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>TCPSegmentationOffload=</varname></term>
 406         <listitem>
 407           <para>The TCP Segmentation Offload (TSO) when true enables
 408           TCP segmentation offload. Takes a boolean value.
 409           Defaults to "unset".</para>
 410         </listitem>
 411       </varlistentry>
 412       <varlistentry>
 413         <term><varname>GenericSegmentationOffload=</varname></term>
 414         <listitem>
 415           <para>The Generic Segmentation Offload (GSO) when true enables
 416           generic segmentation offload. Takes a boolean value.
 417           Defaults to "unset".</para>
 418         </listitem>
 419       </varlistentry>
 420       <varlistentry>
 421         <term><varname>UDPSegmentationOffload=</varname></term>
 422         <listitem>
 423           <para>The UDP Segmentation Offload (USO) when true enables
 424           UDP segmentation offload. Takes a boolean value.
 425           Defaults to "unset".</para>
 426         </listitem>
 427       </varlistentry>
 428     <varlistentry>
 429         <term><varname>GenericReceiveOffload=</varname></term>
 430         <listitem>
 431           <para>The Generic Receive Offload (GRO) when true enables
 432           generic receive offload. Takes a boolean value.
 433           Defaults to "unset".</para>
 434         </listitem>
 435       </varlistentry>
 436       <varlistentry>
 437         <term><varname>LargeReceiveOffload=</varname></term>
 438         <listitem>
 439           <para>The Large Receive Offload (LRO) when true enables
 440           large receive offload. Takes a boolean value.
 441           Defaults to "unset".</para>
 442         </listitem>
 443       </varlistentry>
 444     </variablelist>
 445   </refsect1>
 446
 447   <refsect1>
 448     <title>Examples</title>
 449
 450     <example>
 451       <title>/usr/lib/systemd/network/99-default.link</title>
 452
 453       <para>The link file <filename>99-default.link</filename> that is
 454       shipped with systemd defines the default naming policy for
 455       links.</para>
 456
 457       <programlisting>[Link]
 458 NamePolicy=kernel database onboard slot path
 459 MACAddressPolicy=persistent</programlisting>
 460     </example>
 461
 462     <example>
 463       <title>/etc/systemd/network/10-dmz.link</title>
 464
 465       <para>This example assigns the fixed name
 466       <literal>dmz0</literal> to the interface with the MAC address
 467       00:a0:de:63:7a:e6:</para>
 468
 469       <programlisting>[Match]
 470 MACAddress=00:a0:de:63:7a:e6
 471
 472 [Link]
 473 Name=dmz0</programlisting>
 474     </example>
 475
 476     <example>
 477       <title>/etc/systemd/network/10-internet.link</title>
 478
 479       <para>This example assigns the fixed name
 480       <literal>internet0</literal> to the interface with the device
 481       path <literal>pci-0000:00:1a.0-*</literal>:</para>
 482
 483       <programlisting>[Match]
 484 Path=pci-0000:00:1a.0-*
 485
 486 [Link]
 487 Name=internet0</programlisting>
 488     </example>
 489
 490     <example>
 491       <title>/etc/systemd/network/25-wireless.link</title>
 492
 493       <para>Here's an overly complex example that shows the use of a large number of [Match] and [Link] settings.</para>
 494
 495       <programlisting>[Match]
 496 MACAddress=12:34:56:78:9a:bc
 497 Driver=brcmsmac
 498 Path=pci-0000:02:00.0-*
 499 Type=wlan
 500 Virtualization=no
 501 Host=my-laptop
 502 Architecture=x86-64
 503
 504 [Link]
 505 Name=wireless0
 506 MTUBytes=1450
 507 BitsPerSecond=10M
 508 WakeOnLan=magic
 509 MACAddress=cb:a9:87:65:43:21</programlisting>
 510     </example>
 511   </refsect1>
 512
 513   <refsect1>
 514     <title>See Also</title>
 515     <para>
 516       <citerefentry>
 517         <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
 518       </citerefentry>,
 519       <citerefentry>
 520         <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
 521       </citerefentry>,
 522       <citerefentry>
 523         <refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum>
 524       </citerefentry>,
 525       <citerefentry>
 526         <refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum>
 527       </citerefentry>
 528     </para>
 529   </refsect1>
 530
 531 </refentry>