systemd.link — Network device configuration
link.link
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;
a symlink in /etc with the same name as a
link file in /usr/lib, pointing to
/dev/null, disables the link file
entirely.
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.
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.
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 existing 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.
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:
Example 1. /etc/systemd/network/wireless.link
[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