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.

[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 can not 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.

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)