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 and
/usr/local/lib/systemd/network
[1],
the volatile runtime network directory
/run/systemd/network, and the local administration network directory
/etc/systemd/network. All configuration files are collectively sorted and
processed in alphanumeric order, regardless of the directories in which they live. However, files
with identical filenames replace each other. It is recommended that each filename is prefixed with
a number smaller than "70" (e.g. 10-eth0.link). Otherwise, the
default .link files or those generated by
systemd-network-generator.service(8)
may take precedence over user configured files. 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").
Along with the link file foo.link, a "drop-in" directory
foo.link.d/ may exist. All files with the suffix ".conf"
from this directory will be merged in the alphanumeric order and parsed after the main file itself
has been parsed. This is useful to alter or add configuration settings, without having to modify
the main configuration file. Each drop-in file must have appropriate section headers.
In addition to /etc/systemd/network, drop-in ".d"
directories can be placed in /usr/lib/systemd/network or
/run/systemd/network directories. Drop-in files in /etc/
take precedence over those in /run/ which in turn take precedence over those
in /usr/lib/. Drop-in files under any of these directories take precedence
over the main link file wherever located.
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 an interface 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 interfaces 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 first (in alphanumeric order) of the link files that matches a given interface is applied, all later files are ignored, even if they match as well. The following keys are accepted:
MACAddress=¶A whitespace-separated list of hardware addresses. The acceptable formats are:
colon-delimited hexadecimal¶
Each field must be one byte.
E.g. "12:34:56:78:90:ab" or "AA:BB:CC:DD:EE:FF".
hyphen-delimited hexadecimal¶
Each field must be one byte.
E.g. "12-34-56-78-90-ab" or "AA-BB-CC-DD-EE-FF".
dot-delimited hexadecimal¶
Each field must be two bytes.
E.g. "1234.5678.90ab" or "AABB.CCDD.EEFF".
IPv4 address format¶
E.g. "127.0.0.1" or "192.168.0.1".
IPv6 address format¶
E.g. "2001:0db8:85a3::8a2e:0370:7334" or "::1".
The total length of each MAC address must be 4 (for IPv4 tunnel), 6 (for Ethernet), 16 (for IPv6 tunnel), or 20 (for InfiniBand). 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. Defaults to unset.
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, or IPv4 or IPv6 address format. 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. Defaults to
unset.
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 list. If the list is prefixed with a "!", the test is inverted.
Some valid values are "ether", "loopback", "wlan", "wwan".
Valid types are named either from the udev "DEVTYPE" attribute, or
"ARPHRD_" macros in linux/if_arp.h, so this is not comprehensive.
Kind=¶A whitespace-separated list of shell-style globs matching the device kind, as exposed by
networkctl status INTERFACE or
ip -d link show INTERFACE. If the list is
prefixed with a "!", the test is inverted. Some valid values are "bond",
"bridge", "gre", "tun",
"veth". Valid kinds are given by netlink's "IFLA_INFO_KIND"
attribute, so this is not comprehensive.
Property=¶A whitespace-separated list of udev property names with their values after equals sign
("="). 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, the 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, the 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, the 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, the previously assigned value is cleared.
Credential=¶Checks whether the specified credential was passed to the
systemd-udevd.service service. See System and Service Credentials for details. When
prefixed with an exclamation mark ("!"), the result is negated. If an empty
string is assigned, the 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, the previously assigned value is cleared.
Firmware=¶Checks whether the system is running on a machine with the specified firmware. See
ConditionFirmware= in
systemd.unit(5)
for details. When prefixed with an exclamation mark ("!"), the result is negated.
If an empty string is assigned, the previously assigned value is cleared.
The [Link] section accepts the following keys:
Description=¶A description of the device.
Property=¶Set specified udev properties. This takes space separated list of key-value pairs
concatenated with equal sign ("="). Example:
Property=HOGE=foo BAR=baz
This option supports simple specifier expansion, see the Specifiers section below. This option can be specified multiple times. If an empty string is assigned, then the all previous assignments are cleared.
This setting is useful to configure the "ID_NET_MANAGED_BY=" property which
declares which network management service shall manage the interface, which is respected by
systemd-networkd and others. Use
Property=ID_NET_MANAGED_BY=io.systemd.Network
to declare explicitly that systemd-networkd shall manage the interface, or set the property to something else to declare explicitly it shall not do so. See systemd.network(5) for details how this property is used to match interface names.
ImportProperty=¶Import specified udev properties from the saved database. This takes space separated list of property names. Example:
ImportProperty=HOGE BAR
This option supports simple specifier expansion, see the Specifiers section below. This option can be specified multiple times. If an empty string is assigned, then the all previous assignments are cleared.
If the same property is also set in Property= in the above, then the
imported property value will be overridden by the value specified in Property=.
UnsetProperty=¶Unset specified udev properties. This takes space separated list of property names. Example:
ImportProperty=HOGE BAR
This option supports simple specifier expansion, see the Specifiers section below. This option can be specified multiple times. If an empty string is assigned, then the all previous assignments are cleared.
This setting is applied after ImportProperty= and
Property= are applied. Hence, if the same property is specified in
ImportProperty= or Property=, then the imported or specified
property value will be ignored, and the property will be unset.
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".
Interface names must have a minimum length of 1 character and a maximum length of 15
characters, and may contain any 7bit ASCII character, with the exception of control characters,
":", "/" and "%". While "." is
an allowed character, it's recommended to avoid it when naming interfaces as various tools (such as
resolvconf(1)) use
it as separator character. Also, fully numeric interface names are not allowed (in order to avoid
ambiguity with interface specification by numeric indexes), nor are the special strings
".", "..", "all" and
"default".
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.
Alternative interface names may be used to identify interfaces in various tools. In contrast
to the primary name (as configured with Name= above) there may be multiple
alternative names referring to the same interface. Alternative names may have a maximum length of
127 characters, in contrast to the 15 allowed for the primary interface name, but otherwise are
subject to the same naming constraints.
TransmitQueues=¶Specifies the device's number of transmit queues. An integer in the range 1…4096. When unset, the kernel's default will be used.
ReceiveQueues=¶Specifies the device's number of receive queues. An integer in the range 1…4096. When unset, the kernel's default will be used.
TransmitQueueLength=¶Specifies the transmit queue length of the device in number of packets. An unsigned integer in the range 0…4294967294. When unset, the kernel's default will be used.
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. Takes the special value
"off" which disables Wake-on-LAN, or space separated list of the following
words:
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 password for MagicPacket. Implied when
WakeOnLanPassword= is specified. If specified without
WakeOnLanPassword= option, then the password is read from the
credential "LINK.link.wol.password60-foo.link.wol.password"), and if the credential not found, then
read from "wol.password". See
ImportCredential=/LoadCredential=/SetCredential= in
systemd.exec(5)
for details. The password in the credential, must be 6 bytes in hex format with each
byte separated by a colon (":") like an Ethernet MAC address, e.g.,
"aa:bb:cc:dd:ee:ff".
Defaults to unset, and the device's default will be used. This setting can be specified multiple times. If an empty string is assigned, then the all previous assignments are cleared.
WakeOnLanPassword=¶Specifies the SecureOn password for MagicPacket. Takes an absolute path to a regular
file or an AF_UNIX stream socket, or the plain password. When a path to
a regular file is specified, the password is read from it. When an
AF_UNIX stream socket is specified, a connection is made to it and the
password is read from it. The password must be 6 bytes in hex format with each byte separated
by a colon (":") like an Ethernet MAC address, e.g.,
"aa:bb:cc:dd:ee:ff". This implies WakeOnLan=secureon.
Defaults to unset, and the current value will not be changed.
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-full | 10 | full |
10baset1brr-full | 10 | full |
10baset1l-full | 10 | full |
10baset1s-full | 10 | full |
10baset-half | 10 | half |
10baset1s-half | 10 | half |
10baset1s-p2mp-half | 10 | half |
100basefx-full | 100 | full |
100baset-full | 100 | full |
100baset1-full | 100 | full |
100basefx-half | 100 | half |
100baset-half | 100 | half |
1000basekx-full | 1000 | full |
1000baset-full | 1000 | full |
1000baset1-full | 1000 | full |
1000basex-full | 1000 | full |
1000baset-half | 1000 | half |
2500baset-full | 2500 | full |
2500basex-full | 2500 | full |
5000baset-full | 5000 | full |
10000baser-fec | 10000 | |
10000basecr-full | 10000 | full |
10000baseer-full | 10000 | full |
10000basekr-full | 10000 | full |
10000basekx4-full | 10000 | full |
10000baselr-full | 10000 | full |
10000baselrm-full | 10000 | full |
10000basesr-full | 10000 | full |
10000baset-full | 10000 | full |
20000basekr2-full | 20000 | full |
20000basemld2-full | 20000 | full |
25000basecr-full | 25000 | full |
25000basekr-full | 25000 | full |
25000basesr-full | 25000 | full |
40000basecr4-full | 40000 | full |
40000basekr4-full | 40000 | full |
40000baselr4-full | 40000 | full |
40000basesr4-full | 40000 | full |
50000basecr-full | 50000 | full |
50000basecr2-full | 50000 | full |
50000basedr-full | 50000 | full |
50000basekr-full | 50000 | full |
50000basekr2-full | 50000 | full |
50000baselr-er-fr-full | 50000 | full |
50000basesr-full | 50000 | full |
50000basesr2-full | 50000 | full |
56000basecr4-full | 56000 | full |
56000basekr4-full | 56000 | full |
56000baselr4-full | 56000 | full |
56000basesr4-full | 56000 | full |
100000basecr-full | 100000 | full |
100000basecr2-full | 100000 | full |
100000basecr4-full | 100000 | full |
100000basedr-full | 100000 | full |
100000basedr2-full | 100000 | full |
100000basekr-full | 100000 | full |
100000basekr2-full | 100000 | full |
100000basekr4-full | 100000 | full |
100000baselr-er-fr-full | 100000 | full |
100000baselr2-er2-fr2-full | 100000 | full |
100000baselr4-er4-full | 100000 | full |
100000basesr-full | 100000 | full |
100000basesr2-full | 100000 | full |
100000basesr4-full | 100000 | full |
200000basecr2-full | 200000 | full |
200000basecr4-full | 200000 | full |
200000basedr2-full | 200000 | full |
200000basedr4-full | 200000 | full |
200000basekr2-full | 200000 | full |
200000basekr4-full | 200000 | full |
200000baselr2-er2-fr2-full | 200000 | full |
200000baselr4-er4-fr4-full | 200000 | full |
200000basesr2-full | 200000 | full |
200000basesr4-full | 200000 | full |
400000basecr4-full | 400000 | full |
400000basecr8-full | 400000 | full |
400000basedr4-full | 400000 | full |
400000basedr8-full | 400000 | full |
400000basekr4-full | 400000 | full |
400000basekr8-full | 400000 | full |
400000baselr4-er4-fr4-full | 400000 | full |
400000baselr8-er8-fr8-full | 400000 | full |
400000basesr4-full | 400000 | full |
400000basesr8-full | 400000 | full |
800000basecr8-full | 800000 | full |
800000basedr8-2-full | 800000 | full |
800000basedr8-full | 800000 | full |
800000basekr8-full | 800000 | full |
800000basesr8-full | 800000 | full |
800000basevr8-full | 800000 | full |
asym-pause | ||
aui | ||
autonegotiation | ||
backplane | ||
bnc | ||
fec-baser | ||
fec-llrs | ||
fec-none | ||
fec-rs | ||
fibre | ||
mii | ||
pause | ||
tp |
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, 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, 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, TCP Segmentation Offload (TSO) is enabled. When unset, the kernel's default will be used.
TCP6SegmentationOffload=¶Takes a boolean. If set to true, 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, Generic Segmentation Offload (GSO) is enabled. When unset, the kernel's default will be used.
GenericReceiveOffload=¶Takes a boolean. If set to true, Generic Receive Offload (GRO) is enabled. When unset, the kernel's default will be used.
GenericReceiveOffloadHardware=¶Takes a boolean. If set to true, hardware accelerated Generic Receive Offload (GRO) is enabled. When unset, the kernel's default will be used.
LargeReceiveOffload=¶Takes a boolean. If set to true, Large Receive Offload (LRO) is enabled. When unset, the kernel's default will be used.
ReceivePacketSteeringCPUMask=¶Configures Receive Packet Steering (RPS) list of CPUs to which RPS may forward traffic.
Takes a list of CPU indices or ranges separated by either whitespace or commas. Alternatively,
takes the special value "all" in which will include all available CPUs in the mask.
CPU ranges are specified by the lower and upper CPU indices separated by a dash (e.g. "2-6").
This option may be specified more than once, in which case the specified CPU affinity masks are merged.
If an empty string is assigned, the mask is reset, all assignments prior to this will have no effect.
Defaults to unset and RPS CPU list is unchanged. To disable RPS when it was previously enabled, use the
special value "disable".
ReceiveVLANCTAGHardwareAcceleration=¶Takes a boolean. If set to true, receive VLAN CTAG hardware acceleration is enabled. When unset, the kernel's default will be used.
TransmitVLANCTAGHardwareAcceleration=¶Takes a boolean. If set to true, transmit VLAN CTAG hardware acceleration is enabled. When unset, the kernel's default will be used.
ReceiveVLANCTAGFilter=¶Takes a boolean. If set to true, receive filtering on VLAN CTAGs is enabled. When unset, the kernel's default will be used.
TransmitVLANSTAGHardwareAcceleration=¶Takes a boolean. If set to true, transmit VLAN STAG hardware acceleration is enabled. When unset, the kernel's default will be used.
NTupleFilter=¶Takes a boolean. If set to true, receive N-tuple filters and actions are enabled. When unset, the kernel's default will be used.
RxChannels=, TxChannels=, OtherChannels=, CombinedChannels=¶Specifies the number of receive, transmit, other, or combined channels, respectively.
Takes an unsigned integer in the range 1…4294967295 or "max". If set to
"max", the advertised maximum value of the hardware will be used. When
unset, the number will not be changed. Defaults to unset.
RxBufferSize=, RxMiniBufferSize=, RxJumboBufferSize=, TxBufferSize=¶Specifies the maximum number of pending packets in the NIC receive buffer, mini receive
buffer, jumbo receive buffer, or transmit buffer, respectively. Takes an unsigned integer in
the range 1…4294967295 or "max". If set to "max", the
advertised maximum value of the hardware will be used. When unset, the number will not be
changed. Defaults to unset.
RxFlowControl=¶Takes a boolean. When set, enables 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 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, 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.
GenericSegmentOffloadMaxBytes=¶Specifies the maximum size of a Generic Segment Offload (GSO) packet the device should accept. The usual suffixes K, M, G are supported and are understood to the base of 1024. An unsigned integer in the range 1…65536. Defaults to unset.
GenericSegmentOffloadMaxSegments=¶Specifies the maximum number of Generic Segment Offload (GSO) segments the device should accept. An unsigned integer in the range 1…65535. Defaults to unset.
UseAdaptiveRxCoalesce=, UseAdaptiveTxCoalesce=¶Boolean properties that, when set, enable/disable adaptive Rx/Tx coalescing if the hardware supports it. When unset, the kernel's default will be used.
RxCoalesceSec=, RxCoalesceIrqSec=, RxCoalesceLowSec=, RxCoalesceHighSec=, TxCoalesceSec=, TxCoalesceIrqSec=, TxCoalesceLowSec=, TxCoalesceHighSec=¶These properties configure the delay before Rx/Tx interrupts are generated after a packet is
sent/received. The "Irq" properties come into effect when the host is servicing an
IRQ. The "Low" and "High" properties come into effect when the
packet rate drops below the low packet rate threshold or exceeds the high packet rate threshold
respectively if adaptive Rx/Tx coalescing is enabled. When unset, the kernel's defaults will be
used.
RxMaxCoalescedFrames=, RxMaxCoalescedIrqFrames=, RxMaxCoalescedLowFrames=, RxMaxCoalescedHighFrames=, TxMaxCoalescedFrames=, TxMaxCoalescedIrqFrames=, TxMaxCoalescedLowFrames=, TxMaxCoalescedHighFrames=¶These properties configure the maximum number of frames that are sent/received before a Rx/Tx
interrupt is generated. The "Irq" properties come into effect when the host is
servicing an IRQ. The "Low" and "High" properties come into
effect when the packet rate drops below the low packet rate threshold or exceeds the high packet
rate threshold respectively if adaptive Rx/Tx coalescing is enabled. When unset, the kernel's
defaults will be used.
CoalescePacketRateLow=, CoalescePacketRateHigh=¶These properties configure the low and high packet rate (expressed in packets per second) threshold respectively and are used to determine when the corresponding coalescing settings for low and high packet rates come into effect if adaptive Rx/Tx coalescing is enabled. If unset, the kernel's defaults will be used.
CoalescePacketRateSampleIntervalSec=¶Configures how often to sample the packet rate used for adaptive Rx/Tx coalescing. This property cannot be zero. This lowest time granularity supported by this property is seconds. Partial seconds will be rounded up before being passed to the kernel. If unset, the kernel's default will be used.
StatisticsBlockCoalesceSec=¶How long to delay driver in-memory statistics block updates. If the driver does not have an in-memory statistic block, this property is ignored. This property cannot be zero. If unset, the kernel's default will be used.
MDI=¶Specifies the medium dependent interface (MDI) mode for the interface. A MDI describes
the interface from a physical layer implementation to the physical medium used to carry the
transmission. Takes one of the following words: "straight" (or equivalently:
"mdi"), "crossover" (or equivalently:
"mdi-x", "mdix"), and "auto". When
"straight", the MDI straight through mode will be used. When
"crossover", the MDI crossover (MDI-X) mode will be used. When
"auto", the MDI status is automatically detected. Defaults to unset, and the
kernel's default will be used.
SR-IOVVirtualFunctions=¶Specifies the number of SR-IOV virtual functions. Takes an integer in the range
0…2147483647. Defaults to unset, and automatically determined from the values specified in
the VirtualFunction= settings in the [SR-IOV] sections.
The [SR-IOV] section accepts the following keys. Specify several [SR-IOV] sections to configure several SR-IOVs. SR-IOV provides the ability to partition a single physical PCI resource into virtual PCI functions which can then be injected into a VM. In the case of network VFs, SR-IOV improves north-south network performance (that is, traffic with endpoints outside the host machine) by allowing traffic to bypass the host machine’s network stack.
VirtualFunction=¶Specifies a Virtual Function (VF), lightweight PCIe function designed solely to move data in and out. Takes an integer in the range 0…2147483646. This option is compulsory.
VLANId=¶Specifies VLAN ID of the virtual function. Takes an integer in the range 1…4095.
QualityOfService=¶Specifies quality of service of the virtual function. Takes an integer in the range 1…4294967294.
VLANProtocol=¶Specifies VLAN protocol of the virtual function. Takes "802.1Q" or
"802.1ad".
MACSpoofCheck=¶Takes a boolean. Controls the MAC spoof checking. When unset, the kernel's default will be used.
QueryReceiveSideScaling=¶Takes a boolean. Toggle the ability of querying the receive side scaling (RSS) configuration of the virtual function (VF). The VF RSS information like RSS hash key may be considered sensitive on some devices where this information is shared between VF and the physical function (PF). When unset, the kernel's default will be used.
Trust=¶Takes a boolean. Allows one to set trust mode of the virtual function (VF). When set, VF users can set a specific feature which may impact security and/or performance. When unset, the kernel's default will be used.
LinkState=¶Allows one to set the link state of the virtual function (VF). Takes a boolean or a
special value "auto". Setting to "auto" means a
reflection of the physical function (PF) link state, "yes" lets the VF to
communicate with other VFs on this host even if the PF link state is down,
"no" causes the hardware to drop any packets sent by the VF. When unset,
the kernel's default will be used.
MACAddress=¶Specifies the MAC address for the virtual function.
Some settings resolve specifiers which may be used to write generic unit files referring to runtime or unit parameters that are replaced when the unit files are loaded. Specifiers must be known and resolvable for the setting to be valid. The following specifiers are understood:
Table 2. Specifiers available in unit files
| Specifier | Meaning | Details |
|---|---|---|
"%a" | Architecture | A short string identifying the architecture of the local system. A string such as x86, x86-64 or arm64. See the architectures defined for ConditionArchitecture= in systemd.unit(5) for a full list. |
"%A" | Operating system image version | The operating system image version identifier of the running system, as read from the IMAGE_VERSION= field of /etc/os-release. If not set, resolves to an empty string. See os-release(5) for more information. |
"%b" | Boot ID | The boot ID of the running system, formatted as string. See random(4) for more information. |
"%B" | Operating system build ID | The operating system build identifier of the running system, as read from the BUILD_ID= field of /etc/os-release. If not set, resolves to an empty string. See os-release(5) for more information. |
"%H" | Host name | The hostname of the running system. |
"%l" | Short host name | The hostname of the running system, truncated at the first dot to remove any domain component. |
"%m" | Machine ID | The machine ID of the running system, formatted as string. See machine-id(5) for more information. |
"%M" | Operating system image identifier | The operating system image identifier of the running system, as read from the IMAGE_ID= field of /etc/os-release. If not set, resolves to an empty string. See os-release(5) for more information. |
"%o" | Operating system ID | The operating system identifier of the running system, as read from the ID= field of /etc/os-release. See os-release(5) for more information. |
"%q" | Pretty host name | The pretty hostname of the running system, as read from the PRETTY_HOSTNAME= field of /etc/machine-info. If not set, resolves to the short hostname. See machine-info(5) for more information. |
"%T" | Directory for temporary files | This is either /tmp or the path "$TMPDIR", "$TEMP" or "$TMP" are set to. (Note that the directory may be specified without a trailing slash.) |
"%v" | Kernel release | Identical to uname -r output. |
"%V" | Directory for larger and persistent temporary files | This is either /var/tmp or the path "$TMPDIR", "$TEMP" or "$TMP" are set to. (Note that the directory may be specified without a trailing slash.) |
"%w" | Operating system version ID | The operating system version identifier of the running system, as read from the VERSION_ID= field of /etc/os-release. If not set, resolves to an empty string. See os-release(5) for more information. |
"%W" | Operating system variant ID | The operating system variant identifier of the running system, as read from the VARIANT_ID= field of /etc/os-release. If not set, resolves to an empty string. See os-release(5) for more information. |
Example 1. /usr/lib/systemd/network/99-default.link
The link file 99-default.link that is shipped with systemd defines the
default policies for the interface name, alternative names, and MAC address of links.
[Match] OriginalName=* [Link] NamePolicy=keep kernel database onboard slot path AlternativeNamesPolicy=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-default.link, i.e. it needs a numerical prefix, to have any effect at all.
Example 3. (Re-)applying a .link file to an interface
After a new .link file has been created, or an existing .link file modified, the new settings may be applied to the matching interface with the following commands:
$ sudo udevadm control --reload $ sudo ip link set eth0 down $ sudo udevadm trigger --verbose --settle --action add /sys/class/net/eth0
You may also need to stop the service that manages the network interface, e.g.
systemd-networkd.service(8)
or NetworkManager.service before the above operation, and then restart the service
after that. For more details about udevadm command, see
udevadm(8).
Example 4. 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 5. /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 6. /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), systemd-network-generator.service(8)
[1] 💣💥🧨💥💥💣 Please note that those configuration files must be available at all times. If
/usr/local/ is a separate partition, it may not be available during early boot,
and must not be used for configuration.