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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
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.
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 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
devices 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 following keys are accepted:
MACAddress=
A whitespace-separated list of hardware addresses. Use full
colon-, hyphen- or dot-delimited hexadecimal. See the example
below. This option may appear more than once, in which case the
lists are merged. If the empty string is assigned to this option,
the list of hardware addresses defined prior to this is reset.
Example:
MACAddress=01:23:45:67:89:ab 00-11-22-33-44-55 AABB.CCDD.EEFF
PermanentMACAddress=
A whitespace-separated list of hardware's permanent addresses.
While MACAddress= matches the device's current MAC address, this
matches the device's permanent MAC address, which may be
different from the current one. Use full colon-, hyphen- or
dot-delimited hexadecimal. This option may appear more than once,
in which case the lists are merged. If the empty string is
assigned to this option, the list of hardware addresses defined
prior to this is reset.
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 ID_NET_DRIVER of its parent device, or if that is not
set, the driver as exposed by ethtool -i of the device itself. If
the list is prefixed with a "!", the test is inverted.
Type=
A whitespace-separated list of shell-style globs matching the
device type, as exposed by networkctl status. If the list is
prefixed with a "!", the test is inverted.
Property=
A whitespace-separated list of udev property name with its value
after a equal ("="). If multiple properties are specified, the
test results are ANDed. If the list is prefixed with a "!", the
test is inverted. If a value contains white spaces, then please
quote whole key and value pair. If a value contains quotation,
then please escape the quotation with "\".
Example: if a .link file has the following:
Property=ID_MODEL_ID=9999 "ID_VENDOR_FROM_DATABASE=vendor name" "KEY=with \"quotation\""
then, the .link file matches only when an interface has all the
above three properties.
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.
Host=
Matches against the hostname or machine ID of the host. See
ConditionHost= in systemd.unit(5) for details. When prefixed with
an exclamation mark ("!"), the result is negated. If an empty
string is assigned, then previously assigned value is cleared.
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. When prefixed with an exclamation mark ("!"), the
result is negated. If an empty string is assigned, then
previously assigned value is cleared.
KernelCommandLine=
Checks whether a specific kernel command line option is set. See
ConditionKernelCommandLine= in systemd.unit(5) for details. When
prefixed with an exclamation mark ("!"), the result is negated.
If an empty string is assigned, then previously assigned value is
cleared.
KernelVersion=
Checks whether the kernel version (as reported by uname -r)
matches a certain expression. See ConditionKernelVersion= in
systemd.unit(5) for details. When prefixed with an exclamation
mark ("!"), the result is negated. If an empty string is
assigned, then previously assigned value is cleared.
Architecture=
Checks whether the system is running on a specific architecture.
See ConditionArchitecture= in systemd.unit(5) for details. When
prefixed with an exclamation mark ("!"), the result is negated.
If an empty string is assigned, then previously assigned value is
cleared.
The [Link] section accepts the following keys:
Description=
A description of the device.
Alias=
The ifalias interface property 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(7), rule to set
NAME. 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. See systemd.net-naming-scheme(7).
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. See systemd.net-naming-scheme(7).
path
The name is set based on the device's physical location, as
exported by the udev property ID_NET_NAME_PATH. See
systemd.net-naming-scheme(7).
mac
The name is set based on the device's persistent MAC address,
as exported by the udev property ID_NET_NAME_MAC. See
systemd.net-naming-scheme(7).
keep
If the device already had a name given by userspace (as part
of creation of the device or a rename), keep it.
Name=
The interface name to use. This option has lower precedence than
NamePolicy=, so for this setting to take effect, NamePolicy= must
either be unset, empty, disabled, or all policies configured
there must fail. Also see the example below with "Name=dmz0".
Note that specifying a name that the kernel might use for another
interface (for example "eth0") is dangerous because the name
assignment done by udev will race with the assignment done by the
kernel, and only one interface may use the name. Depending on the
order of operations, either udev or the kernel will win, making
the naming unpredictable. It is best to use some different
prefix, for example "internal0"/"external0" or
"lan0"/"lan1"/"lan3".
AlternativeNamesPolicy=
A space-separated list of policies by which the interface's
alternative names should be set. Each of the policies may fail,
and all successful policies are used. The available policies are
"database", "onboard", "slot", "path", and "mac". If the kernel
does not support the alternative names, then this setting will be
ignored.
AlternativeName=
The alternative interface name to use. This option can be
specified multiple times. If the empty string is assigned to this
option, the list is reset, and all prior assignments have no
effect. If the kernel does not support the alternative names,
then this setting will be ignored.
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=
Takes a boolean. If set to yes, automatic negotiation of
transmission parameters is enabled. Autonegotiation is a
procedure by which two connected ethernet devices choose common
transmission parameters, such as speed, duplex mode, and flow
control. When unset, the kernel's default will be used.
Note that if autonegotiation is enabled, speed and duplex
settings are read-only. If autonegotiation 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.
unicast
Wake on unicast messages.
multicast
Wake on multicast messages.
broadcast
Wake on broadcast messages.
arp
Wake on ARP.
magic
Wake on receipt of a magic packet.
secureon
Enable secureon(tm) password for MagicPacket(tm).
off
Never wake.
Defaults to off.
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.
Advertise=
This sets what speeds and duplex modes of operation are
advertised for auto-negotiation. This implies
"AutoNegotiation=yes". The supported values are:
Table 1. Supported advertise values
┌───────────────────┬──────────────┬─────────────┐
│Advertise │ Speed (Mbps) │ Duplex Mode │
├───────────────────┼──────────────┼─────────────┤
│10baset-half │ 10 │ half │
├───────────────────┼──────────────┼─────────────┤
│10baset-full │ 10 │ full │
├───────────────────┼──────────────┼─────────────┤
│100baset-half │ 100 │ half │
├───────────────────┼──────────────┼─────────────┤
│100baset-full │ 100 │ full │
├───────────────────┼──────────────┼─────────────┤
│1000baset-half │ 1000 │ half │
├───────────────────┼──────────────┼─────────────┤
│1000baset-full │ 1000 │ full │
├───────────────────┼──────────────┼─────────────┤
│10000baset-full │ 10000 │ full │
├───────────────────┼──────────────┼─────────────┤
│2500basex-full │ 2500 │ full │
├───────────────────┼──────────────┼─────────────┤
│1000basekx-full │ 1000 │ full │
├───────────────────┼──────────────┼─────────────┤
│10000basekx4-full │ 10000 │ full │
├───────────────────┼──────────────┼─────────────┤
│10000basekr-full │ 10000 │ full │
├───────────────────┼──────────────┼─────────────┤
│10000baser-fec │ 10000 │ full │
├───────────────────┼──────────────┼─────────────┤
│20000basemld2-full │ 20000 │ full │
├───────────────────┼──────────────┼─────────────┤
│20000basekr2-full │ 20000 │ full │
└───────────────────┴──────────────┴─────────────┘
By default this is unset, i.e. all possible modes will be
advertised. This option may be specified more than once, in which
case all specified speeds and modes are advertised. If the empty
string is assigned to this option, the list is reset, and all
prior assignments have no effect.
ReceiveChecksumOffload=
Takes a boolean. If set to true, the hardware offload for
checksumming of ingress network packets is enabled. When unset,
the kernel's default will be used.
TransmitChecksumOffload=
Takes a boolean. If set to true, the hardware offload for
checksumming of egress network packets is enabled. When unset,
the kernel's default will be used.
TCPSegmentationOffload=
Takes a boolean. If set to true, the TCP Segmentation Offload
(TSO) is enabled. When unset, the kernel's default will be used.
TCP6SegmentationOffload=
Takes a boolean. If set to true, the TCP6 Segmentation Offload
(tx-tcp6-segmentation) is enabled. When unset, the kernel's
default will be used.
GenericSegmentationOffload=
Takes a boolean. If set to true, the Generic Segmentation Offload
(GSO) is enabled. When unset, the kernel's default will be used.
GenericReceiveOffload=
Takes a boolean. If set to true, the Generic Receive Offload
(GRO) is enabled. When unset, the kernel's default will be used.
LargeReceiveOffload=
Takes a boolean. If set to true, the Large Receive Offload (LRO)
is enabled. When unset, the kernel's default will be used.
RxChannels=
Sets the number of receive channels (a number between 1 and
4294967295) .
TxChannels=
Sets the number of transmit channels (a number between 1 and
4294967295).
OtherChannels=
Sets the number of other channels (a number between 1 and
4294967295).
CombinedChannels=
Sets the number of combined set channels (a number between 1 and
4294967295).
RxBufferSize=
Takes an integer. Specifies the maximum number of pending packets
in the NIC receive buffer. When unset, the kernel's default will
be used.
RxMiniBufferSize=
Takes an integer. Specifies the maximum number of pending packets
in the NIC mini receive buffer. When unset, the kernel's default
will be used.
RxJumboBufferSize=
Takes an integer. Specifies the maximum number of pending packets
in the NIC jumbo receive buffer. When unset, the kernel's default
will be used.
TxBufferSize=
Takes an integer. Specifies the maximum number of pending packets
in the NIC transmit buffer. When unset, the kernel's default will
be used.
RxFlowControl=
Takes a boolean. When set, enables the receive flow control, also
known as the ethernet receive PAUSE message (generate and send
ethernet PAUSE frames). When unset, the kernel's default will be
used.
TxFlowControl=
Takes a boolean. When set, enables the transmit flow control,
also known as the ethernet transmit PAUSE message (respond to
received ethernet PAUSE frames). When unset, the kernel's default
will be used.
AutoNegotiationFlowControl=
Takes a boolean. When set, the auto negotiation enables the
interface to exchange state advertisements with the connected
peer so that the two devices can agree on the ethernet PAUSE
configuration. When unset, the kernel's default will be used.
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
NamePolicy= is not set, so Name= takes effect. We use the "10-"
prefix to order this file early in the list. Note that it needs to be
before "99-link", i.e. it needs a numerical prefix, to have any
effect at all.
Example 3. Debugging NamePolicy= assignments
$ 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 didn't yield a name, using specified Name=hub0.
ID_NET_LINK_FILE=/etc/systemd/network/10-eth0.link
ID_NET_NAME=hub0
...
Explicit Name= configuration wins in this case.
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
...
In this case, the interface was already renamed, so the keep policy
specified as the first option in 99-default.link means that the
existing name is preserved. If keep was removed, or if were in boot
before the renaming has happened, we might get the following instead:
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
...
Please note that the details of output are subject to change.
Example 4. /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 5. /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 2020-08-13. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-08-11.) If you discover 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 246 SYSTEMD.LINK(5)
Pages that refer to this page: systemd.netdev(5) , systemd.network(5) , 30-systemd-environment-d-generator(7) , systemd.directives(7) , systemd.index(7) , systemd.net-naming-scheme(7) , systemd.syntax(7) , udev(7) , systemd-networkd(8) , systemd-networkd.service(8) , systemd-network-generator(8) , systemd-network-generator.service(8)