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NAME | DESCRIPTION | PATTERNS | TOKENS | ENVIRONMENT VARIABLES | FILES | SEE ALSO | AUTHORS | COLOPHON |
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SSH_CONFIG(5) File Formats Manual SSH_CONFIG(5)
ssh_config — OpenSSH client configuration file
ssh(1) obtains configuration data from the following sources in
the following order:
1. command-line options
2. user's configuration file (~/.ssh/config)
3. system-wide configuration file (/etc/ssh/ssh_config)
Unless noted otherwise, for each parameter, the first obtained
value will be used. The configuration files contain sections
separated by Host specifications, and that section is only applied
for hosts that match one of the patterns given in the
specification. The matched host name is usually the one given on
the command line (see the CanonicalizeHostname option for
exceptions).
Since the first obtained value for each parameter is used, more
host-specific declarations should be given near the beginning of
the file, and general defaults at the end.
The file contains keyword-argument pairs, one per line. Lines
starting with ‘#’ and empty lines are interpreted as comments.
Arguments may optionally be enclosed in double quotes (") in order
to represent arguments containing spaces. Configuration options
may be separated by whitespace or optional whitespace and exactly
one ‘=’; the latter format is useful to avoid the need to quote
whitespace when specifying configuration options using the ssh,
scp, and sftp -o option.
The possible keywords and their meanings are as follows (note that
keywords are case-insensitive and arguments are case-sensitive):
Host Restricts the following declarations (up to the next Host
or Match keyword) to be only for those hosts that match
one of the patterns given after the keyword. If more than
one pattern is provided, they should be separated by
whitespace. A single ‘*’ as a pattern can be used to
provide global defaults for all hosts. The host is
usually the hostname argument given on the command line
(see the CanonicalizeHostname keyword for exceptions).
A pattern entry may be negated by prefixing it with an
exclamation mark (‘!’). If a negated entry is matched,
then the Host entry is ignored, regardless of whether any
other patterns on the line match. Negated matches are
therefore useful to provide exceptions for wildcard
matches.
See “PATTERNS” for more information on patterns.
Match Restricts the following declarations (up to the next Host
or Match keyword) to be used only when the conditions
following the Match keyword are satisfied. Match
conditions are specified using one or more criteria or the
single token all which always matches. The available
criteria keywords are: canonical, final, exec,
localnetwork, host, originalhost, tagged, user, and
localuser. The all criteria must appear alone or
immediately after canonical or final. Other criteria may
be combined arbitrarily. All criteria but all, canonical,
and final require an argument. Criteria may be negated by
prepending an exclamation mark (‘!’).
The canonical keyword matches only when the configuration
file is being re-parsed after hostname canonicalization
(see the CanonicalizeHostname option). This may be useful
to specify conditions that work with canonical host names
only.
The final keyword requests that the configuration be re-
parsed (regardless of whether CanonicalizeHostname is
enabled), and matches only during this final pass. If
CanonicalizeHostname is enabled, then canonical and final
match during the same pass.
The exec keyword executes the specified command under the
user's shell. If the command returns a zero exit status
then the condition is considered true. Commands
containing whitespace characters must be quoted.
Arguments to exec accept the tokens described in the
“TOKENS” section.
The localnetwork keyword matches the addresses of active
local network interfaces against the supplied list of
networks in CIDR format. This may be convenient for
varying the effective configuration on devices that roam
between networks. Note that network address is not a
trustworthy criteria in many situations (e.g. when the
network is automatically configured using DHCP) and so
caution should be applied if using it to control security-
sensitive configuration.
The other keywords' criteria must be single entries or
comma-separated lists and may use the wildcard and
negation operators described in the “PATTERNS” section.
The criteria for the host keyword are matched against the
target hostname, after any substitution by the Hostname or
CanonicalizeHostname options. The originalhost keyword
matches against the hostname as it was specified on the
command-line. The tagged keyword matches a tag name
specified by a prior Tag directive or on the ssh(1)
command-line using the -P flag. The user keyword matches
against the target username on the remote host. The
localuser keyword matches against the name of the local
user running ssh(1) (this keyword may be useful in system-
wide ssh_config files).
AddKeysToAgent
Specifies whether keys should be automatically added to a
running ssh-agent(1). If this option is set to yes and a
key is loaded from a file, the key and its passphrase are
added to the agent with the default lifetime, as if by
ssh-add(1). If this option is set to ask, ssh(1) will
require confirmation using the SSH_ASKPASS program before
adding a key (see ssh-add(1) for details). If this option
is set to confirm, each use of the key must be confirmed,
as if the -c option was specified to ssh-add(1). If this
option is set to no, no keys are added to the agent.
Alternately, this option may be specified as a time
interval using the format described in the “TIME FORMATS”
section of sshd_config(5) to specify the key's lifetime in
ssh-agent(1), after which it will automatically be
removed. The argument must be no (the default), yes,
confirm (optionally followed by a time interval), ask or a
time interval.
AddressFamily
Specifies which address family to use when connecting.
Valid arguments are any (the default), inet (use IPv4
only), or inet6 (use IPv6 only).
BatchMode
If set to yes, user interaction such as password prompts
and host key confirmation requests will be disabled. This
option is useful in scripts and other batch jobs where no
user is present to interact with ssh(1). The argument
must be yes or no (the default).
BindAddress
Use the specified address on the local machine as the
source address of the connection. Only useful on systems
with more than one address.
BindInterface
Use the address of the specified interface on the local
machine as the source address of the connection.
CanonicalDomains
When CanonicalizeHostname is enabled, this option
specifies the list of domain suffixes in which to search
for the specified destination host.
CanonicalizeFallbackLocal
Specifies whether to fail with an error when hostname
canonicalization fails. The default, yes, will attempt to
look up the unqualified hostname using the system
resolver's search rules. A value of no will cause ssh(1)
to fail instantly if CanonicalizeHostname is enabled and
the target hostname cannot be found in any of the domains
specified by CanonicalDomains.
CanonicalizeHostname
Controls whether explicit hostname canonicalization is
performed. The default, no, is not to perform any name
rewriting and let the system resolver handle all hostname
lookups. If set to yes then, for connections that do not
use a ProxyCommand or ProxyJump, ssh(1) will attempt to
canonicalize the hostname specified on the command line
using the CanonicalDomains suffixes and
CanonicalizePermittedCNAMEs rules. If
CanonicalizeHostname is set to always, then
canonicalization is applied to proxied connections too.
If this option is enabled, then the configuration files
are processed again using the new target name to pick up
any new configuration in matching Host and Match stanzas.
A value of none disables the use of a ProxyJump host.
CanonicalizeMaxDots
Specifies the maximum number of dot characters in a
hostname before canonicalization is disabled. The
default, 1, allows a single dot (i.e. hostname.subdomain).
CanonicalizePermittedCNAMEs
Specifies rules to determine whether CNAMEs should be
followed when canonicalizing hostnames. The rules consist
of one or more arguments of
source_domain_list:target_domain_list, where
source_domain_list is a pattern-list of domains that may
follow CNAMEs in canonicalization, and target_domain_list
is a pattern-list of domains that they may resolve to.
For example,
"*.a.example.com:*.b.example.com,*.c.example.com" will
allow hostnames matching "*.a.example.com" to be
canonicalized to names in the "*.b.example.com" or
"*.c.example.com" domains.
A single argument of "none" causes no CNAMEs to be
considered for canonicalization. This is the default
behaviour.
CASignatureAlgorithms
Specifies which algorithms are allowed for signing of
certificates by certificate authorities (CAs). The
default is:
ssh-ed25519,ecdsa-sha2-nistp256,
ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
sk-ssh-ed25519@openssh.com,
sk-ecdsa-sha2-nistp256@openssh.com,
rsa-sha2-512,rsa-sha2-256
If the specified list begins with a ‘+’ character, then
the specified algorithms will be appended to the default
set instead of replacing them. If the specified list
begins with a ‘-’ character, then the specified algorithms
(including wildcards) will be removed from the default set
instead of replacing them.
ssh(1) will not accept host certificates signed using
algorithms other than those specified.
CertificateFile
Specifies a file from which the user's certificate is
read. A corresponding private key must be provided
separately in order to use this certificate either from an
IdentityFile directive or -i flag to ssh(1), via
ssh-agent(1), or via a PKCS11Provider or
SecurityKeyProvider.
Arguments to CertificateFile may use the tilde syntax to
refer to a user's home directory, the tokens described in
the “TOKENS” section and environment variables as
described in the “ENVIRONMENT VARIABLES” section.
It is possible to have multiple certificate files
specified in configuration files; these certificates will
be tried in sequence. Multiple CertificateFile directives
will add to the list of certificates used for
authentication.
ChannelTimeout
Specifies whether and how quickly ssh(1) should close
inactive channels. Timeouts are specified as one or more
“type=interval” pairs separated by whitespace, where the
“type” must be the special keyword “global” or a channel
type name from the list below, optionally containing
wildcard characters.
The timeout value “interval” is specified in seconds or
may use any of the units documented in the “TIME FORMATS”
section. For example, “session=5m” would cause
interactive sessions to terminate after five minutes of
inactivity. Specifying a zero value disables the
inactivity timeout.
The special timeout “global” applies to all active
channels, taken together. Traffic on any active channel
will reset the timeout, but when the timeout expires then
all open channels will be closed. Note that this global
timeout is not matched by wildcards and must be specified
explicitly.
The available channel type names include:
agent-connection
Open connections to ssh-agent(1).
direct-tcpip, direct-streamlocal@openssh.com
Open TCP or Unix socket (respectively) connections
that have been established from a ssh(1) local
forwarding, i.e. LocalForward or DynamicForward.
forwarded-tcpip, forwarded-streamlocal@openssh.com
Open TCP or Unix socket (respectively) connections
that have been established to a sshd(8) listening
on behalf of a ssh(1) remote forwarding, i.e.
RemoteForward.
session
The interactive main session, including shell
session, command execution, scp(1), sftp(1), etc.
tun-connection
Open TunnelForward connections.
x11-connection
Open X11 forwarding sessions.
Note that in all the above cases, terminating an inactive
session does not guarantee to remove all resources
associated with the session, e.g. shell processes or X11
clients relating to the session may continue to execute.
Moreover, terminating an inactive channel or session does
not necessarily close the SSH connection, nor does it
prevent a client from requesting another channel of the
same type. In particular, expiring an inactive forwarding
session does not prevent another identical forwarding from
being subsequently created.
The default is not to expire channels of any type for
inactivity.
CheckHostIP
If set to yes, ssh(1) will additionally check the host IP
address in the known_hosts file. This allows it to detect
if a host key changed due to DNS spoofing and will add
addresses of destination hosts to ~/.ssh/known_hosts in
the process, regardless of the setting of
StrictHostKeyChecking. If the option is set to no (the
default), the check will not be executed.
Ciphers
Specifies the ciphers allowed and their order of
preference. Multiple ciphers must be comma-separated. If
the specified list begins with a ‘+’ character, then the
specified ciphers will be appended to the default set
instead of replacing them. If the specified list begins
with a ‘-’ character, then the specified ciphers
(including wildcards) will be removed from the default set
instead of replacing them. If the specified list begins
with a ‘^’ character, then the specified ciphers will be
placed at the head of the default set.
The supported ciphers are:
3des-cbc
aes128-cbc
aes192-cbc
aes256-cbc
aes128-ctr
aes192-ctr
aes256-ctr
aes128-gcm@openssh.com
aes256-gcm@openssh.com
chacha20-poly1305@openssh.com
The default is:
chacha20-poly1305@openssh.com,
aes128-ctr,aes192-ctr,aes256-ctr,
aes128-gcm@openssh.com,aes256-gcm@openssh.com
The list of available ciphers may also be obtained using
"ssh -Q cipher".
ClearAllForwardings
Specifies that all local, remote, and dynamic port
forwardings specified in the configuration files or on the
command line be cleared. This option is primarily useful
when used from the ssh(1) command line to clear port
forwardings set in configuration files, and is
automatically set by scp(1) and sftp(1). The argument
must be yes or no (the default).
Compression
Specifies whether to use compression. The argument must
be yes or no (the default).
ConnectionAttempts
Specifies the number of tries (one per second) to make
before exiting. The argument must be an integer. This
may be useful in scripts if the connection sometimes
fails. The default is 1.
ConnectTimeout
Specifies the timeout (in seconds) used when connecting to
the SSH server, instead of using the default system TCP
timeout. This timeout is applied both to establishing the
connection and to performing the initial SSH protocol
handshake and key exchange.
ControlMaster
Enables the sharing of multiple sessions over a single
network connection. When set to yes, ssh(1) will listen
for connections on a control socket specified using the
ControlPath argument. Additional sessions can connect to
this socket using the same ControlPath with ControlMaster
set to no (the default). These sessions will try to reuse
the master instance's network connection rather than
initiating new ones, but will fall back to connecting
normally if the control socket does not exist, or is not
listening.
Setting this to ask will cause ssh(1) to listen for
control connections, but require confirmation using
ssh-askpass(1). If the ControlPath cannot be opened,
ssh(1) will continue without connecting to a master
instance.
X11 and ssh-agent(1) forwarding is supported over these
multiplexed connections, however the display and agent
forwarded will be the one belonging to the master
connection i.e. it is not possible to forward multiple
displays or agents.
Two additional options allow for opportunistic
multiplexing: try to use a master connection but fall back
to creating a new one if one does not already exist.
These options are: auto and autoask. The latter requires
confirmation like the ask option.
ControlPath
Specify the path to the control socket used for connection
sharing as described in the ControlMaster section above or
the string none to disable connection sharing. Arguments
to ControlPath may use the tilde syntax to refer to a
user's home directory, the tokens described in the
“TOKENS” section and environment variables as described in
the “ENVIRONMENT VARIABLES” section. It is recommended
that any ControlPath used for opportunistic connection
sharing include at least %h, %p, and %r (or alternatively
%C) and be placed in a directory that is not writable by
other users. This ensures that shared connections are
uniquely identified.
ControlPersist
When used in conjunction with ControlMaster, specifies
that the master connection should remain open in the
background (waiting for future client connections) after
the initial client connection has been closed. If set to
no (the default), then the master connection will not be
placed into the background, and will close as soon as the
initial client connection is closed. If set to yes or 0,
then the master connection will remain in the background
indefinitely (until killed or closed via a mechanism such
as the "ssh -O exit"). If set to a time in seconds, or a
time in any of the formats documented in sshd_config(5),
then the backgrounded master connection will automatically
terminate after it has remained idle (with no client
connections) for the specified time.
DynamicForward
Specifies that a TCP port on the local machine be
forwarded over the secure channel, and the application
protocol is then used to determine where to connect to
from the remote machine.
The argument must be [bind_address:]port. IPv6 addresses
can be specified by enclosing addresses in square
brackets. By default, the local port is bound in
accordance with the GatewayPorts setting. However, an
explicit bind_address may be used to bind the connection
to a specific address. The bind_address of localhost
indicates that the listening port be bound for local use
only, while an empty address or ‘*’ indicates that the
port should be available from all interfaces.
Currently the SOCKS4 and SOCKS5 protocols are supported,
and ssh(1) will act as a SOCKS server. Multiple
forwardings may be specified, and additional forwardings
can be given on the command line. Only the superuser can
forward privileged ports.
EnableEscapeCommandline
Enables the command line option in the EscapeChar menu for
interactive sessions (default ‘~C’). By default, the
command line is disabled.
EnableSSHKeysign
Setting this option to yes in the global client
configuration file /etc/ssh/ssh_config enables the use of
the helper program ssh-keysign(8) during
HostbasedAuthentication. The argument must be yes or no
(the default). This option should be placed in the non-
hostspecific section. See ssh-keysign(8) for more
information.
EscapeChar
Sets the escape character (default: ‘~’). The escape
character can also be set on the command line. The
argument should be a single character, ‘^’ followed by a
letter, or none to disable the escape character entirely
(making the connection transparent for binary data).
ExitOnForwardFailure
Specifies whether ssh(1) should terminate the connection
if it cannot set up all requested dynamic, tunnel, local,
and remote port forwardings, (e.g. if either end is unable
to bind and listen on a specified port). Note that
ExitOnForwardFailure does not apply to connections made
over port forwardings and will not, for example, cause
ssh(1) to exit if TCP connections to the ultimate
forwarding destination fail. The argument must be yes or
no (the default).
FingerprintHash
Specifies the hash algorithm used when displaying key
fingerprints. Valid options are: md5 and sha256 (the
default).
ForkAfterAuthentication
Requests ssh to go to background just before command
execution. This is useful if ssh is going to ask for
passwords or passphrases, but the user wants it in the
background. This implies the StdinNull configuration
option being set to “yes”. The recommended way to start
X11 programs at a remote site is with something like ssh
-f host xterm, which is the same as ssh host xterm if the
ForkAfterAuthentication configuration option is set to
“yes”.
If the ExitOnForwardFailure configuration option is set to
“yes”, then a client started with the
ForkAfterAuthentication configuration option being set to
“yes” will wait for all remote port forwards to be
successfully established before placing itself in the
background. The argument to this keyword must be yes
(same as the -f option) or no (the default).
ForwardAgent
Specifies whether the connection to the authentication
agent (if any) will be forwarded to the remote machine.
The argument may be yes, no (the default), an explicit
path to an agent socket or the name of an environment
variable (beginning with ‘$’) in which to find the path.
Agent forwarding should be enabled with caution. Users
with the ability to bypass file permissions on the remote
host (for the agent's Unix-domain socket) can access the
local agent through the forwarded connection. An attacker
cannot obtain key material from the agent, however they
can perform operations on the keys that enable them to
authenticate using the identities loaded into the agent.
ForwardX11
Specifies whether X11 connections will be automatically
redirected over the secure channel and DISPLAY set. The
argument must be yes or no (the default).
X11 forwarding should be enabled with caution. Users with
the ability to bypass file permissions on the remote host
(for the user's X11 authorization database) can access the
local X11 display through the forwarded connection. An
attacker may then be able to perform activities such as
keystroke monitoring if the ForwardX11Trusted option is
also enabled.
ForwardX11Timeout
Specify a timeout for untrusted X11 forwarding using the
format described in the “TIME FORMATS” section of
sshd_config(5). X11 connections received by ssh(1) after
this time will be refused. Setting ForwardX11Timeout to
zero will disable the timeout and permit X11 forwarding
for the life of the connection. The default is to disable
untrusted X11 forwarding after twenty minutes has elapsed.
ForwardX11Trusted
If this option is set to yes, remote X11 clients will have
full access to the original X11 display.
If this option is set to no (the default), remote X11
clients will be considered untrusted and prevented from
stealing or tampering with data belonging to trusted X11
clients. Furthermore, the xauth(1) token used for the
session will be set to expire after 20 minutes. Remote
clients will be refused access after this time.
See the X11 SECURITY extension specification for full
details on the restrictions imposed on untrusted clients.
GatewayPorts
Specifies whether remote hosts are allowed to connect to
local forwarded ports. By default, ssh(1) binds local
port forwardings to the loopback address. This prevents
other remote hosts from connecting to forwarded ports.
GatewayPorts can be used to specify that ssh should bind
local port forwardings to the wildcard address, thus
allowing remote hosts to connect to forwarded ports. The
argument must be yes or no (the default).
GlobalKnownHostsFile
Specifies one or more files to use for the global host key
database, separated by whitespace. The default is
/etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
GSSAPIAuthentication
Specifies whether user authentication based on GSSAPI is
allowed. The default is no.
GSSAPIDelegateCredentials
Forward (delegate) credentials to the server. The default
is no.
HashKnownHosts
Indicates that ssh(1) should hash host names and addresses
when they are added to ~/.ssh/known_hosts. These hashed
names may be used normally by ssh(1) and sshd(8), but they
do not visually reveal identifying information if the
file's contents are disclosed. The default is no. Note
that existing names and addresses in known hosts files
will not be converted automatically, but may be manually
hashed using ssh-keygen(1).
HostbasedAcceptedAlgorithms
Specifies the signature algorithms that will be used for
hostbased authentication as a comma-separated list of
patterns. Alternately if the specified list begins with a
‘+’ character, then the specified signature algorithms
will be appended to the default set instead of replacing
them. If the specified list begins with a ‘-’ character,
then the specified signature algorithms (including
wildcards) will be removed from the default set instead of
replacing them. If the specified list begins with a ‘^’
character, then the specified signature algorithms will be
placed at the head of the default set. The default for
this option is:
ssh-ed25519-cert-v01@openssh.com,
ecdsa-sha2-nistp256-cert-v01@openssh.com,
ecdsa-sha2-nistp384-cert-v01@openssh.com,
ecdsa-sha2-nistp521-cert-v01@openssh.com,
sk-ssh-ed25519-cert-v01@openssh.com,
sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
rsa-sha2-512-cert-v01@openssh.com,
rsa-sha2-256-cert-v01@openssh.com,
ssh-ed25519,
ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
sk-ssh-ed25519@openssh.com,
sk-ecdsa-sha2-nistp256@openssh.com,
rsa-sha2-512,rsa-sha2-256
The -Q option of ssh(1) may be used to list supported
signature algorithms. This was formerly named
HostbasedKeyTypes.
HostbasedAuthentication
Specifies whether to try rhosts based authentication with
public key authentication. The argument must be yes or no
(the default).
HostKeyAlgorithms
Specifies the host key signature algorithms that the
client wants to use in order of preference. Alternately
if the specified list begins with a ‘+’ character, then
the specified signature algorithms will be appended to the
default set instead of replacing them. If the specified
list begins with a ‘-’ character, then the specified
signature algorithms (including wildcards) will be removed
from the default set instead of replacing them. If the
specified list begins with a ‘^’ character, then the
specified signature algorithms will be placed at the head
of the default set. The default for this option is:
ssh-ed25519-cert-v01@openssh.com,
ecdsa-sha2-nistp256-cert-v01@openssh.com,
ecdsa-sha2-nistp384-cert-v01@openssh.com,
ecdsa-sha2-nistp521-cert-v01@openssh.com,
sk-ssh-ed25519-cert-v01@openssh.com,
sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
rsa-sha2-512-cert-v01@openssh.com,
rsa-sha2-256-cert-v01@openssh.com,
ssh-ed25519,
ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
sk-ecdsa-sha2-nistp256@openssh.com,
sk-ssh-ed25519@openssh.com,
rsa-sha2-512,rsa-sha2-256
If hostkeys are known for the destination host then this
default is modified to prefer their algorithms.
The list of available signature algorithms may also be
obtained using "ssh -Q HostKeyAlgorithms".
HostKeyAlias
Specifies an alias that should be used instead of the real
host name when looking up or saving the host key in the
host key database files and when validating host
certificates. This option is useful for tunneling SSH
connections or for multiple servers running on a single
host.
Hostname
Specifies the real host name to log into. This can be
used to specify nicknames or abbreviations for hosts.
Arguments to Hostname accept the tokens described in the
“TOKENS” section. Numeric IP addresses are also permitted
(both on the command line and in Hostname specifications).
The default is the name given on the command line.
IdentitiesOnly
Specifies that ssh(1) should only use the configured
authentication identity and certificate files (either the
default files, or those explicitly configured in the
ssh_config files or passed on the ssh(1) command-line),
even if ssh-agent(1) or a PKCS11Provider or
SecurityKeyProvider offers more identities. The argument
to this keyword must be yes or no (the default). This
option is intended for situations where ssh-agent offers
many different identities.
IdentityAgent
Specifies the Unix-domain socket used to communicate with
the authentication agent.
This option overrides the SSH_AUTH_SOCK environment
variable and can be used to select a specific agent.
Setting the socket name to none disables the use of an
authentication agent. If the string "SSH_AUTH_SOCK" is
specified, the location of the socket will be read from
the SSH_AUTH_SOCK environment variable. Otherwise if the
specified value begins with a ‘$’ character, then it will
be treated as an environment variable containing the
location of the socket.
Arguments to IdentityAgent may use the tilde syntax to
refer to a user's home directory, the tokens described in
the “TOKENS” section and environment variables as
described in the “ENVIRONMENT VARIABLES” section.
IdentityFile
Specifies a file from which the user's ECDSA,
authenticator-hosted ECDSA, Ed25519, authenticator-hosted
Ed25519 or RSA authentication identity is read. You can
also specify a public key file to use the corresponding
private key that is loaded in ssh-agent(1) when the
private key file is not present locally. The default is
~/.ssh/id_rsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk,
~/.ssh/id_ed25519 and ~/.ssh/id_ed25519_sk. Additionally,
any identities represented by the authentication agent
will be used for authentication unless IdentitiesOnly is
set. If no certificates have been explicitly specified by
CertificateFile, ssh(1) will try to load certificate
information from the filename obtained by appending
-cert.pub to the path of a specified IdentityFile.
Arguments to IdentityFile may use the tilde syntax to
refer to a user's home directory or the tokens described
in the “TOKENS” section. Alternately an argument of none
may be used to indicate no identity files should be
loaded.
It is possible to have multiple identity files specified
in configuration files; all these identities will be tried
in sequence. Multiple IdentityFile directives will add to
the list of identities tried (this behaviour differs from
that of other configuration directives).
IdentityFile may be used in conjunction with
IdentitiesOnly to select which identities in an agent are
offered during authentication. IdentityFile may also be
used in conjunction with CertificateFile in order to
provide any certificate also needed for authentication
with the identity.
IgnoreUnknown
Specifies a pattern-list of unknown options to be ignored
if they are encountered in configuration parsing. This
may be used to suppress errors if ssh_config contains
options that are unrecognised by ssh(1). It is
recommended that IgnoreUnknown be listed early in the
configuration file as it will not be applied to unknown
options that appear before it.
Include
Include the specified configuration file(s). Multiple
pathnames may be specified and each pathname may contain
glob(7) wildcards, tokens as described in the “TOKENS”
section, environment variables as described in the
“ENVIRONMENT VARIABLES” section and, for user
configurations, shell-like ‘~’ references to user home
directories. Wildcards will be expanded and processed in
lexical order. Files without absolute paths are assumed
to be in ~/.ssh if included in a user configuration file
or /etc/ssh if included from the system configuration
file. Include directive may appear inside a Match or Host
block to perform conditional inclusion.
IPQoS Specifies the IPv4 type-of-service or DSCP class for
connections. Accepted values are af11, af12, af13, af21,
af22, af23, af31, af32, af33, af41, af42, af43, cs0, cs1,
cs2, cs3, cs4, cs5, cs6, cs7, ef, le, lowdelay,
throughput, reliability, a numeric value, or none to use
the operating system default. This option may take one or
two arguments, separated by whitespace. If one argument
is specified, it is used as the packet class
unconditionally. If two values are specified, the first
is automatically selected for interactive sessions and the
second for non-interactive sessions. The default is af21
(Low-Latency Data) for interactive sessions and cs1 (Lower
Effort) for non-interactive sessions.
KbdInteractiveAuthentication
Specifies whether to use keyboard-interactive
authentication. The argument to this keyword must be yes
(the default) or no. ChallengeResponseAuthentication is a
deprecated alias for this.
KbdInteractiveDevices
Specifies the list of methods to use in keyboard-
interactive authentication. Multiple method names must be
comma-separated. The default is to use the server
specified list. The methods available vary depending on
what the server supports. For an OpenSSH server, it may
be zero or more of: bsdauth and pam.
KexAlgorithms
Specifies the permitted KEX (Key Exchange) algorithms that
will be used and their preference order. The selected
algorithm will be the first algorithm in this list that
the server also supports. Multiple algorithms must be
comma-separated.
If the specified list begins with a ‘+’ character, then
the specified algorithms will be appended to the default
set instead of replacing them. If the specified list
begins with a ‘-’ character, then the specified algorithms
(including wildcards) will be removed from the default set
instead of replacing them. If the specified list begins
with a ‘^’ character, then the specified algorithms will
be placed at the head of the default set.
The default is:
sntrup761x25519-sha512,sntrup761x25519-sha512@openssh.com,
mlkem768x25519-sha256,
curve25519-sha256,curve25519-sha256@libssh.org,
ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
diffie-hellman-group-exchange-sha256,
diffie-hellman-group16-sha512,
diffie-hellman-group18-sha512,
diffie-hellman-group14-sha256
The list of supported key exchange algorithms may also be
obtained using "ssh -Q kex".
KnownHostsCommand
Specifies a command to use to obtain a list of host keys,
in addition to those listed in UserKnownHostsFile and
GlobalKnownHostsFile. This command is executed after the
files have been read. It may write host key lines to
standard output in identical format to the usual files
(described in the “VERIFYING HOST KEYS” section in
ssh(1)). Arguments to KnownHostsCommand accept the tokens
described in the “TOKENS” section. The command may be
invoked multiple times per connection: once when preparing
the preference list of host key algorithms to use, again
to obtain the host key for the requested host name and, if
CheckHostIP is enabled, one more time to obtain the host
key matching the server's address. If the command exits
abnormally or returns a non-zero exit status then the
connection is terminated.
LocalCommand
Specifies a command to execute on the local machine after
successfully connecting to the server. The command string
extends to the end of the line, and is executed with the
user's shell. Arguments to LocalCommand accept the tokens
described in the “TOKENS” section.
The command is run synchronously and does not have access
to the session of the ssh(1) that spawned it. It should
not be used for interactive commands.
This directive is ignored unless PermitLocalCommand has
been enabled.
LocalForward
Specifies that a TCP port on the local machine be
forwarded over the secure channel to the specified host
and port from the remote machine. The first argument
specifies the listener and may be [bind_address:]port or a
Unix domain socket path. The second argument is the
destination and may be host:hostport or a Unix domain
socket path if the remote host supports it.
IPv6 addresses can be specified by enclosing addresses in
square brackets. Multiple forwardings may be specified,
and additional forwardings can be given on the command
line. Only the superuser can forward privileged ports.
By default, the local port is bound in accordance with the
GatewayPorts setting. However, an explicit bind_address
may be used to bind the connection to a specific address.
The bind_address of localhost indicates that the listening
port be bound for local use only, while an empty address
or ‘*’ indicates that the port should be available from
all interfaces. Unix domain socket paths may use the
tokens described in the “TOKENS” section and environment
variables as described in the “ENVIRONMENT VARIABLES”
section.
LogLevel
Gives the verbosity level that is used when logging
messages from ssh(1). The possible values are: QUIET,
FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and
DEBUG3. The default is INFO. DEBUG and DEBUG1 are
equivalent. DEBUG2 and DEBUG3 each specify higher levels
of verbose output.
LogVerbose
Specify one or more overrides to LogLevel. An override
consists of one or more pattern lists that matches the
source file, function and line number to force detailed
logging for. For example, an override pattern of:
kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
would enable detailed logging for line 1000 of kex.c,
everything in the kex_exchange_identification() function,
and all code in the packet.c file. This option is
intended for debugging and no overrides are enabled by
default.
MACs Specifies the MAC (message authentication code) algorithms
in order of preference. The MAC algorithm is used for
data integrity protection. Multiple algorithms must be
comma-separated. If the specified list begins with a ‘+’
character, then the specified algorithms will be appended
to the default set instead of replacing them. If the
specified list begins with a ‘-’ character, then the
specified algorithms (including wildcards) will be removed
from the default set instead of replacing them. If the
specified list begins with a ‘^’ character, then the
specified algorithms will be placed at the head of the
default set.
The algorithms that contain "-etm" calculate the MAC after
encryption (encrypt-then-mac). These are considered safer
and their use recommended.
The default is:
umac-64-etm@openssh.com,umac-128-etm@openssh.com,
hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
hmac-sha1-etm@openssh.com,
umac-64@openssh.com,umac-128@openssh.com,
hmac-sha2-256,hmac-sha2-512,hmac-sha1
The list of available MAC algorithms may also be obtained
using "ssh -Q mac".
NoHostAuthenticationForLocalhost
Disable host authentication for localhost (loopback
addresses). The argument to this keyword must be yes or
no (the default).
NumberOfPasswordPrompts
Specifies the number of password prompts before giving up.
The argument to this keyword must be an integer. The
default is 3.
ObscureKeystrokeTiming
Specifies whether ssh(1) should try to obscure inter-
keystroke timings from passive observers of network
traffic. If enabled, then for interactive sessions,
ssh(1) will send keystrokes at fixed intervals of a few
tens of milliseconds and will send fake keystroke packets
for some time after typing ceases. The argument to this
keyword must be yes, no or an interval specifier of the
form interval:milliseconds (e.g. interval:80 for 80
milliseconds). The default is to obscure keystrokes using
a 20ms packet interval. Note that smaller intervals will
result in higher fake keystroke packet rates.
PasswordAuthentication
Specifies whether to use password authentication. The
argument to this keyword must be yes (the default) or no.
PermitLocalCommand
Allow local command execution via the LocalCommand option
or using the !command escape sequence in ssh(1). The
argument must be yes or no (the default).
PermitRemoteOpen
Specifies the destinations to which remote TCP port
forwarding is permitted when RemoteForward is used as a
SOCKS proxy. The forwarding specification must be one of
the following forms:
PermitRemoteOpen host:port
PermitRemoteOpen IPv4_addr:port
PermitRemoteOpen [IPv6_addr]:port
Multiple forwards may be specified by separating them with
whitespace. An argument of any can be used to remove all
restrictions and permit any forwarding requests. An
argument of none can be used to prohibit all forwarding
requests. The wildcard ‘*’ can be used for host or port
to allow all hosts or ports respectively. Otherwise, no
pattern matching or address lookups are performed on
supplied names.
PKCS11Provider
Specifies which PKCS#11 provider to use or none to
indicate that no provider should be used (the default).
The argument to this keyword is a path to the PKCS#11
shared library ssh(1) should use to communicate with a
PKCS#11 token providing keys for user authentication.
Port Specifies the port number to connect on the remote host.
The default is 22.
PreferredAuthentications
Specifies the order in which the client should try
authentication methods. This allows a client to prefer
one method (e.g. keyboard-interactive) over another method
(e.g. password). The default is:
gssapi-with-mic,hostbased,publickey,
keyboard-interactive,password
ProxyCommand
Specifies the command to use to connect to the server.
The command string extends to the end of the line, and is
executed using the user's shell ‘exec’ directive to avoid
a lingering shell process.
Arguments to ProxyCommand accept the tokens described in
the “TOKENS” section. The command can be basically
anything, and should read from its standard input and
write to its standard output. It should eventually
connect an sshd(8) server running on some machine, or
execute sshd -i somewhere. Host key management will be
done using the Hostname of the host being connected
(defaulting to the name typed by the user). Setting the
command to none disables this option entirely. Note that
CheckHostIP is not available for connects with a proxy
command.
This directive is useful in conjunction with nc(1) and its
proxy support. For example, the following directive would
connect via an HTTP proxy at 192.0.2.0:
ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
ProxyJump
Specifies one or more jump proxies as either
[user@]host[:port] or an ssh URI. Multiple proxies may be
separated by comma characters and will be visited
sequentially. Setting this option will cause ssh(1) to
connect to the target host by first making a ssh(1)
connection to the specified ProxyJump host and then
establishing a TCP forwarding to the ultimate target from
there. Setting the host to none disables this option
entirely.
Note that this option will compete with the ProxyCommand
option - whichever is specified first will prevent later
instances of the other from taking effect.
Note also that the configuration for the destination host
(either supplied via the command-line or the configuration
file) is not generally applied to jump hosts.
~/.ssh/config should be used if specific configuration is
required for jump hosts.
ProxyUseFdpass
Specifies that ProxyCommand will pass a connected file
descriptor back to ssh(1) instead of continuing to execute
and pass data. The default is no.
PubkeyAcceptedAlgorithms
Specifies the signature algorithms that will be used for
public key authentication as a comma-separated list of
patterns. If the specified list begins with a ‘+’
character, then the algorithms after it will be appended
to the default instead of replacing it. If the specified
list begins with a ‘-’ character, then the specified
algorithms (including wildcards) will be removed from the
default set instead of replacing them. If the specified
list begins with a ‘^’ character, then the specified
algorithms will be placed at the head of the default set.
The default for this option is:
ssh-ed25519-cert-v01@openssh.com,
ecdsa-sha2-nistp256-cert-v01@openssh.com,
ecdsa-sha2-nistp384-cert-v01@openssh.com,
ecdsa-sha2-nistp521-cert-v01@openssh.com,
sk-ssh-ed25519-cert-v01@openssh.com,
sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
rsa-sha2-512-cert-v01@openssh.com,
rsa-sha2-256-cert-v01@openssh.com,
ssh-ed25519,
ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
sk-ssh-ed25519@openssh.com,
sk-ecdsa-sha2-nistp256@openssh.com,
rsa-sha2-512,rsa-sha2-256
The list of available signature algorithms may also be
obtained using "ssh -Q PubkeyAcceptedAlgorithms".
PubkeyAuthentication
Specifies whether to try public key authentication. The
argument to this keyword must be yes (the default), no,
unbound or host-bound. The final two options enable
public key authentication while respectively disabling or
enabling the OpenSSH host-bound authentication protocol
extension required for restricted ssh-agent(1) forwarding.
RekeyLimit
Specifies the maximum amount of data that may be
transmitted or received before the session key is
renegotiated, optionally followed by a maximum amount of
time that may pass before the session key is renegotiated.
The first argument is specified in bytes and may have a
suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
Megabytes, or Gigabytes, respectively. The default is
between ‘1G’ and ‘4G’, depending on the cipher. The
optional second value is specified in seconds and may use
any of the units documented in the TIME FORMATS section of
sshd_config(5). The default value for RekeyLimit is
default none, which means that rekeying is performed after
the cipher's default amount of data has been sent or
received and no time based rekeying is done.
RemoteCommand
Specifies a command to execute on the remote machine after
successfully connecting to the server. The command string
extends to the end of the line, and is executed with the
user's shell. Arguments to RemoteCommand accept the
tokens described in the “TOKENS” section.
RemoteForward
Specifies that a TCP port on the remote machine be
forwarded over the secure channel. The remote port may
either be forwarded to a specified host and port from the
local machine, or may act as a SOCKS 4/5 proxy that allows
a remote client to connect to arbitrary destinations from
the local machine. The first argument is the listening
specification and may be [bind_address:]port or, if the
remote host supports it, a Unix domain socket path. If
forwarding to a specific destination then the second
argument must be host:hostport or a Unix domain socket
path, otherwise if no destination argument is specified
then the remote forwarding will be established as a SOCKS
proxy. When acting as a SOCKS proxy, the destination of
the connection can be restricted by PermitRemoteOpen.
IPv6 addresses can be specified by enclosing addresses in
square brackets. Multiple forwardings may be specified,
and additional forwardings can be given on the command
line. Privileged ports can be forwarded only when logging
in as root on the remote machine. Unix domain socket
paths may use the tokens described in the “TOKENS” section
and environment variables as described in the “ENVIRONMENT
VARIABLES” section.
If the port argument is 0, the listen port will be
dynamically allocated on the server and reported to the
client at run time.
If the bind_address is not specified, the default is to
only bind to loopback addresses. If the bind_address is
‘*’ or an empty string, then the forwarding is requested
to listen on all interfaces. Specifying a remote
bind_address will only succeed if the server's
GatewayPorts option is enabled (see sshd_config(5)).
RequestTTY
Specifies whether to request a pseudo-tty for the session.
The argument may be one of: no (never request a TTY), yes
(always request a TTY when standard input is a TTY), force
(always request a TTY) or auto (request a TTY when opening
a login session). This option mirrors the -t and -T flags
for ssh(1).
RequiredRSASize
Specifies the minimum RSA key size (in bits) that ssh(1)
will accept. User authentication keys smaller than this
limit will be ignored. Servers that present host keys
smaller than this limit will cause the connection to be
terminated. The default is 1024 bits. Note that this
limit may only be raised from the default.
RevokedHostKeys
Specifies revoked host public keys. Keys listed in this
file will be refused for host authentication. Note that
if this file does not exist or is not readable, then host
authentication will be refused for all hosts. Keys may be
specified as a text file, listing one public key per line,
or as an OpenSSH Key Revocation List (KRL) as generated by
ssh-keygen(1). For more information on KRLs, see the KEY
REVOCATION LISTS section in ssh-keygen(1). Arguments to
RevokedHostKeys may use the tilde syntax to refer to a
user's home directory, the tokens described in the
“TOKENS” section and environment variables as described in
the “ENVIRONMENT VARIABLES” section.
SecurityKeyProvider
Specifies a path to a library that will be used when
loading any FIDO authenticator-hosted keys, overriding the
default of using the built-in USB HID support.
If the specified value begins with a ‘$’ character, then
it will be treated as an environment variable containing
the path to the library.
SendEnv
Specifies what variables from the local environ(7) should
be sent to the server. The server must also support it,
and the server must be configured to accept these
environment variables. Note that the TERM environment
variable is always sent whenever a pseudo-terminal is
requested as it is required by the protocol. Refer to
AcceptEnv in sshd_config(5) for how to configure the
server. Variables are specified by name, which may
contain wildcard characters. Multiple environment
variables may be separated by whitespace or spread across
multiple SendEnv directives.
See “PATTERNS” for more information on patterns.
It is possible to clear previously set SendEnv variable
names by prefixing patterns with -. The default is not to
send any environment variables.
ServerAliveCountMax
Sets the number of server alive messages (see below) which
may be sent without ssh(1) receiving any messages back
from the server. If this threshold is reached while
server alive messages are being sent, ssh will disconnect
from the server, terminating the session. It is important
to note that the use of server alive messages is very
different from TCPKeepAlive (below). The server alive
messages are sent through the encrypted channel and
therefore will not be spoofable. The TCP keepalive option
enabled by TCPKeepAlive is spoofable. The server alive
mechanism is valuable when the client or server depend on
knowing when a connection has become unresponsive.
The default value is 3. If, for example,
ServerAliveInterval (see below) is set to 15 and
ServerAliveCountMax is left at the default, if the server
becomes unresponsive, ssh will disconnect after
approximately 45 seconds.
ServerAliveInterval
Sets a timeout interval in seconds after which if no data
has been received from the server, ssh(1) will send a
message through the encrypted channel to request a
response from the server. The default is 0, indicating
that these messages will not be sent to the server.
SessionType
May be used to either request invocation of a subsystem on
the remote system, or to prevent the execution of a remote
command at all. The latter is useful for just forwarding
ports. The argument to this keyword must be none (same as
the -N option), subsystem (same as the -s option) or
default (shell or command execution).
SetEnv Directly specify one or more environment variables and
their contents to be sent to the server. Similarly to
SendEnv, with the exception of the TERM variable, the
server must be prepared to accept the environment
variable.
StdinNull
Redirects stdin from /dev/null (actually, prevents reading
from stdin). Either this or the equivalent -n option must
be used when ssh is run in the background. The argument
to this keyword must be yes (same as the -n option) or no
(the default).
StreamLocalBindMask
Sets the octal file creation mode mask (umask) used when
creating a Unix-domain socket file for local or remote
port forwarding. This option is only used for port
forwarding to a Unix-domain socket file.
The default value is 0177, which creates a Unix-domain
socket file that is readable and writable only by the
owner. Note that not all operating systems honor the file
mode on Unix-domain socket files.
StreamLocalBindUnlink
Specifies whether to remove an existing Unix-domain socket
file for local or remote port forwarding before creating a
new one. If the socket file already exists and
StreamLocalBindUnlink is not enabled, ssh will be unable
to forward the port to the Unix-domain socket file. This
option is only used for port forwarding to a Unix-domain
socket file.
The argument must be yes or no (the default).
StrictHostKeyChecking
If this flag is set to yes, ssh(1) will never
automatically add host keys to the ~/.ssh/known_hosts
file, and refuses to connect to hosts whose host key has
changed. This provides maximum protection against man-in-
the-middle (MITM) attacks, though it can be annoying when
the /etc/ssh/ssh_known_hosts file is poorly maintained or
when connections to new hosts are frequently made. This
option forces the user to manually add all new hosts.
If this flag is set to accept-new then ssh will
automatically add new host keys to the user's known_hosts
file, but will not permit connections to hosts with
changed host keys. If this flag is set to no or off, ssh
will automatically add new host keys to the user known
hosts files and allow connections to hosts with changed
hostkeys to proceed, subject to some restrictions. If
this flag is set to ask (the default), new host keys will
be added to the user known host files only after the user
has confirmed that is what they really want to do, and ssh
will refuse to connect to hosts whose host key has
changed. The host keys of known hosts will be verified
automatically in all cases.
SyslogFacility
Gives the facility code that is used when logging messages
from ssh(1). The possible values are: DAEMON, USER, AUTH,
LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6,
LOCAL7. The default is USER.
TCPKeepAlive
Specifies whether the system should send TCP keepalive
messages to the other side. If they are sent, death of
the connection or crash of one of the machines will be
properly noticed. However, this means that connections
will die if the route is down temporarily, and some people
find it annoying.
The default is yes (to send TCP keepalive messages), and
the client will notice if the network goes down or the
remote host dies. This is important in scripts, and many
users want it too.
To disable TCP keepalive messages, the value should be set
to no. See also ServerAliveInterval for protocol-level
keepalives.
Tag Specify a configuration tag name that may be later used by
a Match directive to select a block of configuration.
Tunnel Request tun(4) device forwarding between the client and
the server. The argument must be yes, point-to-point
(layer 3), ethernet (layer 2), or no (the default).
Specifying yes requests the default tunnel mode, which is
point-to-point.
TunnelDevice
Specifies the tun(4) devices to open on the client
(local_tun) and the server (remote_tun).
The argument must be local_tun[:remote_tun]. The devices
may be specified by numerical ID or the keyword any, which
uses the next available tunnel device. If remote_tun is
not specified, it defaults to any. The default is
any:any.
UpdateHostKeys
Specifies whether ssh(1) should accept notifications of
additional hostkeys from the server sent after
authentication has completed and add them to
UserKnownHostsFile. The argument must be yes, no or ask.
This option allows learning alternate hostkeys for a
server and supports graceful key rotation by allowing a
server to send replacement public keys before old ones are
removed.
Additional hostkeys are only accepted if the key used to
authenticate the host was already trusted or explicitly
accepted by the user, the host was authenticated via
UserKnownHostsFile (i.e. not GlobalKnownHostsFile) and the
host was authenticated using a plain key and not a
certificate.
UpdateHostKeys is enabled by default if the user has not
overridden the default UserKnownHostsFile setting and has
not enabled VerifyHostKeyDNS, otherwise UpdateHostKeys
will be set to no.
If UpdateHostKeys is set to ask, then the user is asked to
confirm the modifications to the known_hosts file.
Confirmation is currently incompatible with
ControlPersist, and will be disabled if it is enabled.
Presently, only sshd(8) from OpenSSH 6.8 and greater
support the "hostkeys@openssh.com" protocol extension used
to inform the client of all the server's hostkeys.
User Specifies the user to log in as. This can be useful when
a different user name is used on different machines. This
saves the trouble of having to remember to give the user
name on the command line.
UserKnownHostsFile
Specifies one or more files to use for the user host key
database, separated by whitespace. Each filename may use
tilde notation to refer to the user's home directory, the
tokens described in the “TOKENS” section and environment
variables as described in the “ENVIRONMENT VARIABLES”
section. A value of none causes ssh(1) to ignore any
user-specific known hosts files. The default is
~/.ssh/known_hosts, ~/.ssh/known_hosts2.
VerifyHostKeyDNS
Specifies whether to verify the remote key using DNS and
SSHFP resource records. If this option is set to yes, the
client will implicitly trust keys that match a secure
fingerprint from DNS. Insecure fingerprints will be
handled as if this option was set to ask. If this option
is set to ask, information on fingerprint match will be
displayed, but the user will still need to confirm new
host keys according to the StrictHostKeyChecking option.
The default is no.
See also “VERIFYING HOST KEYS” in ssh(1).
VisualHostKey
If this flag is set to yes, an ASCII art representation of
the remote host key fingerprint is printed in addition to
the fingerprint string at login and for unknown host keys.
If this flag is set to no (the default), no fingerprint
strings are printed at login and only the fingerprint
string will be printed for unknown host keys.
XAuthLocation
Specifies the full pathname of the xauth(1) program. The
default is /usr/X11R6/bin/xauth.
A pattern consists of zero or more non-whitespace characters, ‘*’
(a wildcard that matches zero or more characters), or ‘?’ (a
wildcard that matches exactly one character). For example, to
specify a set of declarations for any host in the ".co.uk" set of
domains, the following pattern could be used:
Host *.co.uk
The following pattern would match any host in the 192.168.0.[0-9]
network range:
Host 192.168.0.?
A pattern-list is a comma-separated list of patterns. Patterns
within pattern-lists may be negated by preceding them with an
exclamation mark (‘!’). For example, to allow a key to be used
from anywhere within an organization except from the "dialup"
pool, the following entry (in authorized_keys) could be used:
from="!*.dialup.example.com,*.example.com"
Note that a negated match will never produce a positive result by
itself. For example, attempting to match "host3" against the
following pattern-list will fail:
from="!host1,!host2"
The solution here is to include a term that will yield a positive
match, such as a wildcard:
from="!host1,!host2,*"
Arguments to some keywords can make use of tokens, which are
expanded at runtime:
%% A literal ‘%’.
%C Hash of %l%h%p%r%j.
%d Local user's home directory.
%f The fingerprint of the server's host key.
%H The known_hosts hostname or address that is being
searched for.
%h The remote hostname.
%I A string describing the reason for a KnownHostsCommand
execution: either ADDRESS when looking up a host by
address (only when CheckHostIP is enabled), HOSTNAME
when searching by hostname, or ORDER when preparing
the host key algorithm preference list to use for the
destination host.
%i The local user ID.
%j The contents of the ProxyJump option, or the empty
string if this option is unset.
%K The base64 encoded host key.
%k The host key alias if specified, otherwise the
original remote hostname given on the command line.
%L The local hostname.
%l The local hostname, including the domain name.
%n The original remote hostname, as given on the command
line.
%p The remote port.
%r The remote username.
%T The local tun(4) or tap(4) network interface assigned
if tunnel forwarding was requested, or "NONE"
otherwise.
%t The type of the server host key, e.g. ssh-ed25519.
%u The local username.
CertificateFile, ControlPath, IdentityAgent, IdentityFile,
Include, KnownHostsCommand, LocalForward, Match exec,
RemoteCommand, RemoteForward, RevokedHostKeys, and
UserKnownHostsFile accept the tokens %%, %C, %d, %h, %i, %j, %k,
%L, %l, %n, %p, %r, and %u.
KnownHostsCommand additionally accepts the tokens %f, %H, %I, %K
and %t.
Hostname accepts the tokens %% and %h.
LocalCommand accepts all tokens.
ProxyCommand and ProxyJump accept the tokens %%, %h, %n, %p, and
%r.
Note that some of these directives build commands for execution
via the shell. Because ssh(1) performs no filtering or escaping
of characters that have special meaning in shell commands (e.g.
quotes), it is the user's responsibility to ensure that the
arguments passed to ssh(1) do not contain such characters and that
tokens are appropriately quoted when used.
Arguments to some keywords can be expanded at runtime from
environment variables on the client by enclosing them in ${}, for
example ${HOME}/.ssh would refer to the user's .ssh directory. If
a specified environment variable does not exist then an error will
be returned and the setting for that keyword will be ignored.
The keywords CertificateFile, ControlPath, IdentityAgent,
IdentityFile, Include, KnownHostsCommand, and UserKnownHostsFile
support environment variables. The keywords LocalForward and
RemoteForward support environment variables only for Unix domain
socket paths.
~/.ssh/config
This is the per-user configuration file. The format of
this file is described above. This file is used by the
SSH client. Because of the potential for abuse, this file
must have strict permissions: read/write for the user, and
not writable by others.
/etc/ssh/ssh_config
Systemwide configuration file. This file provides
defaults for those values that are not specified in the
user's configuration file, and for those users who do not
have a configuration file. This file must be world-
readable.
ssh(1)
OpenSSH is a derivative of the original and free ssh 1.2.12
release by Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl,
Niels Provos, Theo de Raadt and Dug Song removed many bugs, re-
added newer features and created OpenSSH. Markus Friedl
contributed the support for SSH protocol versions 1.5 and 2.0.
This page is part of the openssh (Portable OpenSSH) project.
Information about the project can be found at
http://www.openssh.com/portable.html. If you have a bug report
for this manual page, see ⟨http://www.openssh.com/report.html⟩.
This page was obtained from the tarball openssh-9.9p2.tar.gz
fetched from
⟨http://ftp.eu.openbsd.org/pub/OpenBSD/OpenSSH/portable/⟩ on
2025-08-11. 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
man-pages@man7.org
GNU September 9, 2024 SSH_CONFIG(5)
Pages that refer to this page: sshfs(1), systemd-ssh-proxy(1)
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