systemd.link(5)

NAME

systemd.link - Network device configuration

SYNOPSIS

link.link

DESCRIPTION

A plain ini-style text file that encodes configuration for matching network devices, used by systemd-udevd(8) and in particular its net_setup_link builtin. See systemd.syntax(7) 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 and /usr/local/lib/systemd/network, the volatile runtime network directory /run/systemd/network, and the local administration network directory /etc/systemd/network. All configuration files are collectively sorted and processed in alphanumeric order, regardless of the directories in which they live. However, files with identical filenames replace each other. It is recommended that each filename is prefixed with a number smaller than "70" (e.g. 10-eth0.link). Otherwise, the default .link files or those generated by systemd-network-generator.service(8) may take precedence over user configured files. 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").

Along with the link file foo.link, a "drop-in" directory foo.link.d/ may exist. All files with the suffix ".conf" from this directory will be merged in the alphanumeric order and parsed after the main file itself has been parsed. This is useful to alter or add configuration settings, without having to modify the main configuration file. Each drop-in file must have appropriate section headers.

In addition to /etc/systemd/network, drop-in ".d" directories can be placed in /usr/lib/systemd/network or /run/systemd/network directories. Drop-in files in /etc/ take precedence over those in /run/ which in turn take precedence over those in /usr/lib/. Drop-in files under any of these directories take precedence over the main link file wherever located.

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 an interface 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 interfaces 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 first (in alphanumeric order) of the link files that matches a given interface is applied, all later files are ignored, even if they match as well. The following keys are accepted:

MACAddress=

PermanentMACAddress=

Path=

Driver=

Type=

Kind=

Property=

Property=ID_MODEL_ID=9999 "ID_VENDOR_FROM_DATABASE=vendor name" "KEY=with \"quotation\""

OriginalName=

Host=

Virtualization=

KernelCommandLine=

KernelVersion=

Credential=

Architecture=

Firmware=

[LINK] SECTION OPTIONS

The [Link] section accepts the following keys:

Description=

Alias=

MACAddressPolicy=

MACAddress=

NamePolicy=

Name=

AlternativeNamesPolicy=

AlternativeName=

TransmitQueues=

ReceiveQueues=

TransmitQueueLength=

MTUBytes=

BitsPerSecond=

Duplex=

AutoNegotiation=

WakeOnLan=

WakeOnLanPassword=

Port=

Advertise=

ReceiveChecksumOffload=

TransmitChecksumOffload=

TCPSegmentationOffload=

TCP6SegmentationOffload=

GenericSegmentationOffload=

GenericReceiveOffload=

GenericReceiveOffloadHardware=

LargeReceiveOffload=

ReceiveVLANCTAGHardwareAcceleration=

TransmitVLANCTAGHardwareAcceleration=

ReceiveVLANCTAGFilter=

TransmitVLANSTAGHardwareAcceleration=

NTupleFilter=

RxChannels=, TxChannels=, OtherChannels=, CombinedChannels=

RxBufferSize=, RxMiniBufferSize=, RxJumboBufferSize=, TxBufferSize=

RxFlowControl=

TxFlowControl=

AutoNegotiationFlowControl=

GenericSegmentOffloadMaxBytes=

GenericSegmentOffloadMaxSegments=

UseAdaptiveRxCoalesce=, UseAdaptiveTxCoalesce=

RxCoalesceSec=, RxCoalesceIrqSec=, RxCoalesceLowSec=, RxCoalesceHighSec=, TxCoalesceSec=, TxCoalesceIrqSec=, TxCoalesceLowSec=, TxCoalesceHighSec=

RxMaxCoalescedFrames=, RxMaxCoalescedIrqFrames=, RxMaxCoalescedLowFrames=, RxMaxCoalescedHighFrames=, TxMaxCoalescedFrames=, TxMaxCoalescedIrqFrames=, TxMaxCoalescedLowFrames=, TxMaxCoalescedHighFrames=

CoalescePacketRateLow=, CoalescePacketRateHigh=

CoalescePacketRateSampleIntervalSec=

StatisticsBlockCoalesceSec=

MDI=

SR-IOVVirtualFunctions=

[SR-IOV] SECTION OPTIONS

The [SR-IOV] section accepts the following keys. Specify several [SR-IOV] sections to configure several SR-IOVs. SR-IOV provides the ability to partition a single physical PCI resource into virtual PCI functions which can then be injected into a VM. In the case of network VFs, SR-IOV improves north-south network performance (that is, traffic with endpoints outside the host machine) by allowing traffic to bypass the host machine’s network stack.

VirtualFunction=

VLANId=

QualityOfService=

VLANProtocol=

MACSpoofCheck=

QueryReceiveSideScaling=

Trust=

LinkState=

MACAddress=

EXAMPLES

Example 1. /usr/lib/systemd/network/99-default.link

The link file 99-default.link that is shipped with systemd defines the default policies for the interface name, alternative names, and MAC address of links.

[Match]
OriginalName=*
[Link]
NamePolicy=keep kernel database onboard slot path
AlternativeNamesPolicy=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-default.link, i.e. it needs a numerical prefix, to have any effect at all.

Example 3. (Re-)applying a .link file to an interface

After a new .link file has been created, or an existing .link file modified, the new settings may be applied to the matching interface with the following commands:

$ sudo udevadm control --reload
$ sudo ip link set eth0 down
$ sudo udevadm trigger --verbose --settle --action add /sys/class/net/eth0

You may also need to stop the service that manages the network interface, e.g. systemd-networkd.service(8) or NetworkManager.service before the above operation, and then restart the service after that. For more details about udevadm command, see udevadm(8).

Example 4. 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
...

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 5. /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 6. /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), systemd-network-generator.service(8)

NOTES

1.

System and Service Credentials