NAME | SYNOPSIS | DESCRIPTION | [MATCH] SECTION OPTIONS | [LINK] SECTION OPTIONS | EXAMPLES | SEE ALSO | COLOPHON

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

NAME         top

       systemd.link - Network device configuration

SYNOPSIS         top

       link.link

DESCRIPTION         top

       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 /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         top

       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         top

       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         top

       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

       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         top

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

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a bug
       report for this manual page, see 
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.  This
       page was obtained from the project's upstream Git repository 
       ⟨https://github.com/systemd/systemd.git⟩ on 2016-10-04.  If you dis‐
       cover any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail
       to man-pages@man7.org

systemd 231                                                  SYSTEMD.LINK(5)