degenerate form of host discovery that
           simply lists each host of the network(s) specified, without
           sending any packets to the target hosts. By default, Nmap
           still does reverse-DNS resolution on the hosts to learn their
           names. It is often surprising how much useful information
           simple hostnames give out. For example, fw.chi is the name of
           one company's Chicago firewall.

           Nmap also reports the total number of IP addresses at the
           end. The list scan is a good sanity check to ensure that you
           have proper IP addresses for your targets. If the hosts sport
           domain names you do not recognize, it is worth investigating
           further to prevent scanning the wrong company's network.

           Since the idea is to simply print a list of target hosts,
           options for higher level functionality such as port scanning,
           OS detection, or host discovery cannot be combined with this.
           If you wish to disable host discovery while still performing
           such higher level functionality, read up on the -Pn (skip
           host discovery) option.

       -sn (No port scan)
           This option tells Nmap not to do a port scan after host
           discovery, and only print out the available hosts that
           responded to the host discovery probes. This is often known
           as a “ping scan”, but you can also request that traceroute
           and NSE host scripts be run. This is by default one step more
           intrusive than the list scan, and can often be used for the
           same purposes. It allows light reconnaissance of a target
           network without attracting much attention. Knowing how many
           hosts are up is more valuable to attackers than the list
           provided by list scan of every single IP and host name.

           Systems administrators often find this option valuable as
           well. It can easily be used to count available machines on a
           network or monitor server availability. This is often called
           a ping sweep, and is more reliable than pinging the broadcast
           address because many hosts do not reply to broadcast queries.

           The default host discovery done with -sn consists of an ICMP
           echo request, TCP SYN to port 443, TCP ACK to port 80, and an
           ICMP timestamp request by default. When executed by an
           unprivileged user, only SYN packets are sent (using a connect
           call) to ports 80 and 443 on the target. When a privileged
           user tries to scan targets on a local ethernet network, ARP
           requests are used unless --send-ip was specified. The -sn
           option can be combined with any of the discovery probe types
           (the -P* options) for greater flexibility. If any of those
           probe type and port number options are used, the default
           probes are overridden. When strict firewalls are in place
           between the source host running Nmap and the target network,
           using those advanced techniques is recommended. Otherwise
           hosts could be missed when the firewall drops probes or their

           In previous releases of Nmap, -sn was known as -sP.

       -Pn (No ping)
           This option skips the host discovery stage altogether.
           Normally, Nmap uses this stage to determine active machines
           for heavier scanning and to gauge the speed of the network.
           By default, Nmap only performs heavy probing such as port
           scans, version detection, or OS detection against hosts that
           are found to be up. Disabling host discovery with -Pn causes
           Nmap to attempt the requested scanning functions against
           every target IP address specified. So if a /16 sized network
           is specified on the command line, all 65,536 IP addresses are
           scanned. Proper host discovery is skipped as with the list
           scan, but instead of stopping and printing the target list,
           Nmap continues to perform requested functions as if each
           target IP is active. Default timing parameters are used,
           which may result in slower scans. To skip host discovery and
           port scan, while still allowing NSE to run, use the two
           options -Pn -sn together.

           For machines on a local ethernet network, ARP scanning will
           still be performed (unless --disable-arp-ping or --send-ip is
           specified) because Nmap needs MAC addresses to further scan
           target hosts. In previous versions of Nmap, -Pn was -P0 and

       -PS port list (TCP SYN Ping)
           This option sends an empty TCP packet with the SYN flag set.
           The default destination port is 80 (configurable at compile
           time by changing DEFAULT_TCP_PROBE_PORT_SPEC in nmap.h).
           Alternate ports can be specified as a parameter. The syntax
           is the same as for the -p except that port type specifiers
           like T: are not allowed. Examples are -PS22 and
           -PS22-25,80,113,1050,35000. Note that there can be no space
           between -PS and the port list. If multiple probes are
           specified they will be sent in parallel.

           The SYN flag suggests to the remote system that you are
           attempting to establish a connection. Normally the
           destination port will be closed, and a RST (reset) packet
           sent back. If the port happens to be open, the target will
           take the second step of a TCP three-way-handshake by
           responding with a SYN/ACK TCP packet. The machine running
           Nmap then tears down the nascent connection by responding
           with a RST rather than sending an ACK packet which would
           complete the three-way-handshake and establish a full
           connection. The RST packet is sent by the kernel of the
           machine running Nmap in response to the unexpected SYN/ACK,
           not by Nmap itself.

           Nmap does not care whether the port is open or closed. Either
           the RST or SYN/ACK response discussed previously tell Nmap
           that the host is available and responsive.

           On Unix boxes, only the privileged user root is generally
           able to send and receive raw TCP packets.  For unprivileged
           users, a workaround is automatically employed whereby the
           connect system call is initiated against each target port.
           This has the effect of sending a SYN packet to the target
           host, in an attempt to establish a connection. If connect
           returns with a quick success or an ECONNREFUSED failure, the
           underlying TCP stack must have received a SYN/ACK or RST and
           the host is marked available. If the connection attempt is
           left hanging until a timeout is reached, the host is marked
           as down.

       -PA port list (TCP ACK Ping)
           The TCP ACK ping is quite similar to the just-discussed SYN
           ping. The difference, as you could likely guess, is that the
           TCP ACK flag is set instead of the SYN flag. Such an ACK
           packet purports to be acknowledging data over an established
           TCP connection, but no such connection exists. So remote
           hosts should always respond with a RST packet, disclosing
           their existence in the process.

           The -PA option uses the same default port as the SYN probe
           (80) and can also take a list of destination ports in the
           same format. If an unprivileged user tries this, the connect
           workaround discussed previously is used. This workaround is
           imperfect because connect is actually sending a SYN packet
           rather than an ACK.

           The reason for offering both SYN and ACK ping probes is to
           maximize the chances of bypassing firewalls. Many
           administrators configure routers and other simple firewalls
           to block incoming SYN packets except for those destined for
           public services like the company web site or mail server.
           This prevents other incoming connections to the organization,
           while allowing users to make unobstructed outgoing
           connections to the Internet. This non-stateful approach takes
           up few resources on the firewall/router and is widely
           supported by hardware and software filters. The Linux
           Netfilter/iptables firewall software offers the --syn
           convenience option to implement this stateless approach. When
           stateless firewall rules such as this are in place, SYN ping
           probes (-PS) are likely to be blocked when sent to closed
           target ports. In such cases, the ACK probe shines as it cuts
           right through these rules.

           Another common type of firewall uses stateful rules that drop
           unexpected packets. This feature was initially found mostly
           on high-end firewalls, though it has become much more common
           over the years. The Linux Netfilter/iptables system supports
           this through the --state option, which categorizes packets
           based on connection state. A SYN probe is more likely to work
           against such a system, as unexpected ACK packets are
           generally recognized as bogus and dropped. A solution to this
           quandary is to send both SYN and ACK probes by specifying -PS
           and -PA.

       -PU port list (UDP Ping)
           Another host discovery option is the UDP ping, which sends a
           UDP packet to the given ports. For most ports, the packet
           will be empty, though some use a protocol-specific payload
           that is more likely to elicit a response.

           The payloads are the same probes used in service and version
           detection and are defined in the nmap-service-probes

           file. Packet content can also be affected with the --data,
           --data-string, and --data-length options.

           The port list takes the same format as with the previously
           discussed -PS and -PA options. If no ports are specified, the
           default is 40125.  This default can be configured at
           compile-time by changing DEFAULT_UDP_PROBE_PORT_SPEC in
           nmap.h.  A highly uncommon port is used by default because
           sending to open ports is often undesirable for this
           particular scan type.

           Upon hitting a closed port on the target machine, the UDP
           probe should elicit an ICMP port unreachable packet in
           return. This signifies to Nmap that the machine is up and
           available. Many other types of ICMP errors, such as
           host/network unreachables or TTL exceeded are indicative of a
           down or unreachable host. A lack of response is also
           interpreted this way. If an open port is reached, most
           services simply ignore the empty packet and fail to return
           any response. This is why the default probe port is 40125,
           which is highly unlikely to be in use. A few services, such
           as the Character Generator (chargen) protocol, will respond
           to an empty UDP packet, and thus disclose to Nmap that the
           machine is available.

           The primary advantage of this scan type is that it bypasses
           firewalls and filters that only screen TCP. For example, I
           once owned a Linksys BEFW11S4 wireless broadband router. The
           external interface of this device filtered all TCP ports by
           default, but UDP probes would still elicit port unreachable
           messages and thus give away the device.

       -PY port list (SCTP INIT Ping)
           This option sends an SCTP packet containing a minimal INIT
           chunk. The default destination port is 80 (configurable at
           compile time by changing DEFAULT_SCTP_PROBE_PORT_SPEC in
           nmap.h). Alternate ports can be specified as a parameter. The
           syntax is the same as for the -p except that port type
           specifiers like S: are not allowed. Examples are -PY22 and
           -PY22,80,179,5060. Note that there can be no space between
           -PY and the port list. If multiple probes are specified they
           will be sent in parallel.

           The INIT chunk suggests to the remote system that you are
           attempting to establish an association. Normally the
           destination port will be closed, and an ABORT chunk will be
           sent back. If the port happens to be open, the target will
           take the second step of an SCTP four-way-handshake by
           responding with an INIT-ACK chunk. If the machine running
           Nmap has a functional SCTP stack, then it tears down the
           nascent association by responding with an ABORT chunk rather
           than sending a COOKIE-ECHO chunk which would be the next step
           in the four-way-handshake. The ABORT packet is sent by the
           kernel of the machine running Nmap in response to the
           unexpected INIT-ACK, not by Nmap itself.

           Nmap does not care whether the port is open or closed. Either
           the ABORT or INIT-ACK response discussed previously tell Nmap
           that the host is available and responsive.

           On Unix boxes, only the privileged user root is generally
           able to send and receive raw SCTP packets.  Using SCTP INIT
           Pings is currently not possible for unprivileged users.

       -PE; -PP; -PM (ICMP Ping Types)
           In addition to the unusual TCP, UDP and SCTP host discovery
           types discussed previously, Nmap can send the standard
           packets sent by the ubiquitous ping program. Nmap sends an
           ICMP type 8 (echo request) packet to the target IP addresses,
           expecting a type 0 (echo reply) in return from available
           hosts.  Unfortunately for network explorers, many hosts and
           firewalls now block these packets, rather than responding as
           required by RFC 1122[2].  For this reason, ICMP-only scans
           are rarely reliable enough against unknown targets over the
           Internet. But for system administrators monitoring an
           internal network, they can be a practical and efficient
           approach. Use the -PE option to enable this echo request

           While echo request is the standard ICMP ping query, Nmap does
           not stop there. The ICMP standards (RFC 792[3] and RFC 950[4]
           ) also specify timestamp request, information request, and
           address mask request packets as codes 13, 15, and 17,
           respectively. While the ostensible purpose for these queries
           is to learn information such as address masks and current
           times, they can easily be used for host discovery. A system
           that replies is up and available. Nmap does not currently
           implement information request packets, as they are not widely
           supported. RFC 1122 insists that “a host SHOULD NOT implement
           these messages”. Timestamp and address mask queries can be
           sent with the -PP and -PM options, respectively. A timestamp
           reply (ICMP code 14) or address mask reply (code 18)
           discloses that the host is available. These two queries can
           be valuable when administrators specifically block echo
           request packets while forgetting that other ICMP queries can
           be used for the same purpose.

       -PO protocol list (IP Protocol Ping)
           One of the newer host discovery options is the IP protocol
           ping, which sends IP packets with the specified protocol
           number set in their IP header. The protocol list takes the
           same format as do port lists in the previously discussed TCP,
           UDP and SCTP host discovery options. If no protocols are
           specified, the default is to send multiple IP packets for
           ICMP (protocol 1), IGMP (protocol 2), and IP-in-IP (protocol
           4). The default protocols can be configured at compile-time
           by changing DEFAULT_PROTO_PROBE_PORT_SPEC in nmap.h. Note
           that for the ICMP, IGMP, TCP (protocol 6), UDP (protocol 17)
           and SCTP (protocol 132), the packets are sent with the proper
           protocol headers while other protocols are sent with no
           additional data beyond the IP header (unless any of --data,
           --data-string, or --data-length options are specified).

           This host discovery method looks for either responses using
           the same protocol as a probe, or ICMP protocol unreachable
           messages which signify that the given protocol isn't
           supported on the destination host. Either type of response
           signifies that the target host is alive.

       --disable-arp-ping (No ARP or ND Ping)
           Nmap normally does ARP or IPv6 Neighbor Discovery (ND)
           discovery of locally connected ethernet hosts, even if other
           host discovery options such as -Pn or -PE are used. To
           disable this implicit behavior, use the --disable-arp-ping

           The default behavior is normally faster, but this option is
           useful on networks using proxy ARP, in which a router
           speculatively replies to all ARP requests, making every
           target appear to be up according to ARP scan.

           In some cases, firewalls may spoof TCP reset (RST) replies in
           response to probes to unoccupied or disallowed addresses.
           Since Nmap ordinarily considers RST replies to be proof that
           the target is up, this can lead to wasted time scanning
           targets that aren't there. Using the --discovery-ignore-rst
           will prevent Nmap from considering these replies during host
           discovery. You may need to select extra host discovery
           options to ensure you don't miss targets in this case.

       --traceroute (Trace path to host)
           Traceroutes are performed post-scan using information from
           the scan results to determine the port and protocol most
           likely to reach the target. It works with all scan types
           except connect scans (-sT) and idle scans (-sI). All traces
           use Nmap's dynamic timing model and are performed in

           Traceroute works by sending packets with a low TTL
           (time-to-live) in an attempt to elicit ICMP Time Exceeded
           messages from intermediate hops between the scanner and the
           target host. Standard traceroute implementations start with a
           TTL of 1 and increment the TTL until the destination host is
           reached. Nmap's traceroute starts with a high TTL and then
           decrements the TTL until it reaches zero. Doing it backwards
           lets Nmap employ clever caching algorithms to speed up traces
           over multiple hosts. On average Nmap sends 5–10 fewer packets
           per host, depending on network conditions. If a single subnet
           is being scanned (i.e. Nmap may only have to
           send two packets to most hosts.


       While Nmap has grown in functionality over the years, it began as
       an efficient port scanner, and that remains its core function.
       The simple command nmap target scans 1,000 TCP ports on the host
       target. While many port scanners have traditionally lumped all
       ports into the open or closed states, Nmap is much more granular.
       It divides ports into six states: open, closed, filtered,
       unfiltered, open|filtered, or closed|filtered.

       These states are not intrinsic properties of the port itself, but
       describe how Nmap sees them. For example, an Nmap scan from the
       same network as the target may show port 135/tcp as open, while a
       scan at the same time with the same options from across the
       Internet might show that port as filtered.

       The six port states recognized by Nmap

           An application is actively accepting TCP connections, UDP
           datagrams or SCTP associations on this port. Finding these is
           often the primary goal of port scanning. Security-minded
           people know that each open port is an avenue for attack.
           Attackers and pen-testers want to exploit the open ports,
           while administrators try to close or protect them with
           firewalls without thwarting legitimate users. Open ports are
           also interesting for non-security scans because they show
           services available for use on the network.

           A closed port is accessible (it receives and responds to Nmap
           probe packets), but there is no application listening on it.
           They can be helpful in showing that a host is up on an IP
           address (host discovery, or ping scanning), and as part of OS
           detection. Because closed ports are reachable, it may be
           worth scanning later in case some open up. Administrators may
           want to consider blocking such ports with a firewall. Then
           they would appear in the filtered state, discussed next.

           Nmap cannot determine whether the port is open because packet
           filtering prevents its probes from reaching the port. The
           filtering could be from a dedicated firewall device, router
           rules, or host-based firewall software. These ports frustrate
           attackers because they provide so little information.
           Sometimes they respond with ICMP error messages such as type
           3 code 13 (destination unreachable: communication
           administratively prohibited), but filters that simply drop
           probes without responding are far more common. This forces
           Nmap to retry several times just in case the probe was
           dropped due to network congestion rather than filtering. This
           slows down the scan dramatically.

           The unfiltered state means that a port is accessible, but
           Nmap is unable to determine whether it is open or closed.
           Only the ACK scan, which is used to map firewall rulesets,
           classifies ports into this state. Scanning unfiltered ports
           with other scan types such as Window scan, SYN scan, or FIN
           scan, may help resolve whether the port is open.

           Nmap places ports in this state when it is unable to
           determine whether a port is open or filtered. This occurs for
           scan types in which open ports give no response. The lack of
           response could also mean that a packet filter dropped the
           probe or any response it elicited. So Nmap does not know for
           sure whether the port is open or being filtered. The UDP, IP
           protocol, FIN, NULL, and Xmas scans classify ports this way.

           This state is used when Nmap is unable to determine whether a
           port is closed or filtered. It is only used for the IP ID
           idle scan.


       As a novice performing automotive repair, I can struggle for
       hours trying to fit my rudimentary tools (hammer, duct tape,
       wrench, etc.) to the task at hand. When I fail miserably and tow
       my jalopy to a real mechanic, he invariably fishes around in a
       huge tool chest until pulling out the perfect gizmo which makes
       the job seem effortless. The art of port scanning is similar.
       Experts understand the dozens of scan techniques and choose the
       appropriate one (or combination) for a given task. Inexperienced
       users and script kiddies, on the other hand, try to solve every
       problem with the default SYN scan. Since Nmap is free, the only
       barrier to port scanning mastery is knowledge. That certainly
       beats the automotive world, where it may take great skill to
       determine that you need a strut spring compressor, then you still
       have to pay thousands of dollars for it.

       Most of the scan types are only available to privileged users.
       This is because they send and receive raw packets, which requires
       root access on Unix systems. Using an administrator account on
       Windows is recommended, though Nmap sometimes works for
       unprivileged users on that platform when Npcap has already been
       loaded into the OS. Requiring root privileges was a serious
       limitation when Nmap was released in 1997, as many users only had
       access to shared shell accounts. Now, the world is different.
       Computers are cheaper, far more people have always-on direct
       Internet access, and desktop Unix systems (including Linux and
       Mac OS X) are prevalent. A Windows version of Nmap is now
       available, allowing it to run on even more desktops. For all
       these reasons, users have less need to run Nmap from limited
       shared shell accounts. This is fortunate, as the privileged
       options make Nmap far more powerful and flexible.

       While Nmap attempts to produce accurate results, keep in mind
       that all of its insights are based on packets returned by the
       target machines (or firewalls in front of them). Such hosts may
       be untrustworthy and send responses intended to confuse or
       mislead Nmap. Much more common are non-RFC-compliant hosts that
       do not respond as they should to Nmap probes. FIN, NULL, and Xmas
       scans are particularly susceptible to this problem. Such issues
       are specific to certain scan types and so are discussed in the
       individual scan type entries.

       This section documents the dozen or so port scan techniques
       supported by Nmap. Only one method may be used at a time, except
       that UDP scan (-sU) and any one of the SCTP scan types (-sY, -sZ)
       may be combined with any one of the TCP scan types. As a memory
       aid, port scan type options are of the form -sC, where C is a
       prominent character in the scan name, usually the first. The one
       exception to this is the deprecated FTP bounce scan (-b). By
       default, Nmap performs a SYN Scan, though it substitutes a
       connect scan if the user does not have proper privileges to send
       raw packets (requires root access on Unix). Of the scans listed
       in this section, unprivileged users can only execute connect and
       FTP bounce scans.

       -sS (TCP SYN scan)
           SYN scan is the default and most popular scan option for good
           reasons. It can be performed quickly, scanning thousands of
           ports per second on a fast network not hampered by
           restrictive firewalls. It is also relatively unobtrusive and
           stealthy since it never completes TCP connections. SYN scan
           works against any compliant TCP stack rather than depending
           on idiosyncrasies of specific platforms as Nmap's
           FIN/NULL/Xmas, Maimon and idle scans do. It also allows
           clear, reliable differentiation between the open, closed, and
           filtered states.

           This technique is often referred to as half-open scanning,
           because you don't open a full TCP connection. You send a SYN
           packet, as if you are going to open a real connection and
           then wait for a response. A SYN/ACK indicates the port is
           listening (open), while a RST (reset) is indicative of a
           non-listener. If no response is received after several
           retransmissions, the port is marked as filtered. The port is
           also marked filtered if an ICMP unreachable error (type 3,
           code 0, 1, 2, 3, 9, 10, or 13) is received. The port is also
           considered open if a SYN packet (without the ACK flag) is
           received in response. This can be due to an extremely rare
           TCP feature known as a simultaneous open or split handshake
           connection (see https://nmap.org/misc/split-handshake.pdf ).

       -sT (TCP connect scan)
           TCP connect scan is the default TCP scan type when SYN scan
           is not an option. This is the case when a user does not have
           raw packet privileges. Instead of writing raw packets as most
           other scan types do, Nmap asks the underlying operating
           system to establish a connection with the target machine and
           port by issuing the connect system call. This is the same
           high-level system call that web browsers, P2P clients, and
           most other network-enabled applications use to establish a
           connection. It is part of a programming interface known as
           the Berkeley Sockets API. Rather than read raw packet
           responses off the wire, Nmap uses this API to obtain status
           information on each connection attempt.

           When SYN scan is available, it is usually a better choice.
           Nmap has less control over the high level connect call than
           with raw packets, making it less efficient. The system call
           completes connections to open target ports rather than
           performing the half-open reset that SYN scan does. Not only
           does this take longer and require more packets to obtain the
           same information, but target machines are more likely to log
           the connection. A decent IDS will catch either, but most
           machines have no such alarm system. Many services on your
           average Unix system will add a note to syslog, and sometimes
           a cryptic error message, when Nmap connects and then closes
           the connection without sending data. Truly pathetic services
           crash when this happens, though that is uncommon. An
           administrator who sees a bunch of connection attempts in her
           logs from a single system should know that she has been
           connect scanned.

       -sU (UDP scans)
           While most popular services on the Internet run over the TCP
           protocol, UDP[5] services are widely deployed. DNS, SNMP, and
           DHCP (registered ports 53, 161/162, and 67/68) are three of
           the most common. Because UDP scanning is generally slower and
           more difficult than TCP, some security auditors ignore these
           ports. This is a mistake, as exploitable UDP services are
           quite common and attackers certainly don't ignore the whole
           protocol. Fortunately, Nmap can help inventory UDP ports.

           UDP scan is activated with the -sU option. It can be combined
           with a TCP scan type such as SYN scan (-sS) to check both
           protocols during the same run.

           UDP scan works by sending a UDP packet to every targeted
           port. For some common ports such as 53 and 161, a
           protocol-specific payload is sent to increase response rate,
           but for most ports the packet is empty unless the --data,
           --data-string, or --data-length options are specified. If an
           ICMP port unreachable error (type 3, code 3) is returned, the
           port is closed. Other ICMP unreachable errors (type 3, codes
           0, 1, 2, 9, 10, or 13) mark the port as filtered.
           Occasionally, a service will respond with a UDP packet,
           proving that it is open. If no response is received after
           retransmissions, the port is classified as open|filtered.
           This means that the port could be open, or perhaps packet
           filters are blocking the communication. Version detection
           (-sV) can be used to help differentiate the truly open ports
           from the filtered ones.

           A big challenge with UDP scanning is doing it quickly. Open
           and filtered ports rarely send any response, leaving Nmap to
           time out and then conduct retransmissions just in case the
           probe or response were lost. Closed ports are often an even
           bigger problem. They usually send back an ICMP port
           unreachable error. But unlike the RST packets sent by closed
           TCP ports in response to a SYN or connect scan, many hosts
           rate limit ICMP port unreachable messages by default. Linux
           and Solaris are particularly strict about this. For example,
           the Linux 2.4.20 kernel limits destination unreachable
           messages to one per second (in net/ipv4/icmp.c).

           Nmap detects rate limiting and slows down accordingly to
           avoid flooding the network with useless packets that the
           target machine will drop. Unfortunately, a Linux-style limit
           of one packet per second makes a 65,536-port scan take more
           than 18 hours. Ideas for speeding your UDP scans up include
           scanning more hosts in parallel, doing a quick scan of just
           the popular ports first, scanning from behind the firewall,
           and using --host-timeout to skip slow hosts.

       -sY (SCTP INIT scan)
           SCTP[6] is a relatively new alternative to the TCP and UDP
           protocols, combining most characteristics of TCP and UDP, and
           also adding new features like multi-homing and
           multi-streaming. It is mostly being used for SS7/SIGTRAN
           related services but has the potential to be used for other
           applications as well. SCTP INIT scan is the SCTP equivalent
           of a TCP SYN scan. It can be performed quickly, scanning
           thousands of ports per second on a fast network not hampered
           by restrictive firewalls. Like SYN scan, INIT scan is
           relatively unobtrusive and stealthy, since it never completes
           SCTP associations. It also allows clear, reliable
           differentiation between the open, closed, and filtered

           This technique is often referred to as half-open scanning,
           because you don't open a full SCTP association. You send an
           INIT chunk, as if you are going to open a real association
           and then wait for a response. An INIT-ACK chunk indicates the
           port is listening (open), while an ABORT chunk is indicative
           of a non-listener. If no response is received after several
           retransmissions, the port is marked as filtered. The port is
           also marked filtered if an ICMP unreachable error (type 3,
           code 0, 1, 2, 3, 9, 10, or 13) is received.

       -sN; -sF; -sX (TCP NULL, FIN, and Xmas scans)
           These three scan types (even more are possible with the
           --scanflags option described in the next section) exploit a
           subtle loophole in the TCP RFC[7] to differentiate between
           open and closed ports. Page 65 of RFC 793 says that “if the
           [destination] port state is CLOSED .... an incoming segment
           not containing a RST causes a RST to be sent in response.”
           Then the next page discusses packets sent to open ports
           without the SYN, RST, or ACK bits set, stating that: “you are
           unlikely to get here, but if you do, drop the segment, and

           When scanning systems compliant with this RFC text, any
           packet not containing SYN, RST, or ACK bits will result in a
           returned RST if the port is closed and no response at all if
           the port is open. As long as none of those three bits are
           included, any combination of the other three (FIN, PSH, and
           URG) are OK. Nmap exploits this with three scan types:

           Null scan (-sN)
               Does not set any bits (TCP flag header is 0)

           FIN scan (-sF)
               Sets just the TCP FIN bit.

           Xmas scan (-sX)
               Sets the FIN, PSH, and URG flags, lighting the packet up
               like a Christmas tree.

           These three scan types are exactly the same in behavior
           except for the TCP flags set in probe packets. If a RST
           packet is received, the port is considered closed, while no
           response means it is open|filtered. The port is marked
           filtered if an ICMP unreachable error (type 3, code 0, 1, 2,
           3, 9, 10, or 13) is received.

           The key advantage to these scan types is that they can sneak
           through certain non-stateful firewalls and packet filtering
           routers. Another advantage is that these scan types are a
           little more stealthy than even a SYN scan. Don't count on
           this though—most modern IDS products can be configured to
           detect them. The big downside is that not all systems follow
           RFC 793 to the letter. A number of systems send RST responses
           to the probes regardless of whether the port is open or not.
           This causes all of the ports to be labeled closed. Major
           operating systems that do this are Microsoft Windows, many
           Cisco devices, BSDI, and IBM OS/400. This scan does work
           against most Unix-based systems though. Another downside of
           these scans is that they can't distinguish open ports from
           certain filtered ones, leaving you with the response

       -sA (TCP ACK scan)
           This scan is different than the others discussed so far in
           that it never determines open (or even open|filtered) ports.
           It is used to map out firewall rulesets, determining whether
           they are stateful or not and which ports are filtered.

           The ACK scan probe packet has only the ACK flag set (unless
           you use --scanflags). When scanning unfiltered systems, open
           and closed ports will both return a RST packet. Nmap then
           labels them as unfiltered, meaning that they are reachable by
           the ACK packet, but whether they are open or closed is
           undetermined. Ports that don't respond, or send certain ICMP
           error messages back (type 3, code 0, 1, 2, 3, 9, 10, or 13),
           are labeled filtered.

       -sW (TCP Window scan)
           Window scan is exactly the same as ACK scan except that it
           exploits an implementation detail of certain systems to
           differentiate open ports from closed ones, rather than always
           printing unfiltered when a RST is returned. It does this by
           examining the TCP Window field of the RST packets returned.
           On some systems, open ports use a positive window size (even
           for RST packets) while closed ones have a zero window. So
           instead of always listing a port as unfiltered when it
           receives a RST back, Window scan lists the port as open or
           closed if the TCP Window value in that reset is positive or
           zero, respectively.

           This scan relies on an implementation detail of a minority of
           systems out on the Internet, so you can't always trust it.
           Systems that don't support it will usually return all ports
           closed. Of course, it is possible that the machine really has
           no open ports. If most scanned ports are closed but a few
           common port numbers (such as 22, 25, 53) are filtered, the
           system is most likely susceptible. Occasionally, systems will
           even show the exact opposite behavior. If your scan shows
           1,000 open ports and three closed or filtered ports, then
           those three may very well be the truly open ones.

       -sM (TCP Maimon scan)
           The Maimon scan is named after its discoverer, Uriel Maimon.
           He described the technique in Phrack Magazine issue #49
           (November 1996).  Nmap, which included this technique, was
           released two issues later. This technique is exactly the same
           as NULL, FIN, and Xmas scans, except that the probe is
           FIN/ACK. According to RFC 793[7] (TCP), a RST packet should
           be generated in response to such a probe whether the port is
           open or closed. However, Uriel noticed that many BSD-derived
           systems simply drop the packet if the port is open.

       --scanflags (Custom TCP scan)
           Truly advanced Nmap users need not limit themselves to the
           canned scan types offered. The --scanflags option allows you
           to design your own scan by specifying arbitrary TCP flags.
           Let your creative juices flow, while evading intrusion
           detection systems whose vendors simply paged through the Nmap
           man page adding specific rules!

           The --scanflags argument can be a numerical flag value such
           as 9 (PSH and FIN), but using symbolic names is easier. Just
           mash together any combination of URG, ACK, PSH, RST, SYN, and
           FIN. For example, --scanflags URGACKPSHRSTSYNFIN sets
           everything, though it's not very useful for scanning. The
           order these are specified in is irrelevant.

           In addition to specifying the desired flags, you can specify
           a TCP scan type (such as -sA or -sF). That base type tells
           Nmap how to interpret responses. For example, a SYN scan
           considers no-response to indicate a filtered port, while a
           FIN scan treats the same as open|filtered. Nmap will behave
           the same way it does for the base scan type, except that it
           will use the TCP flags you specify instead. If you don't
           specify a base type, SYN scan is used.

       -sZ (SCTP COOKIE ECHO scan)
           SCTP COOKIE ECHO scan is a more advanced SCTP scan. It takes
           advantage of the fact that SCTP implementations should
           silently drop packets containing COOKIE ECHO chunks on open
           ports, but send an ABORT if the port is closed. The advantage
           of this scan type is that it is not as obvious a port scan
           than an INIT scan. Also, there may be non-stateful firewall
           rulesets blocking INIT chunks, but not COOKIE ECHO chunks.
           Don't be fooled into thinking that this will make a port scan
           invisible; a good IDS will be able to detect SCTP COOKIE ECHO
           scans too. The downside is that SCTP COOKIE ECHO scans cannot
           differentiate between open and filtered ports, leaving you
           with the state open|filtered in both cases.

       -sI zombie host[:probeport] (idle scan)
           This advanced scan method allows for a truly blind TCP port
           scan of the target (meaning no packets are sent to the target
           from your real IP address). Instead, a unique side-channel
           attack exploits predictable IP fragmentation ID sequence
           generation on the zombie host to glean information about the
           open ports on the target. IDS systems will display the scan
           as coming from the zombie machine you specify (which must be
           up and meet certain criteria).  This fascinating scan type is
           too complex to fully describe in this reference guide, so I
           wrote and posted an informal paper with full details at
           https://nmap.org/book/idlescan.html .

           Besides being extraordinarily stealthy (due to its blind
           nature), this scan type permits mapping out IP-based trust
           relationships between machines. The port listing shows open
           ports from the perspective of the zombie host.  So you can
           try scanning a target using various zombies that you think
           might be trusted (via router/packet filter rules).

           You can add a colon followed by a port number to the zombie
           host if you wish to probe a particular port on the zombie for
           IP ID changes. Otherwise Nmap will use the port it uses by
           default for TCP pings (80).

       -sO (IP protocol scan)
           IP protocol scan allows you to determine which IP protocols
           (TCP, ICMP, IGMP, etc.) are supported by target machines.
           This isn't technically a port scan, since it cycles through
           IP protocol numbers rather than TCP or UDP port numbers. Yet
           it still uses the -p option to select scanned protocol
           numbers, reports its results within the normal port table
           format, and even uses the same underlying scan engine as the
           true port scanning methods. So it is close enough to a port
           scan that it belongs here.

           Besides being useful in its own right, protocol scan
           demonstrates the power of open-source software. While the
           fundamental idea is pretty simple, I had not thought to add
           it nor received any requests for such functionality. Then in
           the summer of 2000, Gerhard Rieger conceived the idea, wrote
           an excellent patch implementing it, and sent it to the
           announce mailing list (then called nmap-hackers).  I
           incorporated that patch into the Nmap tree and released a new
           version the next day. Few pieces of commercial software have
           users enthusiastic enough to design and contribute their own

           Protocol scan works in a similar fashion to UDP scan. Instead
           of iterating through the port number field of a UDP packet,
           it sends IP packet headers and iterates through the eight-bit
           IP protocol field. The headers are usually empty, containing
           no data and not even the proper header for the claimed
           protocol. The exceptions are TCP, UDP, ICMP, SCTP, and IGMP.
           A proper protocol header for those is included since some
           systems won't send them otherwise and because Nmap already
           has functions to create them. Instead of watching for ICMP
           port unreachable messages, protocol scan is on the lookout
           for ICMP protocol unreachable messages. If Nmap receives any
           response in any protocol from the target host, Nmap marks
           that protocol as open. An ICMP protocol unreachable error
           (type 3, code 2) causes the protocol to be marked as closed
           while port unreachable (type 3, code 3) marks the protocol
           open. Other ICMP unreachable errors (type 3, code 0, 1, 9,
           10, or 13) cause the protocol to be marked filtered (though
           they prove that ICMP is open at the same time). If no
           response is received after retransmissions, the protocol is
           marked open|filtered

       -b FTP relay host (FTP bounce scan)
           An interesting feature of the FTP protocol (RFC 959[8]) is
           support for so-called proxy FTP connections. This allows a
           user to connect to one FTP server, then ask that files be
           sent to a third-party server. Such a feature is ripe for
           abuse on many levels, so most servers have ceased supporting
           it. One of the abuses this feature allows is causing the FTP
           server to port scan other hosts. Simply ask the FTP server to
           send a file to each interesting port of a target host in
           turn. The error message will describe whether the port is
           open or not. This is a good way to bypass firewalls because
           organizational FTP servers are often placed where they have
           more access to other internal hosts than any old Internet
           host would. Nmap supports FTP bounce scan with the -b option.
           It takes an argument of the form
           username:password@server:port.  Server is the name or IP
           address of a vulnerable FTP server. As with a normal URL, you
           may omit username:password, in which case anonymous login
           credentials (user: anonymous password:-wwwuser@) are used.
           The port number (and preceding colon) may be omitted as well,
           in which case the default FTP port (21) on server is used.

           This vulnerability was widespread in 1997 when Nmap was
           released, but has largely been fixed. Vulnerable servers are
           still around, so it is worth trying when all else fails. If
           bypassing a firewall is your goal, scan the target network
           for port 21 (or even for any FTP services if you scan all
           ports with version detection) and use the ftp-bounce NSE
           script. Nmap will tell you whether the host is vulnerable or
           not. If you are just trying to cover your tracks, you don't
           need to (and, in fact, shouldn't) limit yourself to hosts on
           the target network. Before you go scanning random Internet
           addresses for vulnerable FTP servers, consider that sysadmins
           may not appreciate you abusing their servers in this way.


       In addition to all of the scan methods discussed previously, Nmap
       offers options for specifying which ports are scanned and whether
       the scan order is randomized or sequential. By default, Nmap
       scans the most common 1,000 ports for each protocol.

       -p port ranges (Only scan specified ports)
           This option specifies which ports you want to scan and
           overrides the default. Individual port numbers are OK, as are
           ranges separated by a hyphen (e.g.  1-1023). The beginning
           and/or end values of a range may be omitted, causing Nmap to
           use 1 and 65535, respectively. So you can specify -p- to scan
           ports from 1 through 65535. Scanning port zero is allowed if
           you specify it explicitly. For IP protocol scanning (-sO),
           this option specifies the protocol numbers you wish to scan
           for (0–255).

           When scanning a combination of protocols (e.g. TCP and UDP),
           you can specify a particular protocol by preceding the port
           numbers by T: for TCP, U: for UDP, S: for SCTP, or P: for IP
           Protocol. The qualifier lasts until you specify another
           qualifier. For example, the argument -p
           U:53,111,137,T:21-25,80,139,8080 would scan UDP ports 53,
           111,and 137, as well as the listed TCP ports. Note that to
           scan both UDP and TCP, you have to specify -sU and at least
           one TCP scan type (such as -sS, -sF, or -sT). If no protocol
           qualifier is given, the port numbers are added to all
           protocol lists.  Ports can also be specified by name
           according to what the port is referred to in the
           nmap-services. You can even use the wildcards * and ?  with
           the names. For example, to scan FTP and all ports whose names
           begin with “http”, use -p ftp,http*. Be careful about shell
           expansions and quote the argument to -p if unsure.

           Ranges of ports can be surrounded by square brackets to
           indicate ports inside that range that appear in
           nmap-services. For example, the following will scan all ports
           in nmap-services equal to or below 1024: -p [-1024]. Be
           careful with shell expansions and quote the argument to -p if

       --exclude-ports port ranges (Exclude the specified ports from
           This option specifies which ports you do want Nmap to exclude
           from scanning. The port ranges are specified similar to -p.
           For IP protocol scanning (-sO), this option specifies the
           protocol numbers you wish to exclude (0–255).

           When ports are asked to be excluded, they are excluded from
           all types of scans (i.e. they will not be scanned under any
           circumstances). This also includes the discovery phase.

       -F (Fast (limited port) scan)
           Specifies that you wish to scan fewer ports than the default.
           Normally Nmap scans the most common 1,000 ports for each
           scanned protocol. With -F, this is reduced to 100.

           Nmap needs an nmap-services file with frequency information
           in order to know which ports are the most common. If port
           frequency information isn't available, perhaps because of the
           use of a custom nmap-services file, Nmap scans all named
           ports plus ports 1-1024. In that case, -F means to scan only
           ports that are named in the services file.

       -r (Don't randomize ports)
           By default, Nmap randomizes the scanned port order (except
           that certain commonly accessible ports are moved near the
           beginning for efficiency reasons). This randomization is
           normally desirable, but you can specify -r for sequential
           (sorted from lowest to highest) port scanning instead.

       --port-ratio ratio<decimal number between 0 and 1>
           Scans all ports in nmap-services file with a ratio greater
           than the one given.  ratio must be between 0.0 and 1.0.

       --top-ports n
           Scans the n highest-ratio ports found in nmap-services file
           after excluding all ports specified by --exclude-ports.  n
           must be 1 or greater.


       Point Nmap at a remote machine and it might tell you that ports
       25/tcp, 80/tcp, and 53/udp are open. Using its nmap-services
       database of about 2,200 well-known services, Nmap would report
       that those ports probably correspond to a mail server (SMTP), web
       server (HTTP), and name server (DNS) respectively. This lookup is
       usually accurate—the vast majority of daemons listening on TCP
       port 25 are, in fact, mail servers. However, you should not bet
       your security on this! People can and do run services on strange

       Even if Nmap is right, and the hypothetical server above is
       running SMTP, HTTP, and DNS servers, that is not a lot of
       information. When doing vulnerability assessments (or even simple
       network inventories) of your companies or clients, you really
       want to know which mail and DNS servers and versions are running.
       Having an accurate version number helps dramatically in
       determining which exploits a server is vulnerable to. Version
       detection helps you obtain this information.

       After TCP and/or UDP ports are discovered using one of the other
       scan methods, version detection interrogates those ports to
       determine more about what is actually running. The
       nmap-service-probes database contains probes for querying various
       services and match expressions to recognize and parse responses.
       Nmap tries to determine the service protocol (e.g. FTP, SSH,
       Telnet, HTTP), the application name (e.g. ISC BIND, Apache httpd,
       Solaris telnetd), the version number, hostname, device type (e.g.
       printer, router), the OS family (e.g. Windows, Linux). When
       possible, Nmap also gets the Common Platform Enumeration (CPE)
       representation of this information. Sometimes miscellaneous
       details like whether an X server is open to connections, the SSH
       protocol version, or the KaZaA user name, are available. Of
       course, most services don't provide all of this information. If
       Nmap was compiled with OpenSSL support, it will connect to SSL
       servers to deduce the service listening behind that encryption
       layer.  Some UDP ports are left in the open|filtered state after
       a UDP port scan is unable to determine whether the port is open
       or filtered. Version detection will try to elicit a response from
       these ports (just as it does with open ports), and change the
       state to open if it succeeds.  open|filtered TCP ports are
       treated the same way. Note that the Nmap -A option enables
       version detection among other things.  A paper documenting the
       workings, usage, and customization of version detection is
       available at https://nmap.org/book/vscan.html .

       When RPC services are discovered, the Nmap RPC grinder is
       automatically used to determine the RPC program and version
       numbers. It takes all the TCP/UDP ports detected as RPC and
       floods them with SunRPC program NULL commands in an attempt to
       determine whether they are RPC ports, and if so, what program and
       version number they serve up. Thus you can effectively obtain the
       same info as rpcinfo -p even if the target's portmapper is behind
       a firewall (or protected by TCP wrappers). Decoys do not
       currently work with RPC scan.

       When Nmap receives responses from a service but cannot match them
       to its database, it prints out a special fingerprint and a URL
       for you to submit it to if you know for sure what is running on
       the port. Please take a couple minutes to make the submission so
       that your find can benefit everyone. Thanks to these submissions,
       Nmap has about 6,500 pattern matches for more than 650 protocols
       such as SMTP, FTP, HTTP, etc.

       Version detection is enabled and controlled with the following

       -sV (Version detection)
           Enables version detection, as discussed above. Alternatively,
           you can use -A, which enables version detection among other

           -sR is an alias for -sV. Prior to March 2011, it was used to
           active the RPC grinder separately from version detection, but
           now these options are always combined.

       --allports (Don't exclude any ports from version detection)
           By default, Nmap version detection skips TCP port 9100
           because some printers simply print anything sent to that
           port, leading to dozens of pages of HTTP GET requests, binary
           SSL session requests, etc. This behavior can be changed by
           modifying or removing the Exclude directive in
           nmap-service-probes, or you can specify --allports to scan
           all ports regardless of any Exclude directive.

       --version-intensity intensity (Set version scan intensity)
           When performing a version scan (-sV), Nmap sends a series of
           probes, each of which is assigned a rarity value between one
           and nine. The lower-numbered probes are effective against a
           wide variety of common services, while the higher-numbered
           ones are rarely useful. The intensity level specifies which
           probes should be applied. The higher the number, the more
           likely it is the service will be correctly identified.
           However, high intensity scans take longer. The intensity must
           be between 0 and 9.  The default is 7.  When a probe is
           registered to the target port via the nmap-service-probes
           ports directive, that probe is tried regardless of intensity
           level. This ensures that the DNS probes will always be
           attempted against any open port 53, the SSL probe will be
           done against 443, etc.

       --version-light (Enable light mode)
           This is a convenience alias for --version-intensity 2. This
           light mode makes version scanning much faster, but it is
           slightly less likely to identify services.

       --version-all (Try every single probe)
           An alias for --version-intensity 9, ensuring that every
           single probe is attempted against each port.

       --version-trace (Trace version scan activity)
           This causes Nmap to print out extensive debugging info about
           what version scanning is doing. It is a subset of what you
           get with --packet-trace.

OS DETECTION         top

       One of Nmap's best-known features is remote OS detection using
       TCP/IP stack fingerprinting. Nmap sends a series of TCP and UDP
       packets to the remote host and examines practically every bit in
       the responses. After performing dozens of tests such as TCP ISN
       sampling, TCP options support and ordering, IP ID sampling, and
       the initial window size check, Nmap compares the results to its
       nmap-os-db database of more than 2,600 known OS fingerprints and
       prints out the OS details if there is a match. Each fingerprint
       includes a freeform textual description of the OS, and a
       classification which provides the vendor name (e.g. Sun),
       underlying OS (e.g. Solaris), OS generation (e.g. 10), and device
       type (general purpose, router, switch, game console, etc). Most
       fingerprints also have a Common Platform Enumeration (CPE)
       representation, like cpe:/o:linux:linux_kernel:2.6.

       If Nmap is unable to guess the OS of a machine, and conditions
       are good (e.g. at least one open port and one closed port were
       found), Nmap will provide a URL you can use to submit the
       fingerprint if you know (for sure) the OS running on the machine.
       By doing this you contribute to the pool of operating systems
       known to Nmap and thus it will be more accurate for everyone.

       OS detection enables some other tests which make use of
       information that is gathered during the process anyway. One of
       these is TCP Sequence Predictability Classification. This
       measures approximately how hard it is to establish a forged TCP
       connection against the remote host. It is useful for exploiting
       source-IP based trust relationships (rlogin, firewall filters,
       etc) or for hiding the source of an attack. This sort of spoofing
       is rarely performed any more, but many machines are still
       vulnerable to it. The actual difficulty number is based on
       statistical sampling and may fluctuate. It is generally better to
       use the English classification such as “worthy challenge” or
       “trivial joke”. This is only reported in normal output in verbose
       (-v) mode. When verbose mode is enabled along with -O, IP ID
       sequence generation is also reported. Most machines are in the
       “incremental” class, which means that they increment the ID field
       in the IP header for each packet they send. This makes them
       vulnerable to several advanced information gathering and spoofing

       Another bit of extra information enabled by OS detection is a
       guess at a target's uptime. This uses the TCP timestamp option
       (RFC 1323[9]) to guess when a machine was last rebooted. The
       guess can be inaccurate due to the timestamp counter not being
       initialized to zero or the counter overflowing and wrapping
       around, so it is printed only in verbose mode.

       A paper documenting the workings, usage, and customization of OS
       detection is available at https://nmap.org/book/osdetect.html .

       OS detection is enabled and controlled with the following

       -O (Enable OS detection)
           Enables OS detection, as discussed above. Alternatively, you
           can use -A to enable OS detection along with other things.

       --osscan-limit (Limit OS detection to promising targets)
           OS detection is far more effective if at least one open and
           one closed TCP port are found. Set this option and Nmap will
           not even try OS detection against hosts that do not meet this
           criteria. This can save substantial time, particularly on -Pn
           scans against many hosts. It only matters when OS detection
           is requested with -O or -A.

       --osscan-guess; --fuzzy (Guess OS detection results)
           When Nmap is unable to detect a perfect OS match, it
           sometimes offers up near-matches as possibilities. The match
           has to be very close for Nmap to do this by default. Either
           of these (equivalent) options make Nmap guess more
           aggressively. Nmap will still tell you when an imperfect
           match is printed and display its confidence level
           (percentage) for each guess.

       --max-os-tries (Set the maximum number of OS detection tries
       against a target)
           When Nmap performs OS detection against a target and fails to
           find a perfect match, it usually repeats the attempt. By
           default, Nmap tries five times if conditions are favorable
           for OS fingerprint submission, and twice when conditions
           aren't so good. Specifying a lower --max-os-tries value (such
           as 1) speeds Nmap up, though you miss out on retries which
           could potentially identify the OS. Alternatively, a high
           value may be set to allow even more retries when conditions
           are favorable. This is rarely done, except to generate better
           fingerprints for submission and integration into the Nmap OS


       The Nmap Scripting Engine (NSE) is one of Nmap's most powerful
       and flexible features. It allows users to write (and share)
       simple scripts (using the Lua programming language[10]

       ) to automate a wide variety of networking tasks. Those scripts
       are executed in parallel with the speed and efficiency you expect
       from Nmap. Users can rely on the growing and diverse set of
       scripts distributed with Nmap, or write their own to meet custom

       Tasks we had in mind when creating the system include network
       discovery, more sophisticated version detection, vulnerability
       detection. NSE can even be used for vulnerability exploitation.

       To reflect those different uses and to simplify the choice of
       which scripts to run, each script contains a field associating it
       with one or more categories. Currently defined categories are
       auth, broadcast, default.  discovery, dos, exploit, external,
       fuzzer, intrusive, malware, safe, version, and vuln. These are
       all described at
       https://nmap.org/book/nse-usage.html#nse-categories .

       Scripts are not run in a sandbox and thus could accidentally or
       maliciously damage your system or invade your privacy. Never run
       scripts from third parties unless you trust the authors or have
       carefully audited the scripts yourself.

       The Nmap Scripting Engine is described in detail at

       and is controlled by the following options:

           Performs a script scan using the default set of scripts. It
           is equivalent to --script=default. Some of the scripts in
           this category are considered intrusive and should not be run
           against a target network without permission.

       --script filename|category|directory/|expression[,...]
           Runs a script scan using the comma-separated list of
           filenames, script categories, and directories. Each element
           in the list may also be a Boolean expression describing a
           more complex set of scripts. Each element is interpreted
           first as an expression, then as a category, and finally as a
           file or directory name.

           There are two special features for advanced users only. One
           is to prefix script names and expressions with + to force
           them to run even if they normally wouldn't (e.g. the relevant
           service wasn't detected on the target port). The other is
           that the argument all may be used to specify every script in
           Nmap's database. Be cautious with this because NSE contains
           dangerous scripts such as exploits, brute force
           authentication crackers, and denial of service attacks.

           File and directory names may be relative or absolute.
           Absolute names are used directly. Relative paths are looked
           for in the scripts of each of the following places until
               ~/.nmap (not searched on Windows)
               APPDATA\nmap (only on Windows)
               the directory containing the nmap executable
               the directory containing the nmap executable, followed by
               ../share/nmap (not searched on Windows)
               NMAPDATADIR (not searched on Windows)
               the current directory.

           When a directory name ending in / is given, Nmap loads every
           file in the directory whose name ends with .nse. All other
           files are ignored and directories are not searched
           recursively. When a filename is given, it does not have to
           have the .nse extension; it will be added automatically if
           necessary.  Nmap scripts are stored in a scripts subdirectory
           of the Nmap data directory by default (see
           https://nmap.org/book/data-files.html ).

           For efficiency, scripts are indexed in a database stored in
           scripts/script.db, which lists the category or categories in
           which each script belongs.  When referring to scripts from
           script.db by name, you can use a shell-style ‘*’ wildcard.

           nmap --script "http-*"
               Loads all scripts whose name starts with http-, such as
               http-auth and http-open-proxy. The argument to --script
               had to be in quotes to protect the wildcard from the

           More complicated script selection can be done using the and,
           or, and not operators to build Boolean expressions. The
           operators have the same precedence[11] as in Lua: not is the
           highest, followed by and and then or. You can alter
           precedence by using parentheses. Because expressions contain
           space characters it is necessary to quote them.

           nmap --script "not intrusive"
               Loads every script except for those in the intrusive

           nmap --script "default or safe"
               This is functionally equivalent to nmap --script
               "default,safe". It loads all scripts that are in the
               default category or the safe category or both.

           nmap --script "default and safe"
               Loads those scripts that are in both the default and safe

           nmap --script "(default or safe or intrusive) and not http-*"
               Loads scripts in the default, safe, or intrusive
               categories, except for those whose names start with

       --script-args n1=v1,n2={n3=v3},n4={v4,v5}
           Lets you provide arguments to NSE scripts. Arguments are a
           comma-separated list of name=value pairs. Names and values
           may be strings not containing whitespace or the characters
           ‘{’, ‘}’, ‘=’, or ‘,’. To include one of these characters in
           a string, enclose the string in single or double quotes.
           Within a quoted string, ‘\’ escapes a quote. A backslash is
           only used to escape quotation marks in this special case; in
           all other cases a backslash is interpreted literally. Values
           may also be tables enclosed in {}, just as in Lua. A table
           may contain simple string values or more name-value pairs,
           including nested tables. Many scripts qualify their arguments
           with the script name, as in xmpp-info.server_name. You may
           use that full qualified version to affect just the specified
           script, or you may pass the unqualified version (server_name
           in this case) to affect all scripts using that argument name.
           A script will first check for its fully qualified argument
           name (the name specified in its documentation) before it
           accepts an unqualified argument name. A complex example of
           script arguments is --script-args
           The online NSE Documentation Portal at
           https://nmap.org/nsedoc/ lists the arguments that each script

       --script-args-file filename
           Lets you load arguments to NSE scripts from a file. Any
           arguments on the command line supersede ones in the file. The
           file can be an absolute path, or a path relative to Nmap's
           usual search path (NMAPDIR, etc.) Arguments can be
           comma-separated or newline-separated, but otherwise follow
           the same rules as for --script-args, without requiring
           special quoting and escaping, since they are not parsed by
           the shell.

       --script-help filename|category|directory|expression|all[,...]
           Shows help about scripts. For each script matching the given
           specification, Nmap prints the script name, its categories,
           and its description. The specifications are the same as those
           accepted by --script; so for example if you want help about
           the ftp-anon script, you would run nmap --script-help
           ftp-anon. In addition to getting help for individual scripts,
           you can use this as a preview of what scripts will be run for
           a specification, for example with nmap --script-help default.

           This option does what --packet-trace does, just one ISO layer
           higher. If this option is specified all incoming and outgoing
           communication performed by a script is printed. The displayed
           information includes the communication protocol, the source,
           the target and the transmitted data. If more than 5% of all
           transmitted data is not printable, then the trace output is
           in a hex dump format. Specifying --packet-trace enables
           script tracing too.

           This option updates the script database found in
           scripts/script.db which is used by Nmap to determine the
           available default scripts and categories. It is only
           necessary to update the database if you have added or removed
           NSE scripts from the default scripts directory or if you have
           changed the categories of any script. This option is
           generally used by itself: nmap --script-updatedb.


       One of my highest Nmap development priorities has always been
       performance. A default scan (nmap hostname) of a host on my local
       network takes a fifth of a second. That is barely enough time to
       blink, but adds up when you are scanning hundreds or thousands of
       hosts. Moreover, certain scan options such as UDP scanning and
       version detection can increase scan times substantially. So can
       certain firewall configurations, particularly response rate
       limiting. While Nmap utilizes parallelism and many advanced
       algorithms to accelerate these scans, the user has ultimate
       control over how Nmap runs. Expert users carefully craft Nmap
       commands to obtain only the information they care about while
       meeting their time constraints.

       Techniques for improving scan times include omitting non-critical
       tests, and upgrading to the latest version of Nmap (performance
       enhancements are made frequently). Optimizing timing parameters
       can also make a substantial difference. Those options are listed

       Some options accept a time parameter. This is specified in
       seconds by default, though you can append ‘ms’, ‘s’, ‘m’, or ‘h’
       to the value to specify milliseconds, seconds, minutes, or hours.
       So the --host-timeout arguments 900000ms, 900, 900s, and 15m all
       do the same thing.

       --min-hostgroup numhosts; --max-hostgroup numhosts (Adjust
       parallel scan group sizes)
           Nmap has the ability to port scan or version scan multiple
           hosts in parallel. Nmap does this by dividing the target IP
           space into groups and then scanning one group at a time. In
           general, larger groups are more efficient. The downside is
           that host results can't be provided until the whole group is
           finished. So if Nmap started out with a group size of 50, the
           user would not receive any reports (except for the updates
           offered in verbose mode) until the first 50 hosts are

           By default, Nmap takes a compromise approach to this
           conflict. It starts out with a group size as low as five so
           the first results come quickly and then increases the
           groupsize to as high as 1024. The exact default numbers
           depend on the options given. For efficiency reasons, Nmap
           uses larger group sizes for UDP or few-port TCP scans.

           When a maximum group size is specified with --max-hostgroup,
           Nmap will never exceed that size. Specify a minimum size with
           --min-hostgroup and Nmap will try to keep group sizes above
           that level. Nmap may have to use smaller groups than you
           specify if there are not enough target hosts left on a given
           interface to fulfill the specified minimum. Both may be set
           to keep the group size within a specific range, though this
           is rarely desired.

           These options do not have an effect during the host discovery
           phase of a scan. This includes plain ping scans (-sn). Host
           discovery always works in large groups of hosts to improve
           speed and accuracy.

           The primary use of these options is to specify a large
           minimum group size so that the full scan runs more quickly. A
           common choice is 256 to scan a network in /24 sized chunks.
           For a scan with many ports, exceeding that number is unlikely
           to help much. For scans of just a few port numbers, host
           group sizes of 2048 or more may be helpful.

       --min-parallelism numprobes; --max-parallelism numprobes (Adjust
       probe parallelization)
           These options control the total number of probes that may be
           outstanding for a host group. They are used for port scanning
           and host discovery. By default, Nmap calculates an
           ever-changing ideal parallelism based on network performance.
           If packets are being dropped, Nmap slows down and allows
           fewer outstanding probes. The ideal probe number slowly rises
           as the network proves itself worthy. These options place
           minimum or maximum bounds on that variable. By default, the
           ideal parallelism can drop to one if the network proves
           unreliable and rise to several hundred in perfect conditions.

           The most common usage is to set --min-parallelism to a number
           higher than one to speed up scans of poorly performing hosts
           or networks. This is a risky option to play with, as setting
           it too high may affect accuracy. Setting this also reduces
           Nmap's ability to control parallelism dynamically based on
           network conditions. A value of 10 might be reasonable, though
           I only adjust this value as a last resort.

           The --max-parallelism option is sometimes set to one to
           prevent Nmap from sending more than one probe at a time to
           hosts. The --scan-delay option, discussed later, is another
           way to do this.

       --min-rtt-timeout time, --max-rtt-timeout time,
       --initial-rtt-timeout time (Adjust probe timeouts)
           Nmap maintains a running timeout value for determining how
           long it will wait for a probe response before giving up or
           retransmitting the probe. This is calculated based on the
           response times of previous probes.

           If the network latency shows itself to be significant and
           variable, this timeout can grow to several seconds. It also
           starts at a conservative (high) level and may stay that way
           for a while when Nmap scans unresponsive hosts.

           Specifying a lower --max-rtt-timeout and
           --initial-rtt-timeout than the defaults can cut scan times
           significantly. This is particularly true for pingless (-Pn)
           scans, and those against heavily filtered networks. Don't get
           too aggressive though. The scan can end up taking longer if
           you specify such a low value that many probes are timing out
           and retransmitting while the response is in transit.

           If all the hosts are on a local network, 100 milliseconds
           (--max-rtt-timeout 100ms) is a reasonable aggressive value.
           If routing is involved, ping a host on the network first with
           the ICMP ping utility, or with a custom packet crafter such
           as Nping that is more likely to get through a firewall. Look
           at the maximum round trip time out of ten packets or so. You
           might want to double that for the --initial-rtt-timeout and
           triple or quadruple it for the --max-rtt-timeout. I generally
           do not set the maximum RTT below 100 ms, no matter what the
           ping times are. Nor do I exceed 1000 ms.

           --min-rtt-timeout is a rarely used option that could be
           useful when a network is so unreliable that even Nmap's
           default is too aggressive. Since Nmap only reduces the
           timeout down to the minimum when the network seems to be
           reliable, this need is unusual and should be reported as a
           bug to the nmap-dev mailing list.

       --max-retries numtries (Specify the maximum number of port scan
       probe retransmissions)
           When Nmap receives no response to a port scan probe, it could
           mean the port is filtered. Or maybe the probe or response was
           simply lost on the network. It is also possible that the
           target host has rate limiting enabled that temporarily
           blocked the response. So Nmap tries again by retransmitting
           the initial probe. If Nmap detects poor network reliability,
           it may try many more times before giving up on a port. While
           this benefits accuracy, it also lengthens scan times. When
           performance is critical, scans may be sped up by limiting the
           number of retransmissions allowed. You can even specify
           --max-retries 0 to prevent any retransmissions, though that
           is only recommended for situations such as informal surveys
           where occasional missed ports and hosts are acceptable.

           The default (with no -T template) is to allow ten
           retransmissions. If a network seems reliable and the target
           hosts aren't rate limiting, Nmap usually only does one
           retransmission. So most target scans aren't even affected by
           dropping --max-retries to a low value such as three. Such
           values can substantially speed scans of slow (rate limited)
           hosts. You usually lose some information when Nmap gives up
           on ports early, though that may be preferable to letting the
           --host-timeout expire and losing all information about the

       --host-timeout time (Give up on slow target hosts)
           Some hosts simply take a long time to scan. This may be due
           to poorly performing or unreliable networking hardware or
           software, packet rate limiting, or a restrictive firewall.
           The slowest few percent of the scanned hosts can eat up a
           majority of the scan time. Sometimes it is best to cut your
           losses and skip those hosts initially. Specify --host-timeout
           with the maximum amount of time you are willing to wait. For
           example, specify 30m to ensure that Nmap doesn't waste more
           than half an hour on a single host. Note that Nmap may be
           scanning other hosts at the same time during that half an
           hour, so it isn't a complete loss. A host that times out is
           skipped. No port table, OS detection, or version detection
           results are printed for that host.

           The special value 0 can be used to mean “no timeout”, which
           can be used to override the T5 timing template, which sets
           the host timeout to 15 minutes.

       --script-timeout time
           While some scripts complete in fractions of a second, others
           can take hours or more depending on the nature of the script,
           arguments passed in, network and application conditions, and
           more. The --script-timeout option sets a ceiling on script
           execution time. Any script instance which exceeds that time
           will be terminated and no output will be shown. If debugging
           (-d) is enabled, Nmap will report on each timeout. For host
           and service scripts, a script instance only scans a single
           target host or port and the timeout period will be reset for
           the next instance.

           The special value 0 can be used to mean “no timeout”, which
           can be used to override the T5 timing template, which sets
           the script timeout to 10 minutes.

       --scan-delay time; --max-scan-delay time (Adjust delay between
           This option causes Nmap to wait at least the given amount of
           time between each probe it sends to a given host. This is
           particularly useful in the case of rate limiting.  Solaris
           machines (among many others) will usually respond to UDP scan
           probe packets with only one ICMP message per second. Any more
           than that sent by Nmap will be wasteful. A --scan-delay of 1s
           will keep Nmap at that slow rate. Nmap tries to detect rate
           limiting and adjust the scan delay accordingly, but it
           doesn't hurt to specify it explicitly if you already know
           what rate works best.

           When Nmap adjusts the scan delay upward to cope with rate
           limiting, the scan slows down dramatically. The
           --max-scan-delay option specifies the largest delay that Nmap
           will allow. A low --max-scan-delay can speed up Nmap, but it
           is risky. Setting this value too low can lead to wasteful
           packet retransmissions and possible missed ports when the
           target implements strict rate limiting.

           Another use of --scan-delay is to evade threshold based
           intrusion detection and prevention systems (IDS/IPS).

       --min-rate number; --max-rate number (Directly control the
       scanning rate)
           Nmap's dynamic timing does a good job of finding an
           appropriate speed at which to scan. Sometimes, however, you
           may happen to know an appropriate scanning rate for a
           network, or you may have to guarantee that a scan will be
           finished by a certain time. Or perhaps you must keep Nmap
           from scanning too quickly. The --min-rate and --max-rate
           options are designed for these situations.

           When the --min-rate option is given Nmap will do its best to
           send packets as fast as or faster than the given rate. The
           argument is a positive real number representing a packet rate
           in packets per second. For example, specifying --min-rate 300
           means that Nmap will try to keep the sending rate at or above
           300 packets per second. Specifying a minimum rate does not
           keep Nmap from going faster if conditions warrant.

           Likewise, --max-rate limits a scan's sending rate to a given
           maximum. Use --max-rate 100, for example, to limit sending to
           100 packets per second on a fast network. Use --max-rate 0.1
           for a slow scan of one packet every ten seconds. Use
           --min-rate and --max-rate together to keep the rate inside a
           certain range.

           These two options are global, affecting an entire scan, not
           individual hosts. They only affect port scans and host
           discovery scans. Other features like OS detection implement
           their own timing.

           There are two conditions when the actual scanning rate may
           fall below the requested minimum. The first is if the minimum
           is faster than the fastest rate at which Nmap can send, which
           is dependent on hardware. In this case Nmap will simply send
           packets as fast as possible, but be aware that such high
           rates are likely to cause a loss of accuracy. The second case
           is when Nmap has nothing to send, for example at the end of a
           scan when the last probes have been sent and Nmap is waiting
           for them to time out or be responded to. It's normal to see
           the scanning rate drop at the end of a scan or in between
           hostgroups. The sending rate may temporarily exceed the
           maximum to make up for unpredictable delays, but on average
           the rate will stay at or below the maximum.

           Specifying a minimum rate should be done with care. Scanning
           faster than a network can support may lead to a loss of
           accuracy. In some cases, using a faster rate can make a scan
           take longer than it would with a slower rate. This is because
           Nmap's adaptive retransmission algorithms will detect the
           network congestion caused by an excessive scanning rate and
           increase the number of retransmissions in order to improve
           accuracy. So even though packets are sent at a higher rate,
           more packets are sent overall. Cap the number of
           retransmissions with the --max-retries option if you need to
           set an upper limit on total scan time.

           Many hosts have long used rate limiting to reduce the number
           of ICMP error messages (such as port-unreachable errors) they
           send. Some systems now apply similar rate limits to the RST
           (reset) packets they generate. This can slow Nmap down
           dramatically as it adjusts its timing to reflect those rate
           limits. You can tell Nmap to ignore those rate limits (for
           port scans such as SYN scan which don't treat non-responsive
           ports as open) by specifying --defeat-rst-ratelimit.

           Using this option can reduce accuracy, as some ports will
           appear non-responsive because Nmap didn't wait long enough
           for a rate-limited RST response. With a SYN scan, the
           non-response results in the port being labeled filtered
           rather than the closed state we see when RST packets are
           received. This option is useful when you only care about open
           ports, and distinguishing between closed and filtered ports
           isn't worth the extra time.

           Similar to --defeat-rst-ratelimit, the
           --defeat-icmp-ratelimit option trades accuracy for speed,
           increasing UDP scanning speed against hosts that rate-limit
           ICMP error messages. Because this option causes Nmap to not
           delay in order to receive the port unreachable messages, a
           non-responsive port will be labeled closed|filtered instead
           of the default open|filtered. This has the effect of only
           treating ports which actually respond via UDP as open. Since
           many UDP services do not respond in this way, the chance for
           inaccuracy is greater with this option than with

       --nsock-engine iocp|epoll|kqueue|poll|select
           Enforce use of a given nsock IO multiplexing engine. Only the
           select(2)-based fallback engine is guaranteed to be available
           on your system. Engines are named after the name of the IO
           management facility they leverage. Engines currently
           implemented are epoll, kqueue, poll, and select, but not all
           will be present on any platform. By default, Nmap will use
           the "best" engine, i.e. the first one in this list that is
           supported. Use nmap -V to see which engines are supported on
           your platform.

       -T paranoid|sneaky|polite|normal|aggressive|insane (Set a timing
           While the fine-grained timing controls discussed in the
           previous section are powerful and effective, some people find
           them confusing. Moreover, choosing the appropriate values can
           sometimes take more time than the scan you are trying to
           optimize. Fortunately, Nmap offers a simpler approach, with
           six timing templates. You can specify them with the -T option
           and their number (0–5) or their name. The template names are
           paranoid (0), sneaky (1), polite (2), normal (3),
           aggressive (4), and insane (5). The first two are for IDS
           evasion. Polite mode slows down the scan to use less
           bandwidth and target machine resources. Normal mode is the
           default and so -T3 does nothing. Aggressive mode speeds scans
           up by making the assumption that you are on a reasonably fast
           and reliable network. Finally insane mode assumes that you
           are on an extraordinarily fast network or are willing to
           sacrifice some accuracy for speed.

           These templates allow the user to specify how aggressive they
           wish to be, while leaving Nmap to pick the exact timing
           values. The templates also make some minor speed adjustments
           for which fine-grained control options do not currently
           exist. For example, -T4 prohibits the dynamic scan delay from
           exceeding 10 ms for TCP ports and -T5 caps that value at
           5 ms. Templates can be used in combination with fine-grained
           controls, and the fine-grained controls that you specify will
           take precedence over the timing template default for that
           parameter. I recommend using -T4 when scanning reasonably
           modern and reliable networks. Keep that option even when you
           add fine-grained controls so that you benefit from those
           extra minor optimizations that it enables.

           If you are on a decent broadband or ethernet connection, I
           would recommend always using -T4. Some people love -T5 though
           it is too aggressive for my taste. People sometimes specify
           -T2 because they think it is less likely to crash hosts or
           because they consider themselves to be polite in general.
           They often don't realize just how slow -T polite really is.
           Their scan may take ten times longer than a default scan.
           Machine crashes and bandwidth problems are rare with the
           default timing options (-T3) and so I normally recommend that
           for cautious scanners. Omitting version detection is far more
           effective than playing with timing values at reducing these

           While -T0 and -T1 may be useful for avoiding IDS alerts, they
           will take an extraordinarily long time to scan thousands of
           machines or ports. For such a long scan, you may prefer to
           set the exact timing values you need rather than rely on the
           canned -T0 and -T1 values.

           The main effects of T0 are serializing the scan so only one
           port is scanned at a time, and waiting five minutes between
           sending each probe.  T1 and T2 are similar but they only wait
           15 seconds and 0.4 seconds, respectively, between probes.  T3
           is Nmap's default behavior, which includes parallelization.
           -T4 does the equivalent of
            --max-rtt-timeout 1250ms --min-rtt-timeout 100ms
           --initial-rtt-timeout 500ms --max-retries 6 and sets the
           maximum TCP and SCTP scan delay to 10ms.  T5 does the
           equivalent of
            --max-rtt-timeout 300ms --min-rtt-timeout 50ms
           --initial-rtt-timeout 250ms --max-retries 2 --host-timeout
           15m --script-timeout 10m as well as setting the maximum TCP
           and SCTP scan delay to 5ms. Maximum UDP scan delay is not set
           by T4 or T5, but it can be set with the --max-scan-delay


       Many Internet pioneers envisioned a global open network with a
       universal IP address space allowing virtual connections between
       any two nodes. This allows hosts to act as true peers, serving
       and retrieving information from each other. People could access
       all of their home systems from work, changing the climate control
       settings or unlocking the doors for early guests. This vision of
       universal connectivity has been stifled by address space
       shortages and security concerns. In the early 1990s,
       organizations began deploying firewalls for the express purpose
       of reducing connectivity. Huge networks were cordoned off from
       the unfiltered Internet by application proxies, network address
       translation, and packet filters. The unrestricted flow of
       information gave way to tight regulation of approved
       communication channels and the content that passes over them.

       Network obstructions such as firewalls can make mapping a network
       exceedingly difficult. It will not get any easier, as stifling
       casual reconnaissance is often a key goal of implementing the
       devices. Nevertheless, Nmap offers many features to help
       understand these complex networks, and to verify that filters are
       working as intended. It even supports mechanisms for bypassing
       poorly implemented defenses. One of the best methods of
       understanding your network security posture is to try to defeat
       it. Place yourself in the mind-set of an attacker, and deploy
       techniques from this section against your networks. Launch an FTP
       bounce scan, idle scan, fragmentation attack, or try to tunnel
       through one of your own proxies.

       In addition to restricting network activity, companies are
       increasingly monitoring traffic with intrusion detection systems
       (IDS). All of the major IDSs ship with rules designed to detect
       Nmap scans because scans are sometimes a precursor to attacks.
       Many of these products have recently morphed into intrusion
       prevention systems (IPS) that actively block traffic deemed
       malicious. Unfortunately for network administrators and IDS
       vendors, reliably detecting bad intentions by analyzing packet
       data is a tough problem. Attackers with patience, skill, and the
       help of certain Nmap options can usually pass by IDSs undetected.
       Meanwhile, administrators must cope with large numbers of false
       positive results where innocent activity is misdiagnosed and
       alerted on or blocked.

       Occasionally people suggest that Nmap should not offer features
       for evading firewall rules or sneaking past IDSs. They argue that
       these features are just as likely to be misused by attackers as
       used by administrators to enhance security. The problem with this
       logic is that these methods would still be used by attackers, who
       would just find other tools or patch the functionality into Nmap.
       Meanwhile, administrators would find it that much harder to do
       their jobs. Deploying only modern, patched FTP servers is a far
       more powerful defense than trying to prevent the distribution of
       tools implementing the FTP bounce attack.

       There is no magic bullet (or Nmap option) for detecting and
       subverting firewalls and IDS systems. It takes skill and
       experience. A tutorial is beyond the scope of this reference
       guide, which only lists the relevant options and describes what
       they do.

       -f (fragment packets); --mtu (using the specified MTU)
           The -f option causes the requested scan (including host
           discovery scans) to use tiny fragmented IP packets. The idea
           is to split up the TCP header over several packets to make it
           harder for packet filters, intrusion detection systems, and
           other annoyances to detect what you are doing. Be careful
           with this! Some programs have trouble handling these tiny
           packets. The old-school sniffer named Sniffit segmentation
           faulted immediately upon receiving the first fragment.
           Specify this option once, and Nmap splits the packets into
           eight bytes or less after the IP header. So a 20-byte TCP
           header would be split into three packets. Two with eight
           bytes of the TCP header, and one with the final four. Of
           course each fragment also has an IP header. Specify -f again
           to use 16 bytes per fragment (reducing the number of
           fragments).  Or you can specify your own offset size with the
           --mtu option. Don't also specify -f if you use --mtu. The
           offset must be a multiple of eight. While fragmented packets
           won't get by packet filters and firewalls that queue all IP
           fragments, such as the CONFIG_IP_ALWAYS_DEFRAG option in the
           Linux kernel, some networks can't afford the performance hit
           this causes and thus leave it disabled. Others can't enable
           this because fragments may take different routes into their
           networks. Some source systems defragment outgoing packets in
           the kernel. Linux with the iptables connection tracking
           module is one such example. Do a scan while a sniffer such as
           Wireshark is running to ensure that sent packets are
           fragmented. If your host OS is causing problems, try the
           --send-eth option to bypass the IP layer and send raw
           ethernet frames.

           Fragmentation is only supported for Nmap's raw packet
           features, which includes TCP and UDP port scans (except
           connect scan and FTP bounce scan) and OS detection. Features
           such as version detection and the Nmap Scripting Engine
           generally don't support fragmentation because they rely on
           your host's TCP stack to communicate with target services.

       -D decoy1[,decoy2][,ME][,...] (Cloak a scan with decoys)
           Causes a decoy scan to be performed, which makes it appear to
           the remote host that the host(s) you specify as decoys are
           scanning the target network too. Thus their IDS might report
           5–10 port scans from unique IP addresses, but they won't know
           which IP was scanning them and which were innocent decoys.
           While this can be defeated through router path tracing,
           response-dropping, and other active mechanisms, it is
           generally an effective technique for hiding your IP address.

           Separate each decoy host with commas, and you can optionally
           use ME as one of the decoys to represent the position for
           your real IP address. If you put ME in the sixth position or
           later, some common port scan detectors (such as Solar
           Designer's excellent Scanlogd) are unlikely to show your IP
           address at all. If you don't use ME, Nmap will put you in a
           random position. You can also use RND to generate a random,
           non-reserved IP address, or RND:number to generate number

           Note that the hosts you use as decoys should be up or you
           might accidentally SYN flood your targets. Also it will be
           pretty easy to determine which host is scanning if only one
           is actually up on the network. You might want to use IP
           addresses instead of names (so the decoy networks don't see
           you in their nameserver logs). Right now random IP address
           generation is only supported with IPv4

           Decoys are used both in the initial host discovery scan
           (using ICMP, SYN, ACK, or whatever) and during the actual
           port scanning phase. Decoys are also used during remote OS
           detection (-O). Decoys do not work with version detection or
           TCP connect scan. When a scan delay is in effect, the delay
           is enforced between each batch of spoofed probes, not between
           each individual probe. Because decoys are sent as a batch all
           at once, they may temporarily violate congestion control

           It is worth noting that using too many decoys may slow your
           scan and potentially even make it less accurate. Also, some
           ISPs will filter out your spoofed packets, but many do not
           restrict spoofed IP packets at all.

       -S IP_Address (Spoof source address)
           In some circumstances, Nmap may not be able to determine your
           source address (Nmap will tell you if this is the case). In
           this situation, use -S with the IP address of the interface
           you wish to send packets through.

           Another possible use of this flag is to spoof the scan to
           make the targets think that someone else is scanning them.
           Imagine a company being repeatedly port scanned by a
           competitor! The -e option and -Pn are generally required for
           this sort of usage. Note that you usually won't receive reply
           packets back (they will be addressed to the IP you are
           spoofing), so Nmap won't produce useful reports.

       -e interface (Use specified interface)
           Tells Nmap what interface to send and receive packets on.
           Nmap should be able to detect this automatically, but it will
           tell you if it cannot.

       --source-port portnumber; -g portnumber (Spoof source port
           One surprisingly common misconfiguration is to trust traffic
           based only on the source port number. It is easy to
           understand how this comes about. An administrator will set up
           a shiny new firewall, only to be flooded with complaints from
           ungrateful users whose applications stopped working. In
           particular, DNS may be broken because the UDP DNS replies
           from external servers can no longer enter the network. FTP is
           another common example. In active FTP transfers, the remote
           server tries to establish a connection back to the client to
           transfer the requested file.

           Secure solutions to these problems exist, often in the form
           of application-level proxies or protocol-parsing firewall
           modules. Unfortunately there are also easier, insecure
           solutions. Noting that DNS replies come from port 53 and
           active FTP from port 20, many administrators have fallen into
           the trap of simply allowing incoming traffic from those
           ports. They often assume that no attacker would notice and
           exploit such firewall holes. In other cases, administrators
           consider this a short-term stop-gap measure until they can
           implement a more secure solution. Then they forget the
           security upgrade.

           Overworked network administrators are not the only ones to
           fall into this trap. Numerous products have shipped with
           these insecure rules. Even Microsoft has been guilty. The
           IPsec filters that shipped with Windows 2000 and Windows XP
           contain an implicit rule that allows all TCP or UDP traffic
           from port 88 (Kerberos). In another well-known case, versions
           of the Zone Alarm personal firewall up to 2.1.25 allowed any
           incoming UDP packets with the source port 53 (DNS) or 67

           Nmap offers the -g and --source-port options (they are
           equivalent) to exploit these weaknesses. Simply provide a
           port number and Nmap will send packets from that port where
           possible. Most scanning operations that use raw sockets,
           including SYN and UDP scans, support the option completely.
           The option notably doesn't have an effect for any operations
           that use normal operating system sockets, including DNS
           requests, TCP connect scan, version detection, and script
           scanning. Setting the source port also doesn't work for OS
           detection, because Nmap must use different port numbers for
           certain OS detection tests to work properly.

       --data hex string (Append custom binary data to sent packets)
           This option lets you include binary data as payload in sent
           packets.  hex string may be specified in any of the following
           formats: 0xAABBCCDDEEFF..., AABBCCDDEEFF...  or
           \xAA\xBB\xCC\xDD\xEE\xFF.... Examples of use are --data
           0xdeadbeef and --data \xCA\xFE\x09. Note that if you specify
           a number like 0x00ff no byte-order conversion is performed.
           Make sure you specify the information in the byte order
           expected by the receiver.

       --data-string string (Append custom string to sent packets)
           This option lets you include a regular string as payload in
           sent packets.  string can contain any string. However, note
           that some characters may depend on your system's locale and
           the receiver may not see the same information. Also, make
           sure you enclose the string in double quotes and escape any
           special characters from the shell. Examples: --data-string
           "Scan conducted by Security Ops, extension 7192" or
           --data-string "Ph34r my l33t skills". Keep in mind that
           nobody is likely to actually see any comments left by this
           option unless they are carefully monitoring the network with
           a sniffer or custom IDS rules.

       --data-length number (Append random data to sent packets)
           Normally Nmap sends minimalist packets containing only a
           header. So its TCP packets are generally 40 bytes and ICMP
           echo requests are just 28. Some UDP ports and IP protocols
           get a custom payload by default. This option tells Nmap to
           append the given number of random bytes to most of the
           packets it sends, and not to use any protocol-specific
           payloads. (Use --data-length 0 for no random or
           protocol-specific payloads.  OS detection (-O) packets are
           not affected because accuracy there requires probe
           consistency, but most pinging and portscan packets support
           this. It slows things down a little, but can make a scan
           slightly less conspicuous.

       --ip-options R|S [route]|L [route]|T|U ... ; --ip-options hex
       string (Send packets with specified ip options)
           The IP protocol[12] offers several options which may be
           placed in packet headers. Unlike the ubiquitous TCP options,
           IP options are rarely seen due to practicality and security
           concerns. In fact, many Internet routers block the most
           dangerous options such as source routing. Yet options can
           still be useful in some cases for determining and
           manipulating the network route to target machines. For
           example, you may be able to use the record route option to
           determine a path to a target even when more traditional
           traceroute-style approaches fail. Or if your packets are
           being dropped by a certain firewall, you may be able to
           specify a different route with the strict or loose source
           routing options.

           The most powerful way to specify IP options is to simply pass
           in values as the argument to --ip-options. Precede each hex
           number with \x then the two digits. You may repeat certain
           characters by following them with an asterisk and then the
           number of times you wish them to repeat. For example,
           \x01\x07\x04\x00*36\x01 is a hex string containing 36 NUL

           Nmap also offers a shortcut mechanism for specifying options.
           Simply pass the letter R, T, or U to request record-route,
           record-timestamp, or both options together, respectively.
           Loose or strict source routing may be specified with an L or
           S followed by a space and then a space-separated list of IP

           If you wish to see the options in packets sent and received,
           specify --packet-trace. For more information and examples of
           using IP options with Nmap, see
           https://seclists.org/nmap-dev/2006/q3/52 .

       --ttl value (Set IP time-to-live field)
           Sets the IPv4 time-to-live field in sent packets to the given

       --randomize-hosts (Randomize target host order)
           Tells Nmap to shuffle each group of up to 16384 hosts before
           it scans them. This can make the scans less obvious to
           various network monitoring systems, especially when you
           combine it with slow timing options. If you want to randomize
           over larger group sizes, increase PING_GROUP_SZ in nmap.h and
           recompile. An alternative solution is to generate the target
           IP list with a list scan (-sL -n -oN filename), randomize it
           with a Perl script, then provide the whole list to Nmap with

       --spoof-mac MAC address, prefix, or vendor name (Spoof MAC
           Asks Nmap to use the given MAC address

           for all of the raw ethernet frames it sends. This option
           implies --send-eth to ensure that Nmap actually sends
           ethernet-level packets. The MAC given can take several
           formats. If it is simply the number 0, Nmap chooses a
           completely random MAC address for the session. If the given
           string is an even number of hex digits (with the pairs
           optionally separated by a colon), Nmap will use those as the
           MAC. If fewer than 12 hex digits are provided, Nmap fills in
           the remainder of the six bytes with random values. If the
           argument isn't a zero or hex string, Nmap looks through
           nmap-mac-prefixes to find a vendor name containing the given
           string (it is case insensitive). If a match is found, Nmap
           uses the vendor's OUI (three-byte prefix) and fills out the
           remaining three bytes randomly. Valid --spoof-mac argument
           examples are Apple, 0, 01:02:03:04:05:06, deadbeefcafe,
           0020F2, and Cisco. This option only affects raw packet scans
           such as SYN scan or OS detection, not connection-oriented
           features such as version detection or the Nmap Scripting

       --proxies Comma-separated list of proxy URLs (Relay TCP
       connections through a chain of proxies)
           Asks Nmap to establish TCP connections with a final target
           through supplied chain of one or more HTTP or SOCKS4 proxies.
           Proxies can help hide the true source of a scan or evade
           certain firewall restrictions, but they can hamper scan
           performance by increasing latency. Users may need to adjust
           Nmap timeouts and other scan parameters accordingly. In
           particular, a lower --max-parallelism may help because some
           proxies refuse to handle as many concurrent connections as
           Nmap opens by default.

           This option takes a list of proxies as argument, expressed as
           URLs in the format proto://host:port. Use commas to separate
           node URLs in a chain. No authentication is supported yet.
           Valid protocols are HTTP and SOCKS4.

           Warning: this feature is still under development and has
           limitations. It is implemented within the nsock library and
           thus has no effect on the ping, port scanning and OS
           discovery phases of a scan. Only NSE and version scan benefit
           from this option so far—other features may disclose your true
           address. SSL connections are not yet supported, nor is
           proxy-side DNS resolution (hostnames are always resolved by

       --badsum (Send packets with bogus TCP/UDP checksums)
           Asks Nmap to use an invalid TCP, UDP or SCTP checksum for
           packets sent to target hosts. Since virtually all host IP
           stacks properly drop these packets, any responses received
           are likely coming from a firewall or IDS that didn't bother
           to verify the checksum. For more details on this technique,
           see https://nmap.org/p60-12.html 

       --adler32 (Use deprecated Adler32 instead of CRC32C for SCTP
           Asks Nmap to use the deprecated Adler32 algorithm for
           calculating the SCTP checksum. If --adler32 is not given,
           CRC-32C (Castagnoli) is used.  RFC 2960[13] originally
           defined Adler32 as checksum algorithm for SCTP; RFC 4960[6]
           later redefined the SCTP checksums to use CRC-32C. Current
           SCTP implementations should be using CRC-32C, but in order to
           elicit responses from old, legacy SCTP implementations, it
           may be preferable to use Adler32.

OUTPUT         top

       Any security tool is only as useful as the output it generates.
       Complex tests and algorithms are of little value if they aren't
       presented in an organized and comprehensible fashion. Given the
       number of ways Nmap is used by people and other software, no
       single format can please everyone. So Nmap offers several
       formats, including the interactive mode for humans to read
       directly and XML for easy parsing by software.

       In addition to offering different output formats, Nmap provides
       options for controlling the verbosity of output as well as
       debugging messages. Output types may be sent to standard output
       or to named files, which Nmap can append to or clobber. Output
       files may also be used to resume aborted scans.

       Nmap makes output available in five different formats. The
       default is called interactive output, and it is sent to standard
       output (stdout).  There is also normal output, which is similar
       to interactive except that it displays less runtime information
       and warnings since it is expected to be analyzed after the scan
       completes rather than interactively.

       XML output is one of the most important output types, as it can
       be converted to HTML, easily parsed by programs such as Nmap
       graphical user interfaces, or imported into databases.

       The two remaining output types are the simple grepable output
       which includes most information for a target host on a single
       line, and sCRiPt KiDDi3 0utPUt for users who consider themselves

       While interactive output is the default and has no associated
       command-line options, the other four format options use the same
       syntax. They take one argument, which is the filename that
       results should be stored in. Multiple formats may be specified,
       but each format may only be specified once. For example, you may
       wish to save normal output for your own review while saving XML
       of the same scan for programmatic analysis. You might do this
       with the options -oX myscan.xml -oN myscan.nmap. While this
       chapter uses the simple names like myscan.xml for brevity, more
       descriptive names are generally recommended. The names chosen are
       a matter of personal preference, though I use long ones that
       incorporate the scan date and a word or two describing the scan,
       placed in a directory named after the company I'm scanning.

       While these options save results to files, Nmap still prints
       interactive output to stdout as usual. For example, the command
       nmap -oX myscan.xml target prints XML to myscan.xml and fills
       standard output with the same interactive results it would have
       printed if -oX wasn't specified at all. You can change this by
       passing a hyphen character as the argument to one of the format
       types. This causes Nmap to deactivate interactive output, and
       instead print results in the format you specified to the standard
       output stream. So the command nmap -oX - target will send only
       XML output to stdout.  Serious errors may still be printed to the
       normal error stream, stderr.

       Unlike some Nmap arguments, the space between the logfile option
       flag (such as -oX) and the filename or hyphen is mandatory. If
       you omit the flags and give arguments such as -oG- or
       -oXscan.xml, a backwards compatibility feature of Nmap will cause
       the creation of normal format output files named G- and Xscan.xml

       All of these arguments support strftime-like conversions in the
       filename.  %H, %M, %S, %m, %d, %y, and %Y are all exactly the
       same as in strftime.  %T is the same as %H%M%S, %R is the same as
       %H%M, and %D is the same as %m%d%y. A % followed by any other
       character just yields that character (%% gives you a percent
       symbol). So -oX 'scan-%T-%D.xml' will use an XML file with a name
       in the form of scan-144840-121307.xml.

       Nmap also offers options to control scan verbosity and to append
       to output files rather than clobbering them. All of these options
       are described below.

       Nmap Output Formats

       -oN filespec (normal output)
           Requests that normal output be directed to the given
           filename. As discussed above, this differs slightly from
           interactive output.

       -oX filespec (XML output)
           Requests that XML output be directed to the given filename.
           Nmap includes a document type definition (DTD) which allows
           XML parsers to validate Nmap XML output. While it is
           primarily intended for programmatic use, it can also help
           humans interpret Nmap XML output. The DTD defines the legal
           elements of the format, and often enumerates the attributes
           and values they can take on. The latest version is always
           available from https://svn.nmap.org/nmap/docs/nmap.dtd .

           XML offers a stable format that is easily parsed by software.
           Free XML parsers are available for all major computer
           languages, including C/C++, Perl, Python, and Java. People
           have even written bindings for most of these languages to
           handle Nmap output and execution specifically. Examples are
           Nmap::Scanner[14] and Nmap::Parser[15] in Perl CPAN. In
           almost all cases that a non-trivial application interfaces
           with Nmap, XML is the preferred format.

           The XML output references an XSL stylesheet which can be used
           to format the results as HTML. The easiest way to use this is
           simply to load the XML output in a web browser such as
           Firefox or IE. By default, this will only work on the machine
           you ran Nmap on (or a similarly configured one) due to the
           hard-coded nmap.xsl filesystem path. Use the --webxml or
           --stylesheet options to create portable XML files that render
           as HTML on any web-connected machine.

       -oS filespec (ScRipT KIdd|3 oUTpuT)
           Script kiddie output is like interactive output, except that
           it is post-processed to better suit the l33t HaXXorZ who
           previously looked down on Nmap due to its consistent
           capitalization and spelling. Humor impaired people should
           note that this option is making fun of the script kiddies
           before flaming me for supposedly “helping them”.

       -oG filespec (grepable output)
           This output format is covered last because it is deprecated.
           The XML output format is far more powerful, and is nearly as
           convenient for experienced users. XML is a standard for which
           dozens of excellent parsers are available, while grepable
           output is my own simple hack. XML is extensible to support
           new Nmap features as they are released, while I often must
           omit those features from grepable output for lack of a place
           to put them.

           Nevertheless, grepable output is still quite popular. It is a
           simple format that lists each host on one line and can be
           trivially searched and parsed with standard Unix tools such
           as grep, awk, cut, sed, diff, and Perl. Even I usually use it
           for one-off tests done at the command line. Finding all the
           hosts with the SSH port open or that are running Solaris
           takes only a simple grep to identify the hosts, piped to an
           awk or cut command to print the desired fields.

           Grepable output consists of comments (lines starting with a
           pound (#)) and target lines. A target line includes a
           combination of six labeled fields, separated by tabs and
           followed with a colon. The fields are Host, Ports, Protocols,
           Ignored State, OS, Seq Index, IP ID, and Status.

           The most important of these fields is generally Ports, which
           gives details on each interesting port. It is a comma
           separated list of port entries. Each port entry represents
           one interesting port, and takes the form of seven slash (/)
           separated subfields. Those subfields are: Port number, State,
           Protocol, Owner, Service, SunRPC info, and Version info.

           As with XML output, this man page does not allow for
           documenting the entire format. A more detailed look at the
           Nmap grepable output format is available from
           https://nmap.org/book/output-formats-grepable-output.html .

       -oA basename (Output to all formats)
           As a convenience, you may specify -oA basename to store scan
           results in normal, XML, and grepable formats at once. They
           are stored in basename.nmap, basename.xml, and
           basename.gnmap, respectively. As with most programs, you can
           prefix the filenames with a directory path, such as
           ~/nmaplogs/foocorp/ on Unix or c:\hacking\sco on Windows.

       Verbosity and debugging options

       -v (Increase verbosity level), -vlevel (Set verbosity level)
           Increases the verbosity level, causing Nmap to print more
           information about the scan in progress. Open ports are shown
           as they are found and completion time estimates are provided
           when Nmap thinks a scan will take more than a few minutes.
           Use it twice or more for even greater verbosity: -vv, or give
           a verbosity level directly, for example -v3.

           Most changes only affect interactive output, and some also
           affect normal and script kiddie output. The other output
           types are meant to be processed by machines, so Nmap can give
           substantial detail by default in those formats without
           fatiguing a human user. However, there are a few changes in
           other modes where output size can be reduced substantially by
           omitting some detail. For example, a comment line in the
           grepable output that provides a list of all ports scanned is
           only printed in verbose mode because it can be quite long.

       -d (Increase debugging level), -dlevel (Set debugging level)
           When even verbose mode doesn't provide sufficient data for
           you, debugging is available to flood you with much more! As
           with the verbosity option (-v), debugging is enabled with a
           command-line flag (-d) and the debug level can be increased
           by specifying it multiple times, as in -dd, or by setting a
           level directly. For example, -d9 sets level nine. That is the
           highest effective level and will produce thousands of lines
           unless you run a very simple scan with very few ports and

           Debugging output is useful when a bug is suspected in Nmap,
           or if you are simply confused as to what Nmap is doing and
           why. As this feature is mostly intended for developers, debug
           lines aren't always self-explanatory. You may get something
           like: Timeout vals: srtt: -1 rttvar: -1 to: 1000000 delta
           14987 ==> srtt: 14987 rttvar: 14987 to: 100000. If you don't
           understand a line, your only recourses are to ignore it, look
           it up in the source code, or request help from the
           development list (nmap-dev).  Some lines are self
           explanatory, but the messages become more obscure as the
           debug level is increased.

       --reason (Host and port state reasons)
           Shows the reason each port is set to a specific state and the
           reason each host is up or down. This option displays the type
           of the packet that determined a port or hosts state. For
           example, A RST packet from a closed port or an echo reply
           from an alive host. The information Nmap can provide is
           determined by the type of scan or ping. The SYN scan and SYN
           ping (-sS and -PS) are very detailed, but the TCP connect
           scan (-sT) is limited by the implementation of the connect
           system call. This feature is automatically enabled by the
           debug option (-d) and the results are stored in XML log files
           even if this option is not specified.

       --stats-every time (Print periodic timing stats)
           Periodically prints a timing status message after each
           interval of time. The time is a specification of the kind
           described in the section called “TIMING AND PERFORMANCE”; so
           for example, use --stats-every 10s to get a status update
           every 10 seconds. Updates are printed to interactive output
           (the screen) and XML output.

       --packet-trace (Trace packets and data sent and received)
           Causes Nmap to print a summary of every packet sent or
           received. This is often used for debugging, but is also a
           valuable way for new users to understand exactly what Nmap is
           doing under the covers. To avoid printing thousands of lines,
           you may want to specify a limited number of ports to scan,
           such as -p20-30. If you only care about the goings on of the
           version detection subsystem, use --version-trace instead. If
           you only care about script tracing, specify --script-trace.
           With --packet-trace, you get all of the above.

       --open (Show only open (or possibly open) ports)
           Sometimes you only care about ports you can actually connect
           to (open ones), and don't want results cluttered with closed,
           filtered, and closed|filtered ports. Output customization is
           normally done after the scan using tools such as grep, awk,
           and Perl, but this feature was added due to overwhelming
           requests. Specify --open to only see hosts with at least one
           open, open|filtered, or unfiltered port, and only see ports
           in those states. These three states are treated just as they
           normally are, which means that open|filtered and unfiltered
           may be condensed into counts if there are an overwhelming
           number of them.

           Beginning with Nmap 7.40, the --open option implies

           --defeat-rst-ratelimit, because that option only affects
           closed and filtered ports, which are hidden by --open.

       --iflist (List interfaces and routes)
           Prints the interface list and system routes as detected by
           Nmap and quits. This is useful for debugging routing problems
           or device mischaracterization (such as Nmap treating a PPP
           connection as ethernet).

       Miscellaneous output options

       --append-output (Append to rather than clobber output files)
           When you specify a filename to an output format flag such as
           -oX or -oN, that file is overwritten by default. If you
           prefer to keep the existing content of the file and append
           the new results, specify the --append-output option. All
           output filenames specified in that Nmap execution will then
           be appended to rather than clobbered. This doesn't work well
           for XML (-oX) scan data as the resultant file generally won't
           parse properly until you fix it up by hand.

       --resume filename (Resume aborted scan)
           Some extensive Nmap runs take a very long time—on the order
           of days. Such scans don't always run to completion.
           Restrictions may prevent Nmap from being run during working
           hours, the network could go down, the machine Nmap is running
           on might suffer a planned or unplanned reboot, or Nmap itself
           could crash. The administrator running Nmap could cancel it
           for any other reason as well, by pressing ctrl-C. Restarting
           the whole scan from the beginning may be undesirable.
           Fortunately, if scan output files were kept, the user can ask
           Nmap to resume scanning with the target it was working on
           when execution ceased. Simply specify the --resume option and
           pass the output file as its argument. No other arguments are
           permitted, as Nmap parses the output file to use the same
           ones specified previously. Simply call Nmap as nmap --resume
           logfilename. Nmap will append new results to the data files
           specified in the previous execution. Scans can be resumed
           from any of the 3 major output formats: Normal, Grepable, or

       --noninteractive (Disable runtime interactions)
           At times, such as when running Nmap in a shell background, it
           might be undesirable for Nmap to monitor and respond to user
           keyboard input when running. (See the section called “RUNTIME
           INTERACTION” about how to control Nmap during a scan.) Use
           option --noninteractive to prevent Nmap taking control of the

       --stylesheet path or URL (Set XSL stylesheet to transform XML
           Nmap ships with an XSL stylesheet named nmap.xsl for viewing
           or translating XML output to HTML.  The XML output includes
           an xml-stylesheet directive which points to nmap.xml where it
           was initially installed by Nmap. Run the XML file through an
           XSLT processor such as xsltproc[16] to produce an HTML file.
           Directly opening the XML file in a browser no longer works
           well because modern browsers limit the locations a stylesheet
           may be loaded from. If you wish to use a different
           stylesheet, specify it as the argument to --stylesheet. You
           must pass the full pathname or URL. One common invocation is
           --stylesheet https://nmap.org/svn/docs/nmap.xsl. This tells
           an XSLT processor to load the latest version of the
           stylesheet from Nmap.Org. The --webxml option does the same
           thing with less typing and memorization. Loading the XSL from
           Nmap.Org makes it easier to view results on a machine that
           doesn't have Nmap (and thus nmap.xsl) installed. So the URL
           is often more useful, but the local filesystem location of
           nmap.xsl is used by default for privacy reasons.

       --webxml (Load stylesheet from Nmap.Org)
           This is a convenience option, nothing more than an alias for
           --stylesheet https://nmap.org/svn/docs/nmap.xsl.

       --no-stylesheet (Omit XSL stylesheet declaration from XML)
           Specify this option to prevent Nmap from associating any XSL
           stylesheet with its XML output. The xml-stylesheet directive
           is omitted.


       This section describes some important (and not-so-important)
       options that don't really fit anywhere else.

       -6 (Enable IPv6 scanning)
           Nmap has IPv6 support for its most popular features. Ping
           scanning, port scanning, version detection, and the Nmap
           Scripting Engine all support IPv6. The command syntax is the
           same as usual except that you also add the -6 option. Of
           course, you must use IPv6 syntax if you specify an address
           rather than a hostname. An address might look like
           3ffe:7501:4819:2000:210:f3ff:fe03:14d0, so hostnames are
           recommended. The output looks the same as usual, with the
           IPv6 address on the “interesting ports” line being the only
           IPv6 giveaway.

           While IPv6 hasn't exactly taken the world by storm, it gets
           significant use in some (usually Asian) countries and most
           modern operating systems support it. To use Nmap with IPv6,
           both the source and target of your scan must be configured
           for IPv6. If your ISP (like most of them) does not allocate
           IPv6 addresses to you, free tunnel brokers are widely
           available and work fine with Nmap. I use the free IPv6 tunnel
           broker service at http://www.tunnelbroker.net . Other tunnel
           brokers are listed at Wikipedia[17]. 6to4 tunnels are another
           popular, free approach.

           On Windows, raw-socket IPv6 scans are supported only on
           ethernet devices (not tunnels), and only on Windows Vista and
           later. Use the --unprivileged option in other situations.

       -A (Aggressive scan options)
           This option enables additional advanced and aggressive
           options. Presently this enables OS detection (-O), version
           scanning (-sV), script scanning (-sC) and traceroute
           (--traceroute).  More features may be added in the future.
           The point is to enable a comprehensive set of scan options
           without people having to remember a large set of flags.
           However, because script scanning with the default set is
           considered intrusive, you should not use -A against target
           networks without permission. This option only enables
           features, and not timing options (such as -T4) or verbosity
           options (-v) that you might want as well. Options which
           require privileges (e.g. root access) such as OS detection
           and traceroute will only be enabled if those privileges are

       --datadir directoryname (Specify custom Nmap data file location)
           Nmap obtains some special data at runtime in files named
           nmap-service-probes, nmap-services, nmap-protocols, nmap-rpc,
           nmap-mac-prefixes, and nmap-os-db. If the location of any of
           these files has been specified (using the --servicedb or
           --versiondb options), that location is used for that file.
           After that, Nmap searches these files in the directory
           specified with the --datadir option (if any). Any files not
           found there, are searched for in the directory specified by
           the NMAPDIR environment variable. Next comes ~/.nmap for real
           and effective UIDs; or on Windows, HOME\AppData\Roaming\nmap
           (where HOME is the user's home directory, like
           C:\Users\user). This is followed by the location of the nmap
           executable and the same location with ../share/nmap appended.
           Then a compiled-in location such as /usr/local/share/nmap or

       --servicedb services file (Specify custom services file)
           Asks Nmap to use the specified services file rather than the
           nmap-services data file that comes with Nmap. Using this
           option also causes a fast scan (-F) to be used. See the
           description for --datadir for more information on Nmap's data

       --versiondb service probes file (Specify custom service probes
           Asks Nmap to use the specified service probes file rather
           than the nmap-service-probes data file that comes with Nmap.
           See the description for --datadir for more information on
           Nmap's data files.

       --send-eth (Use raw ethernet sending)
           Asks Nmap to send packets at the raw ethernet (data link)
           layer rather than the higher IP (network) layer. By default,
           Nmap chooses the one which is generally best for the platform
           it is running on. Raw sockets (IP layer) are generally most
           efficient for Unix machines, while ethernet frames are
           required for Windows operation since Microsoft disabled raw
           socket support. Nmap still uses raw IP packets on Unix
           despite this option when there is no other choice (such as
           non-ethernet connections).

       --send-ip (Send at raw IP level)
           Asks Nmap to send packets via raw IP sockets rather than
           sending lower level ethernet frames. It is the complement to
           the --send-eth option discussed previously.

       --privileged (Assume that the user is fully privileged)
           Tells Nmap to simply assume that it is privileged enough to
           perform raw socket sends, packet sniffing, and similar
           operations that usually require root privileges on Unix
           systems. By default Nmap quits if such operations are
           requested but geteuid is not zero.  --privileged is useful
           with Linux kernel capabilities and similar systems that may
           be configured to allow unprivileged users to perform
           raw-packet scans. Be sure to provide this option flag before
           any flags for options that require privileges (SYN scan, OS
           detection, etc.). The NMAP_PRIVILEGED environment variable
           may be set as an equivalent alternative to --privileged.

       --unprivileged (Assume that the user lacks raw socket privileges)
           This option is the opposite of --privileged. It tells Nmap to
           treat the user as lacking network raw socket and sniffing
           privileges. This is useful for testing, debugging, or when
           the raw network functionality of your operating system is
           somehow broken. The NMAP_UNPRIVILEGED environment variable
           may be set as an equivalent alternative to --unprivileged.

       --release-memory (Release memory before quitting)
           This option is only useful for memory-leak debugging. It
           causes Nmap to release allocated memory just before it quits
           so that actual memory leaks are easier to spot. Normally Nmap
           skips this as the OS does this anyway upon process

       -V; --version (Print version number)
           Prints the Nmap version number and exits.

       -h; --help (Print help summary page)
           Prints a short help screen with the most common command
           flags. Running Nmap without any arguments does the same


       During the execution of Nmap, all key presses are captured. This
       allows you to interact with the program without aborting and
       restarting it. Certain special keys will change options, while
       any other keys will print out a status message telling you about
       the scan. The convention is that lowercase letters increase the
       amount of printing, and uppercase letters decrease the printing.
       You may also press ‘?’ for help.

       v / V
           Increase / decrease the verbosity level

       d / D
           Increase / decrease the debugging Level

       p / P
           Turn on / off packet tracing

           Print a runtime interaction help screen

       Anything else
           Print out a status message like this:

               Stats: 0:00:07 elapsed; 20 hosts completed (1 up), 1 undergoing Service Scan
               Service scan Timing: About 33.33% done; ETC: 20:57 (0:00:12 remaining)

EXAMPLES         top

       Here are some Nmap usage examples, from the simple and routine to
       a little more complex and esoteric. Some actual IP addresses and
       domain names are used to make things more concrete. In their
       place you should substitute addresses/names from your own
       network. While I don't think port scanning other networks is or
       should be illegal, some network administrators don't appreciate
       unsolicited scanning of their networks and may complain. Getting
       permission first is the best approach.

       For testing purposes, you have permission to scan the host
       scanme.nmap.org.  This permission only includes scanning via Nmap
       and not testing exploits or denial of service attacks. To
       conserve bandwidth, please do not initiate more than a dozen
       scans against that host per day. If this free scanning target
       service is abused, it will be taken down and Nmap will report
       Failed to resolve given hostname/IP: scanme.nmap.org. These
       permissions also apply to the hosts scanme2.nmap.org,
       scanme3.nmap.org, and so on, though those hosts do not currently

       nmap -v scanme.nmap.org

       This option scans all reserved TCP ports on the machine
       scanme.nmap.org . The -v option enables verbose mode.

       nmap -sS -O scanme.nmap.org/24

       Launches a stealth SYN scan against each machine that is up out
       of the 256 IPs on the /24 sized network where Scanme resides. It
       also tries to determine what operating system is running on each
       host that is up and running. This requires root privileges
       because of the SYN scan and OS detection.

       nmap -sV -p 22,53,110,143,4564 198.116.0-255.1-127

       Launches host enumeration and a TCP scan at the first half of
       each of the 255 possible eight-bit subnets in the
       address space. This tests whether the systems run SSH, DNS, POP3,
       or IMAP on their standard ports, or anything on port 4564. For
       any of these ports found open, version detection is used to
       determine what application is running.

       nmap -v -iR 100000 -Pn -p 80

       Asks Nmap to choose 100,000 hosts at random and scan them for web
       servers (port 80). Host enumeration is disabled with -Pn since
       first sending a couple probes to determine whether a host is up
       is wasteful when you are only probing one port on each target
       host anyway.

       nmap -Pn -p80 -oX logs/pb-port80scan.xml -oG

       This scans 4096 IPs for any web servers (without pinging them)
       and saves the output in grepable and XML formats.

NMAP BOOK         top

       While this reference guide details all material Nmap options, it
       can't fully demonstrate how to apply those features to quickly
       solve real-world tasks. For that, we released Nmap Network
       Scanning: The Official Nmap Project Guide to Network Discovery
       and Security Scanning.  Topics include subverting firewalls and
       intrusion detection systems, optimizing Nmap performance, and
       automating common networking tasks with the Nmap Scripting
       Engine. Hints and instructions are provided for common Nmap tasks
       such as taking network inventory, penetration testing, detecting
       rogue wireless access points, and quashing network worm
       outbreaks. Examples and diagrams show actual communication on the
       wire. More than half of the book is available free online. See
       https://nmap.org/book for more information.

BUGS         top

       Like its author, Nmap isn't perfect. But you can help make it
       better by sending bug reports or even writing patches. If Nmap
       doesn't behave the way you expect, first upgrade to the latest
       version available from https://nmap.org . If the problem persists,
       do some research to determine whether it has already been
       discovered and addressed. Try searching for the problem or error
       message on Google since that aggregates so many forums. If
       nothing comes of this, create an Issue on our tracker (‐
       http://issues.nmap.org ) and/or mail a bug report to
       <dev@nmap.org>. If you subscribe to the nmap-dev list before
       posting, your message will bypass moderation and get through more
       quickly. Subscribe at https://nmap.org/mailman/listinfo/dev .
       Please include everything you have learned about the problem, as
       well as what version of Nmap you are using and what operating
       system version it is running on. Other suggestions for improving
       Nmap may be sent to the Nmap dev mailing list as well.

       If you are able to write a patch improving Nmap or fixing a bug,
       that is even better! Instructions for submitting patches or git
       pull requests are available from

       Particularly sensitive issues such as a security reports may be
       sent directly to Nmap's author Fyodor directly at
       <fyodor@nmap.org>. All other reports and comments should use the
       dev list or issue tracker instead because more people read,
       follow, and respond to those.

AUTHORS         top

       Gordon “Fyodor” Lyon <fyodor@nmap.org> wrote and released Nmap in
       1997. Since then, hundreds of people have made valuable
       contributions, as detailed in the CHANGELOG file distributed with
       Nmap and also available from https://nmap.org/changelog.html .
       David Fifield and Daniel Miller deserve special recognition for
       their enormous multi-year contributions!

LEGAL NOTICES         top

   Nmap Copyright and Licensing
       The Nmap Security Scanner is (C) 1996–2022 Nmap Software LLC
       ("The Nmap Project"). Nmap is also a registered trademark of the
       Nmap Project. It is published under the Nmap Public Source
       License[18]. This generally allows end users to download and use
       Nmap for free. It doesn't allow Nmap to be used and redistributed
       within commercial software or hardware products (including
       appliances, virtual machines, and traditional applications). We
       fund the project by selling a special Nmap OEM Edition for this
       purpose, as described at https://nmap.org/oem . Hundreds of large
       and small software vendors have already purchased OEM licenses to
       embed Nmap technology such as host discovery, port scanning, OS
       detection, version detection, and the Nmap Scripting Engine
       within their products.

       The Nmap Project has permission to redistribute Npcap, a packet
       capturing driver and library for the Microsoft Windows platform.
       Npcap is a separate work with it's own license rather than this
       Nmap license. Since the Npcap license does not permit
       redistribution without special permission, our Nmap Windows
       binary packages which contain Npcap may not be redistributed
       without special permission.

       Even though the NPSL is based on GPLv2, it contains different
       provisions and is not directly compatible. It is incompatible
       with some other open source licenses as well. In some cases we
       can relicense portions of Nmap or grant special permissions to
       use it in other open source software. Please contact
       fyodor@nmap.org with any such requests. Similarly, we don't
       incorporate incompatible open source software into Nmap without
       special permission from the copyright holders.

       If you have received a written license agreement or contract for
       Nmap (such as an Nmap OEM license[19]) stating terms other than
       these, you may choose to use and redistribute Nmap under those
       terms instead.

   Creative Commons License for this Nmap Guide
       This Nmap Reference Guide is (C) 2005–2022 Nmap Software LLC. It
       is hereby placed under version 3.0 of the Creative Commons
       Attribution License[20]. This allows you redistribute and modify
       the work as you desire, as long as you credit the original
       source. Alternatively, you may choose to treat this document as
       falling under the same license as Nmap itself (discussed

   Source Code Availability and Community Contributions
       Source is provided to this software because we believe users have
       a right to know exactly what a program is going to do before they
       run it. This also allows you to audit the software for security

       Source code also allows you to port Nmap to new platforms, fix
       bugs, and add new features. You are highly encouraged to submit
       your changes as Github Pull Requests (PR) or send them to
       <dev@nmap.org> for possible incorporation into the main
       distribution. By submitting such changes, it is assumed that you
       are offering the Nmap Project the unlimited, non-exclusive right
       to reuse, modify, and relicense the code. This is important
       because the inability to relicense code has caused devastating
       problems for other Free Software projects (such as KDE and NASM).
       We also sell commercial licenses to Nmap OEM[21]. If you wish to
       specify special license conditions of your contributions, just
       say so when you send them.

   No Warranty
       This program is distributed in the hope that it will be useful,
       but WITHOUT ANY WARRANTY; without even the implied warranty of

       It should also be noted that Nmap has occasionally been known to
       crash poorly written applications, TCP/IP stacks, and even
       operating systems.  While this is extremely rare, it is important
       to keep in mind.  Nmap should never be run against mission
       critical systems unless you are prepared to suffer downtime. We
       acknowledge here that Nmap may crash your systems or networks and
       we disclaim all liability for any damage or problems Nmap could

   Inappropriate Usage
       Because of the slight risk of crashes and because a few black
       hats like to use Nmap for reconnaissance prior to attacking
       systems, there are administrators who become upset and may
       complain when their system is scanned. Thus, it is often
       advisable to request permission before doing even a light scan of
       a network.

       Nmap should never be installed with special privileges (e.g. suid
       root).  That would open up a major security vulnerability as
       other users on the system (or attackers) could use it for
       privilege escalation.

       Nmap is not designed, manufactured, or intended for use in
       hazardous environments requiring fail- safe performance where the
       failure of the software could lead directly to death, personal
       injury, or significant physical or environmental damage.

   Third-Party Software and Funding Notices
       This product includes software developed by the Apache Software
       Foundation[22]. A modified version of the Libpcap portable packet
       capture library[23] is distributed along with Nmap. The Windows
       version of Nmap utilizes the Libpcap-derived Ncap library[24]
       instead. Regular expression support is provided by the PCRE
       library[25], which is open-source software, written by Philip
       Hazel.  Certain raw networking functions use the Libdnet[26]
       networking library, which was written by Dug Song.  A modified
       version is distributed with Nmap. Nmap can optionally link with
       the OpenSSL cryptography toolkit[27] for SSL version detection
       support. The Nmap Scripting Engine uses an embedded version of
       the Lua programming language[10].  The Liblinear linear
       classification library[28] is used for our IPv6 OS detection
       machine learning techniques[29].

       All of the third-party software described in this paragraph is
       freely redistributable under BSD-style software licenses.

       Binary packages for Windows and Mac OS X include support
       libraries necessary to run Zenmap and Ndiff with Python and
       PyGTK. (Unix platforms commonly make these libraries easy to
       install, so they are not part of the packages.) A listing of
       these support libraries and their licenses is included in the
       LICENSES files.

       This software was supported in part through the Google Summer of
       Code[30] and the DARPA CINDER program[31] (DARPA-BAA-10-84).

   United States Export Control
       Nmap only uses encryption when compiled with the optional OpenSSL
       support and linked with OpenSSL. When compiled without OpenSSL
       support, the Nmap Project believes that Nmap is not subject to
       U.S.  Export Administration Regulations (EAR)[32] export control.
       As such, there is no applicable ECCN (export control
       classification number) and exportation does not require any
       special license, permit, or other governmental authorization.

       When compiled with OpenSSL support or distributed as source code,
       the Nmap Project believes that Nmap falls under U.S. ECCN
       5D002[33] (“Information Security Software”). We distribute Nmap
       under the TSU exception for publicly available encryption
       software defined in EAR 740.13(e)[34].

NOTES         top

        1. Nmap Network Scanning: The Official Nmap Project Guide to
           Network Discovery and Security Scanning

        2. RFC 1122

        3. RFC 792

        4. RFC 950

        5. UDP

        6. SCTP

        7. TCP RFC

        8. RFC 959

        9. RFC 1323

       10. Lua programming language

       11. precedence

       12. IP protocol

       13. RFC 2960

       14. Nmap::Scanner

       15. Nmap::Parser

       16. xsltproc

       17. listed at Wikipedia

       18. Nmap Public Source License

       19. Nmap OEM license

       20. Creative Commons Attribution License

       21. Nmap OEM

       22. Apache Software Foundation

       23. Libpcap portable packet capture library

       24. Ncap library

       25. PCRE library

       26. Libdnet

       27. OpenSSL cryptography toolkit

       28. Liblinear linear classification library

       29. IPv6 OS detection machine learning techniques

       30. Google Summer of Code

       31. DARPA CINDER program

       32. Export Administration Regulations (EAR)

       33. 5D002

       34. EAR 740.13(e)

COLOPHON         top

       This page is part of the nmap (a network scanner) project.
       Information about the project can be found at ⟨http://nmap.org/⟩.
       If you have a bug report for this manual page, send it to
       dev@nmap.org.  This page was obtained from the project's upstream
       Git mirror of the Subversion repository
       ⟨https://github.com/nmap/nmap⟩ on 2023-12-22.  (At that time, the
       date of the most recent commit that was found in the repository
       was 2023-12-14.)  If you discover any rendering problems in this
       HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to

Nmap                           05/17/2023                        NMAP(1)