man/systemd.link.xml

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   9 <refentry id="systemd.link">
  10   <refentryinfo>
  11     <title>systemd.link</title>
  12     <productname>systemd</productname>
  13   </refentryinfo>
  14
  15   <refmeta>
  16     <refentrytitle>systemd.link</refentrytitle>
  17     <manvolnum>5</manvolnum>
  18   </refmeta>
  19
  20   <refnamediv>
  21     <refname>systemd.link</refname>
  22     <refpurpose>Network device configuration</refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <para><filename><replaceable>link</replaceable>.link</filename></para>
  27   </refsynopsisdiv>
  28
  29   <refsect1>
  30     <title>Description</title>
  31
  32     <para>Network link configuration is performed by the
  33     <command>net_setup_link</command> udev builtin.</para>
  34
  35     <para>The link files are read from the files located in the system
  36     network directory <filename>/usr/lib/systemd/network</filename>,
  37     the volatile runtime network directory
  38     <filename>/run/systemd/network</filename>, and the local
  39     administration network directory
  40     <filename>/etc/systemd/network</filename>. Link files must have
  41     the extension <filename>.link</filename>; other extensions are
  42     ignored. All link files are collectively sorted and processed in
  43     lexical order, regardless of the directories in which they live.
  44     However, files with identical filenames replace each other. Files
  45     in <filename>/etc</filename> have the highest priority, files in
  46     <filename>/run</filename> take precedence over files with the same
  47     name in <filename>/usr/lib</filename>. This can be used to
  48     override a system-supplied link file with a local file if needed.
  49     As a special case, an empty file (file size 0) or symlink with the
  50     same name pointing to <filename>/dev/null</filename> disables the
  51     configuration file entirely (it is "masked").</para>
  52
  53     <para>The link file contains a <literal>[Match]</literal> section,
  54     which determines if a given link file may be applied to a given
  55     device, as well as a <literal>[Link]</literal> section specifying
  56     how the device should be configured. The first (in lexical order)
  57     of the link files that matches a given device is applied. Note
  58     that a default file <filename>99-default.link</filename> is
  59     shipped by the system. Any user-supplied
  60     <filename>.link</filename> should hence have a lexically earlier
  61     name to be considered at all.</para>
  62
  63     <para>See
  64     <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  65     for diagnosing problems with <filename>.link</filename> files.</para>
  66   </refsect1>
  67
  68   <refsect1>
  69     <title>[Match] Section Options</title>
  70
  71     <para>A link file is said to match a device if each of the entries
  72     in the <literal>[Match]</literal> section matches, or if the
  73     section is empty. The following keys are accepted:</para>
  74
  75     <variablelist class='network-directives'>
  76       <varlistentry>
  77         <term><varname>MACAddress=</varname></term>
  78         <listitem>
  79           <para>A whitespace-separated list of hardware addresses. Use full colon-, hyphen- or dot-delimited hexadecimal. See the example below.
  80           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
  81           of hardware addresses defined prior to this is reset.</para>
  82
  83           <para>Example:
  84           <programlisting>MACAddress=01:23:45:67:89:ab 00-11-22-33-44-55 AABB.CCDD.EEFF</programlisting></para>
  85         </listitem>
  86       </varlistentry>
  87       <varlistentry>
  88         <term><varname>OriginalName=</varname></term>
  89         <listitem>
  90           <para>A whitespace-separated list of shell-style globs matching
  91           the device name, as exposed by the udev property
  92           "INTERFACE". This cannot be used to match on names that have
  93           already been changed from userspace. Caution is advised when matching on
  94           kernel-assigned names, as they are known to be unstable
  95           between reboots.</para>
  96         </listitem>
  97       </varlistentry>
  98       <varlistentry>
  99         <term><varname>Path=</varname></term>
 100         <listitem>
 101           <para>A whitespace-separated list of shell-style globs matching
 102           the persistent path, as exposed by the udev property
 103           <literal>ID_PATH</literal>.</para>
 104         </listitem>
 105       </varlistentry>
 106       <varlistentry>
 107         <term><varname>Driver=</varname></term>
 108         <listitem>
 109           <para>A whitespace-separated list of shell-style globs matching
 110           the driver currently bound to the device,
 111           as exposed by the udev property <literal>DRIVER</literal>
 112           of its parent device, or if that is not set, the
 113           driver as exposed by <literal>ethtool -i</literal>
 114           of the device itself.</para>
 115         </listitem>
 116       </varlistentry>
 117       <varlistentry>
 118         <term><varname>Type=</varname></term>
 119         <listitem>
 120           <para>A whitespace-separated list of shell-style globs matching
 121           the device type, as exposed by the udev
 122           property <literal>DEVTYPE</literal>.</para>
 123         </listitem>
 124       </varlistentry>
 125       <varlistentry>
 126         <term><varname>Host=</varname></term>
 127         <listitem>
 128           <para>Matches against the hostname or machine
 129           ID of the host. See <literal>ConditionHost=</literal> in
 130           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 131           for details.</para>
 132         </listitem>
 133       </varlistentry>
 134       <varlistentry>
 135         <term><varname>Virtualization=</varname></term>
 136         <listitem>
 137           <para>Checks whether the system is executed in
 138           a virtualized environment and optionally test
 139           whether it is a specific implementation. See
 140           <literal>ConditionVirtualization=</literal> in
 141           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 142           for details.</para>
 143         </listitem>
 144       </varlistentry>
 145       <varlistentry>
 146         <term><varname>KernelCommandLine=</varname></term>
 147         <listitem>
 148           <para>Checks whether a specific kernel command line option
 149           is set (or if prefixed with the exclamation mark unset). See
 150           <literal>ConditionKernelCommandLine=</literal> in
 151           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 152           for details.</para>
 153         </listitem>
 154       </varlistentry>
 155         <varlistentry>
 156           <term><varname>KernelVersion=</varname></term>
 157           <listitem>
 158             <para>Checks whether the kernel version (as reported by <command>uname -r</command>) matches a certain
 159             expression (or if prefixed with the exclamation mark does not match it). See
 160             <literal>ConditionKernelVersion=</literal> in
 161             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 162             details.
 163             </para>
 164           </listitem>
 165         </varlistentry>
 166       <varlistentry>
 167         <term><varname>Architecture=</varname></term>
 168         <listitem>
 169           <para>Checks whether the system is running on a specific
 170           architecture. See <literal>ConditionArchitecture=</literal>
 171           in
 172           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 173           for details.</para>
 174         </listitem>
 175       </varlistentry>
 176     </variablelist>
 177
 178   </refsect1>
 179
 180   <refsect1>
 181     <title>[Link] Section Options</title>
 182
 183     <para>The <literal>[Link]</literal> section accepts the following
 184     keys:</para>
 185
 186     <variablelist class='network-directives'>
 187       <varlistentry>
 188         <term><varname>Description=</varname></term>
 189         <listitem>
 190           <para>A description of the device.</para>
 191         </listitem>
 192       </varlistentry>
 193       <varlistentry>
 194         <term><varname>Alias=</varname></term>
 195         <listitem>
 196           <para>The <literal>ifalias</literal> is set to this
 197           value.</para>
 198         </listitem>
 199       </varlistentry>
 200       <varlistentry>
 201         <term><varname>MACAddressPolicy=</varname></term>
 202         <listitem>
 203           <para>The policy by which the MAC address should be set. The
 204           available policies are:
 205           </para>
 206
 207           <variablelist>
 208             <varlistentry>
 209               <term><literal>persistent</literal></term>
 210               <listitem>
 211                 <para>If the hardware has a persistent MAC address, as
 212                 most hardware should, and if it is used by the kernel,
 213                 nothing is done. Otherwise, a new MAC address is
 214                 generated which is guaranteed to be the same on every
 215                 boot for the given machine and the given device, but
 216                 which is otherwise random. This feature depends on ID_NET_NAME_*
 217                 properties to exist for the link. On hardware where these
 218                 properties are not set, the generation of a persistent MAC address
 219                 will fail.</para>
 220               </listitem>
 221             </varlistentry>
 222             <varlistentry>
 223               <term><literal>random</literal></term>
 224               <listitem>
 225                 <para>If the kernel is using a random MAC address,
 226                 nothing is done. Otherwise, a new address is randomly
 227                 generated each time the device appears, typically at
 228                 boot. Either way, the random address will have the
 229                 <literal>unicast</literal> and
 230                 <literal>locally administered</literal> bits set.</para>
 231               </listitem>
 232             </varlistentry>
 233             <varlistentry>
 234               <term><literal>none</literal></term>
 235               <listitem>
 236                 <para>Keeps the MAC address assigned by the kernel.</para>
 237               </listitem>
 238             </varlistentry>
 239           </variablelist>
 240         </listitem>
 241       </varlistentry>
 242       <varlistentry>
 243         <term><varname>MACAddress=</varname></term>
 244         <listitem>
 245           <para>The MAC address to use, if no
 246           <literal>MACAddressPolicy=</literal>
 247           is specified.</para>
 248         </listitem>
 249       </varlistentry>
 250       <varlistentry>
 251         <term><varname>NamePolicy=</varname></term>
 252         <listitem>
 253           <para>An ordered, space-separated list of policies by which
 254           the interface name should be set.
 255           <literal>NamePolicy</literal> may be disabled by specifying
 256           <literal>net.ifnames=0</literal> on the kernel command line.
 257           Each of the policies may fail, and the first successful one
 258           is used. The name is not set directly, but is exported to
 259           udev as the property <literal>ID_NET_NAME</literal>, which
 260           is, by default, used by a udev rule to set
 261           <literal>NAME</literal>. If the name has already been set by
 262           userspace, no renaming is performed. The available policies
 263           are:</para>
 264
 265           <variablelist>
 266             <varlistentry>
 267               <term><literal>kernel</literal></term>
 268               <listitem>
 269                 <para>If the kernel claims that the name it has set
 270                 for a device is predictable, then no renaming is
 271                 performed.</para>
 272               </listitem>
 273             </varlistentry>
 274             <varlistentry>
 275               <term><literal>database</literal></term>
 276               <listitem>
 277                 <para>The name is set based on entries in the udev's
 278                 Hardware Database with the key
 279                 <literal>ID_NET_NAME_FROM_DATABASE</literal>.
 280                 </para>
 281               </listitem>
 282             </varlistentry>
 283             <varlistentry>
 284               <term><literal>onboard</literal></term>
 285               <listitem>
 286                 <para>The name is set based on information given by
 287                 the firmware for on-board devices, as exported by the
 288                 udev property <literal>ID_NET_NAME_ONBOARD</literal>.
 289                 </para>
 290               </listitem>
 291             </varlistentry>
 292             <varlistentry>
 293               <term><literal>slot</literal></term>
 294               <listitem>
 295                 <para>The name is set based on information given by
 296                 the firmware for hot-plug devices, as exported by the
 297                 udev property <literal>ID_NET_NAME_SLOT</literal>.
 298                 </para>
 299               </listitem>
 300             </varlistentry>
 301             <varlistentry>
 302               <term><literal>path</literal></term>
 303               <listitem>
 304                 <para>The name is set based on the device's physical
 305                 location, as exported by the udev property
 306                 <literal>ID_NET_NAME_PATH</literal>.</para>
 307               </listitem>
 308             </varlistentry>
 309             <varlistentry>
 310               <term><literal>mac</literal></term>
 311               <listitem>
 312                 <para>The name is set based on the device's persistent
 313                 MAC address, as exported by the udev property
 314                 <literal>ID_NET_NAME_MAC</literal>.</para>
 315               </listitem>
 316             </varlistentry>
 317           </variablelist>
 318         </listitem>
 319       </varlistentry>
 320       <varlistentry>
 321         <term><varname>Name=</varname></term>
 322         <listitem>
 323           <para>The interface name to use in case all the
 324           policies specified in
 325           <varname>NamePolicy=</varname> fail, or in case
 326           <varname>NamePolicy=</varname> is missing or
 327           disabled.</para>
 328
 329           <para>Note that specifying a name that the kernel might use for another
 330           interface (for example <literal>eth0</literal>) is dangerous because the
 331           name assignment done by udev will race with the assignment done by the
 332           kernel, and only one interface may use the name. Depending on the order of
 333           operations, either udev or the kernel will win, making the naming
 334           unpredictable. It is best to use some different prefix, for example
 335           <literal>internal0</literal>/<literal>external0</literal> or
 336           <literal>lan0</literal>/<literal>lan1</literal>/<literal>lan3</literal>.
 337           </para>
 338         </listitem>
 339       </varlistentry>
 340       <varlistentry>
 341         <term><varname>MTUBytes=</varname></term>
 342         <listitem>
 343           <para>The maximum transmission unit in bytes to set for the
 344           device. The usual suffixes K, M, G, are supported and are
 345           understood to the base of 1024.</para>
 346         </listitem>
 347       </varlistentry>
 348       <varlistentry>
 349         <term><varname>BitsPerSecond=</varname></term>
 350         <listitem>
 351           <para>The speed to set for the device, the value is rounded
 352           down to the nearest Mbps. The usual suffixes K, M, G, are
 353           supported and are understood to the base of 1000.</para>
 354         </listitem>
 355       </varlistentry>
 356       <varlistentry>
 357         <term><varname>Duplex=</varname></term>
 358         <listitem>
 359           <para>The duplex mode to set for the device. The accepted
 360           values are <literal>half</literal> and
 361           <literal>full</literal>.</para>
 362         </listitem>
 363       </varlistentry>
 364       <varlistentry>
 365         <term><varname>AutoNegotiation=</varname></term>
 366         <listitem>
 367           <para>Enables or disables automatic negotiation of transmission parameters.
 368           Autonegotiation is a procedure by which two connected ethernet devices choose
 369           common transmission parameters, such as speed, duplex mode, and flow control.
 370           Takes a boolean value. Unset by default, which means that the kernel default
 371           will be used.</para>
 372
 373           <para>Note that if autonegotiation is enabled, speed and duplex settings are
 374           read-only. If autonegotation is disabled, speed and duplex settings are writable
 375           if the driver supports multiple link modes.</para>
 376         </listitem>
 377       </varlistentry>
 378       <varlistentry>
 379         <term><varname>WakeOnLan=</varname></term>
 380         <listitem>
 381           <para>The Wake-on-LAN policy to set for the device. The
 382           supported values are:</para>
 383
 384           <variablelist>
 385             <varlistentry>
 386               <term><literal>phy</literal></term>
 387               <listitem>
 388                 <para>Wake on PHY activity.</para>
 389               </listitem>
 390             </varlistentry>
 391             <varlistentry>
 392               <term><literal>unicast</literal></term>
 393               <listitem>
 394                 <para>Wake on unicast messages.</para>
 395               </listitem>
 396             </varlistentry>
 397             <varlistentry>
 398               <term><literal>multicast</literal></term>
 399               <listitem>
 400                 <para>Wake on multicast messages.</para>
 401               </listitem>
 402             </varlistentry>
 403             <varlistentry>
 404               <term><literal>broadcast</literal></term>
 405               <listitem>
 406                 <para>Wake on broadcast messages.</para>
 407               </listitem>
 408             </varlistentry>
 409             <varlistentry>
 410               <term><literal>arp</literal></term>
 411               <listitem>
 412                 <para>Wake on ARP.</para>
 413               </listitem>
 414             </varlistentry>
 415             <varlistentry>
 416               <term><literal>magic</literal></term>
 417               <listitem>
 418                 <para>Wake on receipt of a magic packet.
 419                 </para>
 420               </listitem>
 421             </varlistentry>
 422             <varlistentry>
 423               <term><literal>secureon</literal></term>
 424               <listitem>
 425                 <para>Enable secureon(tm) password for MagicPacket(tm).
 426                 </para>
 427               </listitem>
 428             </varlistentry>
 429             <varlistentry>
 430               <term><literal>off</literal></term>
 431               <listitem>
 432                 <para>Never wake.</para>
 433               </listitem>
 434             </varlistentry>
 435           </variablelist>
 436
 437           <para>Defaults to <literal>off</literal>.</para>
 438         </listitem>
 439       </varlistentry>
 440       <varlistentry>
 441         <term><varname>Port=</varname></term>
 442         <listitem>
 443           <para>The port option is used to select the device port. The
 444           supported values are:</para>
 445
 446           <variablelist>
 447             <varlistentry>
 448               <term><literal>tp</literal></term>
 449               <listitem>
 450                 <para>An Ethernet interface using Twisted-Pair cable as the medium.</para>
 451               </listitem>
 452             </varlistentry>
 453             <varlistentry>
 454               <term><literal>aui</literal></term>
 455               <listitem>
 456                 <para>Attachment Unit Interface (AUI). Normally used with hubs.
 457                 </para>
 458               </listitem>
 459             </varlistentry>
 460             <varlistentry>
 461               <term><literal>bnc</literal></term>
 462               <listitem>
 463                 <para>An Ethernet interface using BNC connectors and co-axial cable.</para>
 464               </listitem>
 465             </varlistentry>
 466             <varlistentry>
 467               <term><literal>mii</literal></term>
 468               <listitem>
 469                 <para>An Ethernet interface using a Media Independent Interface (MII).</para>
 470               </listitem>
 471             </varlistentry>
 472             <varlistentry>
 473               <term><literal>fibre</literal></term>
 474               <listitem>
 475                 <para>An Ethernet interface using Optical Fibre as the medium.</para>
 476               </listitem>
 477             </varlistentry>
 478           </variablelist>
 479         </listitem>
 480       </varlistentry>
 481       <varlistentry>
 482         <term><varname>TCPSegmentationOffload=</varname></term>
 483         <listitem>
 484           <para>The TCP Segmentation Offload (TSO) when true enables
 485           TCP segmentation offload. Takes a boolean value.
 486           Defaults to "unset".</para>
 487         </listitem>
 488       </varlistentry>
 489        <varlistentry>
 490       <term><varname>TCP6SegmentationOffload=</varname></term>
 491         <listitem>
 492           <para>The TCP6 Segmentation Offload (tx-tcp6-segmentation) when true enables
 493           TCP6 segmentation offload. Takes a boolean value.
 494           Defaults to "unset".</para>
 495         </listitem>
 496       </varlistentry>
 497       <varlistentry>
 498         <term><varname>GenericSegmentationOffload=</varname></term>
 499         <listitem>
 500           <para>The Generic Segmentation Offload (GSO) when true enables
 501           generic segmentation offload. Takes a boolean value.
 502           Defaults to "unset".</para>
 503         </listitem>
 504       </varlistentry>
 505     <varlistentry>
 506         <term><varname>GenericReceiveOffload=</varname></term>
 507         <listitem>
 508           <para>The Generic Receive Offload (GRO) when true enables
 509           generic receive offload. Takes a boolean value.
 510           Defaults to "unset".</para>
 511         </listitem>
 512       </varlistentry>
 513       <varlistentry>
 514         <term><varname>LargeReceiveOffload=</varname></term>
 515         <listitem>
 516           <para>The Large Receive Offload (LRO) when true enables
 517           large receive offload. Takes a boolean value.
 518           Defaults to "unset".</para>
 519         </listitem>
 520       </varlistentry>
 521       <varlistentry>
 522         <term><varname>RxChannels=</varname></term>
 523         <listitem>
 524           <para>Sets the number of receive channels (a number between 1 and 4294967295) .</para>
 525         </listitem>
 526       </varlistentry>
 527       <varlistentry>
 528         <term><varname>TxChannels=</varname></term>
 529         <listitem>
 530           <para>Sets the number of transmit channels (a number between 1 and 4294967295).</para>
 531         </listitem>
 532       </varlistentry>
 533       <varlistentry>
 534         <term><varname>OtherChannels=</varname></term>
 535         <listitem>
 536           <para>Sets the number of other channels (a number between 1 and 4294967295).</para>
 537         </listitem>
 538       </varlistentry>
 539       <varlistentry>
 540         <term><varname>CombinedChannels=</varname></term>
 541         <listitem>
 542           <para>Sets the number of combined set channels (a number between 1 and 4294967295).</para>
 543         </listitem>
 544       </varlistentry>
 545     </variablelist>
 546   </refsect1>
 547
 548   <refsect1>
 549     <title>Examples</title>
 550
 551     <example>
 552       <title>/usr/lib/systemd/network/99-default.link</title>
 553
 554       <para>The link file <filename>99-default.link</filename> that is
 555       shipped with systemd defines the default naming policy for
 556       links.</para>
 557
 558       <programlisting>[Link]
 559 NamePolicy=kernel database onboard slot path
 560 MACAddressPolicy=persistent</programlisting>
 561     </example>
 562
 563     <example>
 564       <title>/etc/systemd/network/10-dmz.link</title>
 565
 566       <para>This example assigns the fixed name
 567       <literal>dmz0</literal> to the interface with the MAC address
 568       00:a0:de:63:7a:e6:</para>
 569
 570       <programlisting>[Match]
 571 MACAddress=00:a0:de:63:7a:e6
 572
 573 [Link]
 574 Name=dmz0</programlisting>
 575     </example>
 576
 577     <example>
 578       <title>/etc/systemd/network/10-internet.link</title>
 579
 580       <para>This example assigns the fixed name
 581       <literal>internet0</literal> to the interface with the device
 582       path <literal>pci-0000:00:1a.0-*</literal>:</para>
 583
 584       <programlisting>[Match]
 585 Path=pci-0000:00:1a.0-*
 586
 587 [Link]
 588 Name=internet0</programlisting>
 589     </example>
 590
 591     <example>
 592       <title>/etc/systemd/network/25-wireless.link</title>
 593
 594       <para>Here's an overly complex example that shows the use of a large number of [Match] and [Link] settings.</para>
 595
 596       <programlisting>[Match]
 597 MACAddress=12:34:56:78:9a:bc
 598 Driver=brcmsmac
 599 Path=pci-0000:02:00.0-*
 600 Type=wlan
 601 Virtualization=no
 602 Host=my-laptop
 603 Architecture=x86-64
 604
 605 [Link]
 606 Name=wireless0
 607 MTUBytes=1450
 608 BitsPerSecond=10M
 609 WakeOnLan=magic
 610 MACAddress=cb:a9:87:65:43:21</programlisting>
 611     </example>
 612   </refsect1>
 613
 614   <refsect1>
 615     <title>See Also</title>
 616     <para>
 617       <citerefentry>
 618         <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
 619       </citerefentry>,
 620       <citerefentry>
 621         <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
 622       </citerefentry>,
 623       <citerefentry>
 624         <refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum>
 625       </citerefentry>,
 626       <citerefentry>
 627         <refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum>
 628       </citerefentry>
 629     </para>
 630   </refsect1>
 631
 632 </refentry>