man/systemd.link.xml

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