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:
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. /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 /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 /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 /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=/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=/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