systemd.link(5)

.SH "NAME" systemd.link - Network device configuration

.SH "SYNOPSIS"

.PP link.link

.SH "DESCRIPTION"

.PP 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.

.PP Note that some distributions may incorporate .link files in their early boot facilities (e.g. by including copies of the .link files in initramfs). As such it may be necessary to take manual steps to ensure that any local changes are consistent with early-boot storage facilities. The relevant distribution-specific documentation should be consulted.

.PP The .link files are read from the files located in the system network directory /usr/lib/systemd/network and /usr/local/lib/systemd/network [1], 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").

.PP 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.

.PP 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.

.PP 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 lexicographic 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 lexicographically earlier name to be considered at all.

.PP See udevadm(8) for diagnosing problems with .link files.

.SH "[MATCH] SECTION OPTIONS"

.PP 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:

.PP MACAddress=

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

Property=HOGE=foo BAR=baz

Property=ID_NET_MANAGED_BY=io.systemd.Network

ImportProperty=HOGE BAR

UnsetProperty=HOGE BAR

[Match]
OriginalName=*
[Link]
NamePolicy=keep kernel database onboard slot path
AlternativeNamesPolicy=database onboard slot path
MACAddressPolicy=persistent

[Match]
MACAddress=00:a0:de:63:7a:e6
[Link]
Name=dmz0

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

$ 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 did not yield a name, using specified Name=hub0.
ID_NET_LINK_FILE=/etc/systemd/network/10-eth0.link
ID_NET_NAME=hub0
...

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
...

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
...

[Match]
Path=pci-0000:00:1a.0-*
[Link]
Name=internet0

[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