focal (5) systemd.link.5.gz

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NAME

       systemd.link - Network device configuration

SYNOPSIS

       link.link

DESCRIPTION

       A plain ini-style text file that encodes configuration for matching network devices, used by systemd-
       udev(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 /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 /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

       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

       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
           ┌───────────────────┬──────────────┬─────────────┐
           │AdvertiseSpeed (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 a integer. Specifies the NIC receive ring buffer size. When unset, the kernel's default will be
           used.

       TxBufferSize=
           Takes a integer. Specifies the NIC transmit ring buffer size. When unset, the kernel's default will
           be used.

EXAMPLES

       Example 1. /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 /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 /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 /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=/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=/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

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