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=
    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

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.

KernelVersion=
    Checks whether the kernel version (as reported by uname -r) matches a certain expression (or if prefixed with the exclamation mark does not match it). See ConditionKernelVersion= 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 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 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.

    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.

    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 in case all the policies specified in NamePolicy= fail, or in case NamePolicy= is missing or disabled.

    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".

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 autonegotation 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.

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).

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)