man/systemd.link.xml

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   8   This file is part of systemd.
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  10   Copyright 2014 Tom Gundersen
  11 -->
  12
  13 <refentry id="systemd.link">
  14   <refentryinfo>
  15     <title>systemd.link</title>
  16     <productname>systemd</productname>
  17
  18     <authorgroup>
  19       <author>
  20         <contrib>Developer</contrib>
  21         <firstname>Tom</firstname>
  22         <surname>Gundersen</surname>
  23       </author>
  24     </authorgroup>
  25   </refentryinfo>
  26
  27   <refmeta>
  28     <refentrytitle>systemd.link</refentrytitle>
  29     <manvolnum>5</manvolnum>
  30   </refmeta>
  31
  32   <refnamediv>
  33     <refname>systemd.link</refname>
  34     <refpurpose>Network device configuration</refpurpose>
  35   </refnamediv>
  36
  37   <refsynopsisdiv>
  38     <para><filename><replaceable>link</replaceable>.link</filename></para>
  39   </refsynopsisdiv>
  40
  41   <refsect1>
  42     <title>Description</title>
  43
  44     <para>Network link configuration is performed by the
  45     <command>net_setup_link</command> udev builtin.</para>
  46
  47     <para>The link files are read from the files located in the system
  48     network directory <filename>/usr/lib/systemd/network</filename>,
  49     the volatile runtime network directory
  50     <filename>/run/systemd/network</filename>, and the local
  51     administration network directory
  52     <filename>/etc/systemd/network</filename>. Link files must have
  53     the extension <filename>.link</filename>; other extensions are
  54     ignored. All link files are collectively sorted and processed in
  55     lexical order, regardless of the directories in which they live.
  56     However, files with identical filenames replace each other. Files
  57     in <filename>/etc</filename> have the highest priority, files in
  58     <filename>/run</filename> take precedence over files with the same
  59     name in <filename>/usr/lib</filename>. This can be used to
  60     override a system-supplied link file with a local file if needed.
  61     As a special case, an empty file (file size 0) or symlink with the
  62     same name pointing to <filename>/dev/null</filename> disables the
  63     configuration file entirely (it is "masked").</para>
  64
  65     <para>The link file contains a <literal>[Match]</literal> section,
  66     which determines if a given link file may be applied to a given
  67     device, as well as a <literal>[Link]</literal> section specifying
  68     how the device should be configured. The first (in lexical order)
  69     of the link files that matches a given device is applied. Note
  70     that a default file <filename>99-default.link</filename> is
  71     shipped by the system. Any user-supplied
  72     <filename>.link</filename> should hence have a lexically earlier
  73     name to be considered at all.</para>
  74
  75     <para>See
  76     <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  77     for diagnosing problems with <filename>.link</filename> files.</para>
  78   </refsect1>
  79
  80   <refsect1>
  81     <title>[Match] Section Options</title>
  82
  83     <para>A link file is said to match a device if each of the entries
  84     in the <literal>[Match]</literal> section matches, or if the
  85     section is empty. The following keys are accepted:</para>
  86
  87     <variablelist class='network-directives'>
  88       <varlistentry>
  89         <term><varname>MACAddress=</varname></term>
  90         <listitem>
  91           <para>A whitespace-separated list of hardware addresses. Use full colon-, hyphen- or dot-delimited hexadecimal. See the example below.
  92           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
  93           of hardware addresses defined prior to this is reset.</para>
  94
  95           <para>Example:
  96           <programlisting>MACAddress=01:23:45:67:89:ab 00-11-22-33-44-55 AABB.CCDD.EEFF</programlisting></para>
  97         </listitem>
  98       </varlistentry>
  99       <varlistentry>
 100         <term><varname>OriginalName=</varname></term>
 101         <listitem>
 102           <para>A whitespace-separated list of shell-style globs matching
 103           the device name, as exposed by the udev property
 104           "INTERFACE". This cannot be used to match on names that have
 105           already been changed from userspace. Caution is advised when matching on
 106           kernel-assigned names, as they are known to be unstable
 107           between reboots.</para>
 108         </listitem>
 109       </varlistentry>
 110       <varlistentry>
 111         <term><varname>Path=</varname></term>
 112         <listitem>
 113           <para>A whitespace-separated list of shell-style globs matching
 114           the persistent path, as exposed by the udev property
 115           <literal>ID_PATH</literal>.</para>
 116         </listitem>
 117       </varlistentry>
 118       <varlistentry>
 119         <term><varname>Driver=</varname></term>
 120         <listitem>
 121           <para>A whitespace-separated list of shell-style globs matching
 122           the driver currently bound to the device,
 123           as exposed by the udev property <literal>DRIVER</literal>
 124           of its parent device, or if that is not set, the
 125           driver as exposed by <literal>ethtool -i</literal>
 126           of the device itself.</para>
 127         </listitem>
 128       </varlistentry>
 129       <varlistentry>
 130         <term><varname>Type=</varname></term>
 131         <listitem>
 132           <para>A whitespace-separated list of shell-style globs matching
 133           the device type, as exposed by the udev
 134           property <literal>DEVTYPE</literal>.</para>
 135         </listitem>
 136       </varlistentry>
 137       <varlistentry>
 138         <term><varname>Host=</varname></term>
 139         <listitem>
 140           <para>Matches against the hostname or machine
 141           ID of the host. See <literal>ConditionHost=</literal> in
 142           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 143           for details.</para>
 144         </listitem>
 145       </varlistentry>
 146       <varlistentry>
 147         <term><varname>Virtualization=</varname></term>
 148         <listitem>
 149           <para>Checks whether the system is executed in
 150           a virtualized environment and optionally test
 151           whether it is a specific implementation. See
 152           <literal>ConditionVirtualization=</literal> in
 153           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 154           for details.</para>
 155         </listitem>
 156       </varlistentry>
 157       <varlistentry>
 158         <term><varname>KernelCommandLine=</varname></term>
 159         <listitem>
 160           <para>Checks whether a specific kernel command line option
 161           is set (or if prefixed with the exclamation mark unset). See
 162           <literal>ConditionKernelCommandLine=</literal> in
 163           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 164           for details.</para>
 165         </listitem>
 166       </varlistentry>
 167         <varlistentry>
 168           <term><varname>KernelVersion=</varname></term>
 169           <listitem>
 170             <para>Checks whether the kernel version (as reported by <command>uname -r</command>) matches a certain
 171             expression (or if prefixed with the exclamation mark does not match it). See
 172             <literal>ConditionKernelVersion=</literal> in
 173             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 174             details.
 175             </para>
 176           </listitem>
 177         </varlistentry>
 178       <varlistentry>
 179         <term><varname>Architecture=</varname></term>
 180         <listitem>
 181           <para>Checks whether the system is running on a specific
 182           architecture. See <literal>ConditionArchitecture=</literal>
 183           in
 184           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 185           for details.</para>
 186         </listitem>
 187       </varlistentry>
 188     </variablelist>
 189
 190   </refsect1>
 191
 192   <refsect1>
 193     <title>[Link] Section Options</title>
 194
 195     <para>The <literal>[Link]</literal> section accepts the following
 196     keys:</para>
 197
 198     <variablelist class='network-directives'>
 199       <varlistentry>
 200         <term><varname>Description=</varname></term>
 201         <listitem>
 202           <para>A description of the device.</para>
 203         </listitem>
 204       </varlistentry>
 205       <varlistentry>
 206         <term><varname>Alias=</varname></term>
 207         <listitem>
 208           <para>The <literal>ifalias</literal> is set to this
 209           value.</para>
 210         </listitem>
 211       </varlistentry>
 212       <varlistentry>
 213         <term><varname>MACAddressPolicy=</varname></term>
 214         <listitem>
 215           <para>The policy by which the MAC address should be set. The
 216           available policies are:
 217           </para>
 218
 219           <variablelist>
 220             <varlistentry>
 221               <term><literal>persistent</literal></term>
 222               <listitem>
 223                 <para>If the hardware has a persistent MAC address, as
 224                 most hardware should, and if it is used by the kernel,
 225                 nothing is done. Otherwise, a new MAC address is
 226                 generated which is guaranteed to be the same on every
 227                 boot for the given machine and the given device, but
 228                 which is otherwise random. This feature depends on ID_NET_NAME_*
 229                 properties to exist for the link. On hardware where these
 230                 properties are not set, the generation of a persistent MAC address
 231                 will fail.</para>
 232               </listitem>
 233             </varlistentry>
 234             <varlistentry>
 235               <term><literal>random</literal></term>
 236               <listitem>
 237                 <para>If the kernel is using a random MAC address,
 238                 nothing is done. Otherwise, a new address is randomly
 239                 generated each time the device appears, typically at
 240                 boot. Either way, the random address will have the
 241                 <literal>unicast</literal> and
 242                 <literal>locally administered</literal> bits set.</para>
 243               </listitem>
 244             </varlistentry>
 245             <varlistentry>
 246               <term><literal>none</literal></term>
 247               <listitem>
 248                 <para>Keeps the MAC address assigned by the kernel.</para>
 249               </listitem>
 250             </varlistentry>
 251           </variablelist>
 252         </listitem>
 253       </varlistentry>
 254       <varlistentry>
 255         <term><varname>MACAddress=</varname></term>
 256         <listitem>
 257           <para>The MAC address to use, if no
 258           <literal>MACAddressPolicy=</literal>
 259           is specified.</para>
 260         </listitem>
 261       </varlistentry>
 262       <varlistentry>
 263         <term><varname>NamePolicy=</varname></term>
 264         <listitem>
 265           <para>An ordered, space-separated list of policies by which
 266           the interface name should be set.
 267           <literal>NamePolicy</literal> may be disabled by specifying
 268           <literal>net.ifnames=0</literal> on the kernel command line.
 269           Each of the policies may fail, and the first successful one
 270           is used. The name is not set directly, but is exported to
 271           udev as the property <literal>ID_NET_NAME</literal>, which
 272           is, by default, used by a udev rule to set
 273           <literal>NAME</literal>. If the name has already been set by
 274           userspace, no renaming is performed. The available policies
 275           are:</para>
 276
 277           <variablelist>
 278             <varlistentry>
 279               <term><literal>kernel</literal></term>
 280               <listitem>
 281                 <para>If the kernel claims that the name it has set
 282                 for a device is predictable, then no renaming is
 283                 performed.</para>
 284               </listitem>
 285             </varlistentry>
 286             <varlistentry>
 287               <term><literal>database</literal></term>
 288               <listitem>
 289                 <para>The name is set based on entries in the udev's
 290                 Hardware Database with the key
 291                 <literal>ID_NET_NAME_FROM_DATABASE</literal>.
 292                 </para>
 293               </listitem>
 294             </varlistentry>
 295             <varlistentry>
 296               <term><literal>onboard</literal></term>
 297               <listitem>
 298                 <para>The name is set based on information given by
 299                 the firmware for on-board devices, as exported by the
 300                 udev property <literal>ID_NET_NAME_ONBOARD</literal>.
 301                 </para>
 302               </listitem>
 303             </varlistentry>
 304             <varlistentry>
 305               <term><literal>slot</literal></term>
 306               <listitem>
 307                 <para>The name is set based on information given by
 308                 the firmware for hot-plug devices, as exported by the
 309                 udev property <literal>ID_NET_NAME_SLOT</literal>.
 310                 </para>
 311               </listitem>
 312             </varlistentry>
 313             <varlistentry>
 314               <term><literal>path</literal></term>
 315               <listitem>
 316                 <para>The name is set based on the device's physical
 317                 location, as exported by the udev property
 318                 <literal>ID_NET_NAME_PATH</literal>.</para>
 319               </listitem>
 320             </varlistentry>
 321             <varlistentry>
 322               <term><literal>mac</literal></term>
 323               <listitem>
 324                 <para>The name is set based on the device's persistent
 325                 MAC address, as exported by the udev property
 326                 <literal>ID_NET_NAME_MAC</literal>.</para>
 327               </listitem>
 328             </varlistentry>
 329           </variablelist>
 330         </listitem>
 331       </varlistentry>
 332       <varlistentry>
 333         <term><varname>Name=</varname></term>
 334         <listitem>
 335           <para>The interface name to use in case all the
 336           policies specified in
 337           <varname>NamePolicy=</varname> fail, or in case
 338           <varname>NamePolicy=</varname> is missing or
 339           disabled.</para>
 340
 341           <para>Note that specifying a name that the kernel might use for another
 342           interface (for example <literal>eth0</literal>) is dangerous because the
 343           name assignment done by udev will race with the assignment done by the
 344           kernel, and only one interface may use the name. Depending on the order of
 345           operations, either udev or the kernel will win, making the naming
 346           unpredictable. It is best to use some different prefix, for example
 347           <literal>internal0</literal>/<literal>external0</literal> or
 348           <literal>lan0</literal>/<literal>lan1</literal>/<literal>lan3</literal>.
 349           </para>
 350         </listitem>
 351       </varlistentry>
 352       <varlistentry>
 353         <term><varname>MTUBytes=</varname></term>
 354         <listitem>
 355           <para>The maximum transmission unit in bytes to set for the
 356           device. The usual suffixes K, M, G, are supported and are
 357           understood to the base of 1024.</para>
 358         </listitem>
 359       </varlistentry>
 360       <varlistentry>
 361         <term><varname>BitsPerSecond=</varname></term>
 362         <listitem>
 363           <para>The speed to set for the device, the value is rounded
 364           down to the nearest Mbps. The usual suffixes K, M, G, are
 365           supported and are understood to the base of 1000.</para>
 366         </listitem>
 367       </varlistentry>
 368       <varlistentry>
 369         <term><varname>Duplex=</varname></term>
 370         <listitem>
 371           <para>The duplex mode to set for the device. The accepted
 372           values are <literal>half</literal> and
 373           <literal>full</literal>.</para>
 374         </listitem>
 375       </varlistentry>
 376       <varlistentry>
 377         <term><varname>AutoNegotiation=</varname></term>
 378         <listitem>
 379           <para>Enables or disables automatic negotiation of transmission parameters.
 380           Autonegotiation is a procedure by which two connected ethernet devices choose
 381           common transmission parameters, such as speed, duplex mode, and flow control.
 382           Takes a boolean value. Unset by default, which means that the kernel default
 383           will be used.</para>
 384
 385           <para>Note that if autonegotiation is enabled, speed and duplex settings are
 386           read-only. If autonegotation is disabled, speed and duplex settings are writable
 387           if the driver supports multiple link modes.</para>
 388         </listitem>
 389       </varlistentry>
 390       <varlistentry>
 391         <term><varname>WakeOnLan=</varname></term>
 392         <listitem>
 393           <para>The Wake-on-LAN policy to set for the device. The
 394           supported values are:</para>
 395
 396           <variablelist>
 397             <varlistentry>
 398               <term><literal>phy</literal></term>
 399               <listitem>
 400                 <para>Wake on PHY activity.</para>
 401               </listitem>
 402             </varlistentry>
 403             <varlistentry>
 404               <term><literal>unicast</literal></term>
 405               <listitem>
 406                 <para>Wake on unicast messages.</para>
 407               </listitem>
 408             </varlistentry>
 409             <varlistentry>
 410               <term><literal>multicast</literal></term>
 411               <listitem>
 412                 <para>Wake on multicast messages.</para>
 413               </listitem>
 414             </varlistentry>
 415             <varlistentry>
 416               <term><literal>broadcast</literal></term>
 417               <listitem>
 418                 <para>Wake on broadcast messages.</para>
 419               </listitem>
 420             </varlistentry>
 421             <varlistentry>
 422               <term><literal>arp</literal></term>
 423               <listitem>
 424                 <para>Wake on ARP.</para>
 425               </listitem>
 426             </varlistentry>
 427             <varlistentry>
 428               <term><literal>magic</literal></term>
 429               <listitem>
 430                 <para>Wake on receipt of a magic packet.
 431                 </para>
 432               </listitem>
 433             </varlistentry>
 434             <varlistentry>
 435               <term><literal>secureon</literal></term>
 436               <listitem>
 437                 <para>Enable secureon(tm) password for MagicPacket(tm).
 438                 </para>
 439               </listitem>
 440             </varlistentry>
 441             <varlistentry>
 442               <term><literal>off</literal></term>
 443               <listitem>
 444                 <para>Never wake.</para>
 445               </listitem>
 446             </varlistentry>
 447           </variablelist>
 448
 449           <para>Defaults to <literal>off</literal>.</para>
 450         </listitem>
 451       </varlistentry>
 452       <varlistentry>
 453         <term><varname>Port=</varname></term>
 454         <listitem>
 455           <para>The port option is used to select the device port. The
 456           supported values are:</para>
 457
 458           <variablelist>
 459             <varlistentry>
 460               <term><literal>tp</literal></term>
 461               <listitem>
 462                 <para>An Ethernet interface using Twisted-Pair cable as the medium.</para>
 463               </listitem>
 464             </varlistentry>
 465             <varlistentry>
 466               <term><literal>aui</literal></term>
 467               <listitem>
 468                 <para>Attachment Unit Interface (AUI). Normally used with hubs.
 469                 </para>
 470               </listitem>
 471             </varlistentry>
 472             <varlistentry>
 473               <term><literal>bnc</literal></term>
 474               <listitem>
 475                 <para>An Ethernet interface using BNC connectors and co-axial cable.</para>
 476               </listitem>
 477             </varlistentry>
 478             <varlistentry>
 479               <term><literal>mii</literal></term>
 480               <listitem>
 481                 <para>An Ethernet interface using a Media Independent Interface (MII).</para>
 482               </listitem>
 483             </varlistentry>
 484             <varlistentry>
 485               <term><literal>fibre</literal></term>
 486               <listitem>
 487                 <para>An Ethernet interface using Optical Fibre as the medium.</para>
 488               </listitem>
 489             </varlistentry>
 490           </variablelist>
 491         </listitem>
 492       </varlistentry>
 493       <varlistentry>
 494         <term><varname>TCPSegmentationOffload=</varname></term>
 495         <listitem>
 496           <para>The TCP Segmentation Offload (TSO) when true enables
 497           TCP segmentation offload. Takes a boolean value.
 498           Defaults to "unset".</para>
 499         </listitem>
 500       </varlistentry>
 501        <varlistentry>
 502       <term><varname>TCP6SegmentationOffload=</varname></term>
 503         <listitem>
 504           <para>The TCP6 Segmentation Offload (tx-tcp6-segmentation) when true enables
 505           TCP6 segmentation offload. Takes a boolean value.
 506           Defaults to "unset".</para>
 507         </listitem>
 508       </varlistentry>
 509       <varlistentry>
 510         <term><varname>GenericSegmentationOffload=</varname></term>
 511         <listitem>
 512           <para>The Generic Segmentation Offload (GSO) when true enables
 513           generic segmentation offload. Takes a boolean value.
 514           Defaults to "unset".</para>
 515         </listitem>
 516       </varlistentry>
 517     <varlistentry>
 518         <term><varname>GenericReceiveOffload=</varname></term>
 519         <listitem>
 520           <para>The Generic Receive Offload (GRO) when true enables
 521           generic receive offload. Takes a boolean value.
 522           Defaults to "unset".</para>
 523         </listitem>
 524       </varlistentry>
 525       <varlistentry>
 526         <term><varname>LargeReceiveOffload=</varname></term>
 527         <listitem>
 528           <para>The Large Receive Offload (LRO) when true enables
 529           large receive offload. Takes a boolean value.
 530           Defaults to "unset".</para>
 531         </listitem>
 532       </varlistentry>
 533       <varlistentry>
 534         <term><varname>RxChannels=</varname></term>
 535         <listitem>
 536           <para>Sets the number of receive channels (a number between 1 and 4294967295) .</para>
 537         </listitem>
 538       </varlistentry>
 539       <varlistentry>
 540         <term><varname>TxChannels=</varname></term>
 541         <listitem>
 542           <para>Sets the number of transmit channels (a number between 1 and 4294967295).</para>
 543         </listitem>
 544       </varlistentry>
 545       <varlistentry>
 546         <term><varname>OtherChannels=</varname></term>
 547         <listitem>
 548           <para>Sets the number of other channels (a number between 1 and 4294967295).</para>
 549         </listitem>
 550       </varlistentry>
 551       <varlistentry>
 552         <term><varname>CombinedChannels=</varname></term>
 553         <listitem>
 554           <para>Sets the number of combined set channels (a number between 1 and 4294967295).</para>
 555         </listitem>
 556       </varlistentry>
 557     </variablelist>
 558   </refsect1>
 559
 560   <refsect1>
 561     <title>Examples</title>
 562
 563     <example>
 564       <title>/usr/lib/systemd/network/99-default.link</title>
 565
 566       <para>The link file <filename>99-default.link</filename> that is
 567       shipped with systemd defines the default naming policy for
 568       links.</para>
 569
 570       <programlisting>[Link]
 571 NamePolicy=kernel database onboard slot path
 572 MACAddressPolicy=persistent</programlisting>
 573     </example>
 574
 575     <example>
 576       <title>/etc/systemd/network/10-dmz.link</title>
 577
 578       <para>This example assigns the fixed name
 579       <literal>dmz0</literal> to the interface with the MAC address
 580       00:a0:de:63:7a:e6:</para>
 581
 582       <programlisting>[Match]
 583 MACAddress=00:a0:de:63:7a:e6
 584
 585 [Link]
 586 Name=dmz0</programlisting>
 587     </example>
 588
 589     <example>
 590       <title>/etc/systemd/network/10-internet.link</title>
 591
 592       <para>This example assigns the fixed name
 593       <literal>internet0</literal> to the interface with the device
 594       path <literal>pci-0000:00:1a.0-*</literal>:</para>
 595
 596       <programlisting>[Match]
 597 Path=pci-0000:00:1a.0-*
 598
 599 [Link]
 600 Name=internet0</programlisting>
 601     </example>
 602
 603     <example>
 604       <title>/etc/systemd/network/25-wireless.link</title>
 605
 606       <para>Here's an overly complex example that shows the use of a large number of [Match] and [Link] settings.</para>
 607
 608       <programlisting>[Match]
 609 MACAddress=12:34:56:78:9a:bc
 610 Driver=brcmsmac
 611 Path=pci-0000:02:00.0-*
 612 Type=wlan
 613 Virtualization=no
 614 Host=my-laptop
 615 Architecture=x86-64
 616
 617 [Link]
 618 Name=wireless0
 619 MTUBytes=1450
 620 BitsPerSecond=10M
 621 WakeOnLan=magic
 622 MACAddress=cb:a9:87:65:43:21</programlisting>
 623     </example>
 624   </refsect1>
 625
 626   <refsect1>
 627     <title>See Also</title>
 628     <para>
 629       <citerefentry>
 630         <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
 631       </citerefentry>,
 632       <citerefentry>
 633         <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
 634       </citerefentry>,
 635       <citerefentry>
 636         <refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum>
 637       </citerefentry>,
 638       <citerefentry>
 639         <refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum>
 640       </citerefentry>
 641     </para>
 642   </refsect1>
 643
 644 </refentry>