man/systemd.link.xml

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