systemd.link






systemd.link − Network device configuration



     link.link



     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(5)
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.



     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:









                             ‐2‐


     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\""









                             ‐3‐


     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.













                             ‐4‐




     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









                             ‐5‐


          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









                             ‐6‐


     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.









                             ‐7‐


          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:

     valuesTable 1. Supportedadvertise
















                             ‐8‐


     ┌───────────────────┬──────────────┬─────────────┐
     │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.










                             ‐9‐


     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.

     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.



     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]









                            ‐10‐


     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
     ...











                            ‐11‐


     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



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