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 /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; a symlink in /etc with the same name as a link file in /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; and 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.
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.
Path=
The persistent path, as exposed by the udev property "ID_PATH". May contain shell style globs.
Driver=
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=
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.
"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 commandline. 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:
"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.
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