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NAME | SYNOPSIS | DESCRIPTION | [MATCH] SECTION OPTIONS | [LINK] SECTION OPTIONS | EXAMPLES | SEE ALSO | COLOPHON |
SYSTEMD.LINK(5) systemd.link SYSTEMD.LINK(5)
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. 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.
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.
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".
AutoNegotiation=
Enables or disables automatic negotiation of transmission
parameters. Autonegotiation is a procedure by which two connected
ethernet devices choose common transmission parameters, such as
speed, duplex mode, and flow control. Takes a boolean value.
Unset by default, which means that the kernel default will be
used.
Note that if autonegotiation is enabled, speed and duplex
settings are read-only. If autonegotation is disabled, speed and
duplex settings are writable if the driver supports multiple link
modes.
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.
Port=
The port option is used to select the device port. The supported
values are:
"tp"
An Ethernet interface using Twisted-Pair cable as the medium.
"aui"
Attachment Unit Interface (AUI). Normally used with hubs.
"bnc"
An Ethernet interface using BNC connectors and co-axial
cable.
"mii"
An Ethernet interface using a Media Independent Interface
(MII).
"fibre"
An Ethernet interface using Optical Fibre as the medium.
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".
Example 1. /usr/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
systemd-udevd.service(8), udevadm(8), systemd.netdev(5),
systemd.network(5)
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2017-07-05. If you dis‐
cover any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
systemd 234 SYSTEMD.LINK(5)
Pages that refer to this page: systemd.netdev(5), systemd.network(5), systemd.directives(7), systemd.index(7), udev(7), systemd-networkd.service(8)