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=
The hardware address.
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.
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" 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". 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:
"phy"
Wake on PHY activity.
"magic"
Wake on receipt of a magic packet.
"off"
Never wake.
TCPSegmentationOffload=
The TCP Segmentation Offload (TSO) when true enables TCP
segmentation offload. Takes a boolean value. Defaults to "unset".
GenericSegmentationOffload=
The Generic Segmentation Offload (GSO) when true enables generic
segmentation offload. Takes a boolean value. Defaults to "unset".
UDPSegmentationOffload=
The UDP Segmentation Offload (USO) when true enables UDP
segmentation offload. Takes a boolean value. Defaults to "unset".
GenericReceiveOffload=
The Generic Receive Offload (GRO) when true enables generic receive
offload. Takes a boolean value. Defaults to "unset".
LargeReceiveOffload=
The Large Receive Offload (LRO) when true enables large receive
offload. Takes a boolean value. Defaults to "unset".
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)
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