man/systemd.link.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="systemd.link"
   7           xmlns:xi="http://www.w3.org/2001/XInclude">
   8   <refentryinfo>
   9     <title>systemd.link</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>systemd.link</refentrytitle>
  15     <manvolnum>5</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>systemd.link</refname>
  20     <refpurpose>Network device configuration</refpurpose>
  21   </refnamediv>
  22
  23   <refsynopsisdiv>
  24     <para><filename><replaceable>link</replaceable>.link</filename></para>
  25   </refsynopsisdiv>
  26
  27   <refsect1>
  28     <title>Description</title>
  29
  30     <para>A plain ini-style text file that encodes configuration for matching network devices, used by
  31     <citerefentry><refentrytitle>systemd-udevd</refentrytitle><manvolnum>8</manvolnum></citerefentry> and in
  32     particular its <command>net_setup_link</command> builtin. See
  33     <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>7</manvolnum></citerefentry> for a
  34     general description of the syntax.</para>
  35
  36     <para>The <filename>.link</filename> files are read from the files located in the system network
  37     directory <filename>/usr/lib/systemd/network</filename> and
  38     <filename>/usr/local/lib/systemd/network</filename>, the volatile runtime network directory
  39     <filename>/run/systemd/network</filename>, and the local administration network directory
  40     <filename>/etc/systemd/network</filename>. All configuration files are collectively sorted and
  41     processed in alphanumeric order, regardless of the directories in which they live. However, files
  42     with identical filenames replace each other. It is recommended that each filename is prefixed with
  43     a number smaller than <literal>70</literal> (e.g. <filename>10-eth0.link</filename>). Otherwise, the
  44     default <filename>.link</filename> files or those generated by
  45     <citerefentry><refentrytitle>systemd-network-generator.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  46     may take precedence over user configured files. Files in <filename>/etc/</filename> have the
  47     highest priority, files in <filename>/run/</filename> take precedence over files with the same name
  48     in <filename>/usr/lib/</filename>. This can be used to override a system-supplied link file with a
  49     local file if needed. As a special case, an empty file (file size 0) or symlink with the same name
  50     pointing to <filename>/dev/null</filename> disables the configuration file entirely (it is
  51     "masked").</para>
  52
  53     <para>Along with the link file <filename>foo.link</filename>, a "drop-in" directory
  54     <filename>foo.link.d/</filename> may exist. All files with the suffix <literal>.conf</literal>
  55     from this directory will be merged in the alphanumeric order and parsed after the main file itself
  56     has been parsed. This is useful to alter or add configuration settings, without having to modify
  57     the main configuration file. Each drop-in file must have appropriate section headers.</para>
  58
  59     <para>In addition to <filename>/etc/systemd/network</filename>, drop-in <literal>.d</literal>
  60     directories can be placed in <filename>/usr/lib/systemd/network</filename> or
  61     <filename>/run/systemd/network</filename> directories. Drop-in files in <filename>/etc/</filename>
  62     take precedence over those in <filename>/run/</filename> which in turn take precedence over those
  63     in <filename>/usr/lib/</filename>. Drop-in files under any of these directories take precedence
  64     over the main link file wherever located.</para>
  65
  66     <para>The link file contains a [Match] section, which determines if a given link file may be applied to a
  67     given device, as well as a [Link] section specifying how the device should be configured. The first (in
  68     lexical order) of the link files that matches a given device is applied. Note that a default file
  69     <filename>99-default.link</filename> is shipped by the system. Any user-supplied
  70     <filename>.link</filename> should hence have a lexically earlier name to be considered at all.</para>
  71
  72     <para>See <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
  73     diagnosing problems with <filename>.link</filename> files.</para>
  74   </refsect1>
  75
  76   <refsect1>
  77     <title>[Match] Section Options</title>
  78
  79     <para>A link file is said to match an interface if all matches specified by the [Match] section are
  80     satisfied. When a link file does not contain valid settings in [Match] section, then the file will
  81     match all interfaces and <command>systemd-udevd</command> warns about that. Hint: to avoid the
  82     warning and to make it clear that all interfaces shall be matched, add the following:
  83     <programlisting>OriginalName=*</programlisting>
  84     The first (in alphanumeric order) of the link files that matches a given interface is applied, all
  85     later files are ignored, even if they match as well. The following keys are accepted:</para>
  86
  87     <variablelist class='network-directives'>
  88       <!-- This list is reused in systemd.network(3), hence maintain a specific order:
  89            1. device matches shared between the two lists
  90            2. non-shared settings
  91            3. host matches shared between the two lists
  92         -->
  93
  94       <varlistentry id='mac-address'>
  95         <term><varname>MACAddress=</varname></term>
  96         <listitem>
  97           <para>A whitespace-separated list of hardware addresses. The acceptable formats are:</para>
  98
  99           <variablelist>
 100             <varlistentry>
 101               <term><option>colon-delimited hexadecimal</option></term>
 102               <listitem><para>
 103                 Each field must be one byte.
 104                 E.g. <literal>12:34:56:78:90:ab</literal> or <literal>AA:BB:CC:DD:EE:FF</literal>.
 105               </para>
 106
 107                 <xi:include href="version-info.xml" xpointer="v250"/></listitem>
 108             </varlistentry>
 109             <varlistentry>
 110               <term><option>hyphen-delimited hexadecimal</option></term>
 111               <listitem><para>
 112                 Each field must be one byte.
 113                 E.g. <literal>12-34-56-78-90-ab</literal> or <literal>AA-BB-CC-DD-EE-FF</literal>.
 114               </para>
 115
 116                 <xi:include href="version-info.xml" xpointer="v250"/></listitem>
 117             </varlistentry>
 118             <varlistentry>
 119               <term><option>dot-delimited hexadecimal</option></term>
 120               <listitem><para>
 121                 Each field must be two bytes.
 122                 E.g. <literal>1234.5678.90ab</literal> or <literal>AABB.CCDD.EEFF</literal>.
 123               </para>
 124
 125                 <xi:include href="version-info.xml" xpointer="v250"/></listitem>
 126             </varlistentry>
 127             <varlistentry>
 128               <term><option>IPv4 address format</option></term>
 129               <listitem><para>
 130                 E.g. <literal>127.0.0.1</literal> or <literal>192.168.0.1</literal>.
 131               </para>
 132
 133                 <xi:include href="version-info.xml" xpointer="v250"/></listitem>
 134             </varlistentry>
 135             <varlistentry>
 136               <term><option>IPv6 address format</option></term>
 137               <listitem><para>
 138                 E.g. <literal>2001:0db8:85a3::8a2e:0370:7334</literal> or <literal>::1</literal>.
 139               </para>
 140
 141                 <xi:include href="version-info.xml" xpointer="v250"/></listitem>
 142             </varlistentry>
 143           </variablelist>
 144
 145           <para>The total length of each MAC address must be 4 (for IPv4 tunnel), 6 (for Ethernet), 16
 146           (for IPv6 tunnel), or 20 (for InfiniBand). This option may appear more than once, in which
 147           case the lists are merged. If the empty string is assigned to this option, the list of
 148           hardware addresses defined prior to this is reset. Defaults to unset.</para>
 149
 150           <xi:include href="version-info.xml" xpointer="v211"/>
 151         </listitem>
 152       </varlistentry>
 153
 154       <varlistentry id='permanent-mac-address'>
 155         <term><varname>PermanentMACAddress=</varname></term>
 156         <listitem>
 157           <para>A whitespace-separated list of hardware's permanent addresses. While
 158           <varname>MACAddress=</varname> matches the device's current MAC address, this matches the
 159           device's permanent MAC address, which may be different from the current one. Use full
 160           colon-, hyphen- or dot-delimited hexadecimal, or IPv4 or IPv6 address format. This option may
 161           appear more than once, in which case the lists are merged. If the empty string is assigned to
 162           this option, the list of hardware addresses defined prior to this is reset. Defaults to
 163           unset.</para>
 164
 165           <xi:include href="version-info.xml" xpointer="v245"/>
 166         </listitem>
 167       </varlistentry>
 168
 169       <varlistentry id='path'>
 170         <term><varname>Path=</varname></term>
 171         <listitem>
 172           <para>A whitespace-separated list of shell-style globs matching
 173           the persistent path, as exposed by the udev property
 174           <varname>ID_PATH</varname>.</para>
 175
 176           <xi:include href="version-info.xml" xpointer="v211"/>
 177         </listitem>
 178       </varlistentry>
 179
 180       <varlistentry id='driver'>
 181         <term><varname>Driver=</varname></term>
 182         <listitem>
 183           <para>A whitespace-separated list of shell-style globs matching the driver currently bound to the
 184           device, as exposed by the udev property <varname>ID_NET_DRIVER</varname> of its parent device, or
 185           if that is not set, the driver as exposed by <command>ethtool -i</command> of the device itself.
 186           If the list is prefixed with a "!", the test is inverted.</para>
 187
 188           <xi:include href="version-info.xml" xpointer="v211"/>
 189         </listitem>
 190       </varlistentry>
 191
 192       <varlistentry id='type'>
 193         <term><varname>Type=</varname></term>
 194         <listitem>
 195           <para>A whitespace-separated list of shell-style globs matching the device type, as exposed by
 196           <command>networkctl list</command>. If the list is prefixed with a "!", the test is inverted.
 197           Some valid values are <literal>ether</literal>, <literal>loopback</literal>, <literal>wlan</literal>, <literal>wwan</literal>.
 198           Valid types are named either from the udev <literal>DEVTYPE</literal> attribute, or
 199           <literal>ARPHRD_</literal> macros in <filename>linux/if_arp.h</filename>, so this is not comprehensive.
 200           </para>
 201
 202           <xi:include href="version-info.xml" xpointer="v211"/>
 203         </listitem>
 204       </varlistentry>
 205
 206       <varlistentry id='kind'>
 207         <term><varname>Kind=</varname></term>
 208         <listitem>
 209           <para>A whitespace-separated list of shell-style globs matching the device kind, as exposed by
 210           <command>networkctl status <replaceable>INTERFACE</replaceable></command> or
 211           <command>ip -d link show <replaceable>INTERFACE</replaceable></command>. If the list is
 212           prefixed with a "!", the test is inverted. Some valid values are <literal>bond</literal>,
 213           <literal>bridge</literal>, <literal>gre</literal>, <literal>tun</literal>,
 214           <literal>veth</literal>. Valid kinds are given by netlink's <literal>IFLA_INFO_KIND</literal>
 215           attribute, so this is not comprehensive.
 216           </para>
 217
 218           <xi:include href="version-info.xml" xpointer="v251"/>
 219         </listitem>
 220       </varlistentry>
 221
 222       <varlistentry id='property'>
 223         <term><varname>Property=</varname></term>
 224         <listitem>
 225           <para>A whitespace-separated list of udev property names with their values after equals sign
 226           (<literal>=</literal>). If multiple properties are specified, the test results are ANDed.
 227           If the list is prefixed with a "!", the test is inverted. If a value contains white
 228           spaces, then please quote whole key and value pair. If a value contains quotation, then
 229           please escape the quotation with <literal>\</literal>.</para>
 230
 231           <para>Example: if a .link file has the following:
 232           <programlisting>Property=ID_MODEL_ID=9999 "ID_VENDOR_FROM_DATABASE=vendor name" "KEY=with \"quotation\""</programlisting>
 233           then, the .link file matches only when an interface has all the above three properties.
 234           </para>
 235
 236           <xi:include href="version-info.xml" xpointer="v243"/>
 237         </listitem>
 238       </varlistentry>
 239
 240       <varlistentry>
 241         <term><varname>OriginalName=</varname></term>
 242         <listitem>
 243           <para>A whitespace-separated list of shell-style globs matching the device name, as exposed by the
 244           udev property "INTERFACE". This cannot be used to match on names that have already been changed
 245           from userspace. Caution is advised when matching on kernel-assigned names, as they are known to be
 246           unstable between reboots.</para>
 247
 248           <xi:include href="version-info.xml" xpointer="v218"/>
 249         </listitem>
 250       </varlistentry>
 251
 252       <varlistentry id='host'>
 253         <term><varname>Host=</varname></term>
 254         <listitem>
 255           <para>Matches against the hostname or machine ID of the host. See <varname>ConditionHost=</varname> in
 256           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 257           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 258           If an empty string is assigned, the previously assigned value is cleared.
 259           </para>
 260
 261         <xi:include href="version-info.xml" xpointer="v211"/>
 262         </listitem>
 263       </varlistentry>
 264
 265       <varlistentry id='virtualization'>
 266         <term><varname>Virtualization=</varname></term>
 267         <listitem>
 268           <para>Checks whether the system is executed in a virtualized environment and optionally test
 269           whether it is a specific implementation. See <varname>ConditionVirtualization=</varname> in
 270           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 271           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 272           If an empty string is assigned, the previously assigned value is cleared.
 273           </para>
 274
 275           <xi:include href="version-info.xml" xpointer="v211"/>
 276         </listitem>
 277       </varlistentry>
 278
 279       <varlistentry id='kernel-command-line'>
 280         <term><varname>KernelCommandLine=</varname></term>
 281         <listitem>
 282           <para>Checks whether a specific kernel command line option is set. See
 283           <varname>ConditionKernelCommandLine=</varname> in
 284           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 285           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 286           If an empty string is assigned, the previously assigned value is cleared.
 287           </para>
 288
 289           <xi:include href="version-info.xml" xpointer="v211"/>
 290         </listitem>
 291       </varlistentry>
 292
 293       <varlistentry id='kernel-version'>
 294         <term><varname>KernelVersion=</varname></term>
 295         <listitem>
 296           <para>Checks whether the kernel version (as reported by <command>uname -r</command>) matches a certain
 297           expression. See <varname>ConditionKernelVersion=</varname> in
 298           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 299           details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 300           If an empty string is assigned, the previously assigned value is cleared.
 301           </para>
 302
 303         <xi:include href="version-info.xml" xpointer="v237"/>
 304         </listitem>
 305       </varlistentry>
 306
 307       <varlistentry id='credential'>
 308         <term><varname>Credential=</varname></term>
 309         <listitem>
 310           <para>Checks whether the specified credential was passed to the
 311           <filename>systemd-udevd.service</filename> service. See <ulink
 312           url="https://systemd.io/CREDENTIALS">System and Service Credentials</ulink> for details. When
 313           prefixed with an exclamation mark (<literal>!</literal>), the result is negated.  If an empty
 314           string is assigned, the previously assigned value is cleared.
 315           </para>
 316
 317           <xi:include href="version-info.xml" xpointer="v252"/>
 318         </listitem>
 319       </varlistentry>
 320
 321       <varlistentry id='architecture'>
 322         <term><varname>Architecture=</varname></term>
 323         <listitem>
 324           <para>Checks whether the system is running on a specific architecture. See
 325           <varname>ConditionArchitecture=</varname> in
 326           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 327           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 328           If an empty string is assigned, the previously assigned value is cleared.
 329           </para>
 330
 331           <xi:include href="version-info.xml" xpointer="v211"/>
 332         </listitem>
 333       </varlistentry>
 334
 335       <varlistentry id='firmware'>
 336         <term><varname>Firmware=</varname></term>
 337         <listitem>
 338           <para>Checks whether the system is running on a machine with the specified firmware. See
 339           <varname>ConditionFirmware=</varname> in
 340           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 341           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 342           If an empty string is assigned, the previously assigned value is cleared.
 343           </para>
 344
 345           <xi:include href="version-info.xml" xpointer="v249"/>
 346         </listitem>
 347       </varlistentry>
 348     </variablelist>
 349
 350   </refsect1>
 351
 352   <refsect1>
 353     <title>[Link] Section Options</title>
 354
 355     <para>The [Link] section accepts the following
 356     keys:</para>
 357
 358     <variablelist class='network-directives'>
 359       <varlistentry>
 360         <term><varname>Description=</varname></term>
 361         <listitem>
 362           <para>A description of the device.</para>
 363
 364           <xi:include href="version-info.xml" xpointer="v211"/>
 365         </listitem>
 366       </varlistentry>
 367       <varlistentry>
 368         <term><varname>Property=</varname></term>
 369         <listitem>
 370           <para>Set specified udev properties. This takes space separated list of key-value pairs
 371           concatenated with equal sign (<literal>=</literal>). Example:
 372           <programlisting>Property=HOGE=foo BAR=baz</programlisting>
 373           This option supports simple specifier expansion, see the Specifiers section below.
 374           This option can be specified multiple times. If an empty string is assigned, then the all previous
 375           assignments are cleared.</para>
 376
 377           <para>This setting is useful to configure the <literal>ID_NET_MANAGED_BY=</literal> property which
 378           declares which network management service shall manage the interface, which is respected by
 379           systemd-networkd and others. Use
 380           <programlisting>Property=ID_NET_MANAGED_BY=io.systemd.Network</programlisting>
 381           to declare explicitly that <command>systemd-networkd</command> shall manage the interface, or set
 382           the property to something else to declare explicitly it shall not do so. See
 383           <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 384           for details how this property is used to match interface names.</para>
 385
 386           <xi:include href="version-info.xml" xpointer="v256"/>
 387         </listitem>
 388       </varlistentry>
 389       <varlistentry>
 390         <term><varname>ImportProperty=</varname></term>
 391         <listitem>
 392           <para>Import specified udev properties from the saved database. This takes space separated list of
 393           property names. Example: <programlisting>ImportProperty=HOGE BAR</programlisting>
 394           This option supports simple specifier expansion, see the Specifiers section below.
 395           This option can be specified multiple times. If an empty string is assigned, then the all previous
 396           assignments are cleared.</para>
 397           <para>If the same property is also set in <varname>Property=</varname> in the above, then the
 398           imported property value will be overridden by the value specified in <varname>Property=</varname>.
 399           </para>
 400
 401           <xi:include href="version-info.xml" xpointer="v256"/>
 402         </listitem>
 403       </varlistentry>
 404       <varlistentry>
 405         <term><varname>UnsetProperty=</varname></term>
 406         <listitem>
 407           <para>Unset specified udev properties. This takes space separated list of
 408           property names. Example: <programlisting>ImportProperty=HOGE BAR</programlisting>
 409           This option supports simple specifier expansion, see the Specifiers section below.
 410           This option can be specified multiple times. If an empty string is assigned, then the all previous
 411           assignments are cleared.</para>
 412           <para>This setting is applied after <varname>ImportProperty=</varname> and
 413           <varname>Property=</varname> are applied. Hence, if the same property is specified in
 414           <varname>ImportProperty=</varname> or <varname>Property=</varname>, then the imported or specified
 415           property value will be ignored, and the property will be unset.</para>
 416
 417           <xi:include href="version-info.xml" xpointer="v256"/>
 418         </listitem>
 419       </varlistentry>
 420       <varlistentry>
 421         <term><varname>Alias=</varname></term>
 422         <listitem>
 423           <para>The <varname>ifalias</varname> interface property is set to this value.</para>
 424
 425           <xi:include href="version-info.xml" xpointer="v211"/>
 426         </listitem>
 427       </varlistentry>
 428       <varlistentry>
 429         <term><varname>MACAddressPolicy=</varname></term>
 430         <listitem>
 431           <para>The policy by which the MAC address should be set. The
 432           available policies are:
 433           </para>
 434
 435           <variablelist>
 436             <varlistentry>
 437               <term><option>persistent</option></term>
 438               <listitem>
 439                 <para>If the hardware has a persistent MAC address, as
 440                 most hardware should, and if it is used by the kernel,
 441                 nothing is done. Otherwise, a new MAC address is
 442                 generated which is guaranteed to be the same on every
 443                 boot for the given machine and the given device, but
 444                 which is otherwise random. This feature depends on ID_NET_NAME_*
 445                 properties to exist for the link. On hardware where these
 446                 properties are not set, the generation of a persistent MAC address
 447                 will fail.</para>
 448
 449                 <xi:include href="version-info.xml" xpointer="v211"/>
 450               </listitem>
 451             </varlistentry>
 452             <varlistentry>
 453               <term><option>random</option></term>
 454               <listitem>
 455                 <para>If the kernel is using a random MAC address,
 456                 nothing is done. Otherwise, a new address is randomly
 457                 generated each time the device appears, typically at
 458                 boot. Either way, the random address will have the
 459                 <literal>unicast</literal> and
 460                 <literal>locally administered</literal> bits set.</para>
 461
 462                 <xi:include href="version-info.xml" xpointer="v211"/>
 463               </listitem>
 464             </varlistentry>
 465             <varlistentry>
 466               <term><option>none</option></term>
 467               <listitem>
 468                 <para>Keeps the MAC address assigned by the kernel. Or use the MAC address specified in
 469                 <varname>MACAddress=</varname>.</para>
 470
 471                 <xi:include href="version-info.xml" xpointer="v227"/>
 472               </listitem>
 473             </varlistentry>
 474           </variablelist>
 475
 476           <para>An empty string assignment is equivalent to setting <literal>none</literal>.</para>
 477
 478           <xi:include href="version-info.xml" xpointer="v211"/>
 479         </listitem>
 480       </varlistentry>
 481       <varlistentry>
 482         <term><varname>MACAddress=</varname></term>
 483         <listitem>
 484           <para>The interface MAC address to use. For this setting to take effect,
 485           <varname>MACAddressPolicy=</varname> must either be unset, empty, or <literal>none</literal>.
 486           </para>
 487
 488           <xi:include href="version-info.xml" xpointer="v211"/>
 489         </listitem>
 490       </varlistentry>
 491       <varlistentry>
 492         <term><varname>NamePolicy=</varname></term>
 493         <listitem>
 494           <para>An ordered, space-separated list of policies by which the interface name should be set.
 495           <varname>NamePolicy=</varname> may be disabled by specifying <option>net.ifnames=0</option> on the
 496           kernel command line. Each of the policies may fail, and the first successful one is used. The name
 497           is not set directly, but is exported to udev as the property <option>ID_NET_NAME</option>, which
 498           is, by default, used by a
 499           <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 500           rule to set <varname>NAME</varname>. The available policies are:
 501           </para>
 502
 503           <variablelist>
 504             <varlistentry>
 505               <term><option>kernel</option></term>
 506               <listitem>
 507                 <para>If the kernel claims that the name it has set
 508                 for a device is predictable, then no renaming is
 509                 performed.</para>
 510
 511                 <xi:include href="version-info.xml" xpointer="v216"/>
 512               </listitem>
 513             </varlistentry>
 514             <varlistentry>
 515               <term><option>database</option></term>
 516               <listitem>
 517                 <para>The name is set based on entries in the udev's
 518                 Hardware Database with the key
 519                 <varname>ID_NET_NAME_FROM_DATABASE</varname>.
 520                 </para>
 521
 522                 <xi:include href="version-info.xml" xpointer="v211"/>
 523               </listitem>
 524             </varlistentry>
 525             <varlistentry>
 526               <term><option>onboard</option></term>
 527               <listitem>
 528                 <para>The name is set based on information given by
 529                 the firmware for on-board devices, as exported by the
 530                 udev property <varname>ID_NET_NAME_ONBOARD</varname>.
 531                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 532                 </para>
 533
 534                 <xi:include href="version-info.xml" xpointer="v211"/>
 535               </listitem>
 536             </varlistentry>
 537             <varlistentry>
 538               <term><option>slot</option></term>
 539               <listitem>
 540                 <para>The name is set based on information given by
 541                 the firmware for hot-plug devices, as exported by the
 542                 udev property <varname>ID_NET_NAME_SLOT</varname>.
 543                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 544                 </para>
 545
 546                 <xi:include href="version-info.xml" xpointer="v211"/>
 547               </listitem>
 548             </varlistentry>
 549             <varlistentry>
 550               <term><option>path</option></term>
 551               <listitem>
 552                 <para>The name is set based on the device's physical
 553                 location, as exported by the udev property
 554                 <varname>ID_NET_NAME_PATH</varname>.
 555                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 556                 </para>
 557
 558                 <xi:include href="version-info.xml" xpointer="v211"/>
 559               </listitem>
 560             </varlistentry>
 561             <varlistentry>
 562               <term><option>mac</option></term>
 563               <listitem>
 564                 <para>The name is set based on the device's persistent
 565                 MAC address, as exported by the udev property
 566                 <varname>ID_NET_NAME_MAC</varname>.
 567                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 568                 </para>
 569
 570                 <xi:include href="version-info.xml" xpointer="v211"/>
 571               </listitem>
 572             </varlistentry>
 573             <varlistentry>
 574               <term><option>keep</option></term>
 575               <listitem>
 576                 <para>If the device already had a name given by userspace (as part of creation of the device
 577                 or a rename), keep it.</para>
 578
 579                 <xi:include href="version-info.xml" xpointer="v241"/>
 580               </listitem>
 581             </varlistentry>
 582           </variablelist>
 583
 584             <xi:include href="version-info.xml" xpointer="v211"/>
 585         </listitem>
 586       </varlistentry>
 587       <varlistentry>
 588         <term><varname>Name=</varname></term>
 589         <listitem>
 590           <para>The interface name to use. This option has lower precedence than
 591           <varname>NamePolicy=</varname>, so for this setting to take effect, <varname>NamePolicy=</varname>
 592           must either be unset, empty, disabled, or all policies configured there must fail. Also see the
 593           example below with <literal>Name=dmz0</literal>.</para>
 594
 595           <para>Note that specifying a name that the kernel might use for another interface (for example
 596           <literal>eth0</literal>) is dangerous because the name assignment done by udev will race with the
 597           assignment done by the kernel, and only one interface may use the name. Depending on the order of
 598           operations, either udev or the kernel will win, making the naming unpredictable. It is best to use
 599           some different prefix, for example <literal>internal0</literal>/<literal>external0</literal> or
 600           <literal>lan0</literal>/<literal>lan1</literal>/<literal>lan3</literal>.</para>
 601
 602           <para>Interface names must have a minimum length of 1 character and a maximum length of 15
 603           characters, and may contain any 7bit ASCII character, with the exception of control characters,
 604           <literal>:</literal>, <literal>/</literal> and <literal>%</literal>. While <literal>.</literal> is
 605           an allowed character, it's recommended to avoid it when naming interfaces as various tools (such as
 606           <citerefentry><refentrytitle>resolvconf</refentrytitle><manvolnum>1</manvolnum></citerefentry>) use
 607           it as separator character. Also, fully numeric interface names are not allowed (in order to avoid
 608           ambiguity with interface specification by numeric indexes), as are the special strings
 609           <literal>.</literal>, <literal>..</literal>, <literal>all</literal> and
 610           <literal>default</literal>.</para>
 611
 612           <xi:include href="version-info.xml" xpointer="v211"/>
 613         </listitem>
 614       </varlistentry>
 615       <varlistentry>
 616         <term><varname>AlternativeNamesPolicy=</varname></term>
 617         <listitem>
 618           <para>A space-separated list of policies by which the interface's alternative names
 619           should be set. Each of the policies may fail, and all successful policies are used. The
 620           available policies are <literal>database</literal>, <literal>onboard</literal>,
 621           <literal>slot</literal>, <literal>path</literal>, and <literal>mac</literal>. If the
 622           kernel does not support the alternative names, then this setting will be ignored.
 623           </para>
 624
 625           <xi:include href="version-info.xml" xpointer="v245"/>
 626         </listitem>
 627       </varlistentry>
 628       <varlistentry>
 629         <term><varname>AlternativeName=</varname></term>
 630         <listitem>
 631           <para>The alternative interface name to use. This option can be specified multiple times.
 632           If the empty string is assigned to this option, the list is reset, and all prior assignments
 633           have no effect. If the kernel does not support the alternative names, then this setting will
 634           be ignored.</para>
 635
 636           <para>Alternative interface names may be used to identify interfaces in various tools. In contrast
 637           to the primary name (as configured with <varname>Name=</varname> above) there may be multiple
 638           alternative names referring to the same interface. Alternative names may have a maximum length of
 639           127 characters, in contrast to the 15 allowed for the primary interface name, but otherwise are
 640           subject to the same naming constraints.</para>
 641
 642           <xi:include href="version-info.xml" xpointer="v245"/>
 643         </listitem>
 644       </varlistentry>
 645       <varlistentry>
 646         <term><varname>TransmitQueues=</varname></term>
 647         <listitem>
 648           <para>Specifies the device's number of transmit queues. An integer in the range 1…4096.
 649           When unset, the kernel's default will be used.</para>
 650
 651           <xi:include href="version-info.xml" xpointer="v248"/>
 652         </listitem>
 653       </varlistentry>
 654       <varlistentry>
 655         <term><varname>ReceiveQueues=</varname></term>
 656         <listitem>
 657           <para>Specifies the device's number of receive queues. An integer in the range 1…4096.
 658           When unset, the kernel's default will be used.</para>
 659
 660           <xi:include href="version-info.xml" xpointer="v248"/>
 661         </listitem>
 662       </varlistentry>
 663       <varlistentry>
 664         <term><varname>TransmitQueueLength=</varname></term>
 665         <listitem>
 666           <para>Specifies the transmit queue length of the device in number of packets. An unsigned integer
 667           in the range 0…4294967294. When unset, the kernel's default will be used.</para>
 668
 669           <xi:include href="version-info.xml" xpointer="v248"/>
 670         </listitem>
 671       </varlistentry>
 672       <varlistentry>
 673         <term><varname>MTUBytes=</varname></term>
 674         <listitem>
 675           <para>The maximum transmission unit in bytes to set for the
 676           device. The usual suffixes K, M, G are supported and are
 677           understood to the base of 1024.</para>
 678
 679           <xi:include href="version-info.xml" xpointer="v211"/>
 680         </listitem>
 681       </varlistentry>
 682       <varlistentry>
 683         <term><varname>BitsPerSecond=</varname></term>
 684         <listitem>
 685           <para>The speed to set for the device, the value is rounded
 686           down to the nearest Mbps. The usual suffixes K, M, G are
 687           supported and are understood to the base of 1000.</para>
 688
 689           <xi:include href="version-info.xml" xpointer="v211"/>
 690         </listitem>
 691       </varlistentry>
 692       <varlistentry>
 693         <term><varname>Duplex=</varname></term>
 694         <listitem>
 695           <para>The duplex mode to set for the device. The accepted values are <option>half</option> and
 696           <option>full</option>.</para>
 697
 698         <xi:include href="version-info.xml" xpointer="v211"/>
 699         </listitem>
 700       </varlistentry>
 701       <varlistentry>
 702         <term><varname>AutoNegotiation=</varname></term>
 703         <listitem>
 704           <para>Takes a boolean. If set to yes, automatic negotiation of transmission parameters is enabled.
 705           Autonegotiation is a procedure by which two connected ethernet devices choose
 706           common transmission parameters, such as speed, duplex mode, and flow control.
 707           When unset, the kernel's default will be used.</para>
 708
 709           <para>Note that if autonegotiation is enabled, speed and duplex settings are
 710           read-only. If autonegotiation is disabled, speed and duplex settings are writable
 711           if the driver supports multiple link modes.</para>
 712
 713           <xi:include href="version-info.xml" xpointer="v233"/>
 714         </listitem>
 715       </varlistentry>
 716       <varlistentry>
 717         <term><varname>WakeOnLan=</varname></term>
 718         <listitem>
 719           <para>The Wake-on-LAN policy to set for the device. Takes the special value
 720           <literal>off</literal> which disables Wake-on-LAN, or space separated list of the following
 721           words:</para>
 722
 723           <variablelist>
 724             <varlistentry>
 725               <term><option>phy</option></term>
 726               <listitem>
 727                 <para>Wake on PHY activity.</para>
 728
 729               <xi:include href="version-info.xml" xpointer="v211"/>
 730               </listitem>
 731             </varlistentry>
 732             <varlistentry>
 733               <term><option>unicast</option></term>
 734               <listitem>
 735                 <para>Wake on unicast messages.</para>
 736
 737               <xi:include href="version-info.xml" xpointer="v235"/>
 738               </listitem>
 739             </varlistentry>
 740             <varlistentry>
 741               <term><option>multicast</option></term>
 742               <listitem>
 743                 <para>Wake on multicast messages.</para>
 744
 745               <xi:include href="version-info.xml" xpointer="v235"/>
 746               </listitem>
 747             </varlistentry>
 748             <varlistentry>
 749               <term><option>broadcast</option></term>
 750               <listitem>
 751                 <para>Wake on broadcast messages.</para>
 752
 753               <xi:include href="version-info.xml" xpointer="v235"/>
 754               </listitem>
 755             </varlistentry>
 756             <varlistentry>
 757               <term><option>arp</option></term>
 758               <listitem>
 759                 <para>Wake on ARP.</para>
 760
 761               <xi:include href="version-info.xml" xpointer="v235"/>
 762               </listitem>
 763             </varlistentry>
 764             <varlistentry>
 765               <term><option>magic</option></term>
 766               <listitem>
 767                 <para>Wake on receipt of a magic packet.
 768                 </para>
 769
 770                 <xi:include href="version-info.xml" xpointer="v211"/>
 771               </listitem>
 772             </varlistentry>
 773             <varlistentry>
 774               <term><option>secureon</option></term>
 775               <listitem>
 776                 <para>Enable SecureOn password for MagicPacket. Implied when
 777                 <varname>WakeOnLanPassword=</varname> is specified. If specified without
 778                 <varname>WakeOnLanPassword=</varname> option, then the password is read from the
 779                 credential <literal><replaceable>LINK</replaceable>.link.wol.password</literal> (e.g.,
 780                 <literal>60-foo.link.wol.password</literal>), and if the credential not found, then
 781                 read from <literal>wol.password</literal>. See
 782                 <varname>ImportCredential=</varname>/<varname>LoadCredential=</varname>/<varname>SetCredential=</varname> in
 783                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 784                 for details. The password in the credential, must be 6 bytes in hex format with each
 785                 byte separated by a colon (<literal>:</literal>) like an Ethernet MAC address, e.g.,
 786                 <literal>aa:bb:cc:dd:ee:ff</literal>.</para>
 787
 788                 <xi:include href="version-info.xml" xpointer="v235"/>
 789               </listitem>
 790             </varlistentry>
 791           </variablelist>
 792
 793           <para>Defaults to unset, and the device's default will be used. This setting can be specified
 794           multiple times. If an empty string is assigned, then the all previous assignments are
 795           cleared.</para>
 796
 797           <xi:include href="version-info.xml" xpointer="v211"/>
 798         </listitem>
 799       </varlistentry>
 800       <varlistentry>
 801         <term><varname>WakeOnLanPassword=</varname></term>
 802         <listitem>
 803           <para>Specifies the SecureOn password for MagicPacket. Takes an absolute path to a regular
 804           file or an <constant>AF_UNIX</constant> stream socket, or the plain password. When a path to
 805           a regular file is specified, the password is read from it. When an
 806           <constant>AF_UNIX</constant> stream socket is specified, a connection is made to it and the
 807           password is read from it. The password must be 6 bytes in hex format with each byte separated
 808           by a colon (<literal>:</literal>) like an Ethernet MAC address, e.g.,
 809           <literal>aa:bb:cc:dd:ee:ff</literal>. This implies <varname>WakeOnLan=secureon</varname>.
 810           Defaults to unset, and the current value will not be changed.</para>
 811
 812           <xi:include href="version-info.xml" xpointer="v250"/>
 813         </listitem>
 814       </varlistentry>
 815       <varlistentry>
 816         <term><varname>Port=</varname></term>
 817         <listitem>
 818           <para>The port option is used to select the device port. The
 819           supported values are:</para>
 820
 821           <variablelist>
 822             <varlistentry>
 823               <term><option>tp</option></term>
 824               <listitem>
 825                 <para>An Ethernet interface using Twisted-Pair cable as the medium.</para>
 826
 827               <xi:include href="version-info.xml" xpointer="v234"/>
 828               </listitem>
 829             </varlistentry>
 830             <varlistentry>
 831               <term><option>aui</option></term>
 832               <listitem>
 833                 <para>Attachment Unit Interface (AUI). Normally used with hubs.
 834                 </para>
 835
 836                 <xi:include href="version-info.xml" xpointer="v234"/>
 837               </listitem>
 838             </varlistentry>
 839             <varlistentry>
 840               <term><option>bnc</option></term>
 841               <listitem>
 842                 <para>An Ethernet interface using BNC connectors and co-axial cable.</para>
 843
 844               <xi:include href="version-info.xml" xpointer="v234"/>
 845               </listitem>
 846             </varlistentry>
 847             <varlistentry>
 848               <term><option>mii</option></term>
 849               <listitem>
 850                 <para>An Ethernet interface using a Media Independent Interface (MII).</para>
 851
 852               <xi:include href="version-info.xml" xpointer="v234"/>
 853               </listitem>
 854             </varlistentry>
 855             <varlistentry>
 856               <term><option>fibre</option></term>
 857               <listitem>
 858                 <para>An Ethernet interface using Optical Fibre as the medium.</para>
 859
 860               <xi:include href="version-info.xml" xpointer="v234"/>
 861               </listitem>
 862             </varlistentry>
 863           </variablelist>
 864
 865             <xi:include href="version-info.xml" xpointer="v234"/>
 866         </listitem>
 867       </varlistentry>
 868       <varlistentry>
 869         <term><varname>Advertise=</varname></term>
 870         <listitem>
 871           <para>This sets what speeds and duplex modes of operation are advertised for auto-negotiation.
 872           This implies <literal>AutoNegotiation=yes</literal>. The supported values are:
 873
 874           <table>
 875             <title>Supported advertise values</title>
 876             <tgroup cols='3'>
 877               <colspec colname='Advertise' />
 878               <colspec colname='Speed' />
 879               <colspec colname='Duplex Mode' />
 880
 881               <thead><row>
 882                 <entry>Advertise</entry>
 883                 <entry>Speed (Mbps)</entry>
 884                 <entry>Duplex Mode</entry>
 885               </row></thead>
 886               <xi:include href="ethtool-link-mode.xml" />
 887             </tgroup>
 888           </table>
 889
 890           By default this is unset, i.e. all possible modes will be advertised.
 891           This option may be specified more than once, in which case all specified speeds and modes are advertised.
 892           If the empty string is assigned to this option, the list is reset, and all prior assignments have no effect.
 893           </para>
 894
 895           <xi:include href="version-info.xml" xpointer="v240"/>
 896         </listitem>
 897       </varlistentry>
 898       <varlistentry>
 899         <term><varname>ReceiveChecksumOffload=</varname></term>
 900         <listitem>
 901           <para>Takes a boolean. If set to true, hardware offload for checksumming of ingress
 902           network packets is enabled. When unset, the kernel's default will be used.</para>
 903
 904           <xi:include href="version-info.xml" xpointer="v245"/>
 905         </listitem>
 906       </varlistentry>
 907       <varlistentry>
 908         <term><varname>TransmitChecksumOffload=</varname></term>
 909         <listitem>
 910           <para>Takes a boolean. If set to true, hardware offload for checksumming of egress
 911           network packets is enabled. When unset, the kernel's default will be used.</para>
 912
 913           <xi:include href="version-info.xml" xpointer="v245"/>
 914         </listitem>
 915       </varlistentry>
 916       <varlistentry>
 917         <term><varname>TCPSegmentationOffload=</varname></term>
 918         <listitem>
 919           <para>Takes a boolean. If set to true, TCP Segmentation Offload (TSO) is enabled.
 920           When unset, the kernel's default will be used.</para>
 921
 922           <xi:include href="version-info.xml" xpointer="v232"/>
 923         </listitem>
 924       </varlistentry>
 925        <varlistentry>
 926       <term><varname>TCP6SegmentationOffload=</varname></term>
 927         <listitem>
 928           <para>Takes a boolean. If set to true, TCP6 Segmentation Offload (tx-tcp6-segmentation) is enabled.
 929           When unset, the kernel's default will be used.</para>
 930
 931           <xi:include href="version-info.xml" xpointer="v235"/>
 932         </listitem>
 933       </varlistentry>
 934       <varlistentry>
 935         <term><varname>GenericSegmentationOffload=</varname></term>
 936         <listitem>
 937           <para>Takes a boolean. If set to true, Generic Segmentation Offload (GSO) is enabled.
 938           When unset, the kernel's default will be used.</para>
 939
 940           <xi:include href="version-info.xml" xpointer="v232"/>
 941         </listitem>
 942       </varlistentry>
 943       <varlistentry>
 944         <term><varname>GenericReceiveOffload=</varname></term>
 945         <listitem>
 946           <para>Takes a boolean. If set to true, Generic Receive Offload (GRO) is enabled.
 947           When unset, the kernel's default will be used.</para>
 948
 949           <xi:include href="version-info.xml" xpointer="v232"/>
 950         </listitem>
 951       </varlistentry>
 952       <varlistentry>
 953         <term><varname>GenericReceiveOffloadHardware=</varname></term>
 954         <listitem>
 955           <para>Takes a boolean. If set to true, hardware accelerated Generic Receive Offload (GRO) is
 956           enabled. When unset, the kernel's default will be used.</para>
 957
 958           <xi:include href="version-info.xml" xpointer="v250"/>
 959         </listitem>
 960       </varlistentry>
 961       <varlistentry>
 962         <term><varname>LargeReceiveOffload=</varname></term>
 963         <listitem>
 964           <para>Takes a boolean. If set to true, Large Receive Offload (LRO) is enabled.
 965           When unset, the kernel's default will be used.</para>
 966
 967           <xi:include href="version-info.xml" xpointer="v232"/>
 968         </listitem>
 969       </varlistentry>
 970       <varlistentry>
 971         <term><varname>ReceiveVLANCTAGHardwareAcceleration=</varname></term>
 972         <listitem>
 973           <para>Takes a boolean. If set to true, receive VLAN CTAG hardware acceleration is enabled.
 974           When unset, the kernel's default will be used.</para>
 975
 976           <xi:include href="version-info.xml" xpointer="v250"/>
 977         </listitem>
 978       </varlistentry>
 979       <varlistentry>
 980         <term><varname>TransmitVLANCTAGHardwareAcceleration=</varname></term>
 981         <listitem>
 982           <para>Takes a boolean. If set to true, transmit VLAN CTAG hardware acceleration is enabled.
 983           When unset, the kernel's default will be used.</para>
 984
 985           <xi:include href="version-info.xml" xpointer="v250"/>
 986         </listitem>
 987       </varlistentry>
 988       <varlistentry>
 989         <term><varname>ReceiveVLANCTAGFilter=</varname></term>
 990         <listitem>
 991           <para>Takes a boolean. If set to true, receive filtering on VLAN CTAGs is enabled.
 992           When unset, the kernel's default will be used.</para>
 993
 994           <xi:include href="version-info.xml" xpointer="v250"/>
 995         </listitem>
 996       </varlistentry>
 997       <varlistentry>
 998         <term><varname>TransmitVLANSTAGHardwareAcceleration=</varname></term>
 999         <listitem>
1000           <para>Takes a boolean. If set to true, transmit VLAN STAG hardware acceleration is enabled.
1001           When unset, the kernel's default will be used.</para>
1002
1003           <xi:include href="version-info.xml" xpointer="v250"/>
1004         </listitem>
1005       </varlistentry>
1006       <varlistentry>
1007         <term><varname>NTupleFilter=</varname></term>
1008         <listitem>
1009           <para>Takes a boolean. If set to true, receive N-tuple filters and actions are enabled.
1010           When unset, the kernel's default will be used.</para>
1011
1012           <xi:include href="version-info.xml" xpointer="v250"/>
1013         </listitem>
1014       </varlistentry>
1015       <varlistentry>
1016         <term><varname>RxChannels=</varname></term>
1017         <term><varname>TxChannels=</varname></term>
1018         <term><varname>OtherChannels=</varname></term>
1019         <term><varname>CombinedChannels=</varname></term>
1020         <listitem>
1021           <para>Specifies the number of receive, transmit, other, or combined channels, respectively.
1022           Takes an unsigned integer in the range 1…4294967295 or <literal>max</literal>. If set to
1023           <literal>max</literal>, the advertised maximum value of the hardware will be used. When
1024           unset, the number will not be changed. Defaults to unset.</para>
1025
1026           <xi:include href="version-info.xml" xpointer="v239"/>
1027         </listitem>
1028       </varlistentry>
1029       <varlistentry>
1030         <term><varname>RxBufferSize=</varname></term>
1031         <term><varname>RxMiniBufferSize=</varname></term>
1032         <term><varname>RxJumboBufferSize=</varname></term>
1033         <term><varname>TxBufferSize=</varname></term>
1034         <listitem>
1035           <para>Specifies the maximum number of pending packets in the NIC receive buffer, mini receive
1036           buffer, jumbo receive buffer, or transmit buffer, respectively. Takes an unsigned integer in
1037           the range 1…4294967295 or <literal>max</literal>. If set to <literal>max</literal>, the
1038           advertised maximum value of the hardware will be used. When unset, the number will not be
1039           changed. Defaults to unset.</para>
1040
1041           <xi:include href="version-info.xml" xpointer="v244"/>
1042         </listitem>
1043       </varlistentry>
1044       <varlistentry>
1045         <term><varname>RxFlowControl=</varname></term>
1046         <listitem>
1047           <para>Takes a boolean. When set, enables receive flow control, also known as the ethernet
1048           receive PAUSE message (generate and send ethernet PAUSE frames). When unset, the kernel's
1049           default will be used.</para>
1050
1051           <xi:include href="version-info.xml" xpointer="v246"/>
1052         </listitem>
1053       </varlistentry>
1054       <varlistentry>
1055         <term><varname>TxFlowControl=</varname></term>
1056         <listitem>
1057           <para>Takes a boolean. When set, enables transmit flow control, also known as the ethernet
1058           transmit PAUSE message (respond to received ethernet PAUSE frames). When unset, the kernel's
1059           default will be used.</para>
1060
1061           <xi:include href="version-info.xml" xpointer="v246"/>
1062         </listitem>
1063       </varlistentry>
1064       <varlistentry>
1065         <term><varname>AutoNegotiationFlowControl=</varname></term>
1066         <listitem>
1067           <para>Takes a boolean. When set, auto negotiation enables the interface to exchange state
1068           advertisements with the connected peer so that the two devices can agree on the ethernet
1069           PAUSE configuration. When unset, the kernel's default will be used.</para>
1070
1071           <xi:include href="version-info.xml" xpointer="v246"/>
1072         </listitem>
1073       </varlistentry>
1074       <varlistentry>
1075         <term><varname>GenericSegmentOffloadMaxBytes=</varname></term>
1076         <listitem>
1077           <para>Specifies the maximum size of a Generic Segment Offload (GSO) packet the
1078           device should accept. The usual suffixes K, M, G are supported and are
1079           understood to the base of 1024. An unsigned integer in the range 1…65536.
1080           Defaults to unset.</para>
1081
1082           <xi:include href="version-info.xml" xpointer="v248"/>
1083         </listitem>
1084       </varlistentry>
1085       <varlistentry>
1086         <term><varname>GenericSegmentOffloadMaxSegments=</varname></term>
1087         <listitem>
1088           <para>Specifies the maximum number of Generic Segment Offload (GSO) segments the device should
1089           accept. An unsigned integer in the range 1…65535. Defaults to unset.</para>
1090
1091           <xi:include href="version-info.xml" xpointer="v248"/>
1092         </listitem>
1093       </varlistentry>
1094       <varlistentry>
1095         <term><varname>UseAdaptiveRxCoalesce=</varname></term>
1096         <term><varname>UseAdaptiveTxCoalesce=</varname></term>
1097         <listitem>
1098           <para>Boolean properties that, when set, enable/disable adaptive Rx/Tx coalescing if the hardware
1099           supports it. When unset, the kernel's default will be used.</para>
1100
1101           <xi:include href="version-info.xml" xpointer="v250"/>
1102         </listitem>
1103       </varlistentry>
1104       <varlistentry>
1105         <term><varname>RxCoalesceSec=</varname></term>
1106         <term><varname>RxCoalesceIrqSec=</varname></term>
1107         <term><varname>RxCoalesceLowSec=</varname></term>
1108         <term><varname>RxCoalesceHighSec=</varname></term>
1109         <term><varname>TxCoalesceSec=</varname></term>
1110         <term><varname>TxCoalesceIrqSec=</varname></term>
1111         <term><varname>TxCoalesceLowSec=</varname></term>
1112         <term><varname>TxCoalesceHighSec=</varname></term>
1113         <listitem>
1114           <para>These properties configure the delay before Rx/Tx interrupts are generated after a packet is
1115           sent/received. The <literal>Irq</literal> properties come into effect when the host is servicing an
1116           IRQ. The <literal>Low</literal> and <literal>High</literal> properties come into effect when the
1117           packet rate drops below the low packet rate threshold or exceeds the high packet rate threshold
1118           respectively if adaptive Rx/Tx coalescing is enabled. When unset, the kernel's defaults will be
1119           used.</para>
1120
1121           <xi:include href="version-info.xml" xpointer="v250"/>
1122         </listitem>
1123       </varlistentry>
1124         <varlistentry>
1125         <term><varname>RxMaxCoalescedFrames=</varname></term>
1126         <term><varname>RxMaxCoalescedIrqFrames=</varname></term>
1127         <term><varname>RxMaxCoalescedLowFrames=</varname></term>
1128         <term><varname>RxMaxCoalescedHighFrames=</varname></term>
1129         <term><varname>TxMaxCoalescedFrames=</varname></term>
1130         <term><varname>TxMaxCoalescedIrqFrames=</varname></term>
1131         <term><varname>TxMaxCoalescedLowFrames=</varname></term>
1132         <term><varname>TxMaxCoalescedHighFrames=</varname></term>
1133         <listitem>
1134           <para>These properties configure the maximum number of frames that are sent/received before a Rx/Tx
1135           interrupt is generated. The <literal>Irq</literal> properties come into effect when the host is
1136           servicing an IRQ. The <literal>Low</literal> and <literal>High</literal> properties come into
1137           effect when the packet rate drops below the low packet rate threshold or exceeds the high packet
1138           rate threshold respectively if adaptive Rx/Tx coalescing is enabled. When unset, the kernel's
1139           defaults will be used.</para>
1140
1141           <xi:include href="version-info.xml" xpointer="v250"/>
1142         </listitem>
1143       </varlistentry>
1144       <varlistentry>
1145         <term><varname>CoalescePacketRateLow=</varname></term>
1146         <term><varname>CoalescePacketRateHigh=</varname></term>
1147         <listitem>
1148           <para>These properties configure the low and high packet rate (expressed in packets per second)
1149           threshold respectively and are used to determine when the corresponding coalescing settings for low
1150           and high packet rates come into effect if adaptive Rx/Tx coalescing is enabled. If unset, the
1151           kernel's defaults will be used.</para>
1152
1153           <xi:include href="version-info.xml" xpointer="v250"/>
1154         </listitem>
1155       </varlistentry>
1156       <varlistentry>
1157         <term><varname>CoalescePacketRateSampleIntervalSec=</varname></term>
1158         <listitem>
1159           <para>Configures how often to sample the packet rate used for adaptive Rx/Tx coalescing. This
1160           property cannot be zero. This lowest time granularity supported by this property is seconds.
1161           Partial seconds will be rounded up before being passed to the kernel. If unset, the kernel's
1162           default will be used.</para>
1163
1164           <xi:include href="version-info.xml" xpointer="v250"/>
1165         </listitem>
1166       </varlistentry>
1167       <varlistentry>
1168         <term><varname>StatisticsBlockCoalesceSec=</varname></term>
1169         <listitem>
1170           <para>How long to delay driver in-memory statistics block updates. If the driver does not have an
1171           in-memory statistic block, this property is ignored. This property cannot be zero. If unset, the
1172           kernel's default will be used.</para>
1173
1174           <xi:include href="version-info.xml" xpointer="v250"/>
1175         </listitem>
1176       </varlistentry>
1177
1178       <varlistentry>
1179         <term><varname>MDI=</varname></term>
1180         <listitem>
1181           <para>Specifies the medium dependent interface (MDI) mode for the interface. A MDI describes
1182           the interface from a physical layer implementation to the physical medium used to carry the
1183           transmission. Takes one of the following words: <literal>straight</literal> (or equivalently:
1184           <literal>mdi</literal>), <literal>crossover</literal> (or equivalently:
1185           <literal>mdi-x</literal>, <literal>mdix</literal>), and <literal>auto</literal>. When
1186           <literal>straight</literal>, the MDI straight through mode will be used. When
1187           <literal>crossover</literal>, the MDI crossover (MDI-X) mode will be used. When
1188           <literal>auto</literal>, the MDI status is automatically detected. Defaults to unset, and the
1189           kernel's default will be used.</para>
1190
1191           <xi:include href="version-info.xml" xpointer="v251"/>
1192         </listitem>
1193       </varlistentry>
1194
1195       <varlistentry>
1196         <term><varname>SR-IOVVirtualFunctions=</varname></term>
1197         <listitem>
1198           <para>Specifies the number of SR-IOV virtual functions. Takes an integer in the range
1199           0…2147483647. Defaults to unset, and automatically determined from the values specified in
1200           the <varname>VirtualFunction=</varname> settings in the [SR-IOV] sections.</para>
1201
1202           <xi:include href="version-info.xml" xpointer="v251"/>
1203         </listitem>
1204       </varlistentry>
1205
1206     </variablelist>
1207   </refsect1>
1208
1209   <refsect1 id='sr-iov'>
1210     <title>[SR-IOV] Section Options</title>
1211     <para>The [SR-IOV] section accepts the following keys. Specify several [SR-IOV] sections to
1212     configure several SR-IOVs. SR-IOV provides the ability to partition a single physical PCI resource
1213     into virtual PCI functions which can then be injected into a VM. In the case of network VFs, SR-IOV
1214     improves north-south network performance (that is, traffic with endpoints outside the host machine)
1215     by allowing traffic to bypass the host machine’s network stack.</para>
1216
1217     <variablelist class='network-directives'>
1218       <varlistentry>
1219         <term><varname>VirtualFunction=</varname></term>
1220         <listitem>
1221           <para>Specifies a Virtual Function (VF), lightweight PCIe function designed solely to move
1222           data in and out. Takes an integer in the range 0…2147483646. This option is compulsory.
1223           </para>
1224
1225           <xi:include href="version-info.xml" xpointer="v251"/>
1226         </listitem>
1227       </varlistentry>
1228
1229       <varlistentry>
1230         <term><varname>VLANId=</varname></term>
1231         <listitem>
1232           <para>Specifies VLAN ID of the virtual function. Takes an integer in the range 1…4095.</para>
1233
1234         <xi:include href="version-info.xml" xpointer="v251"/>
1235         </listitem>
1236       </varlistentry>
1237
1238       <varlistentry>
1239         <term><varname>QualityOfService=</varname></term>
1240         <listitem>
1241           <para>Specifies quality of service of the virtual function. Takes an integer in the range
1242           1…4294967294.</para>
1243
1244           <xi:include href="version-info.xml" xpointer="v251"/>
1245         </listitem>
1246       </varlistentry>
1247
1248       <varlistentry>
1249         <term><varname>VLANProtocol=</varname></term>
1250         <listitem>
1251           <para>Specifies VLAN protocol of the virtual function. Takes <literal>802.1Q</literal> or
1252           <literal>802.1ad</literal>.</para>
1253
1254         <xi:include href="version-info.xml" xpointer="v251"/>
1255         </listitem>
1256       </varlistentry>
1257
1258       <varlistentry>
1259         <term><varname>MACSpoofCheck=</varname></term>
1260         <listitem>
1261           <para>Takes a boolean. Controls the MAC spoof checking. When unset, the kernel's default will
1262           be used.</para>
1263
1264           <xi:include href="version-info.xml" xpointer="v251"/>
1265         </listitem>
1266       </varlistentry>
1267
1268       <varlistentry>
1269         <term><varname>QueryReceiveSideScaling=</varname></term>
1270         <listitem>
1271           <para>Takes a boolean. Toggle the ability of querying the receive side scaling (RSS)
1272           configuration of the virtual function (VF). The VF RSS information like RSS hash key may be
1273           considered sensitive on some devices where this information is shared between VF and the
1274           physical function (PF). When unset, the kernel's default will be used.</para>
1275
1276           <xi:include href="version-info.xml" xpointer="v251"/>
1277         </listitem>
1278       </varlistentry>
1279
1280       <varlistentry>
1281         <term><varname>Trust=</varname></term>
1282         <listitem>
1283           <para>Takes a boolean. Allows one to set trust mode of the virtual function (VF). When set,
1284           VF users can set a specific feature which may impact security and/or performance. When unset,
1285           the kernel's default will be used.</para>
1286
1287           <xi:include href="version-info.xml" xpointer="v251"/>
1288         </listitem>
1289       </varlistentry>
1290
1291       <varlistentry>
1292         <term><varname>LinkState=</varname></term>
1293         <listitem>
1294           <para>Allows one to set the link state of the virtual function (VF). Takes a boolean or a
1295           special value <literal>auto</literal>. Setting to <literal>auto</literal> means a
1296           reflection of the physical function (PF) link state, <literal>yes</literal> lets the VF to
1297           communicate with other VFs on this host even if the PF link state is down,
1298           <literal>no</literal> causes the hardware to drop any packets sent by the VF. When unset,
1299           the kernel's default will be used.</para>
1300
1301           <xi:include href="version-info.xml" xpointer="v251"/>
1302         </listitem>
1303       </varlistentry>
1304
1305       <varlistentry>
1306         <term><varname>MACAddress=</varname></term>
1307         <listitem>
1308           <para>Specifies the MAC address for the virtual function.</para>
1309
1310         <xi:include href="version-info.xml" xpointer="v251"/>
1311         </listitem>
1312       </varlistentry>
1313     </variablelist>
1314   </refsect1>
1315
1316   <refsect1>
1317     <title>Specifiers</title>
1318
1319     <para>Some settings resolve specifiers which may be used to write generic unit files referring to runtime
1320     or unit parameters that are replaced when the unit files are loaded. Specifiers must be known and
1321     resolvable for the setting to be valid. The following specifiers are understood:</para>
1322
1323     <table class='specifiers'>
1324       <title>Specifiers available in unit files</title>
1325       <tgroup cols='3' align='left' colsep='1' rowsep='1'>
1326         <colspec colname="spec" />
1327         <colspec colname="mean" />
1328         <colspec colname="detail" />
1329         <thead>
1330           <row>
1331             <entry>Specifier</entry>
1332             <entry>Meaning</entry>
1333             <entry>Details</entry>
1334           </row>
1335         </thead>
1336         <tbody>
1337           <xi:include href="standard-specifiers.xml" xpointer="a"/>
1338           <xi:include href="standard-specifiers.xml" xpointer="A"/>
1339           <xi:include href="standard-specifiers.xml" xpointer="b"/>
1340           <xi:include href="standard-specifiers.xml" xpointer="B"/>
1341           <xi:include href="standard-specifiers.xml" xpointer="H"/>
1342           <xi:include href="standard-specifiers.xml" xpointer="l"/>
1343           <xi:include href="standard-specifiers.xml" xpointer="m"/>
1344           <xi:include href="standard-specifiers.xml" xpointer="M"/>
1345           <xi:include href="standard-specifiers.xml" xpointer="o"/>
1346           <xi:include href="standard-specifiers.xml" xpointer="q"/>
1347           <xi:include href="standard-specifiers.xml" xpointer="T"/>
1348           <xi:include href="standard-specifiers.xml" xpointer="v"/>
1349           <xi:include href="standard-specifiers.xml" xpointer="V"/>
1350           <xi:include href="standard-specifiers.xml" xpointer="w"/>
1351           <xi:include href="standard-specifiers.xml" xpointer="W"/>
1352         </tbody>
1353       </tgroup>
1354     </table>
1355   </refsect1>
1356
1357   <refsect1>
1358     <title>Examples</title>
1359
1360     <example>
1361       <title>/usr/lib/systemd/network/99-default.link</title>
1362
1363       <para>The link file <filename>99-default.link</filename> that is shipped with systemd defines the
1364       default policies for the interface name, alternative names, and MAC address of links.</para>
1365
1366       <programlisting>[Match]
1367 OriginalName=*
1368
1369 [Link]
1370 NamePolicy=keep kernel database onboard slot path
1371 AlternativeNamesPolicy=database onboard slot path
1372 MACAddressPolicy=persistent</programlisting>
1373     </example>
1374
1375     <example>
1376       <title>/etc/systemd/network/10-dmz.link</title>
1377
1378       <para>This example assigns the fixed name <literal>dmz0</literal> to the interface with the MAC address
1379       00:a0:de:63:7a:e6:</para>
1380
1381       <programlisting>[Match]
1382 MACAddress=00:a0:de:63:7a:e6
1383
1384 [Link]
1385 Name=dmz0</programlisting>
1386
1387       <para><varname>NamePolicy=</varname> is not set, so <varname>Name=</varname> takes effect. We use the
1388       <literal>10-</literal> prefix to order this file early in the list. Note that it needs to be before
1389       <filename>99-default.link</filename>, i.e. it needs a numerical prefix, to have any effect at all.</para>
1390     </example>
1391
1392     <example>
1393       <title>(Re-)applying a .link file to an interface</title>
1394
1395       <para>After a new .link file has been created, or an existing .link file modified, the new settings
1396       may be applied to the matching interface with the following commands:</para>
1397
1398       <programlisting>$ sudo udevadm control --reload
1399 $ sudo ip link set eth0 down
1400 $ sudo udevadm trigger --verbose --settle --action add /sys/class/net/eth0</programlisting>
1401
1402       <para>You may also need to stop the service that manages the network interface, e.g.
1403       <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1404       or <filename>NetworkManager.service</filename> before the above operation, and then restart the service
1405       after that. For more details about <command>udevadm</command> command, see
1406       <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
1407     </example>
1408
1409     <example>
1410       <title>Debugging <varname>NamePolicy=</varname> assignments</title>
1411
1412       <programlisting>$ sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/hub0
1413 …
1414 Parsed configuration file /usr/lib/systemd/network/99-default.link
1415 Parsed configuration file /etc/systemd/network/10-eth0.link
1416 ID_NET_DRIVER=cdc_ether
1417 Config file /etc/systemd/network/10-eth0.link applies to device hub0
1418 link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
1419 hub0: Device has name_assign_type=4
1420 Using default interface naming scheme 'v240'.
1421 hub0: Policies didn't yield a name, using specified Name=hub0.
1422 ID_NET_LINK_FILE=/etc/systemd/network/10-eth0.link
1423 ID_NET_NAME=hub0
1424 …</programlisting>
1425
1426      <para>Explicit <varname>Name=</varname> configuration wins in this case.</para>
1427
1428      <programlisting>sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/enp0s31f6
1429 …
1430 Parsed configuration file /usr/lib/systemd/network/99-default.link
1431 Parsed configuration file /etc/systemd/network/10-eth0.link
1432 Created link configuration context.
1433 ID_NET_DRIVER=e1000e
1434 Config file /usr/lib/systemd/network/99-default.link applies to device enp0s31f6
1435 link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
1436 enp0s31f6: Device has name_assign_type=4
1437 Using default interface naming scheme 'v240'.
1438 enp0s31f6: Policy *keep*: keeping existing userspace name
1439 enp0s31f6: Device has addr_assign_type=0
1440 enp0s31f6: MAC on the device already matches policy *persistent*
1441 ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
1442 …
1443 </programlisting>
1444
1445      <para>In this case, the interface was already renamed, so the <option>keep</option> policy specified as
1446      the first option in <filename index="false">99-default.link</filename> means that the existing name is
1447      preserved. If <option>keep</option> was removed, or if were in boot before the renaming has happened,
1448      we might get the following instead:</para>
1449
1450      <programlisting>enp0s31f6: Policy *path* yields "enp0s31f6".
1451 enp0s31f6: Device has addr_assign_type=0
1452 enp0s31f6: MAC on the device already matches policy *persistent*
1453 ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
1454 ID_NET_NAME=enp0s31f6
1455 …
1456 </programlisting>
1457
1458       <para>Please note that the details of output are subject to change.</para>
1459     </example>
1460
1461     <example>
1462       <title>/etc/systemd/network/10-internet.link</title>
1463
1464       <para>This example assigns the fixed name
1465       <literal>internet0</literal> to the interface with the device
1466       path <literal>pci-0000:00:1a.0-*</literal>:</para>
1467
1468       <programlisting>[Match]
1469 Path=pci-0000:00:1a.0-*
1470
1471 [Link]
1472 Name=internet0</programlisting>
1473     </example>
1474
1475     <example>
1476       <title>/etc/systemd/network/25-wireless.link</title>
1477
1478       <para>Here's an overly complex example that shows the use of a large number of [Match] and [Link] settings.</para>
1479
1480       <programlisting>[Match]
1481 MACAddress=12:34:56:78:9a:bc
1482 Driver=brcmsmac
1483 Path=pci-0000:02:00.0-*
1484 Type=wlan
1485 Virtualization=no
1486 Host=my-laptop
1487 Architecture=x86-64
1488
1489 [Link]
1490 Name=wireless0
1491 MTUBytes=1450
1492 BitsPerSecond=10M
1493 WakeOnLan=magic
1494 MACAddress=cb:a9:87:65:43:21</programlisting>
1495     </example>
1496   </refsect1>
1497
1498   <refsect1>
1499     <title>See Also</title>
1500     <para><simplelist type="inline">
1501       <member><citerefentry>
1502         <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
1503       </citerefentry></member>
1504       <member><citerefentry>
1505         <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
1506       </citerefentry></member>
1507       <member><citerefentry>
1508         <refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum>
1509       </citerefentry></member>
1510       <member><citerefentry>
1511         <refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum>
1512       </citerefentry></member>
1513       <member><citerefentry>
1514         <refentrytitle>systemd-network-generator.service</refentrytitle><manvolnum>8</manvolnum>
1515       </citerefentry></member>
1516     </simplelist></para>
1517   </refsect1>
1518
1519 </refentry>