man/systemd.link.xml

   1 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
   9
  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>The hardware address.</para>
  92         </listitem>
  93       </varlistentry>
  94       <varlistentry>
  95         <term><varname>OriginalName=</varname></term>
  96         <listitem>
  97           <para>A whitespace-separated list of shell-style globs matching
  98           the device name, as exposed by the udev property
  99           "INTERFACE". This cannot be used to match on names that have
 100           already been changed from userspace. Caution is advised when matching on
 101           kernel-assigned names, as they are known to be unstable
 102           between reboots.</para>
 103         </listitem>
 104       </varlistentry>
 105       <varlistentry>
 106         <term><varname>Path=</varname></term>
 107         <listitem>
 108           <para>A whitespace-separated list of shell-style globs matching
 109           the persistent path, as exposed by the udev property
 110           <literal>ID_PATH</literal>.</para>
 111         </listitem>
 112       </varlistentry>
 113       <varlistentry>
 114         <term><varname>Driver=</varname></term>
 115         <listitem>
 116           <para>A whitespace-separated list of shell-style globs matching
 117           the driver currently bound to the device,
 118           as exposed by the udev property <literal>DRIVER</literal>
 119           of its parent device, or if that is not set, the
 120           driver as exposed by <literal>ethtool -i</literal>
 121           of the device itself.</para>
 122         </listitem>
 123       </varlistentry>
 124       <varlistentry>
 125         <term><varname>Type=</varname></term>
 126         <listitem>
 127           <para>A whitespace-separated list of shell-style globs matching
 128           the device type, as exposed by the udev
 129           property <literal>DEVTYPE</literal>.</para>
 130         </listitem>
 131       </varlistentry>
 132       <varlistentry>
 133         <term><varname>Host=</varname></term>
 134         <listitem>
 135           <para>Matches against the hostname or machine
 136           ID of the host. See <literal>ConditionHost=</literal> in
 137           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 138           for details.</para>
 139         </listitem>
 140       </varlistentry>
 141       <varlistentry>
 142         <term><varname>Virtualization=</varname></term>
 143         <listitem>
 144           <para>Checks whether the system is executed in
 145           a virtualized environment and optionally test
 146           whether it is a specific implementation. See
 147           <literal>ConditionVirtualization=</literal> in
 148           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 149           for details.</para>
 150         </listitem>
 151       </varlistentry>
 152       <varlistentry>
 153         <term><varname>KernelCommandLine=</varname></term>
 154         <listitem>
 155           <para>Checks whether a specific kernel command line option
 156           is set (or if prefixed with the exclamation mark unset). See
 157           <literal>ConditionKernelCommandLine=</literal> in
 158           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 159           for details.</para>
 160         </listitem>
 161       </varlistentry>
 162         <varlistentry>
 163           <term><varname>KernelVersion=</varname></term>
 164           <listitem>
 165             <para>Checks whether the kernel version (as reported by <command>uname -r</command>) matches a certain
 166             expression (or if prefixed with the exclamation mark does not match it). See
 167             <literal>ConditionKernelVersion=</literal> in
 168             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 169             details.
 170             </para>
 171           </listitem>
 172         </varlistentry>
 173       <varlistentry>
 174         <term><varname>Architecture=</varname></term>
 175         <listitem>
 176           <para>Checks whether the system is running on a specific
 177           architecture. See <literal>ConditionArchitecture=</literal>
 178           in
 179           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 180           for details.</para>
 181         </listitem>
 182       </varlistentry>
 183     </variablelist>
 184
 185   </refsect1>
 186
 187   <refsect1>
 188     <title>[Link] Section Options</title>
 189
 190     <para>The <literal>[Link]</literal> section accepts the following
 191     keys:</para>
 192
 193     <variablelist class='network-directives'>
 194       <varlistentry>
 195         <term><varname>Description=</varname></term>
 196         <listitem>
 197           <para>A description of the device.</para>
 198         </listitem>
 199       </varlistentry>
 200       <varlistentry>
 201         <term><varname>Alias=</varname></term>
 202         <listitem>
 203           <para>The <literal>ifalias</literal> is set to this
 204           value.</para>
 205         </listitem>
 206       </varlistentry>
 207       <varlistentry>
 208         <term><varname>MACAddressPolicy=</varname></term>
 209         <listitem>
 210           <para>The policy by which the MAC address should be set. The
 211           available policies are:
 212           </para>
 213
 214           <variablelist>
 215             <varlistentry>
 216               <term><literal>persistent</literal></term>
 217               <listitem>
 218                 <para>If the hardware has a persistent MAC address, as
 219                 most hardware should, and if it is used by the kernel,
 220                 nothing is done. Otherwise, a new MAC address is
 221                 generated which is guaranteed to be the same on every
 222                 boot for the given machine and the given device, but
 223                 which is otherwise random. This feature depends on ID_NET_NAME_*
 224                 properties to exist for the link. On hardware where these
 225                 properties are not set, the generation of a persistent MAC address
 226                 will fail.</para>
 227               </listitem>
 228             </varlistentry>
 229             <varlistentry>
 230               <term><literal>random</literal></term>
 231               <listitem>
 232                 <para>If the kernel is using a random MAC address,
 233                 nothing is done. Otherwise, a new address is randomly
 234                 generated each time the device appears, typically at
 235                 boot. Either way, the random address will have the
 236                 <literal>unicast</literal> and
 237                 <literal>locally administered</literal> bits set.</para>
 238               </listitem>
 239             </varlistentry>
 240             <varlistentry>
 241               <term><literal>none</literal></term>
 242               <listitem>
 243                 <para>Keeps the MAC address assigned by the kernel.</para>
 244               </listitem>
 245             </varlistentry>
 246           </variablelist>
 247         </listitem>
 248       </varlistentry>
 249       <varlistentry>
 250         <term><varname>MACAddress=</varname></term>
 251         <listitem>
 252           <para>The MAC address to use, if no
 253           <literal>MACAddressPolicy=</literal>
 254           is specified.</para>
 255         </listitem>
 256       </varlistentry>
 257       <varlistentry>
 258         <term><varname>NamePolicy=</varname></term>
 259         <listitem>
 260           <para>An ordered, space-separated list of policies by which
 261           the interface name should be set.
 262           <literal>NamePolicy</literal> may be disabled by specifying
 263           <literal>net.ifnames=0</literal> on the kernel command line.
 264           Each of the policies may fail, and the first successful one
 265           is used. The name is not set directly, but is exported to
 266           udev as the property <literal>ID_NET_NAME</literal>, which
 267           is, by default, used by a udev rule to set
 268           <literal>NAME</literal>. If the name has already been set by
 269           userspace, no renaming is performed. The available policies
 270           are:</para>
 271
 272           <variablelist>
 273             <varlistentry>
 274               <term><literal>kernel</literal></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><literal>database</literal></term>
 283               <listitem>
 284                 <para>The name is set based on entries in the udev's
 285                 Hardware Database with the key
 286                 <literal>ID_NET_NAME_FROM_DATABASE</literal>.
 287                 </para>
 288               </listitem>
 289             </varlistentry>
 290             <varlistentry>
 291               <term><literal>onboard</literal></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 <literal>ID_NET_NAME_ONBOARD</literal>.
 296                 </para>
 297               </listitem>
 298             </varlistentry>
 299             <varlistentry>
 300               <term><literal>slot</literal></term>
 301               <listitem>
 302                 <para>The name is set based on information given by
 303                 the firmware for hot-plug devices, as exported by the
 304                 udev property <literal>ID_NET_NAME_SLOT</literal>.
 305                 </para>
 306               </listitem>
 307             </varlistentry>
 308             <varlistentry>
 309               <term><literal>path</literal></term>
 310               <listitem>
 311                 <para>The name is set based on the device's physical
 312                 location, as exported by the udev property
 313                 <literal>ID_NET_NAME_PATH</literal>.</para>
 314               </listitem>
 315             </varlistentry>
 316             <varlistentry>
 317               <term><literal>mac</literal></term>
 318               <listitem>
 319                 <para>The name is set based on the device's persistent
 320                 MAC address, as exported by the udev property
 321                 <literal>ID_NET_NAME_MAC</literal>.</para>
 322               </listitem>
 323             </varlistentry>
 324           </variablelist>
 325         </listitem>
 326       </varlistentry>
 327       <varlistentry>
 328         <term><varname>Name=</varname></term>
 329         <listitem>
 330           <para>The interface name to use in case all the
 331           policies specified in
 332           <varname>NamePolicy=</varname> fail, or in case
 333           <varname>NamePolicy=</varname> is missing or
 334           disabled.</para>
 335
 336           <para>Note that specifying a name that the kernel might use for another
 337           interface (for example <literal>eth0</literal>) is dangerous because the
 338           name assignment done by udev will race with the assignment done by the
 339           kernel, and only one interface may use the name. Depending on the order of
 340           operations, either udev or the kernel will win, making the naming
 341           unpredictable. It is best to use some different prefix, for example
 342           <literal>internal0</literal>/<literal>external0</literal> or
 343           <literal>lan0</literal>/<literal>lan1</literal>/<literal>lan3</literal>.
 344           </para>
 345         </listitem>
 346       </varlistentry>
 347       <varlistentry>
 348         <term><varname>MTUBytes=</varname></term>
 349         <listitem>
 350           <para>The maximum transmission unit in bytes to set for the
 351           device. The usual suffixes K, M, G, are supported and are
 352           understood to the base of 1024.</para>
 353         </listitem>
 354       </varlistentry>
 355       <varlistentry>
 356         <term><varname>BitsPerSecond=</varname></term>
 357         <listitem>
 358           <para>The speed to set for the device, the value is rounded
 359           down to the nearest Mbps. The usual suffixes K, M, G, are
 360           supported and are understood to the base of 1000.</para>
 361         </listitem>
 362       </varlistentry>
 363       <varlistentry>
 364         <term><varname>Duplex=</varname></term>
 365         <listitem>
 366           <para>The duplex mode to set for the device. The accepted
 367           values are <literal>half</literal> and
 368           <literal>full</literal>.</para>
 369         </listitem>
 370       </varlistentry>
 371       <varlistentry>
 372         <term><varname>AutoNegotiation=</varname></term>
 373         <listitem>
 374           <para>Enables or disables automatic negotiation of transmission parameters.
 375           Autonegotiation is a procedure by which two connected ethernet devices choose
 376           common transmission parameters, such as speed, duplex mode, and flow control.
 377           Takes a boolean value. Unset by default, which means that the kernel default
 378           will be used.</para>
 379
 380           <para>Note that if autonegotiation is enabled, speed and duplex settings are
 381           read-only. If autonegotation is disabled, speed and duplex settings are writable
 382           if the driver supports multiple link modes.</para>
 383         </listitem>
 384       </varlistentry>
 385       <varlistentry>
 386         <term><varname>WakeOnLan=</varname></term>
 387         <listitem>
 388           <para>The Wake-on-LAN policy to set for the device. The
 389           supported values are:</para>
 390
 391           <variablelist>
 392             <varlistentry>
 393               <term><literal>phy</literal></term>
 394               <listitem>
 395                 <para>Wake on PHY activity.</para>
 396               </listitem>
 397             </varlistentry>
 398             <varlistentry>
 399               <term><literal>unicast</literal></term>
 400               <listitem>
 401                 <para>Wake on unicast messages.</para>
 402               </listitem>
 403             </varlistentry>
 404             <varlistentry>
 405               <term><literal>multicast</literal></term>
 406               <listitem>
 407                 <para>Wake on multicast messages.</para>
 408               </listitem>
 409             </varlistentry>
 410             <varlistentry>
 411               <term><literal>broadcast</literal></term>
 412               <listitem>
 413                 <para>Wake on broadcast messages.</para>
 414               </listitem>
 415             </varlistentry>
 416             <varlistentry>
 417               <term><literal>arp</literal></term>
 418               <listitem>
 419                 <para>Wake on ARP.</para>
 420               </listitem>
 421             </varlistentry>
 422             <varlistentry>
 423               <term><literal>magic</literal></term>
 424               <listitem>
 425                 <para>Wake on receipt of a magic packet.
 426                 </para>
 427               </listitem>
 428             </varlistentry>
 429             <varlistentry>
 430               <term><literal>secureon</literal></term>
 431               <listitem>
 432                 <para>Enable secureon(tm) password for MagicPacket(tm).
 433                 </para>
 434               </listitem>
 435             </varlistentry>
 436             <varlistentry>
 437               <term><literal>off</literal></term>
 438               <listitem>
 439                 <para>Never wake.</para>
 440               </listitem>
 441             </varlistentry>
 442           </variablelist>
 443
 444           <para>Defaults to <literal>off</literal>.</para>
 445         </listitem>
 446       </varlistentry>
 447       <varlistentry>
 448         <term><varname>Port=</varname></term>
 449         <listitem>
 450           <para>The port option is used to select the device port. The
 451           supported values are:</para>
 452
 453           <variablelist>
 454             <varlistentry>
 455               <term><literal>tp</literal></term>
 456               <listitem>
 457                 <para>An Ethernet interface using Twisted-Pair cable as the medium.</para>
 458               </listitem>
 459             </varlistentry>
 460             <varlistentry>
 461               <term><literal>aui</literal></term>
 462               <listitem>
 463                 <para>Attachment Unit Interface (AUI). Normally used with hubs.
 464                 </para>
 465               </listitem>
 466             </varlistentry>
 467             <varlistentry>
 468               <term><literal>bnc</literal></term>
 469               <listitem>
 470                 <para>An Ethernet interface using BNC connectors and co-axial cable.</para>
 471               </listitem>
 472             </varlistentry>
 473             <varlistentry>
 474               <term><literal>mii</literal></term>
 475               <listitem>
 476                 <para>An Ethernet interface using a Media Independent Interface (MII).</para>
 477               </listitem>
 478             </varlistentry>
 479             <varlistentry>
 480               <term><literal>fibre</literal></term>
 481               <listitem>
 482                 <para>An Ethernet interface using Optical Fibre as the medium.</para>
 483               </listitem>
 484             </varlistentry>
 485           </variablelist>
 486         </listitem>
 487       </varlistentry>
 488       <varlistentry>
 489         <term><varname>TCPSegmentationOffload=</varname></term>
 490         <listitem>
 491           <para>The TCP Segmentation Offload (TSO) when true enables
 492           TCP segmentation offload. Takes a boolean value.
 493           Defaults to "unset".</para>
 494         </listitem>
 495       </varlistentry>
 496        <varlistentry>
 497       <term><varname>TCP6SegmentationOffload=</varname></term>
 498         <listitem>
 499           <para>The TCP6 Segmentation Offload (tx-tcp6-segmentation) when true enables
 500           TCP6 segmentation offload. Takes a boolean value.
 501           Defaults to "unset".</para>
 502         </listitem>
 503       </varlistentry>
 504       <varlistentry>
 505         <term><varname>GenericSegmentationOffload=</varname></term>
 506         <listitem>
 507           <para>The Generic Segmentation Offload (GSO) when true enables
 508           generic segmentation offload. Takes a boolean value.
 509           Defaults to "unset".</para>
 510         </listitem>
 511       </varlistentry>
 512     <varlistentry>
 513         <term><varname>GenericReceiveOffload=</varname></term>
 514         <listitem>
 515           <para>The Generic Receive Offload (GRO) when true enables
 516           generic receive offload. Takes a boolean value.
 517           Defaults to "unset".</para>
 518         </listitem>
 519       </varlistentry>
 520       <varlistentry>
 521         <term><varname>LargeReceiveOffload=</varname></term>
 522         <listitem>
 523           <para>The Large Receive Offload (LRO) when true enables
 524           large receive offload. Takes a boolean value.
 525           Defaults to "unset".</para>
 526         </listitem>
 527       </varlistentry>
 528     </variablelist>
 529   </refsect1>
 530
 531   <refsect1>
 532     <title>Examples</title>
 533
 534     <example>
 535       <title>/usr/lib/systemd/network/99-default.link</title>
 536
 537       <para>The link file <filename>99-default.link</filename> that is
 538       shipped with systemd defines the default naming policy for
 539       links.</para>
 540
 541       <programlisting>[Link]
 542 NamePolicy=kernel database onboard slot path
 543 MACAddressPolicy=persistent</programlisting>
 544     </example>
 545
 546     <example>
 547       <title>/etc/systemd/network/10-dmz.link</title>
 548
 549       <para>This example assigns the fixed name
 550       <literal>dmz0</literal> to the interface with the MAC address
 551       00:a0:de:63:7a:e6:</para>
 552
 553       <programlisting>[Match]
 554 MACAddress=00:a0:de:63:7a:e6
 555
 556 [Link]
 557 Name=dmz0</programlisting>
 558     </example>
 559
 560     <example>
 561       <title>/etc/systemd/network/10-internet.link</title>
 562
 563       <para>This example assigns the fixed name
 564       <literal>internet0</literal> to the interface with the device
 565       path <literal>pci-0000:00:1a.0-*</literal>:</para>
 566
 567       <programlisting>[Match]
 568 Path=pci-0000:00:1a.0-*
 569
 570 [Link]
 571 Name=internet0</programlisting>
 572     </example>
 573
 574     <example>
 575       <title>/etc/systemd/network/25-wireless.link</title>
 576
 577       <para>Here's an overly complex example that shows the use of a large number of [Match] and [Link] settings.</para>
 578
 579       <programlisting>[Match]
 580 MACAddress=12:34:56:78:9a:bc
 581 Driver=brcmsmac
 582 Path=pci-0000:02:00.0-*
 583 Type=wlan
 584 Virtualization=no
 585 Host=my-laptop
 586 Architecture=x86-64
 587
 588 [Link]
 589 Name=wireless0
 590 MTUBytes=1450
 591 BitsPerSecond=10M
 592 WakeOnLan=magic
 593 MACAddress=cb:a9:87:65:43:21</programlisting>
 594     </example>
 595   </refsect1>
 596
 597   <refsect1>
 598     <title>See Also</title>
 599     <para>
 600       <citerefentry>
 601         <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
 602       </citerefentry>,
 603       <citerefentry>
 604         <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
 605       </citerefentry>,
 606       <citerefentry>
 607         <refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum>
 608       </citerefentry>,
 609       <citerefentry>
 610         <refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum>
 611       </citerefentry>
 612     </para>
 613   </refsect1>
 614
 615 </refentry>