systemd.link

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



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-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
       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
           ┌───────────────────┬──────────────┬─────────────┐
           │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
       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
       systemd-udevd.service(8), udevadm(8), systemd.netdev(5),
       systemd.network(5)



systemd 246                                                      SYSTEMD.LINK(5)