Provided by: udev_242-7ubuntu3_amd64 bug

NAME

       systemd.link - Network device configuration

SYNOPSIS

       link.link

DESCRIPTION

       Network link configuration is performed by the net_setup_link udev builtin.

       The link files are read from the files located in the system network directory
       /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 /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.

[MATCH] SECTION OPTIONS

       A link file is said to match a device if each of the entries in the [Match] section
       matches, or if the section is empty. The following keys are accepted:

       MACAddress=
           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

       OriginalName=
           A whitespace-separated list of shell-style globs matching the device name, as exposed
           by the udev property "INTERFACE". This cannot be used to match on names that have
           already been changed from userspace. Caution is advised when matching on
           kernel-assigned names, as they are known to be unstable between reboots.

       Path=
           A whitespace-separated list of shell-style globs matching the persistent path, as
           exposed by the udev property ID_PATH.

       Driver=
           A whitespace-separated list of shell-style globs matching the driver currently bound
           to the device, as exposed by the udev property DRIVER of its parent device, or if that
           is not set, the driver as exposed by ethtool -i of the device itself.

       Type=
           A whitespace-separated list of shell-style globs matching the device type, as exposed
           by the udev property DEVTYPE.

       Host=
           Matches against the hostname or machine ID of the host. See ConditionHost= in
           systemd.unit(5) for details. 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.

[LINK] SECTION OPTIONS

       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.

           slot
               The name is set based on information given by the firmware for hot-plug devices,
               as exported by the udev property ID_NET_NAME_SLOT.

           path
               The name is set based on the device's physical location, as exported by the udev
               property ID_NET_NAME_PATH.

           mac
               The name is set based on the device's persistent MAC address, as exported by the
               udev property ID_NET_NAME_MAC.

           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".

       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
           autonegotation is disabled, speed and duplex settings are writable if the driver
           supports multiple link modes.

       WakeOnLan=
           The Wake-on-LAN policy to set for the device. The supported values are:

           phy
               Wake on PHY activity.

           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
           ┌───────────────────┬──────────────┬─────────────┐
           │AdvertiseSpeed (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.

       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).

EXAMPLES

       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 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

SEE ALSO

       systemd-udevd.service(8), udevadm(8), systemd.netdev(5), systemd.network(5)