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<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>
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<para > Network link configuration is performed by the <command > net_setup_link</command>
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udev builtin.</para>
<para > The link files are read from the files located in the
system network directory <filename > /usr/lib/systemd/network</filename> ,
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the volatile runtime network directory <filename > /run/systemd/network</filename> ,
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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;
a symlink in <filename > /etc</filename> with the same name as a link file in
<filename > /usr/lib</filename> , pointing to <filename > /dev/null</filename> ,
disables the link file entirely.</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; and 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.</para>
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</refsect1>
<refsect1 >
<title > [Match] Section Options</title>
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<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 > Path=</varname> </term>
<listitem >
<para > The persistent path, as exposed by the
udev property <literal > ID_PATH</literal> . May
contain shell style globs.</para>
</listitem>
</varlistentry>
<varlistentry >
<term > <varname > Driver=</varname> </term>
<listitem >
<para > The driver currently bound to the device,
as exposed by the udev property <literal > DRIVER</literal>
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of its parent device, or if that is not set, the
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driver as exposed by <literal > ethtool -i</literal>
of the device itself.</para>
</listitem>
</varlistentry>
<varlistentry >
<term > <varname > Type=</varname> </term>
<listitem >
<para > 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>
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</refsect1>
<refsect1 >
<title > [Link] Section Options</title>
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<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,
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and if it is used by the kernel, nothing
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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.</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.</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
commandline. 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> . The available policies
are:</para>
<variablelist >
<varlistentry >
<term > <literal > database</literal> </term>
<listitem >
<para > The name is set based on entries in
the udev's Hardware Database with the key
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<literal > ID_NET_NAME_FROM_DATABASE</literal> .
</para>
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</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
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the udev property <literal > ID_NET_NAME_ONBOARD</literal> .
</para>
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</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
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the udev property <literal > ID_NET_NAME_SLOT</literal> .
</para>
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</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 >
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<para > Wake on receipt of a magic packet.
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</para>
</listitem>
</varlistentry>
<varlistentry >
<term > <literal > off</literal> </term>
<listitem >
<para > Never wake.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 >
<title > Example</title>
<example >
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<title > /etc/systemd/network/wireless.link</title>
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<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
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[Link]
Name=wireless0
MTUBytes=1450
BitsPerSecond=10M
WakeOnLan=magic
MACAddress=cb:a9:87:65:43:21</programlisting>
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</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>
</para>
</refsect1>
</refentry>
