man/systemd.link.xml

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  23
  24 <refentry id="systemd.link">
  25   <refentryinfo>
  26     <title>systemd.link</title>
  27     <productname>systemd</productname>
  28
  29     <authorgroup>
  30       <author>
  31         <contrib>Developer</contrib>
  32         <firstname>Tom</firstname>
  33         <surname>Gundersen</surname>
  34       </author>
  35     </authorgroup>
  36   </refentryinfo>
  37
  38   <refmeta>
  39     <refentrytitle>systemd.link</refentrytitle>
  40     <manvolnum>5</manvolnum>
  41   </refmeta>
  42
  43   <refnamediv>
  44     <refname>systemd.link</refname>
  45     <refpurpose>Network device configuration</refpurpose>
  46   </refnamediv>
  47
  48   <refsynopsisdiv>
  49     <para><filename><replaceable>link</replaceable>.link</filename></para>
  50   </refsynopsisdiv>
  51
  52   <refsect1>
  53     <title>Description</title>
  54
  55     <para>Network link configuration is performed by the
  56     <command>net_setup_link</command> udev builtin.</para>
  57
  58     <para>The link files are read from the files located in the system
  59     network directory <filename>/usr/lib/systemd/network</filename>,
  60     the volatile runtime network directory
  61     <filename>/run/systemd/network</filename>, and the local
  62     administration network directory
  63     <filename>/etc/systemd/network</filename>. Link files must have
  64     the extension <filename>.link</filename>; other extensions are
  65     ignored. All link files are collectively sorted and processed in
  66     lexical order, regardless of the directories in which they live.
  67     However, files with identical filenames replace each other. Files
  68     in <filename>/etc</filename> have the highest priority, files in
  69     <filename>/run</filename> take precedence over files with the same
  70     name in <filename>/usr/lib</filename>. This can be used to
  71     override a system-supplied link file with a local file if needed.
  72     As a special case, an empty file (file size 0) or symlink with the
  73     same name pointing to <filename>/dev/null</filename> disables the
  74     configuration file entirely (it is "masked").</para>
  75
  76     <para>The link file contains a <literal>[Match]</literal> section,
  77     which determines if a given link file may be applied to a given
  78     device, as well as a <literal>[Link]</literal> section specifying
  79     how the device should be configured. The first (in lexical order)
  80     of the link files that matches a given device is applied. Note
  81     that a default file <filename>99-default.link</filename> is
  82     shipped by the system, any user-supplied
  83     <filename>.link</filename> should hence have a lexically earlier
  84     name to be considered at all.</para>
  85
  86     <para>See
  87     <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  88     for diagnosing problems with <filename>.link</filename> files.</para>
  89   </refsect1>
  90
  91   <refsect1>
  92     <title>[Match] Section Options</title>
  93
  94     <para>A link file is said to match a device if each of the entries
  95     in the <literal>[Match]</literal> section matches, or if the
  96     section is empty. The following keys are accepted:</para>
  97
  98     <variablelist class='network-directives'>
  99       <varlistentry>
 100         <term><varname>MACAddress=</varname></term>
 101         <listitem>
 102           <para>The hardware address.</para>
 103         </listitem>
 104       </varlistentry>
 105       <varlistentry>
 106         <term><varname>OriginalName=</varname></term>
 107         <listitem>
 108           <para>A whitespace-separated list of shell-style globs matching
 109           the device name, as exposed by the udev property
 110           "INTERFACE". This cannot be used to match on names that have
 111           already been changed from userspace. Caution is advised when matching on
 112           kernel-assigned names, as they are known to be unstable
 113           between reboots.</para>
 114         </listitem>
 115       </varlistentry>
 116       <varlistentry>
 117         <term><varname>Path=</varname></term>
 118         <listitem>
 119           <para>A whitespace-separated list of shell-style globs matching
 120           the persistent path, as exposed by the udev property
 121           <literal>ID_PATH</literal>.</para>
 122         </listitem>
 123       </varlistentry>
 124       <varlistentry>
 125         <term><varname>Driver=</varname></term>
 126         <listitem>
 127           <para>A whitespace-separated list of shell-style globs matching
 128           the driver currently bound to the device,
 129           as exposed by the udev property <literal>DRIVER</literal>
 130           of its parent device, or if that is not set, the
 131           driver as exposed by <literal>ethtool -i</literal>
 132           of the device itself.</para>
 133         </listitem>
 134       </varlistentry>
 135       <varlistentry>
 136         <term><varname>Type=</varname></term>
 137         <listitem>
 138           <para>A whitespace-separated list of shell-style globs matching
 139           the device type, as exposed by the udev
 140           property <literal>DEVTYPE</literal>.</para>
 141         </listitem>
 142       </varlistentry>
 143       <varlistentry>
 144         <term><varname>Host=</varname></term>
 145         <listitem>
 146           <para>Matches against the hostname or machine
 147           ID of the host. See <literal>ConditionHost=</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>Virtualization=</varname></term>
 154         <listitem>
 155           <para>Checks whether the system is executed in
 156           a virtualized environment and optionally test
 157           whether it is a specific implementation. See
 158           <literal>ConditionVirtualization=</literal> in
 159           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 160           for details.</para>
 161         </listitem>
 162       </varlistentry>
 163       <varlistentry>
 164         <term><varname>KernelCommandLine=</varname></term>
 165         <listitem>
 166           <para>Checks whether a specific kernel command line option
 167           is set (or if prefixed with the exclamation mark unset). See
 168           <literal>ConditionKernelCommandLine=</literal> in
 169           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 170           for details.</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         </listitem>
 336       </varlistentry>
 337       <varlistentry>
 338         <term><varname>MTUBytes=</varname></term>
 339         <listitem>
 340           <para>The maximum transmission unit in bytes to set for the
 341           device. The usual suffixes K, M, G, are supported and are
 342           understood to the base of 1024.</para>
 343         </listitem>
 344       </varlistentry>
 345       <varlistentry>
 346         <term><varname>BitsPerSecond=</varname></term>
 347         <listitem>
 348           <para>The speed to set for the device, the value is rounded
 349           down to the nearest Mbps. The usual suffixes K, M, G, are
 350           supported and are understood to the base of 1000.</para>
 351         </listitem>
 352       </varlistentry>
 353       <varlistentry>
 354         <term><varname>Duplex=</varname></term>
 355         <listitem>
 356           <para>The duplex mode to set for the device. The accepted
 357           values are <literal>half</literal> and
 358           <literal>full</literal>.</para>
 359         </listitem>
 360       </varlistentry>
 361       <varlistentry>
 362         <term><varname>AutoNegotiation=</varname></term>
 363         <listitem>
 364           <para>Enables or disables automatic negotiation of transmission parameters.
 365           Autonegotiation is a procedure by which two connected ethernet devices choose
 366           common transmission parameters, such as speed, duplex mode, and flow control.
 367           Takes a boolean value. Unset by default, which means that the kernel default
 368           will be used.</para>
 369
 370           <para>Note that if autonegotiation is enabled, speed and duplex settings are
 371           read-only. If autonegotation is disabled, speed and duplex settings are writable
 372           if the driver supports multiple link modes.</para>
 373         </listitem>
 374       </varlistentry>
 375       <varlistentry>
 376         <term><varname>WakeOnLan=</varname></term>
 377         <listitem>
 378           <para>The Wake-on-LAN policy to set for the device. The
 379           supported values are:</para>
 380
 381           <variablelist>
 382             <varlistentry>
 383               <term><literal>phy</literal></term>
 384               <listitem>
 385                 <para>Wake on PHY activity.</para>
 386               </listitem>
 387             </varlistentry>
 388             <varlistentry>
 389               <term><literal>magic</literal></term>
 390               <listitem>
 391                 <para>Wake on receipt of a magic packet.
 392                 </para>
 393               </listitem>
 394             </varlistentry>
 395             <varlistentry>
 396               <term><literal>off</literal></term>
 397               <listitem>
 398                 <para>Never wake.</para>
 399               </listitem>
 400             </varlistentry>
 401           </variablelist>
 402         </listitem>
 403       </varlistentry>
 404       <varlistentry>
 405         <term><varname>Port=</varname></term>
 406         <listitem>
 407           <para>The port option is used to select the device port. The
 408           supported values are:</para>
 409
 410           <variablelist>
 411             <varlistentry>
 412               <term><literal>tp</literal></term>
 413               <listitem>
 414                 <para>An Ethernet interface using Twisted-Pair cable as the medium.</para>
 415               </listitem>
 416             </varlistentry>
 417             <varlistentry>
 418               <term><literal>aui</literal></term>
 419               <listitem>
 420                 <para>Attachment Unit Interface (AUI). Normally used with hubs.
 421                 </para>
 422               </listitem>
 423             </varlistentry>
 424             <varlistentry>
 425               <term><literal>bnc</literal></term>
 426               <listitem>
 427                 <para>An Ethernet interface using BNC connectors and co-axial cable.</para>
 428               </listitem>
 429             </varlistentry>
 430             <varlistentry>
 431               <term><literal>mii</literal></term>
 432               <listitem>
 433                 <para>An Ethernet interface using a Media Independent Interface (MII).</para>
 434               </listitem>
 435             </varlistentry>
 436             <varlistentry>
 437               <term><literal>fibre</literal></term>
 438               <listitem>
 439                 <para>An Ethernet interface using Optical Fibre as the medium.</para>
 440               </listitem>
 441             </varlistentry>
 442           </variablelist>
 443         </listitem>
 444       </varlistentry>
 445       <varlistentry>
 446         <term><varname>TCPSegmentationOffload=</varname></term>
 447         <listitem>
 448           <para>The TCP Segmentation Offload (TSO) when true enables
 449           TCP segmentation offload. Takes a boolean value.
 450           Defaults to "unset".</para>
 451         </listitem>
 452       </varlistentry>
 453       <varlistentry>
 454         <term><varname>GenericSegmentationOffload=</varname></term>
 455         <listitem>
 456           <para>The Generic Segmentation Offload (GSO) when true enables
 457           generic segmentation offload. Takes a boolean value.
 458           Defaults to "unset".</para>
 459         </listitem>
 460       </varlistentry>
 461       <varlistentry>
 462         <term><varname>UDPSegmentationOffload=</varname></term>
 463         <listitem>
 464           <para>The UDP Segmentation Offload (USO) when true enables
 465           UDP segmentation offload. Takes a boolean value.
 466           Defaults to "unset".</para>
 467         </listitem>
 468       </varlistentry>
 469     <varlistentry>
 470         <term><varname>GenericReceiveOffload=</varname></term>
 471         <listitem>
 472           <para>The Generic Receive Offload (GRO) when true enables
 473           generic receive offload. Takes a boolean value.
 474           Defaults to "unset".</para>
 475         </listitem>
 476       </varlistentry>
 477       <varlistentry>
 478         <term><varname>LargeReceiveOffload=</varname></term>
 479         <listitem>
 480           <para>The Large Receive Offload (LRO) when true enables
 481           large receive offload. Takes a boolean value.
 482           Defaults to "unset".</para>
 483         </listitem>
 484       </varlistentry>
 485     </variablelist>
 486   </refsect1>
 487
 488   <refsect1>
 489     <title>Examples</title>
 490
 491     <example>
 492       <title>/usr/lib/systemd/network/99-default.link</title>
 493
 494       <para>The link file <filename>99-default.link</filename> that is
 495       shipped with systemd defines the default naming policy for
 496       links.</para>
 497
 498       <programlisting>[Link]
 499 NamePolicy=kernel database onboard slot path
 500 MACAddressPolicy=persistent</programlisting>
 501     </example>
 502
 503     <example>
 504       <title>/etc/systemd/network/10-dmz.link</title>
 505
 506       <para>This example assigns the fixed name
 507       <literal>dmz0</literal> to the interface with the MAC address
 508       00:a0:de:63:7a:e6:</para>
 509
 510       <programlisting>[Match]
 511 MACAddress=00:a0:de:63:7a:e6
 512
 513 [Link]
 514 Name=dmz0</programlisting>
 515     </example>
 516
 517     <example>
 518       <title>/etc/systemd/network/10-internet.link</title>
 519
 520       <para>This example assigns the fixed name
 521       <literal>internet0</literal> to the interface with the device
 522       path <literal>pci-0000:00:1a.0-*</literal>:</para>
 523
 524       <programlisting>[Match]
 525 Path=pci-0000:00:1a.0-*
 526
 527 [Link]
 528 Name=internet0</programlisting>
 529     </example>
 530
 531     <example>
 532       <title>/etc/systemd/network/25-wireless.link</title>
 533
 534       <para>Here's an overly complex example that shows the use of a large number of [Match] and [Link] settings.</para>
 535
 536       <programlisting>[Match]
 537 MACAddress=12:34:56:78:9a:bc
 538 Driver=brcmsmac
 539 Path=pci-0000:02:00.0-*
 540 Type=wlan
 541 Virtualization=no
 542 Host=my-laptop
 543 Architecture=x86-64
 544
 545 [Link]
 546 Name=wireless0
 547 MTUBytes=1450
 548 BitsPerSecond=10M
 549 WakeOnLan=magic
 550 MACAddress=cb:a9:87:65:43:21</programlisting>
 551     </example>
 552   </refsect1>
 553
 554   <refsect1>
 555     <title>See Also</title>
 556     <para>
 557       <citerefentry>
 558         <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
 559       </citerefentry>,
 560       <citerefentry>
 561         <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
 562       </citerefentry>,
 563       <citerefentry>
 564         <refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum>
 565       </citerefentry>,
 566       <citerefentry>
 567         <refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum>
 568       </citerefentry>
 569     </para>
 570   </refsect1>
 571
 572 </refentry>