systemd.link(5)

NAME

   systemd.link - Network device configuration

SYNOPSIS

   link.link

DESCRIPTION

   Network link configuration is performed by the net_setup_link udev
   builtin.

   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 each of the entries in the
   "[Match]" section matches, or if the section is empty. The following
   keys are accepted:

   MACAddress=
       The hardware address.

   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.

   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 "DRIVER" of its parent device, or if that is not set, the
       driver as exposed by "ethtool -i" of the device itself.

   Type=
       A whitespace-separated list of shell-style globs matching the
       device type, as exposed by the udev property "DEVTYPE".

   Host=
       Matches against the hostname or machine ID of the host. See
       "ConditionHost=" in systemd.unit(5) for details.

   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.

   KernelCommandLine=
       Checks whether a specific kernel command line option is set (or if
       prefixed with the exclamation mark unset). See
       "ConditionKernelCommandLine=" in systemd.unit(5) for details.

   Architecture=
       Checks whether the system is running on a specific architecture.
       See "ConditionArchitecture=" in systemd.unit(5) for details.

[LINK] SECTION OPTIONS

   The "[Link]" section accepts the following keys:

   Description=
       A description of the device.

   Alias=
       The "ifalias" 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 rule to set "NAME". If the
       name has already been set by userspace, no renaming is performed.
       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".

       "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".

       "path"
           The name is set based on the device's physical location, as
           exported by the udev property "ID_NET_NAME_PATH".

       "mac"
           The name is set based on the device's persistent MAC address,
           as exported by the udev property "ID_NET_NAME_MAC".

   Name=
       The interface name to use in case all the policies specified in
       NamePolicy= fail, or in case NamePolicy= is missing or disabled.

   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".

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

       "phy"
           Wake on PHY activity.

       "magic"
           Wake on receipt of a magic packet.

       "off"
           Never wake.

   TCPSegmentationOffload=
       The TCP Segmentation Offload (TSO) when true enables TCP
       segmentation offload. Takes a boolean value. Defaults to "unset".

   GenericSegmentationOffload=
       The Generic Segmentation Offload (GSO) when true enables generic
       segmentation offload. Takes a boolean value. Defaults to "unset".

   UDPSegmentationOffload=
       The UDP Segmentation Offload (USO) when true enables UDP
       segmentation offload. Takes a boolean value. Defaults to "unset".

   GenericReceiveOffload=
       The Generic Receive Offload (GRO) when true enables generic receive
       offload. Takes a boolean value. Defaults to "unset".

   LargeReceiveOffload=
       The Large Receive Offload (LRO) when true enables large receive
       offload. Takes a boolean value. Defaults to "unset".

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

   Example 3. /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 4. /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)

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