man/systemd.link.xml

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