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NAME | SYNOPSIS | DESCRIPTION | [MATCH] SECTION OPTIONS | [LINK] SECTION OPTIONS | EXAMPLES | SEE ALSO | COLOPHON |
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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. Or use the
MAC address specified in MACAddress=.
An empty string assignment is equivalent to setting "none".
MACAddress=
The interface MAC address to use. For this setting to take
effect, MACAddressPolicy= must either be unset, empty, or
"none".
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 2020-12-18. (At that
time, the date of the most recent commit that was found in the
repository was 2020-12-18.) 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 247 SYSTEMD.LINK(5)
Pages that refer to this page: systemd.netdev(5), systemd.network(5), systemd.directives(7), systemd.index(7), systemd.net-naming-scheme(7), systemd.syntax(7), udev(7), systemd-networkd.service(8), systemd-network-generator.service(8)
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