man/systemd.link.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="systemd.link">
   7   <refentryinfo>
   8     <title>systemd.link</title>
   9     <productname>systemd</productname>
  10   </refentryinfo>
  11
  12   <refmeta>
  13     <refentrytitle>systemd.link</refentrytitle>
  14     <manvolnum>5</manvolnum>
  15   </refmeta>
  16
  17   <refnamediv>
  18     <refname>systemd.link</refname>
  19     <refpurpose>Network device configuration</refpurpose>
  20   </refnamediv>
  21
  22   <refsynopsisdiv>
  23     <para><filename><replaceable>link</replaceable>.link</filename></para>
  24   </refsynopsisdiv>
  25
  26   <refsect1>
  27     <title>Description</title>
  28
  29     <para>Network link configuration is performed by the
  30     <command>net_setup_link</command> udev builtin.</para>
  31
  32     <para>The link files are read from the files located in the system
  33     network directory <filename>/usr/lib/systemd/network</filename>,
  34     the volatile runtime network directory
  35     <filename>/run/systemd/network</filename>, and the local
  36     administration network directory
  37     <filename>/etc/systemd/network</filename>. Link files must have
  38     the extension <filename>.link</filename>; other extensions are
  39     ignored. All link files are collectively sorted and processed in
  40     lexical order, regardless of the directories in which they live.
  41     However, files with identical filenames replace each other. Files
  42     in <filename>/etc</filename> have the highest priority, files in
  43     <filename>/run</filename> take precedence over files with the same
  44     name in <filename>/usr/lib</filename>. This can be used to
  45     override a system-supplied link file with a local file if needed.
  46     As a special case, an empty file (file size 0) or symlink with the
  47     same name pointing to <filename>/dev/null</filename> disables the
  48     configuration file entirely (it is "masked").</para>
  49
  50     <para>The link file contains a [Match] section, which determines if a given link file may be applied to a
  51     given device, as well as a [Link] section specifying how the device should be configured. The first (in
  52     lexical order) of the link files that matches a given device is applied. Note that a default file
  53     <filename>99-default.link</filename> is shipped by the system. Any user-supplied
  54     <filename>.link</filename> should hence have a lexically earlier name to be considered at all.</para>
  55
  56     <para>See <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
  57     diagnosing problems with <filename>.link</filename> files.</para>
  58   </refsect1>
  59
  60   <refsect1>
  61     <title>[Match] Section Options</title>
  62
  63     <para>A link file is said to match a device if all matches specified by the
  64     <literal>[Match]</literal> section are satisfied. When a link file does not contain valid settings
  65     in <literal>[Match]</literal> section, then the file will match all devices and
  66     <command>systemd-udevd</command> warns about that. Hint: to avoid the warning and to make it clear
  67     that all interfaces shall be matched, add the following:
  68     <programlisting>OriginalName=*</programlisting>
  69     The following keys are accepted:</para>
  70
  71     <variablelist class='network-directives'>
  72       <varlistentry>
  73         <term><varname>MACAddress=</varname></term>
  74         <listitem>
  75           <para>A whitespace-separated list of hardware addresses. Use full colon-, hyphen- or dot-delimited hexadecimal. See the example below.
  76           This option may appear more than once, in which case the lists are merged. If the empty string is assigned to this option, the list
  77           of hardware addresses defined prior to this is reset.</para>
  78
  79           <para>Example:
  80           <programlisting>MACAddress=01:23:45:67:89:ab 00-11-22-33-44-55 AABB.CCDD.EEFF</programlisting></para>
  81         </listitem>
  82       </varlistentry>
  83       <varlistentry>
  84         <term><varname>OriginalName=</varname></term>
  85         <listitem>
  86           <para>A whitespace-separated list of shell-style globs matching
  87           the device name, as exposed by the udev property
  88           "INTERFACE". This cannot be used to match on names that have
  89           already been changed from userspace. Caution is advised when matching on
  90           kernel-assigned names, as they are known to be unstable
  91           between reboots.</para>
  92         </listitem>
  93       </varlistentry>
  94       <varlistentry>
  95         <term><varname>Path=</varname></term>
  96         <listitem>
  97           <para>A whitespace-separated list of shell-style globs matching
  98           the persistent path, as exposed by the udev property
  99           <varname>ID_PATH</varname>.</para>
 100         </listitem>
 101       </varlistentry>
 102       <varlistentry>
 103         <term><varname>Driver=</varname></term>
 104         <listitem>
 105           <para>A whitespace-separated list of shell-style globs matching the driver currently bound to the
 106           device, as exposed by the udev property <varname>ID_NET_DRIVER</varname> of its parent device, or if that
 107           is not set, the driver as exposed by <command>ethtool -i</command> of the device itself.</para>
 108         </listitem>
 109       </varlistentry>
 110       <varlistentry>
 111         <term><varname>Type=</varname></term>
 112         <listitem>
 113           <para>A whitespace-separated list of shell-style globs matching
 114           the device type, as exposed by the udev
 115           property <varname>DEVTYPE</varname>.</para>
 116         </listitem>
 117       </varlistentry>
 118       <varlistentry>
 119         <term><varname>Property=</varname></term>
 120         <listitem>
 121           <para>A whitespace-separated list of udev property name with its value after a equal
 122           (<literal>=</literal>). If multiple properties are specified, the test results are ANDed.
 123           If the list is prefixed with a "!", the test is inverted. If a value contains white
 124           spaces, then please quote whole key and value pair. If a value contains quotation, then
 125           please escape the quotation with <literal>\</literal>.</para>
 126
 127           <para>Example: if a .link file has the following:
 128           <programlisting>Property=ID_MODEL_ID=9999 "ID_VENDOR_FROM_DATABASE=vendor name" "KEY=with \"quotation\""</programlisting>
 129           then, the .link file matches only when an interface has all the above three properties.
 130           </para>
 131         </listitem>
 132       </varlistentry>
 133       <varlistentry>
 134         <term><varname>Host=</varname></term>
 135         <listitem>
 136           <para>Matches against the hostname or machine ID of the host. See <varname>ConditionHost=</varname> in
 137           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 138           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 139           If an empty string is assigned, then previously assigned value is cleared.
 140           </para>
 141         </listitem>
 142       </varlistentry>
 143       <varlistentry>
 144         <term><varname>Virtualization=</varname></term>
 145         <listitem>
 146           <para>Checks whether the system is executed in a virtualized environment and optionally test
 147           whether it is a specific implementation. See <varname>ConditionVirtualization=</varname> in
 148           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 149           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 150           If an empty string is assigned, then previously assigned value is cleared.
 151           </para>
 152         </listitem>
 153       </varlistentry>
 154       <varlistentry>
 155         <term><varname>KernelCommandLine=</varname></term>
 156         <listitem>
 157           <para>Checks whether a specific kernel command line option is set. See
 158           <varname>ConditionKernelCommandLine=</varname> in
 159           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 160           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 161           If an empty string is assigned, then previously assigned value is cleared.
 162           </para>
 163         </listitem>
 164       </varlistentry>
 165       <varlistentry>
 166         <term><varname>KernelVersion=</varname></term>
 167         <listitem>
 168           <para>Checks whether the kernel version (as reported by <command>uname -r</command>) matches a certain
 169           expression. See <varname>ConditionKernelVersion=</varname> in
 170           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 171           details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 172           If an empty string is assigned, then previously assigned value is cleared.
 173           </para>
 174         </listitem>
 175       </varlistentry>
 176       <varlistentry>
 177         <term><varname>Architecture=</varname></term>
 178         <listitem>
 179           <para>Checks whether the system is running on a specific architecture. See
 180           <varname>ConditionArchitecture=</varname> in
 181           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 182           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 183           If an empty string is assigned, then previously assigned value is cleared.
 184           </para>
 185         </listitem>
 186       </varlistentry>
 187     </variablelist>
 188
 189   </refsect1>
 190
 191   <refsect1>
 192     <title>[Link] Section Options</title>
 193
 194     <para>The [Link] section accepts the following
 195     keys:</para>
 196
 197     <variablelist class='network-directives'>
 198       <varlistentry>
 199         <term><varname>Description=</varname></term>
 200         <listitem>
 201           <para>A description of the device.</para>
 202         </listitem>
 203       </varlistentry>
 204       <varlistentry>
 205         <term><varname>Alias=</varname></term>
 206         <listitem>
 207           <para>The <varname>ifalias</varname> interface property is set to this value.</para>
 208         </listitem>
 209       </varlistentry>
 210       <varlistentry>
 211         <term><varname>MACAddressPolicy=</varname></term>
 212         <listitem>
 213           <para>The policy by which the MAC address should be set. The
 214           available policies are:
 215           </para>
 216
 217           <variablelist>
 218             <varlistentry>
 219               <term><option>persistent</option></term>
 220               <listitem>
 221                 <para>If the hardware has a persistent MAC address, as
 222                 most hardware should, and if it is used by the kernel,
 223                 nothing is done. Otherwise, a new MAC address is
 224                 generated which is guaranteed to be the same on every
 225                 boot for the given machine and the given device, but
 226                 which is otherwise random. This feature depends on ID_NET_NAME_*
 227                 properties to exist for the link. On hardware where these
 228                 properties are not set, the generation of a persistent MAC address
 229                 will fail.</para>
 230               </listitem>
 231             </varlistentry>
 232             <varlistentry>
 233               <term><option>random</option></term>
 234               <listitem>
 235                 <para>If the kernel is using a random MAC address,
 236                 nothing is done. Otherwise, a new address is randomly
 237                 generated each time the device appears, typically at
 238                 boot. Either way, the random address will have the
 239                 <literal>unicast</literal> and
 240                 <literal>locally administered</literal> bits set.</para>
 241               </listitem>
 242             </varlistentry>
 243             <varlistentry>
 244               <term><option>none</option></term>
 245               <listitem>
 246                 <para>Keeps the MAC address assigned by the kernel.</para>
 247               </listitem>
 248             </varlistentry>
 249           </variablelist>
 250         </listitem>
 251       </varlistentry>
 252       <varlistentry>
 253         <term><varname>MACAddress=</varname></term>
 254         <listitem>
 255           <para>The MAC address to use, if no
 256           <varname>MACAddressPolicy=</varname>
 257           is specified.</para>
 258         </listitem>
 259       </varlistentry>
 260       <varlistentry>
 261         <term><varname>NamePolicy=</varname></term>
 262         <listitem>
 263           <para>An ordered, space-separated list of policies by which the interface name should be set.
 264           <varname>NamePolicy=</varname> may be disabled by specifying <option>net.ifnames=0</option> on the
 265           kernel command line. Each of the policies may fail, and the first successful one is used. The name
 266           is not set directly, but is exported to udev as the property <option>ID_NET_NAME</option>, which
 267           is, by default, used by a
 268           <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 269           rule to set <varname>NAME</varname>. The available policies are:
 270           </para>
 271
 272           <variablelist>
 273             <varlistentry>
 274               <term><option>kernel</option></term>
 275               <listitem>
 276                 <para>If the kernel claims that the name it has set
 277                 for a device is predictable, then no renaming is
 278                 performed.</para>
 279               </listitem>
 280             </varlistentry>
 281             <varlistentry>
 282               <term><option>database</option></term>
 283               <listitem>
 284                 <para>The name is set based on entries in the udev's
 285                 Hardware Database with the key
 286                 <varname>ID_NET_NAME_FROM_DATABASE</varname>.
 287                 </para>
 288               </listitem>
 289             </varlistentry>
 290             <varlistentry>
 291               <term><option>onboard</option></term>
 292               <listitem>
 293                 <para>The name is set based on information given by
 294                 the firmware for on-board devices, as exported by the
 295                 udev property <varname>ID_NET_NAME_ONBOARD</varname>.
 296                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 297                 </para>
 298               </listitem>
 299             </varlistentry>
 300             <varlistentry>
 301               <term><option>slot</option></term>
 302               <listitem>
 303                 <para>The name is set based on information given by
 304                 the firmware for hot-plug devices, as exported by the
 305                 udev property <varname>ID_NET_NAME_SLOT</varname>.
 306                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 307                 </para>
 308               </listitem>
 309             </varlistentry>
 310             <varlistentry>
 311               <term><option>path</option></term>
 312               <listitem>
 313                 <para>The name is set based on the device's physical
 314                 location, as exported by the udev property
 315                 <varname>ID_NET_NAME_PATH</varname>.
 316                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 317                 </para>
 318               </listitem>
 319             </varlistentry>
 320             <varlistentry>
 321               <term><option>mac</option></term>
 322               <listitem>
 323                 <para>The name is set based on the device's persistent
 324                 MAC address, as exported by the udev property
 325                 <varname>ID_NET_NAME_MAC</varname>.
 326                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 327                 </para>
 328               </listitem>
 329             </varlistentry>
 330             <varlistentry>
 331               <term><option>keep</option></term>
 332               <listitem>
 333                 <para>If the device already had a name given by userspace (as part of creation of the device
 334                 or a rename), keep it.</para>
 335               </listitem>
 336             </varlistentry>
 337           </variablelist>
 338         </listitem>
 339       </varlistentry>
 340       <varlistentry>
 341         <term><varname>Name=</varname></term>
 342         <listitem>
 343           <para>The interface name to use. This option has lower precedence than
 344           <varname>NamePolicy=</varname>, so for this setting to take effect, <varname>NamePolicy=</varname>
 345           must either be unset, empty, disabled, or all policies configured there must fail. Also see the
 346           example below with <literal>Name=dmz0</literal>.</para>
 347
 348           <para>Note that specifying a name that the kernel might use for another
 349           interface (for example <literal>eth0</literal>) is dangerous because the
 350           name assignment done by udev will race with the assignment done by the
 351           kernel, and only one interface may use the name. Depending on the order of
 352           operations, either udev or the kernel will win, making the naming
 353           unpredictable. It is best to use some different prefix, for example
 354           <literal>internal0</literal>/<literal>external0</literal> or
 355           <literal>lan0</literal>/<literal>lan1</literal>/<literal>lan3</literal>.
 356           </para>
 357         </listitem>
 358       </varlistentry>
 359       <varlistentry>
 360         <term><varname>MTUBytes=</varname></term>
 361         <listitem>
 362           <para>The maximum transmission unit in bytes to set for the
 363           device. The usual suffixes K, M, G, are supported and are
 364           understood to the base of 1024.</para>
 365         </listitem>
 366       </varlistentry>
 367       <varlistentry>
 368         <term><varname>BitsPerSecond=</varname></term>
 369         <listitem>
 370           <para>The speed to set for the device, the value is rounded
 371           down to the nearest Mbps. The usual suffixes K, M, G, are
 372           supported and are understood to the base of 1000.</para>
 373         </listitem>
 374       </varlistentry>
 375       <varlistentry>
 376         <term><varname>Duplex=</varname></term>
 377         <listitem>
 378           <para>The duplex mode to set for the device. The accepted values are <option>half</option> and
 379           <option>full</option>.</para>
 380         </listitem>
 381       </varlistentry>
 382       <varlistentry>
 383         <term><varname>AutoNegotiation=</varname></term>
 384         <listitem>
 385           <para>Takes a boolean. If set to yes, automatic negotiation of transmission parameters is enabled.
 386           Autonegotiation is a procedure by which two connected ethernet devices choose
 387           common transmission parameters, such as speed, duplex mode, and flow control.
 388           When unset, the kernel's default will be used.</para>
 389
 390           <para>Note that if autonegotiation is enabled, speed and duplex settings are
 391           read-only. If autonegotation is disabled, speed and duplex settings are writable
 392           if the driver supports multiple link modes.</para>
 393         </listitem>
 394       </varlistentry>
 395       <varlistentry>
 396         <term><varname>WakeOnLan=</varname></term>
 397         <listitem>
 398           <para>The Wake-on-LAN policy to set for the device. The
 399           supported values are:</para>
 400
 401           <variablelist>
 402             <varlistentry>
 403               <term><option>phy</option></term>
 404               <listitem>
 405                 <para>Wake on PHY activity.</para>
 406               </listitem>
 407             </varlistentry>
 408             <varlistentry>
 409               <term><option>unicast</option></term>
 410               <listitem>
 411                 <para>Wake on unicast messages.</para>
 412               </listitem>
 413             </varlistentry>
 414             <varlistentry>
 415               <term><option>multicast</option></term>
 416               <listitem>
 417                 <para>Wake on multicast messages.</para>
 418               </listitem>
 419             </varlistentry>
 420             <varlistentry>
 421               <term><option>broadcast</option></term>
 422               <listitem>
 423                 <para>Wake on broadcast messages.</para>
 424               </listitem>
 425             </varlistentry>
 426             <varlistentry>
 427               <term><option>arp</option></term>
 428               <listitem>
 429                 <para>Wake on ARP.</para>
 430               </listitem>
 431             </varlistentry>
 432             <varlistentry>
 433               <term><option>magic</option></term>
 434               <listitem>
 435                 <para>Wake on receipt of a magic packet.
 436                 </para>
 437               </listitem>
 438             </varlistentry>
 439             <varlistentry>
 440               <term><option>secureon</option></term>
 441               <listitem>
 442                 <para>Enable secureon(tm) password for MagicPacket(tm).
 443                 </para>
 444               </listitem>
 445             </varlistentry>
 446             <varlistentry>
 447               <term><option>off</option></term>
 448               <listitem>
 449                 <para>Never wake.</para>
 450               </listitem>
 451             </varlistentry>
 452           </variablelist>
 453
 454           <para>Defaults to <option>off</option>.</para>
 455         </listitem>
 456       </varlistentry>
 457       <varlistentry>
 458         <term><varname>Port=</varname></term>
 459         <listitem>
 460           <para>The port option is used to select the device port. The
 461           supported values are:</para>
 462
 463           <variablelist>
 464             <varlistentry>
 465               <term><option>tp</option></term>
 466               <listitem>
 467                 <para>An Ethernet interface using Twisted-Pair cable as the medium.</para>
 468               </listitem>
 469             </varlistentry>
 470             <varlistentry>
 471               <term><option>aui</option></term>
 472               <listitem>
 473                 <para>Attachment Unit Interface (AUI). Normally used with hubs.
 474                 </para>
 475               </listitem>
 476             </varlistentry>
 477             <varlistentry>
 478               <term><option>bnc</option></term>
 479               <listitem>
 480                 <para>An Ethernet interface using BNC connectors and co-axial cable.</para>
 481               </listitem>
 482             </varlistentry>
 483             <varlistentry>
 484               <term><option>mii</option></term>
 485               <listitem>
 486                 <para>An Ethernet interface using a Media Independent Interface (MII).</para>
 487               </listitem>
 488             </varlistentry>
 489             <varlistentry>
 490               <term><option>fibre</option></term>
 491               <listitem>
 492                 <para>An Ethernet interface using Optical Fibre as the medium.</para>
 493               </listitem>
 494             </varlistentry>
 495           </variablelist>
 496         </listitem>
 497       </varlistentry>
 498       <varlistentry>
 499         <term><varname>Advertise=</varname></term>
 500         <listitem>
 501           <para>This sets what speeds and duplex modes of operation are advertised for auto-negotiation.
 502           This implies <literal>AutoNegotiation=yes</literal>. The supported values are:
 503
 504           <table>
 505             <title>Supported advertise values</title>
 506             <tgroup cols='3'>
 507               <colspec colname='Advertise' />
 508               <colspec colname='Speed' />
 509               <colspec colname='Duplex Mode' />
 510
 511               <thead><row>
 512                 <entry>Advertise</entry>
 513                 <entry>Speed (Mbps)</entry>
 514                 <entry>Duplex Mode</entry>
 515               </row></thead>
 516               <tbody>
 517                 <row><entry><option>10baset-half</option></entry>
 518                 <entry>10</entry><entry>half</entry></row>
 519
 520                 <row><entry><option>10baset-full</option></entry>
 521                 <entry>10</entry><entry>full</entry></row>
 522
 523                 <row><entry><option>100baset-half</option></entry>
 524                 <entry>100</entry><entry>half</entry></row>
 525
 526                 <row><entry><option>100baset-full</option></entry>
 527                 <entry>100</entry><entry>full</entry></row>
 528
 529                 <row><entry><option>1000baset-half</option></entry>
 530                 <entry>1000</entry><entry>half</entry></row>
 531
 532                 <row><entry><option>1000baset-full</option></entry>
 533                 <entry>1000</entry><entry>full</entry></row>
 534
 535                 <row><entry><option>10000baset-full</option></entry>
 536                 <entry>10000</entry><entry>full</entry></row>
 537
 538                 <row><entry><option>2500basex-full</option></entry>
 539                 <entry>2500</entry><entry>full</entry></row>
 540
 541                 <row><entry><option>1000basekx-full</option></entry>
 542                 <entry>1000</entry><entry>full</entry></row>
 543
 544                 <row><entry><option>10000basekx4-full</option></entry>
 545                 <entry>10000</entry><entry>full</entry></row>
 546
 547                 <row><entry><option>10000basekr-full</option></entry>
 548                 <entry>10000</entry><entry>full</entry></row>
 549
 550                 <row><entry><option>10000baser-fec</option></entry>
 551                 <entry>10000</entry><entry>full</entry></row>
 552
 553                 <row><entry><option>20000basemld2-full</option></entry>
 554                 <entry>20000</entry><entry>full</entry></row>
 555
 556                 <row><entry><option>20000basekr2-full</option></entry>
 557                 <entry>20000</entry><entry>full</entry></row>
 558               </tbody>
 559             </tgroup>
 560           </table>
 561
 562           By default this is unset, i.e. all possible modes will be advertised.
 563           This option may be specified more than once, in which case all specified speeds and modes are advertised.
 564           If the empty string is assigned to this option, the list is reset, and all prior assignments have no effect.
 565           </para>
 566         </listitem>
 567       </varlistentry>
 568       <varlistentry>
 569         <term><varname>TCPSegmentationOffload=</varname></term>
 570         <listitem>
 571           <para>Takes a boolean. If set to true, the TCP Segmentation Offload (TSO) is enabled.
 572           When unset, the kernel's default will be used.</para>
 573         </listitem>
 574       </varlistentry>
 575        <varlistentry>
 576       <term><varname>TCP6SegmentationOffload=</varname></term>
 577         <listitem>
 578           <para>Takes a boolean. If set to true, the TCP6 Segmentation Offload (tx-tcp6-segmentation) is enabled.
 579           When unset, the kernel's default will be used.</para>
 580         </listitem>
 581       </varlistentry>
 582       <varlistentry>
 583         <term><varname>GenericSegmentationOffload=</varname></term>
 584         <listitem>
 585           <para>Takes a boolean. If set to true, the Generic Segmentation Offload (GSO) is enabled.
 586           When unset, the kernel's default will be used.</para>
 587         </listitem>
 588       </varlistentry>
 589     <varlistentry>
 590         <term><varname>GenericReceiveOffload=</varname></term>
 591         <listitem>
 592           <para>Takes a boolean. If set to true, the Generic Receive Offload (GRO) is enabled.
 593           When unset, the kernel's default will be used.</para>
 594         </listitem>
 595       </varlistentry>
 596       <varlistentry>
 597         <term><varname>LargeReceiveOffload=</varname></term>
 598         <listitem>
 599           <para>Takes a boolean. If set to true, the Large Receive Offload (LRO) is enabled.
 600           When unset, the kernel's default will be used.</para>
 601         </listitem>
 602       </varlistentry>
 603       <varlistentry>
 604         <term><varname>RxChannels=</varname></term>
 605         <listitem>
 606           <para>Sets the number of receive channels (a number between 1 and 4294967295) .</para>
 607         </listitem>
 608       </varlistentry>
 609       <varlistentry>
 610         <term><varname>TxChannels=</varname></term>
 611         <listitem>
 612           <para>Sets the number of transmit channels (a number between 1 and 4294967295).</para>
 613         </listitem>
 614       </varlistentry>
 615       <varlistentry>
 616         <term><varname>OtherChannels=</varname></term>
 617         <listitem>
 618           <para>Sets the number of other channels (a number between 1 and 4294967295).</para>
 619         </listitem>
 620       </varlistentry>
 621       <varlistentry>
 622         <term><varname>CombinedChannels=</varname></term>
 623         <listitem>
 624           <para>Sets the number of combined set channels (a number between 1 and 4294967295).</para>
 625         </listitem>
 626       </varlistentry>
 627       <varlistentry>
 628         <term><varname>RxBufferSize=</varname></term>
 629         <listitem>
 630           <para>Takes a integer. Specifies the NIC receive ring buffer size. When unset, the kernel's default will be used.</para>
 631         </listitem>
 632       </varlistentry>
 633       <varlistentry>
 634         <term><varname>TxBufferSize=</varname></term>
 635         <listitem>
 636           <para>Takes a integer. Specifies the NIC transmit ring buffer size. When unset, the kernel's default will be used.</para>
 637         </listitem>
 638       </varlistentry>
 639
 640     </variablelist>
 641   </refsect1>
 642
 643   <refsect1>
 644     <title>Examples</title>
 645
 646     <example>
 647       <title>/usr/lib/systemd/network/99-default.link</title>
 648
 649       <para>The link file <filename>99-default.link</filename> that is
 650       shipped with systemd defines the default naming policy for
 651       links.</para>
 652
 653       <programlisting>[Link]
 654 NamePolicy=kernel database onboard slot path
 655 MACAddressPolicy=persistent</programlisting>
 656     </example>
 657
 658     <example>
 659       <title>/etc/systemd/network/10-dmz.link</title>
 660
 661       <para>This example assigns the fixed name <literal>dmz0</literal> to the interface with the MAC address
 662       00:a0:de:63:7a:e6:</para>
 663
 664       <programlisting>[Match]
 665 MACAddress=00:a0:de:63:7a:e6
 666
 667 [Link]
 668 Name=dmz0</programlisting>
 669
 670       <para><varname>NamePolicy=</varname> is not set, so <varname>Name=</varname> takes effect. We use the
 671       <literal>10-</literal> prefix to order this file early in the list. Note that it needs to before
 672       <literal>99-link</literal>, i.e. it needs a numerical prefix, to have any effect at all.</para>
 673     </example>
 674
 675     <example>
 676       <title>Debugging <varname>NamePolicy=</varname> assignments</title>
 677
 678       <programlisting>$ sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/hub0
 679 …
 680 Parsed configuration file /usr/lib/systemd/network/99-default.link
 681 Parsed configuration file /etc/systemd/network/10-eth0.link
 682 ID_NET_DRIVER=cdc_ether
 683 Config file /etc/systemd/network/10-eth0.link applies to device hub0
 684 link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
 685 hub0: Device has name_assign_type=4
 686 Using default interface naming scheme 'v240'.
 687 hub0: Policies didn't yield a name, using specified Name=hub0.
 688 ID_NET_LINK_FILE=/etc/systemd/network/10-eth0.link
 689 ID_NET_NAME=hub0
 690 …</programlisting>
 691
 692      <para>Explicit <varname>Name=</varname> configuration wins in this case.</para>
 693
 694      <programlisting>sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/enp0s31f6
 695 …
 696 Parsed configuration file /usr/lib/systemd/network/99-default.link
 697 Parsed configuration file /etc/systemd/network/10-eth0.link
 698 Created link configuration context.
 699 ID_NET_DRIVER=e1000e
 700 Config file /usr/lib/systemd/network/99-default.link applies to device enp0s31f6
 701 link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
 702 enp0s31f6: Device has name_assign_type=4
 703 Using default interface naming scheme 'v240'.
 704 enp0s31f6: Policy *keep*: keeping existing userspace name
 705 enp0s31f6: Device has addr_assign_type=0
 706 enp0s31f6: MAC on the device already matches policy *persistent*
 707 ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
 708 …
 709 </programlisting>
 710
 711      <para>In this case, the interface was already renamed, so the <option>keep</option> policy specified as
 712      the first option in <filename index="false">99-default.link</filename> means that the existing name is
 713      preserved. If <option>keep</option> was removed, or if were in boot before the renaming has happened,
 714      we might get the following instead:</para>
 715
 716      <programlisting>enp0s31f6: Policy *path* yields "enp0s31f6".
 717 enp0s31f6: Device has addr_assign_type=0
 718 enp0s31f6: MAC on the device already matches policy *persistent*
 719 ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
 720 ID_NET_NAME=enp0s31f6
 721 …
 722 </programlisting>
 723
 724       <para>Please note that the details of output are subject to change.</para>
 725     </example>
 726
 727     <example>
 728       <title>/etc/systemd/network/10-internet.link</title>
 729
 730       <para>This example assigns the fixed name
 731       <literal>internet0</literal> to the interface with the device
 732       path <literal>pci-0000:00:1a.0-*</literal>:</para>
 733
 734       <programlisting>[Match]
 735 Path=pci-0000:00:1a.0-*
 736
 737 [Link]
 738 Name=internet0</programlisting>
 739     </example>
 740
 741     <example>
 742       <title>/etc/systemd/network/25-wireless.link</title>
 743
 744       <para>Here's an overly complex example that shows the use of a large number of [Match] and [Link] settings.</para>
 745
 746       <programlisting>[Match]
 747 MACAddress=12:34:56:78:9a:bc
 748 Driver=brcmsmac
 749 Path=pci-0000:02:00.0-*
 750 Type=wlan
 751 Virtualization=no
 752 Host=my-laptop
 753 Architecture=x86-64
 754
 755 [Link]
 756 Name=wireless0
 757 MTUBytes=1450
 758 BitsPerSecond=10M
 759 WakeOnLan=magic
 760 MACAddress=cb:a9:87:65:43:21</programlisting>
 761     </example>
 762   </refsect1>
 763
 764   <refsect1>
 765     <title>See Also</title>
 766     <para>
 767       <citerefentry>
 768         <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
 769       </citerefentry>,
 770       <citerefentry>
 771         <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
 772       </citerefentry>,
 773       <citerefentry>
 774         <refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum>
 775       </citerefentry>,
 776       <citerefentry>
 777         <refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum>
 778       </citerefentry>
 779     </para>
 780   </refsect1>
 781
 782 </refentry>