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+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+ This file is part of systemd.
+
+ Copyright 2014 Tom Gundersen
+
+ systemd is free software; you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
+
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="systemd.link">
+ <refentryinfo>
+ <title>systemd.link</title>
+ <productname>systemd</productname>
+
+ <authorgroup>
+ <author>
+ <contrib>Developer</contrib>
+ <firstname>Tom</firstname>
+ <surname>Gundersen</surname>
+ </author>
+ </authorgroup>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>systemd.link</refentrytitle>
+ <manvolnum>5</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>systemd.link</refname>
+ <refpurpose>Network device configuration</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <para><filename><replaceable>link</replaceable>.link</filename></para>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>Network link configuration is performed by the
+ <command>net_setup_link</command> udev builtin.</para>
+
+ <para>The link files are read from the files located in the system
+ network directory <filename>/usr/lib/systemd/network</filename>,
+ the volatile runtime network directory
+ <filename>/run/systemd/network</filename>, and the local
+ administration network directory
+ <filename>/etc/systemd/network</filename>. Link files must have
+ the extension <filename>.link</filename>; 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 <filename>/etc</filename> have the highest priority, files in
+ <filename>/run</filename> take precedence over files with the same
+ name in <filename>/usr/lib</filename>. 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 <filename>/dev/null</filename> disables the
+ configuration file entirely (it is "masked").</para>
+
+ <para>The link file contains a <literal>[Match]</literal> section,
+ which determines if a given link file may be applied to a given
+ device, as well as a <literal>[Link]</literal> 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 <filename>99-default.link</filename> is
+ shipped by the system, any user-supplied
+ <filename>.link</filename> should hence have a lexically earlier
+ name to be considered at all.</para>
+
+ <para>See
+ <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for diagnosing problems with <filename>.link</filename> files.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>[Match] Section Options</title>
+
+ <para>A link file is said to match a device if each of the entries
+ in the <literal>[Match]</literal> section matches, or if the
+ section is empty. The following keys are accepted:</para>
+
+ <variablelist class='network-directives'>
+ <varlistentry>
+ <term><varname>MACAddress=</varname></term>
+ <listitem>
+ <para>The hardware address.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>OriginalName=</varname></term>
+ <listitem>
+ <para>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.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>Path=</varname></term>
+ <listitem>
+ <para>A whitespace-separated list of shell-style globs matching
+ the persistent path, as exposed by the udev property
+ <literal>ID_PATH</literal>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>Driver=</varname></term>
+ <listitem>
+ <para>A whitespace-separated list of shell-style globs matching
+ the driver currently bound to the device,
+ as exposed by the udev property <literal>DRIVER</literal>
+ of its parent device, or if that is not set, the
+ driver as exposed by <literal>ethtool -i</literal>
+ of the device itself.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>Type=</varname></term>
+ <listitem>
+ <para>A whitespace-separated list of shell-style globs matching
+ the device type, as exposed by the udev
+ property <literal>DEVTYPE</literal>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>Host=</varname></term>
+ <listitem>
+ <para>Matches against the hostname or machine
+ ID of the host. See <literal>ConditionHost=</literal> in
+ <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>Virtualization=</varname></term>
+ <listitem>
+ <para>Checks whether the system is executed in
+ a virtualized environment and optionally test
+ whether it is a specific implementation. See
+ <literal>ConditionVirtualization=</literal> in
+ <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>KernelCommandLine=</varname></term>
+ <listitem>
+ <para>Checks whether a specific kernel command line option
+ is set (or if prefixed with the exclamation mark unset). See
+ <literal>ConditionKernelCommandLine=</literal> in
+ <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>Architecture=</varname></term>
+ <listitem>
+ <para>Checks whether the system is running on a specific
+ architecture. See <literal>ConditionArchitecture=</literal>
+ in
+ <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ </refsect1>
+
+ <refsect1>
+ <title>[Link] Section Options</title>
+
+ <para>The <literal>[Link]</literal> section accepts the following
+ keys:</para>
+
+ <variablelist class='network-directives'>
+ <varlistentry>
+ <term><varname>Description=</varname></term>
+ <listitem>
+ <para>A description of the device.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>Alias=</varname></term>
+ <listitem>
+ <para>The <literal>ifalias</literal> is set to this
+ value.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>MACAddressPolicy=</varname></term>
+ <listitem>
+ <para>The policy by which the MAC address should be set. The
+ available policies are:
+ </para>
+
+ <variablelist>
+ <varlistentry>
+ <term><literal>persistent</literal></term>
+ <listitem>
+ <para>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.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>random</literal></term>
+ <listitem>
+ <para>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
+ <literal>unicast</literal> and
+ <literal>locally administered</literal> bits set.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>none</literal></term>
+ <listitem>
+ <para>Keeps the MAC address assigned by the kernel.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>MACAddress=</varname></term>
+ <listitem>
+ <para>The MAC address to use, if no
+ <literal>MACAddressPolicy=</literal>
+ is specified.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>NamePolicy=</varname></term>
+ <listitem>
+ <para>An ordered, space-separated list of policies by which
+ the interface name should be set.
+ <literal>NamePolicy</literal> may be disabled by specifying
+ <literal>net.ifnames=0</literal> 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 <literal>ID_NET_NAME</literal>, which
+ is, by default, used by a udev rule to set
+ <literal>NAME</literal>. If the name has already been set by
+ userspace, no renaming is performed. The available policies
+ are:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><literal>kernel</literal></term>
+ <listitem>
+ <para>If the kernel claims that the name it has set
+ for a device is predictable, then no renaming is
+ performed.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>database</literal></term>
+ <listitem>
+ <para>The name is set based on entries in the udev's
+ Hardware Database with the key
+ <literal>ID_NET_NAME_FROM_DATABASE</literal>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>onboard</literal></term>
+ <listitem>
+ <para>The name is set based on information given by
+ the firmware for on-board devices, as exported by the
+ udev property <literal>ID_NET_NAME_ONBOARD</literal>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>slot</literal></term>
+ <listitem>
+ <para>The name is set based on information given by
+ the firmware for hot-plug devices, as exported by the
+ udev property <literal>ID_NET_NAME_SLOT</literal>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>path</literal></term>
+ <listitem>
+ <para>The name is set based on the device's physical
+ location, as exported by the udev property
+ <literal>ID_NET_NAME_PATH</literal>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>mac</literal></term>
+ <listitem>
+ <para>The name is set based on the device's persistent
+ MAC address, as exported by the udev property
+ <literal>ID_NET_NAME_MAC</literal>.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>Name=</varname></term>
+ <listitem>
+ <para>The interface name to use in case all the
+ policies specified in
+ <varname>NamePolicy=</varname> fail, or in case
+ <varname>NamePolicy=</varname> is missing or
+ disabled.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>MTUBytes=</varname></term>
+ <listitem>
+ <para>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.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>BitsPerSecond=</varname></term>
+ <listitem>
+ <para>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.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>Duplex=</varname></term>
+ <listitem>
+ <para>The duplex mode to set for the device. The accepted
+ values are <literal>half</literal> and
+ <literal>full</literal>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>WakeOnLan=</varname></term>
+ <listitem>
+ <para>The Wake-on-LAN policy to set for the device. The
+ supported values are:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><literal>phy</literal></term>
+ <listitem>
+ <para>Wake on PHY activity.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>magic</literal></term>
+ <listitem>
+ <para>Wake on receipt of a magic packet.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>off</literal></term>
+ <listitem>
+ <para>Never wake.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>TCPSegmentationOffload=</varname></term>
+ <listitem>
+ <para>The TCP Segmentation Offload (TSO) when true enables
+ TCP segmentation offload. Takes a boolean value.
+ Defaults to "unset".</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>GenericSegmentationOffload=</varname></term>
+ <listitem>
+ <para>The Generic Segmentation Offload (GSO) when true enables
+ generic segmentation offload. Takes a boolean value.
+ Defaults to "unset".</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>UDPSegmentationOffload=</varname></term>
+ <listitem>
+ <para>The UDP Segmentation Offload (USO) when true enables
+ UDP segmentation offload. Takes a boolean value.
+ Defaults to "unset".</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>GenericReceiveOffload=</varname></term>
+ <listitem>
+ <para>The Generic Receive Offload (GRO) when true enables
+ generic receive offload. Takes a boolean value.
+ Defaults to "unset".</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>LargeReceiveOffload=</varname></term>
+ <listitem>
+ <para>The Large Receive Offload (LRO) when true enables
+ large receive offload. Takes a boolean value.
+ Defaults to "unset".</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <refsect1>
+ <title>Examples</title>
+
+ <example>
+ <title>/usr/lib/systemd/network/99-default.link</title>
+
+ <para>The link file <filename>99-default.link</filename> that is
+ shipped with systemd defines the default naming policy for
+ links.</para>
+
+ <programlisting>[Link]
+NamePolicy=kernel database onboard slot path
+MACAddressPolicy=persistent</programlisting>
+ </example>
+
+ <example>
+ <title>/etc/systemd/network/10-dmz.link</title>
+
+ <para>This example assigns the fixed name
+ <literal>dmz0</literal> to the interface with the MAC address
+ 00:a0:de:63:7a:e6:</para>
+
+ <programlisting>[Match]
+MACAddress=00:a0:de:63:7a:e6
+
+[Link]
+Name=dmz0</programlisting>
+ </example>
+
+ <example>
+ <title>/etc/systemd/network/10-internet.link</title>
+
+ <para>This example assigns the fixed name
+ <literal>internet0</literal> to the interface with the device
+ path <literal>pci-0000:00:1a.0-*</literal>:</para>
+
+ <programlisting>[Match]
+Path=pci-0000:00:1a.0-*
+
+[Link]
+Name=internet0</programlisting>
+ </example>
+
+ <example>
+ <title>/etc/systemd/network/25-wireless.link</title>
+
+ <para>Here's an overly complex example that shows the use of a large number of [Match] and [Link] settings.</para>
+
+ <programlisting>[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</programlisting>
+ </example>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry>
+ <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum>
+ </citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>