systemd.link(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | [MATCH] SECTION OPTIONS | [LINK] SECTION OPTIONS | EXAMPLES | SEE ALSO | COLOPHON

SYSTEMD.LINK(5)                 systemd.link                 SYSTEMD.LINK(5)

NAME         top

       systemd.link - Network device configuration

SYNOPSIS         top

       link.link

DESCRIPTION         top

       A plain ini-style text file that encodes configuration for matching
       network devices, used by systemd-udevd(8) and in particular its
       net_setup_link builtin. See systemd.syntax(7) for a general
       description of the syntax.

       The link files are read from the files located in the system network
       directory /usr/lib/systemd/network, the volatile runtime network
       directory /run/systemd/network, and the local administration network
       directory /etc/systemd/network. Link files must have the extension
       .link; other extensions are ignored. All link files are collectively
       sorted and processed in lexical order, regardless of the directories
       in which they live. However, files with identical filenames replace
       each other. Files in /etc have the highest priority, files in /run
       take precedence over files with the same name in /usr/lib. This can
       be used to override a system-supplied link file with a local file if
       needed. As a special case, an empty file (file size 0) or symlink
       with the same name pointing to /dev/null disables the configuration
       file entirely (it is "masked").

       The link file contains a [Match] section, which determines if a given
       link file may be applied to a given device, as well as a [Link]
       section specifying how the device should be configured. The first (in
       lexical order) of the link files that matches a given device is
       applied. Note that a default file 99-default.link is shipped by the
       system. Any user-supplied .link should hence have a lexically earlier
       name to be considered at all.

       See udevadm(8) for diagnosing problems with .link files.

[MATCH] SECTION OPTIONS         top

       A link file is said to match a device if all matches specified by the
       [Match] section are satisfied. When a link file does not contain
       valid settings in [Match] section, then the file will match all
       devices and systemd-udevd warns about that. Hint: to avoid the
       warning and to make it clear that all interfaces shall be matched,
       add the following:

           OriginalName=*

       The following keys are accepted:

       MACAddress=
           A whitespace-separated list of hardware addresses. Use full
           colon-, hyphen- or dot-delimited hexadecimal. See the example
           below. This option may appear more than once, in which case the
           lists are merged. If the empty string is assigned to this option,
           the list of hardware addresses defined prior to this is reset.

           Example:

               MACAddress=01:23:45:67:89:ab 00-11-22-33-44-55 AABB.CCDD.EEFF

       PermanentMACAddress=
           A whitespace-separated list of hardware's permanent addresses.
           While MACAddress= matches the device's current MAC address, this
           matches the device's permanent MAC address, which may be
           different from the current one. Use full colon-, hyphen- or
           dot-delimited hexadecimal. This option may appear more than once,
           in which case the lists are merged. If the empty string is
           assigned to this option, the list of hardware addresses defined
           prior to this is reset.

       Path=
           A whitespace-separated list of shell-style globs matching the
           persistent path, as exposed by the udev property ID_PATH.

       Driver=
           A whitespace-separated list of shell-style globs matching the
           driver currently bound to the device, as exposed by the udev
           property ID_NET_DRIVER of its parent device, or if that is not
           set, the driver as exposed by ethtool -i of the device itself. If
           the list is prefixed with a "!", the test is inverted.

       Type=
           A whitespace-separated list of shell-style globs matching the
           device type, as exposed by networkctl status. If the list is
           prefixed with a "!", the test is inverted.

       Property=
           A whitespace-separated list of udev property name with its value
           after a equal ("="). If multiple properties are specified, the
           test results are ANDed. If the list is prefixed with a "!", the
           test is inverted. If a value contains white spaces, then please
           quote whole key and value pair. If a value contains quotation,
           then please escape the quotation with "\".

           Example: if a .link file has the following:

               Property=ID_MODEL_ID=9999 "ID_VENDOR_FROM_DATABASE=vendor name" "KEY=with \"quotation\""

           then, the .link file matches only when an interface has all the
           above three properties.

       OriginalName=
           A whitespace-separated list of shell-style globs matching the
           device name, as exposed by the udev property "INTERFACE". This
           cannot be used to match on names that have already been changed
           from userspace. Caution is advised when matching on
           kernel-assigned names, as they are known to be unstable between
           reboots.

       Host=
           Matches against the hostname or machine ID of the host. See
           ConditionHost= in systemd.unit(5) for details. When prefixed with
           an exclamation mark ("!"), the result is negated. If an empty
           string is assigned, then previously assigned value is cleared.

       Virtualization=
           Checks whether the system is executed in a virtualized
           environment and optionally test whether it is a specific
           implementation. See ConditionVirtualization= in systemd.unit(5)
           for details. When prefixed with an exclamation mark ("!"), the
           result is negated. If an empty string is assigned, then
           previously assigned value is cleared.

       KernelCommandLine=
           Checks whether a specific kernel command line option is set. See
           ConditionKernelCommandLine= in systemd.unit(5) for details. When
           prefixed with an exclamation mark ("!"), the result is negated.
           If an empty string is assigned, then previously assigned value is
           cleared.

       KernelVersion=
           Checks whether the kernel version (as reported by uname -r)
           matches a certain expression. See ConditionKernelVersion= in
           systemd.unit(5) for details. When prefixed with an exclamation
           mark ("!"), the result is negated. If an empty string is
           assigned, then previously assigned value is cleared.

       Architecture=
           Checks whether the system is running on a specific architecture.
           See ConditionArchitecture= in systemd.unit(5) for details. When
           prefixed with an exclamation mark ("!"), the result is negated.
           If an empty string is assigned, then previously assigned value is
           cleared.

[LINK] SECTION OPTIONS         top

       The [Link] section accepts the following keys:

       Description=
           A description of the device.

       Alias=
           The ifalias interface property is set to this value.

       MACAddressPolicy=
           The policy by which the MAC address should be set. The available
           policies are:

           persistent
               If the hardware has a persistent MAC address, as most
               hardware should, and if it is used by the kernel, nothing is
               done. Otherwise, a new MAC address is generated which is
               guaranteed to be the same on every boot for the given machine
               and the given device, but which is otherwise random. This
               feature depends on ID_NET_NAME_* properties to exist for the
               link. On hardware where these properties are not set, the
               generation of a persistent MAC address will fail.

           random
               If the kernel is using a random MAC address, nothing is done.
               Otherwise, a new address is randomly generated each time the
               device appears, typically at boot. Either way, the random
               address will have the "unicast" and "locally administered"
               bits set.

           none
               Keeps the MAC address assigned by the kernel.

       MACAddress=
           The MAC address to use, if no MACAddressPolicy= is specified.

       NamePolicy=
           An ordered, space-separated list of policies by which the
           interface name should be set.  NamePolicy= may be disabled by
           specifying net.ifnames=0 on the kernel command line. Each of the
           policies may fail, and the first successful one is used. The name
           is not set directly, but is exported to udev as the property
           ID_NET_NAME, which is, by default, used by a udev(7), rule to set
           NAME. The available policies are:

           kernel
               If the kernel claims that the name it has set for a device is
               predictable, then no renaming is performed.

           database
               The name is set based on entries in the udev's Hardware
               Database with the key ID_NET_NAME_FROM_DATABASE.

           onboard
               The name is set based on information given by the firmware
               for on-board devices, as exported by the udev property
               ID_NET_NAME_ONBOARD. See systemd.net-naming-scheme(7).

           slot
               The name is set based on information given by the firmware
               for hot-plug devices, as exported by the udev property
               ID_NET_NAME_SLOT. See systemd.net-naming-scheme(7).

           path
               The name is set based on the device's physical location, as
               exported by the udev property ID_NET_NAME_PATH. See
               systemd.net-naming-scheme(7).

           mac
               The name is set based on the device's persistent MAC address,
               as exported by the udev property ID_NET_NAME_MAC. See
               systemd.net-naming-scheme(7).

           keep
               If the device already had a name given by userspace (as part
               of creation of the device or a rename), keep it.

       Name=
           The interface name to use. This option has lower precedence than
           NamePolicy=, so for this setting to take effect, NamePolicy= must
           either be unset, empty, disabled, or all policies configured
           there must fail. Also see the example below with "Name=dmz0".

           Note that specifying a name that the kernel might use for another
           interface (for example "eth0") is dangerous because the name
           assignment done by udev will race with the assignment done by the
           kernel, and only one interface may use the name. Depending on the
           order of operations, either udev or the kernel will win, making
           the naming unpredictable. It is best to use some different
           prefix, for example "internal0"/"external0" or
           "lan0"/"lan1"/"lan3".

       AlternativeNamesPolicy=
           A space-separated list of policies by which the interface's
           alternative names should be set. Each of the policies may fail,
           and all successful policies are used. The available policies are
           "database", "onboard", "slot", "path", and "mac". If the kernel
           does not support the alternative names, then this setting will be
           ignored.

       AlternativeName=
           The alternative interface name to use. This option can be
           specified multiple times. If the empty string is assigned to this
           option, the list is reset, and all prior assignments have no
           effect. If the kernel does not support the alternative names,
           then this setting will be ignored.

       MTUBytes=
           The maximum transmission unit in bytes to set for the device. The
           usual suffixes K, M, G, are supported and are understood to the
           base of 1024.

       BitsPerSecond=
           The speed to set for the device, the value is rounded down to the
           nearest Mbps. The usual suffixes K, M, G, are supported and are
           understood to the base of 1000.

       Duplex=
           The duplex mode to set for the device. The accepted values are
           half and full.

       AutoNegotiation=
           Takes a boolean. If set to yes, automatic negotiation of
           transmission parameters is enabled. Autonegotiation is a
           procedure by which two connected ethernet devices choose common
           transmission parameters, such as speed, duplex mode, and flow
           control. When unset, the kernel's default will be used.

           Note that if autonegotiation is enabled, speed and duplex
           settings are read-only. If autonegotiation is disabled, speed and
           duplex settings are writable if the driver supports multiple link
           modes.

       WakeOnLan=
           The Wake-on-LAN policy to set for the device. The supported
           values are:

           phy
               Wake on PHY activity.

           unicast
               Wake on unicast messages.

           multicast
               Wake on multicast messages.

           broadcast
               Wake on broadcast messages.

           arp
               Wake on ARP.

           magic
               Wake on receipt of a magic packet.

           secureon
               Enable secureon(tm) password for MagicPacket(tm).

           off
               Never wake.

           Defaults to off.

       Port=
           The port option is used to select the device port. The supported
           values are:

           tp
               An Ethernet interface using Twisted-Pair cable as the medium.

           aui
               Attachment Unit Interface (AUI). Normally used with hubs.

           bnc
               An Ethernet interface using BNC connectors and co-axial
               cable.

           mii
               An Ethernet interface using a Media Independent Interface
               (MII).

           fibre
               An Ethernet interface using Optical Fibre as the medium.

       Advertise=
           This sets what speeds and duplex modes of operation are
           advertised for auto-negotiation. This implies
           "AutoNegotiation=yes". The supported values are:

           Table 1. Supported advertise values
           ┌───────────────────┬──────────────┬─────────────┐
           │Advertise          Speed (Mbps) Duplex Mode │
           ├───────────────────┼──────────────┼─────────────┤
           │10baset-half       │ 10           │ half        │
           ├───────────────────┼──────────────┼─────────────┤
           │10baset-full       │ 10           │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │100baset-half      │ 100          │ half        │
           ├───────────────────┼──────────────┼─────────────┤
           │100baset-full      │ 100          │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │1000baset-half     │ 1000         │ half        │
           ├───────────────────┼──────────────┼─────────────┤
           │1000baset-full     │ 1000         │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │10000baset-full    │ 10000        │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │2500basex-full     │ 2500         │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │1000basekx-full    │ 1000         │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │10000basekx4-full  │ 10000        │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │10000basekr-full   │ 10000        │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │10000baser-fec     │ 10000        │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │20000basemld2-full │ 20000        │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │20000basekr2-full  │ 20000        │ full        │
           └───────────────────┴──────────────┴─────────────┘
           By default this is unset, i.e. all possible modes will be
           advertised. This option may be specified more than once, in which
           case all specified speeds and modes are advertised. If the empty
           string is assigned to this option, the list is reset, and all
           prior assignments have no effect.

       ReceiveChecksumOffload=
           Takes a boolean. If set to true, the hardware offload for
           checksumming of ingress network packets is enabled. When unset,
           the kernel's default will be used.

       TransmitChecksumOffload=
           Takes a boolean. If set to true, the hardware offload for
           checksumming of egress network packets is enabled. When unset,
           the kernel's default will be used.

       TCPSegmentationOffload=
           Takes a boolean. If set to true, the TCP Segmentation Offload
           (TSO) is enabled. When unset, the kernel's default will be used.

       TCP6SegmentationOffload=
           Takes a boolean. If set to true, the TCP6 Segmentation Offload
           (tx-tcp6-segmentation) is enabled. When unset, the kernel's
           default will be used.

       GenericSegmentationOffload=
           Takes a boolean. If set to true, the Generic Segmentation Offload
           (GSO) is enabled. When unset, the kernel's default will be used.

       GenericReceiveOffload=
           Takes a boolean. If set to true, the Generic Receive Offload
           (GRO) is enabled. When unset, the kernel's default will be used.

       LargeReceiveOffload=
           Takes a boolean. If set to true, the Large Receive Offload (LRO)
           is enabled. When unset, the kernel's default will be used.

       RxChannels=
           Sets the number of receive channels (a number between 1 and
           4294967295) .

       TxChannels=
           Sets the number of transmit channels (a number between 1 and
           4294967295).

       OtherChannels=
           Sets the number of other channels (a number between 1 and
           4294967295).

       CombinedChannels=
           Sets the number of combined set channels (a number between 1 and
           4294967295).

       RxBufferSize=
           Takes an integer. Specifies the maximum number of pending packets
           in the NIC receive buffer. When unset, the kernel's default will
           be used.

       RxMiniBufferSize=
           Takes an integer. Specifies the maximum number of pending packets
           in the NIC mini receive buffer. When unset, the kernel's default
           will be used.

       RxJumboBufferSize=
           Takes an integer. Specifies the maximum number of pending packets
           in the NIC jumbo receive buffer. When unset, the kernel's default
           will be used.

       TxBufferSize=
           Takes an integer. Specifies the maximum number of pending packets
           in the NIC transmit buffer. When unset, the kernel's default will
           be used.

       RxFlowControl=
           Takes a boolean. When set, enables the receive flow control, also
           known as the ethernet receive PAUSE message (generate and send
           ethernet PAUSE frames). When unset, the kernel's default will be
           used.

       TxFlowControl=
           Takes a boolean. When set, enables the transmit flow control,
           also known as the ethernet transmit PAUSE message (respond to
           received ethernet PAUSE frames). When unset, the kernel's default
           will be used.

       AutoNegotiationFlowControl=
           Takes a boolean. When set, the auto negotiation enables the
           interface to exchange state advertisements with the connected
           peer so that the two devices can agree on the ethernet PAUSE
           configuration. When unset, the kernel's default will be used.

EXAMPLES         top

       Example 1. /usr/lib/systemd/network/99-default.link

       The link file 99-default.link that is shipped with systemd defines
       the default naming policy for links.

           [Link]
           NamePolicy=kernel database onboard slot path
           MACAddressPolicy=persistent

       Example 2. /etc/systemd/network/10-dmz.link

       This example assigns the fixed name "dmz0" to the interface with the
       MAC address 00:a0:de:63:7a:e6:

           [Match]
           MACAddress=00:a0:de:63:7a:e6

           [Link]
           Name=dmz0

       NamePolicy= is not set, so Name= takes effect. We use the "10-"
       prefix to order this file early in the list. Note that it needs to be
       before "99-link", i.e. it needs a numerical prefix, to have any
       effect at all.

       Example 3. Debugging NamePolicy= assignments

           $ sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/hub0
           ...
           Parsed configuration file /usr/lib/systemd/network/99-default.link
           Parsed configuration file /etc/systemd/network/10-eth0.link
           ID_NET_DRIVER=cdc_ether
           Config file /etc/systemd/network/10-eth0.link applies to device hub0
           link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
           hub0: Device has name_assign_type=4
           Using default interface naming scheme 'v240'.
           hub0: Policies didn't yield a name, using specified Name=hub0.
           ID_NET_LINK_FILE=/etc/systemd/network/10-eth0.link
           ID_NET_NAME=hub0
           ...

       Explicit Name= configuration wins in this case.

           sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/enp0s31f6
           ...
           Parsed configuration file /usr/lib/systemd/network/99-default.link
           Parsed configuration file /etc/systemd/network/10-eth0.link
           Created link configuration context.
           ID_NET_DRIVER=e1000e
           Config file /usr/lib/systemd/network/99-default.link applies to device enp0s31f6
           link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
           enp0s31f6: Device has name_assign_type=4
           Using default interface naming scheme 'v240'.
           enp0s31f6: Policy *keep*: keeping existing userspace name
           enp0s31f6: Device has addr_assign_type=0
           enp0s31f6: MAC on the device already matches policy *persistent*
           ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
           ...

       In this case, the interface was already renamed, so the keep policy
       specified as the first option in 99-default.link means that the
       existing name is preserved. If keep was removed, or if were in boot
       before the renaming has happened, we might get the following instead:

           enp0s31f6: Policy *path* yields "enp0s31f6".
           enp0s31f6: Device has addr_assign_type=0
           enp0s31f6: MAC on the device already matches policy *persistent*
           ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
           ID_NET_NAME=enp0s31f6
           ...

       Please note that the details of output are subject to change.

       Example 4. /etc/systemd/network/10-internet.link

       This example assigns the fixed name "internet0" to the interface with
       the device path "pci-0000:00:1a.0-*":

           [Match]
           Path=pci-0000:00:1a.0-*

           [Link]
           Name=internet0

       Example 5. /etc/systemd/network/25-wireless.link

       Here's an overly complex example that shows the use of a large number
       of [Match] and [Link] settings.

           [Match]
           MACAddress=12:34:56:78:9a:bc
           Driver=brcmsmac
           Path=pci-0000:02:00.0-*
           Type=wlan
           Virtualization=no
           Host=my-laptop
           Architecture=x86-64

           [Link]
           Name=wireless0
           MTUBytes=1450
           BitsPerSecond=10M
           WakeOnLan=magic
           MACAddress=cb:a9:87:65:43:21

SEE ALSO         top

       systemd-udevd.service(8), udevadm(8), systemd.netdev(5),
       systemd.network(5)

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a bug
       report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2020-07-14.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-07-14.)  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 man-pages@man7.org

systemd 246                                                  SYSTEMD.LINK(5)

Pages that refer to this page: systemd.netdev(5)systemd.network(5)30-systemd-environment-d-generator(7)systemd.directives(7)systemd.index(7)systemd.net-naming-scheme(7)systemd.syntax(7)udev(7)systemd-networkd(8)systemd-networkd.service(8)systemd-network-generator(8)systemd-network-generator.service(8)