man/systemd.link.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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   5
   6 <refentry id="systemd.link">
   7   <refentryinfo>
   8     <title>systemd.link</title>
   9     <productname>systemd</productname>
  10   </refentryinfo>
  11
  12   <refmeta>
  13     <refentrytitle>systemd.link</refentrytitle>
  14     <manvolnum>5</manvolnum>
  15   </refmeta>
  16
  17   <refnamediv>
  18     <refname>systemd.link</refname>
  19     <refpurpose>Network device configuration</refpurpose>
  20   </refnamediv>
  21
  22   <refsynopsisdiv>
  23     <para><filename><replaceable>link</replaceable>.link</filename></para>
  24   </refsynopsisdiv>
  25
  26   <refsect1>
  27     <title>Description</title>
  28
  29     <para>A plain ini-style text file that encodes configuration for matching network devices, used by
  30     <citerefentry><refentrytitle>systemd-udevd</refentrytitle><manvolnum>8</manvolnum></citerefentry> and in
  31     particular its <command>net_setup_link</command> builtin. See
  32     <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>7</manvolnum></citerefentry> for a
  33     general description of the syntax.</para>
  34
  35     <para>The link files are read from the files located in the system network directory
  36     <filename>/usr/lib/systemd/network</filename>, the volatile runtime network directory
  37     <filename>/run/systemd/network</filename>, and the local administration network directory
  38     <filename>/etc/systemd/network</filename>. Link files must have the extension
  39     <filename>.link</filename>; other extensions are ignored. All link files are collectively sorted
  40     and processed in lexical order, regardless of the directories in which they live. However, files
  41     with identical filenames replace each other. Files in <filename>/etc/</filename> have the highest
  42     priority, files in <filename>/run/</filename> take precedence over files with the same name in
  43     <filename>/usr/lib/</filename>. This can be used to override a system-supplied link file with a
  44     local file if needed. As a special case, an empty file (file size 0) or symlink with the same name
  45     pointing to <filename>/dev/null</filename> disables the configuration file entirely (it is
  46     "masked").</para>
  47
  48     <para>Along with the link file <filename>foo.link</filename>, a "drop-in" directory
  49     <filename>foo.link.d/</filename> may exist. All files with the suffix <literal>.conf</literal>
  50     from this directory will be merged in the alphanumeric order and parsed after the main file itself
  51     has been parsed. This is useful to alter or add configuration settings, without having to modify
  52     the main configuration file. Each drop-in file must have appropriate section headers.</para>
  53
  54     <para>In addition to <filename>/etc/systemd/network</filename>, drop-in <literal>.d</literal>
  55     directories can be placed in <filename>/usr/lib/systemd/network</filename> or
  56     <filename>/run/systemd/network</filename> directories. Drop-in files in <filename>/etc/</filename>
  57     take precedence over those in <filename>/run/</filename> which in turn take precedence over those
  58     in <filename>/usr/lib/</filename>. Drop-in files under any of these directories take precedence
  59     over the main link file wherever located.</para>
  60
  61     <para>The link file contains a [Match] section, which determines if a given link file may be applied to a
  62     given device, as well as a [Link] section specifying how the device should be configured. The first (in
  63     lexical order) of the link files that matches a given device is applied. Note that a default file
  64     <filename>99-default.link</filename> is shipped by the system. Any user-supplied
  65     <filename>.link</filename> should hence have a lexically earlier name to be considered at all.</para>
  66
  67     <para>See <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
  68     diagnosing problems with <filename>.link</filename> files.</para>
  69   </refsect1>
  70
  71   <refsect1>
  72     <title>[Match] Section Options</title>
  73
  74     <para>A link file is said to match a device if all matches specified by the
  75     [Match] section are satisfied. When a link file does not contain valid settings
  76     in [Match] section, then the file will match all devices and
  77     <command>systemd-udevd</command> warns about that. Hint: to avoid the warning and to make it clear
  78     that all interfaces shall be matched, add the following:
  79     <programlisting>OriginalName=*</programlisting>
  80     The following keys are accepted:</para>
  81
  82     <variablelist class='network-directives'>
  83       <!-- This list is reused in systemd.network(3), hence maintain a specific order:
  84            1. device matches shared between the two lists
  85            2. non-shared settings
  86            3. host matches shared between the two lists
  87         -->
  88
  89       <varlistentry id='mac-address'>
  90         <term><varname>MACAddress=</varname></term>
  91         <listitem>
  92           <para>A whitespace-separated list of hardware addresses. Use full colon-, hyphen- or dot-delimited hexadecimal. See the example below.
  93           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
  94           of hardware addresses defined prior to this is reset.</para>
  95
  96           <para>Example:
  97           <programlisting>MACAddress=01:23:45:67:89:ab 00-11-22-33-44-55 AABB.CCDD.EEFF</programlisting></para>
  98         </listitem>
  99       </varlistentry>
 100
 101       <varlistentry id='permanent-mac-address'>
 102         <term><varname>PermanentMACAddress=</varname></term>
 103         <listitem>
 104           <para>A whitespace-separated list of hardware's permanent addresses. While
 105           <varname>MACAddress=</varname> matches the device's current MAC address, this matches the
 106           device's permanent MAC address, which may be different from the current one. Use full
 107           colon-, hyphen- or dot-delimited hexadecimal. This option may appear more than once, in
 108           which case the lists are merged. If the empty string is assigned to this option, the list
 109           of hardware addresses defined prior to this is reset.</para>
 110         </listitem>
 111       </varlistentry>
 112
 113       <varlistentry id='path'>
 114         <term><varname>Path=</varname></term>
 115         <listitem>
 116           <para>A whitespace-separated list of shell-style globs matching
 117           the persistent path, as exposed by the udev property
 118           <varname>ID_PATH</varname>.</para>
 119         </listitem>
 120       </varlistentry>
 121
 122       <varlistentry id='driver'>
 123         <term><varname>Driver=</varname></term>
 124         <listitem>
 125           <para>A whitespace-separated list of shell-style globs matching the driver currently bound to the
 126           device, as exposed by the udev property <varname>ID_NET_DRIVER</varname> of its parent device, or
 127           if that is not set, the driver as exposed by <command>ethtool -i</command> of the device itself.
 128           If the list is prefixed with a "!", the test is inverted.</para>
 129         </listitem>
 130       </varlistentry>
 131
 132       <varlistentry id='type'>
 133         <term><varname>Type=</varname></term>
 134         <listitem>
 135           <para>A whitespace-separated list of shell-style globs matching the device type, as exposed by
 136           <command>networkctl list</command>. If the list is prefixed with a "!", the test is inverted.
 137           Some valid values are <literal>ether</literal>, <literal>loopback</literal>, <literal>wlan</literal>, <literal>wwan</literal>.
 138           Valid types are named either from the udev <literal>DEVTYPE</literal> attribute, or
 139           <literal>ARPHRD_</literal> macros in <filename>linux/if_arp.h</filename>, so this is not comprehensive.
 140           </para>
 141         </listitem>
 142       </varlistentry>
 143
 144       <varlistentry id='property'>
 145         <term><varname>Property=</varname></term>
 146         <listitem>
 147           <para>A whitespace-separated list of udev property name with its value after a equal
 148           (<literal>=</literal>). If multiple properties are specified, the test results are ANDed.
 149           If the list is prefixed with a "!", the test is inverted. If a value contains white
 150           spaces, then please quote whole key and value pair. If a value contains quotation, then
 151           please escape the quotation with <literal>\</literal>.</para>
 152
 153           <para>Example: if a .link file has the following:
 154           <programlisting>Property=ID_MODEL_ID=9999 "ID_VENDOR_FROM_DATABASE=vendor name" "KEY=with \"quotation\""</programlisting>
 155           then, the .link file matches only when an interface has all the above three properties.
 156           </para>
 157         </listitem>
 158       </varlistentry>
 159
 160       <varlistentry>
 161         <term><varname>OriginalName=</varname></term>
 162         <listitem>
 163           <para>A whitespace-separated list of shell-style globs matching the device name, as exposed by the
 164           udev property "INTERFACE". This cannot be used to match on names that have already been changed
 165           from userspace. Caution is advised when matching on kernel-assigned names, as they are known to be
 166           unstable between reboots.</para>
 167         </listitem>
 168       </varlistentry>
 169
 170       <varlistentry id='host'>
 171         <term><varname>Host=</varname></term>
 172         <listitem>
 173           <para>Matches against the hostname or machine ID of the host. See <varname>ConditionHost=</varname> in
 174           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 175           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 176           If an empty string is assigned, then previously assigned value is cleared.
 177           </para>
 178         </listitem>
 179       </varlistentry>
 180
 181       <varlistentry id='virtualization'>
 182         <term><varname>Virtualization=</varname></term>
 183         <listitem>
 184           <para>Checks whether the system is executed in a virtualized environment and optionally test
 185           whether it is a specific implementation. See <varname>ConditionVirtualization=</varname> in
 186           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 187           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 188           If an empty string is assigned, then previously assigned value is cleared.
 189           </para>
 190         </listitem>
 191       </varlistentry>
 192
 193       <varlistentry id='kernel-command-line'>
 194         <term><varname>KernelCommandLine=</varname></term>
 195         <listitem>
 196           <para>Checks whether a specific kernel command line option is set. See
 197           <varname>ConditionKernelCommandLine=</varname> in
 198           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 199           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 200           If an empty string is assigned, then previously assigned value is cleared.
 201           </para>
 202         </listitem>
 203       </varlistentry>
 204
 205       <varlistentry id='kernel-version'>
 206         <term><varname>KernelVersion=</varname></term>
 207         <listitem>
 208           <para>Checks whether the kernel version (as reported by <command>uname -r</command>) matches a certain
 209           expression. See <varname>ConditionKernelVersion=</varname> in
 210           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 211           details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 212           If an empty string is assigned, then previously assigned value is cleared.
 213           </para>
 214         </listitem>
 215       </varlistentry>
 216
 217       <varlistentry id='architecture'>
 218         <term><varname>Architecture=</varname></term>
 219         <listitem>
 220           <para>Checks whether the system is running on a specific architecture. See
 221           <varname>ConditionArchitecture=</varname> in
 222           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 223           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 224           If an empty string is assigned, then previously assigned value is cleared.
 225           </para>
 226         </listitem>
 227       </varlistentry>
 228
 229       <varlistentry id='firmware'>
 230         <term><varname>Firmware=</varname></term>
 231         <listitem>
 232           <para>Checks whether the system is running on a machine with the specified firmware. See
 233           <varname>ConditionFirmware=</varname> in
 234           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 235           for details. When prefixed with an exclamation mark (<literal>!</literal>), the result is negated.
 236           If an empty string is assigned, then previously assigned value is cleared.
 237           </para>
 238         </listitem>
 239       </varlistentry>
 240     </variablelist>
 241
 242   </refsect1>
 243
 244   <refsect1>
 245     <title>[Link] Section Options</title>
 246
 247     <para>The [Link] section accepts the following
 248     keys:</para>
 249
 250     <variablelist class='network-directives'>
 251       <varlistentry>
 252         <term><varname>Description=</varname></term>
 253         <listitem>
 254           <para>A description of the device.</para>
 255         </listitem>
 256       </varlistentry>
 257       <varlistentry>
 258         <term><varname>Alias=</varname></term>
 259         <listitem>
 260           <para>The <varname>ifalias</varname> interface property is set to this value.</para>
 261         </listitem>
 262       </varlistentry>
 263       <varlistentry>
 264         <term><varname>MACAddressPolicy=</varname></term>
 265         <listitem>
 266           <para>The policy by which the MAC address should be set. The
 267           available policies are:
 268           </para>
 269
 270           <variablelist>
 271             <varlistentry>
 272               <term><option>persistent</option></term>
 273               <listitem>
 274                 <para>If the hardware has a persistent MAC address, as
 275                 most hardware should, and if it is used by the kernel,
 276                 nothing is done. Otherwise, a new MAC address is
 277                 generated which is guaranteed to be the same on every
 278                 boot for the given machine and the given device, but
 279                 which is otherwise random. This feature depends on ID_NET_NAME_*
 280                 properties to exist for the link. On hardware where these
 281                 properties are not set, the generation of a persistent MAC address
 282                 will fail.</para>
 283               </listitem>
 284             </varlistentry>
 285             <varlistentry>
 286               <term><option>random</option></term>
 287               <listitem>
 288                 <para>If the kernel is using a random MAC address,
 289                 nothing is done. Otherwise, a new address is randomly
 290                 generated each time the device appears, typically at
 291                 boot. Either way, the random address will have the
 292                 <literal>unicast</literal> and
 293                 <literal>locally administered</literal> bits set.</para>
 294               </listitem>
 295             </varlistentry>
 296             <varlistentry>
 297               <term><option>none</option></term>
 298               <listitem>
 299                 <para>Keeps the MAC address assigned by the kernel. Or use the MAC address specified in
 300                 <varname>MACAddress=</varname>.</para>
 301               </listitem>
 302             </varlistentry>
 303           </variablelist>
 304
 305           <para>An empty string assignment is equivalent to setting <literal>none</literal>.</para>
 306         </listitem>
 307       </varlistentry>
 308       <varlistentry>
 309         <term><varname>MACAddress=</varname></term>
 310         <listitem>
 311           <para>The interface MAC address to use. For this setting to take effect,
 312           <varname>MACAddressPolicy=</varname> must either be unset, empty, or <literal>none</literal>.
 313           </para>
 314         </listitem>
 315       </varlistentry>
 316       <varlistentry>
 317         <term><varname>NamePolicy=</varname></term>
 318         <listitem>
 319           <para>An ordered, space-separated list of policies by which the interface name should be set.
 320           <varname>NamePolicy=</varname> may be disabled by specifying <option>net.ifnames=0</option> on the
 321           kernel command line. Each of the policies may fail, and the first successful one is used. The name
 322           is not set directly, but is exported to udev as the property <option>ID_NET_NAME</option>, which
 323           is, by default, used by a
 324           <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 325           rule to set <varname>NAME</varname>. The available policies are:
 326           </para>
 327
 328           <variablelist>
 329             <varlistentry>
 330               <term><option>kernel</option></term>
 331               <listitem>
 332                 <para>If the kernel claims that the name it has set
 333                 for a device is predictable, then no renaming is
 334                 performed.</para>
 335               </listitem>
 336             </varlistentry>
 337             <varlistentry>
 338               <term><option>database</option></term>
 339               <listitem>
 340                 <para>The name is set based on entries in the udev's
 341                 Hardware Database with the key
 342                 <varname>ID_NET_NAME_FROM_DATABASE</varname>.
 343                 </para>
 344               </listitem>
 345             </varlistentry>
 346             <varlistentry>
 347               <term><option>onboard</option></term>
 348               <listitem>
 349                 <para>The name is set based on information given by
 350                 the firmware for on-board devices, as exported by the
 351                 udev property <varname>ID_NET_NAME_ONBOARD</varname>.
 352                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 353                 </para>
 354               </listitem>
 355             </varlistentry>
 356             <varlistentry>
 357               <term><option>slot</option></term>
 358               <listitem>
 359                 <para>The name is set based on information given by
 360                 the firmware for hot-plug devices, as exported by the
 361                 udev property <varname>ID_NET_NAME_SLOT</varname>.
 362                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 363                 </para>
 364               </listitem>
 365             </varlistentry>
 366             <varlistentry>
 367               <term><option>path</option></term>
 368               <listitem>
 369                 <para>The name is set based on the device's physical
 370                 location, as exported by the udev property
 371                 <varname>ID_NET_NAME_PATH</varname>.
 372                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 373                 </para>
 374               </listitem>
 375             </varlistentry>
 376             <varlistentry>
 377               <term><option>mac</option></term>
 378               <listitem>
 379                 <para>The name is set based on the device's persistent
 380                 MAC address, as exported by the udev property
 381                 <varname>ID_NET_NAME_MAC</varname>.
 382                 See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 383                 </para>
 384               </listitem>
 385             </varlistentry>
 386             <varlistentry>
 387               <term><option>keep</option></term>
 388               <listitem>
 389                 <para>If the device already had a name given by userspace (as part of creation of the device
 390                 or a rename), keep it.</para>
 391               </listitem>
 392             </varlistentry>
 393           </variablelist>
 394         </listitem>
 395       </varlistentry>
 396       <varlistentry>
 397         <term><varname>Name=</varname></term>
 398         <listitem>
 399           <para>The interface name to use. This option has lower precedence than
 400           <varname>NamePolicy=</varname>, so for this setting to take effect, <varname>NamePolicy=</varname>
 401           must either be unset, empty, disabled, or all policies configured there must fail. Also see the
 402           example below with <literal>Name=dmz0</literal>.</para>
 403
 404           <para>Note that specifying a name that the kernel might use for another
 405           interface (for example <literal>eth0</literal>) is dangerous because the
 406           name assignment done by udev will race with the assignment done by the
 407           kernel, and only one interface may use the name. Depending on the order of
 408           operations, either udev or the kernel will win, making the naming
 409           unpredictable. It is best to use some different prefix, for example
 410           <literal>internal0</literal>/<literal>external0</literal> or
 411           <literal>lan0</literal>/<literal>lan1</literal>/<literal>lan3</literal>.
 412           </para>
 413         </listitem>
 414       </varlistentry>
 415       <varlistentry>
 416         <term><varname>AlternativeNamesPolicy=</varname></term>
 417         <listitem>
 418           <para>A space-separated list of policies by which the interface's alternative names
 419           should be set. Each of the policies may fail, and all successful policies are used. The
 420           available policies are <literal>database</literal>, <literal>onboard</literal>,
 421           <literal>slot</literal>, <literal>path</literal>, and <literal>mac</literal>. If the
 422           kernel does not support the alternative names, then this setting will be ignored.
 423           </para>
 424         </listitem>
 425       </varlistentry>
 426       <varlistentry>
 427         <term><varname>AlternativeName=</varname></term>
 428         <listitem>
 429           <para>The alternative interface name to use. This option can be specified multiple times.
 430           If the empty string is assigned to this option, the list is reset, and all prior assignments
 431           have no effect. If the kernel does not support the alternative names, then this setting will
 432           be ignored.</para>
 433         </listitem>
 434       </varlistentry>
 435       <varlistentry>
 436         <term><varname>TransmitQueues=</varname></term>
 437         <listitem>
 438           <para>Specifies the device's number of transmit queues. An integer in the range 1…4096.
 439           When unset, the kernel's default will be used.</para>
 440         </listitem>
 441       </varlistentry>
 442       <varlistentry>
 443         <term><varname>ReceiveQueues=</varname></term>
 444         <listitem>
 445           <para>Specifies the device's number of receive queues. An integer in the range 1…4096.
 446           When unset, the kernel's default will be used.</para>
 447         </listitem>
 448       </varlistentry>
 449       <varlistentry>
 450         <term><varname>TransmitQueueLength=</varname></term>
 451         <listitem>
 452           <para>Specifies the transmit queue length of the device in number of packets. An unsigned integer
 453           in the range 0…4294967294. When unset, the kernel's default will be used.</para>
 454         </listitem>
 455       </varlistentry>
 456       <varlistentry>
 457         <term><varname>MTUBytes=</varname></term>
 458         <listitem>
 459           <para>The maximum transmission unit in bytes to set for the
 460           device. The usual suffixes K, M, G, are supported and are
 461           understood to the base of 1024.</para>
 462         </listitem>
 463       </varlistentry>
 464       <varlistentry>
 465         <term><varname>BitsPerSecond=</varname></term>
 466         <listitem>
 467           <para>The speed to set for the device, the value is rounded
 468           down to the nearest Mbps. The usual suffixes K, M, G, are
 469           supported and are understood to the base of 1000.</para>
 470         </listitem>
 471       </varlistentry>
 472       <varlistentry>
 473         <term><varname>Duplex=</varname></term>
 474         <listitem>
 475           <para>The duplex mode to set for the device. The accepted values are <option>half</option> and
 476           <option>full</option>.</para>
 477         </listitem>
 478       </varlistentry>
 479       <varlistentry>
 480         <term><varname>AutoNegotiation=</varname></term>
 481         <listitem>
 482           <para>Takes a boolean. If set to yes, automatic negotiation of transmission parameters is enabled.
 483           Autonegotiation is a procedure by which two connected ethernet devices choose
 484           common transmission parameters, such as speed, duplex mode, and flow control.
 485           When unset, the kernel's default will be used.</para>
 486
 487           <para>Note that if autonegotiation is enabled, speed and duplex settings are
 488           read-only. If autonegotiation is disabled, speed and duplex settings are writable
 489           if the driver supports multiple link modes.</para>
 490         </listitem>
 491       </varlistentry>
 492       <varlistentry>
 493         <term><varname>WakeOnLan=</varname></term>
 494         <listitem>
 495           <para>The Wake-on-LAN policy to set for the device. The
 496           supported values are:</para>
 497
 498           <variablelist>
 499             <varlistentry>
 500               <term><option>phy</option></term>
 501               <listitem>
 502                 <para>Wake on PHY activity.</para>
 503               </listitem>
 504             </varlistentry>
 505             <varlistentry>
 506               <term><option>unicast</option></term>
 507               <listitem>
 508                 <para>Wake on unicast messages.</para>
 509               </listitem>
 510             </varlistentry>
 511             <varlistentry>
 512               <term><option>multicast</option></term>
 513               <listitem>
 514                 <para>Wake on multicast messages.</para>
 515               </listitem>
 516             </varlistentry>
 517             <varlistentry>
 518               <term><option>broadcast</option></term>
 519               <listitem>
 520                 <para>Wake on broadcast messages.</para>
 521               </listitem>
 522             </varlistentry>
 523             <varlistentry>
 524               <term><option>arp</option></term>
 525               <listitem>
 526                 <para>Wake on ARP.</para>
 527               </listitem>
 528             </varlistentry>
 529             <varlistentry>
 530               <term><option>magic</option></term>
 531               <listitem>
 532                 <para>Wake on receipt of a magic packet.
 533                 </para>
 534               </listitem>
 535             </varlistentry>
 536             <varlistentry>
 537               <term><option>secureon</option></term>
 538               <listitem>
 539                 <para>Enable secureon(tm) password for MagicPacket(tm).
 540                 </para>
 541               </listitem>
 542             </varlistentry>
 543             <varlistentry>
 544               <term><option>off</option></term>
 545               <listitem>
 546                 <para>Never wake.</para>
 547               </listitem>
 548             </varlistentry>
 549           </variablelist>
 550
 551           <para>Defaults to <option>off</option>.</para>
 552         </listitem>
 553       </varlistentry>
 554       <varlistentry>
 555         <term><varname>Port=</varname></term>
 556         <listitem>
 557           <para>The port option is used to select the device port. The
 558           supported values are:</para>
 559
 560           <variablelist>
 561             <varlistentry>
 562               <term><option>tp</option></term>
 563               <listitem>
 564                 <para>An Ethernet interface using Twisted-Pair cable as the medium.</para>
 565               </listitem>
 566             </varlistentry>
 567             <varlistentry>
 568               <term><option>aui</option></term>
 569               <listitem>
 570                 <para>Attachment Unit Interface (AUI). Normally used with hubs.
 571                 </para>
 572               </listitem>
 573             </varlistentry>
 574             <varlistentry>
 575               <term><option>bnc</option></term>
 576               <listitem>
 577                 <para>An Ethernet interface using BNC connectors and co-axial cable.</para>
 578               </listitem>
 579             </varlistentry>
 580             <varlistentry>
 581               <term><option>mii</option></term>
 582               <listitem>
 583                 <para>An Ethernet interface using a Media Independent Interface (MII).</para>
 584               </listitem>
 585             </varlistentry>
 586             <varlistentry>
 587               <term><option>fibre</option></term>
 588               <listitem>
 589                 <para>An Ethernet interface using Optical Fibre as the medium.</para>
 590               </listitem>
 591             </varlistentry>
 592           </variablelist>
 593         </listitem>
 594       </varlistentry>
 595       <varlistentry>
 596         <term><varname>Advertise=</varname></term>
 597         <listitem>
 598           <para>This sets what speeds and duplex modes of operation are advertised for auto-negotiation.
 599           This implies <literal>AutoNegotiation=yes</literal>. The supported values are:
 600
 601           <table>
 602             <title>Supported advertise values</title>
 603             <tgroup cols='3'>
 604               <colspec colname='Advertise' />
 605               <colspec colname='Speed' />
 606               <colspec colname='Duplex Mode' />
 607
 608               <thead><row>
 609                 <entry>Advertise</entry>
 610                 <entry>Speed (Mbps)</entry>
 611                 <entry>Duplex Mode</entry>
 612               </row></thead>
 613               <tbody>
 614                 <row><entry><option>10baset-half</option></entry>
 615                 <entry>10</entry><entry>half</entry></row>
 616
 617                 <row><entry><option>10baset-full</option></entry>
 618                 <entry>10</entry><entry>full</entry></row>
 619
 620                 <row><entry><option>100baset-half</option></entry>
 621                 <entry>100</entry><entry>half</entry></row>
 622
 623                 <row><entry><option>100baset-full</option></entry>
 624                 <entry>100</entry><entry>full</entry></row>
 625
 626                 <row><entry><option>1000baset-half</option></entry>
 627                 <entry>1000</entry><entry>half</entry></row>
 628
 629                 <row><entry><option>1000baset-full</option></entry>
 630                 <entry>1000</entry><entry>full</entry></row>
 631
 632                 <row><entry><option>10000baset-full</option></entry>
 633                 <entry>10000</entry><entry>full</entry></row>
 634
 635                 <row><entry><option>2500basex-full</option></entry>
 636                 <entry>2500</entry><entry>full</entry></row>
 637
 638                 <row><entry><option>1000basekx-full</option></entry>
 639                 <entry>1000</entry><entry>full</entry></row>
 640
 641                 <row><entry><option>10000basekx4-full</option></entry>
 642                 <entry>10000</entry><entry>full</entry></row>
 643
 644                 <row><entry><option>10000basekr-full</option></entry>
 645                 <entry>10000</entry><entry>full</entry></row>
 646
 647                 <row><entry><option>10000baser-fec</option></entry>
 648                 <entry>10000</entry><entry>full</entry></row>
 649
 650                 <row><entry><option>20000basemld2-full</option></entry>
 651                 <entry>20000</entry><entry>full</entry></row>
 652
 653                 <row><entry><option>20000basekr2-full</option></entry>
 654                 <entry>20000</entry><entry>full</entry></row>
 655               </tbody>
 656             </tgroup>
 657           </table>
 658
 659           By default this is unset, i.e. all possible modes will be advertised.
 660           This option may be specified more than once, in which case all specified speeds and modes are advertised.
 661           If the empty string is assigned to this option, the list is reset, and all prior assignments have no effect.
 662           </para>
 663         </listitem>
 664       </varlistentry>
 665       <varlistentry>
 666         <term><varname>ReceiveChecksumOffload=</varname></term>
 667         <listitem>
 668           <para>Takes a boolean. If set to true, the hardware offload for checksumming of ingress
 669           network packets is enabled. When unset, the kernel's default will be used.</para>
 670         </listitem>
 671       </varlistentry>
 672       <varlistentry>
 673         <term><varname>TransmitChecksumOffload=</varname></term>
 674         <listitem>
 675           <para>Takes a boolean. If set to true, the hardware offload for checksumming of egress
 676           network packets is enabled. When unset, the kernel's default will be used.</para>
 677         </listitem>
 678       </varlistentry>
 679       <varlistentry>
 680         <term><varname>TCPSegmentationOffload=</varname></term>
 681         <listitem>
 682           <para>Takes a boolean. If set to true, the TCP Segmentation Offload (TSO) is enabled.
 683           When unset, the kernel's default will be used.</para>
 684         </listitem>
 685       </varlistentry>
 686        <varlistentry>
 687       <term><varname>TCP6SegmentationOffload=</varname></term>
 688         <listitem>
 689           <para>Takes a boolean. If set to true, the TCP6 Segmentation Offload (tx-tcp6-segmentation) is enabled.
 690           When unset, the kernel's default will be used.</para>
 691         </listitem>
 692       </varlistentry>
 693       <varlistentry>
 694         <term><varname>GenericSegmentationOffload=</varname></term>
 695         <listitem>
 696           <para>Takes a boolean. If set to true, the Generic Segmentation Offload (GSO) is enabled.
 697           When unset, the kernel's default will be used.</para>
 698         </listitem>
 699       </varlistentry>
 700       <varlistentry>
 701         <term><varname>GenericReceiveOffload=</varname></term>
 702         <listitem>
 703           <para>Takes a boolean. If set to true, the Generic Receive Offload (GRO) is enabled.
 704           When unset, the kernel's default will be used.</para>
 705         </listitem>
 706       </varlistentry>
 707       <varlistentry>
 708         <term><varname>LargeReceiveOffload=</varname></term>
 709         <listitem>
 710           <para>Takes a boolean. If set to true, the Large Receive Offload (LRO) is enabled.
 711           When unset, the kernel's default will be used.</para>
 712         </listitem>
 713       </varlistentry>
 714       <varlistentry>
 715         <term><varname>RxChannels=</varname></term>
 716         <listitem>
 717           <para>Sets the number of receive channels (a number between 1 and 4294967295) .</para>
 718         </listitem>
 719       </varlistentry>
 720       <varlistentry>
 721         <term><varname>TxChannels=</varname></term>
 722         <listitem>
 723           <para>Sets the number of transmit channels (a number between 1 and 4294967295).</para>
 724         </listitem>
 725       </varlistentry>
 726       <varlistentry>
 727         <term><varname>OtherChannels=</varname></term>
 728         <listitem>
 729           <para>Sets the number of other channels (a number between 1 and 4294967295).</para>
 730         </listitem>
 731       </varlistentry>
 732       <varlistentry>
 733         <term><varname>CombinedChannels=</varname></term>
 734         <listitem>
 735           <para>Sets the number of combined set channels (a number between 1 and 4294967295).</para>
 736         </listitem>
 737       </varlistentry>
 738       <varlistentry>
 739         <term><varname>RxBufferSize=</varname></term>
 740         <listitem>
 741           <para>Takes an integer. Specifies the maximum number of pending packets in the NIC receive buffer.
 742           When unset, the kernel's default will be used.</para>
 743         </listitem>
 744       </varlistentry>
 745       <varlistentry>
 746         <term><varname>RxMiniBufferSize=</varname></term>
 747         <listitem>
 748           <para>Takes an integer. Specifies the maximum number of pending packets in the NIC mini receive buffer.
 749           When unset, the kernel's default will be used.</para>
 750         </listitem>
 751       </varlistentry>
 752       <varlistentry>
 753         <term><varname>RxJumboBufferSize=</varname></term>
 754         <listitem>
 755           <para>Takes an integer. Specifies the maximum number of pending packets in the NIC jumbo receive buffer.
 756           When unset, the kernel's default will be used.</para>
 757         </listitem>
 758       </varlistentry>
 759       <varlistentry>
 760         <term><varname>TxBufferSize=</varname></term>
 761         <listitem>
 762           <para>Takes an integer. Specifies the maximum number of pending packets in the NIC transmit buffer.
 763           When unset, the kernel's default will be used.</para>
 764         </listitem>
 765       </varlistentry>
 766       <varlistentry>
 767         <term><varname>RxFlowControl=</varname></term>
 768         <listitem>
 769           <para>Takes a boolean. When set, enables the receive flow control, also known as the ethernet
 770           receive PAUSE message (generate and send ethernet PAUSE frames). When unset, the kernel's
 771           default will be used.</para>
 772         </listitem>
 773       </varlistentry>
 774       <varlistentry>
 775         <term><varname>TxFlowControl=</varname></term>
 776         <listitem>
 777           <para>Takes a boolean. When set, enables the transmit flow control, also known as the ethernet
 778           transmit PAUSE message (respond to received ethernet PAUSE frames). When unset, the kernel's
 779           default will be used.</para>
 780         </listitem>
 781       </varlistentry>
 782       <varlistentry>
 783         <term><varname>AutoNegotiationFlowControl=</varname></term>
 784         <listitem>
 785           <para>Takes a boolean. When set, the auto negotiation enables the interface to exchange state
 786           advertisements with the connected peer so that the two devices can agree on the ethernet
 787           PAUSE configuration. When unset, the kernel's default will be used.</para>
 788         </listitem>
 789       </varlistentry>
 790       <varlistentry>
 791         <term><varname>GenericSegmentOffloadMaxBytes=</varname></term>
 792         <listitem>
 793           <para>Specifies the maximum size of a Generic Segment Offload (GSO) packet the
 794           device should accept. The usual suffixes K, M, G, are supported and are
 795           understood to the base of 1024. An unsigned integer in the range 1…65536.
 796           Defaults to unset.</para>
 797         </listitem>
 798       </varlistentry>
 799       <varlistentry>
 800         <term><varname>GenericSegmentOffloadMaxSegments=</varname></term>
 801         <listitem>
 802           <para>Specifies the maximum number of a Generic Segment Offload (GSO) segments the device should
 803           accept.  An unsigned integer in the range 1…65535. Defaults to unset.</para>
 804         </listitem>
 805       </varlistentry>
 806
 807     </variablelist>
 808   </refsect1>
 809
 810   <refsect1>
 811     <title>Examples</title>
 812
 813     <example>
 814       <title>/usr/lib/systemd/network/99-default.link</title>
 815
 816       <para>The link file <filename>99-default.link</filename> that is
 817       shipped with systemd defines the default naming policy for
 818       links.</para>
 819
 820       <programlisting>[Link]
 821 NamePolicy=kernel database onboard slot path
 822 MACAddressPolicy=persistent</programlisting>
 823     </example>
 824
 825     <example>
 826       <title>/etc/systemd/network/10-dmz.link</title>
 827
 828       <para>This example assigns the fixed name <literal>dmz0</literal> to the interface with the MAC address
 829       00:a0:de:63:7a:e6:</para>
 830
 831       <programlisting>[Match]
 832 MACAddress=00:a0:de:63:7a:e6
 833
 834 [Link]
 835 Name=dmz0</programlisting>
 836
 837       <para><varname>NamePolicy=</varname> is not set, so <varname>Name=</varname> takes effect. We use the
 838       <literal>10-</literal> prefix to order this file early in the list. Note that it needs to be before
 839       <literal>99-link</literal>, i.e. it needs a numerical prefix, to have any effect at all.</para>
 840     </example>
 841
 842     <example>
 843       <title>Debugging <varname>NamePolicy=</varname> assignments</title>
 844
 845       <programlisting>$ sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/hub0
 846 …
 847 Parsed configuration file /usr/lib/systemd/network/99-default.link
 848 Parsed configuration file /etc/systemd/network/10-eth0.link
 849 ID_NET_DRIVER=cdc_ether
 850 Config file /etc/systemd/network/10-eth0.link applies to device hub0
 851 link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
 852 hub0: Device has name_assign_type=4
 853 Using default interface naming scheme 'v240'.
 854 hub0: Policies didn't yield a name, using specified Name=hub0.
 855 ID_NET_LINK_FILE=/etc/systemd/network/10-eth0.link
 856 ID_NET_NAME=hub0
 857 …</programlisting>
 858
 859      <para>Explicit <varname>Name=</varname> configuration wins in this case.</para>
 860
 861      <programlisting>sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/enp0s31f6
 862 …
 863 Parsed configuration file /usr/lib/systemd/network/99-default.link
 864 Parsed configuration file /etc/systemd/network/10-eth0.link
 865 Created link configuration context.
 866 ID_NET_DRIVER=e1000e
 867 Config file /usr/lib/systemd/network/99-default.link applies to device enp0s31f6
 868 link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
 869 enp0s31f6: Device has name_assign_type=4
 870 Using default interface naming scheme 'v240'.
 871 enp0s31f6: Policy *keep*: keeping existing userspace name
 872 enp0s31f6: Device has addr_assign_type=0
 873 enp0s31f6: MAC on the device already matches policy *persistent*
 874 ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
 875 …
 876 </programlisting>
 877
 878      <para>In this case, the interface was already renamed, so the <option>keep</option> policy specified as
 879      the first option in <filename index="false">99-default.link</filename> means that the existing name is
 880      preserved. If <option>keep</option> was removed, or if were in boot before the renaming has happened,
 881      we might get the following instead:</para>
 882
 883      <programlisting>enp0s31f6: Policy *path* yields "enp0s31f6".
 884 enp0s31f6: Device has addr_assign_type=0
 885 enp0s31f6: MAC on the device already matches policy *persistent*
 886 ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
 887 ID_NET_NAME=enp0s31f6
 888 …
 889 </programlisting>
 890
 891       <para>Please note that the details of output are subject to change.</para>
 892     </example>
 893
 894     <example>
 895       <title>/etc/systemd/network/10-internet.link</title>
 896
 897       <para>This example assigns the fixed name
 898       <literal>internet0</literal> to the interface with the device
 899       path <literal>pci-0000:00:1a.0-*</literal>:</para>
 900
 901       <programlisting>[Match]
 902 Path=pci-0000:00:1a.0-*
 903
 904 [Link]
 905 Name=internet0</programlisting>
 906     </example>
 907
 908     <example>
 909       <title>/etc/systemd/network/25-wireless.link</title>
 910
 911       <para>Here's an overly complex example that shows the use of a large number of [Match] and [Link] settings.</para>
 912
 913       <programlisting>[Match]
 914 MACAddress=12:34:56:78:9a:bc
 915 Driver=brcmsmac
 916 Path=pci-0000:02:00.0-*
 917 Type=wlan
 918 Virtualization=no
 919 Host=my-laptop
 920 Architecture=x86-64
 921
 922 [Link]
 923 Name=wireless0
 924 MTUBytes=1450
 925 BitsPerSecond=10M
 926 WakeOnLan=magic
 927 MACAddress=cb:a9:87:65:43:21</programlisting>
 928     </example>
 929   </refsect1>
 930
 931   <refsect1>
 932     <title>See Also</title>
 933     <para>
 934       <citerefentry>
 935         <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
 936       </citerefentry>,
 937       <citerefentry>
 938         <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
 939       </citerefentry>,
 940       <citerefentry>
 941         <refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum>
 942       </citerefentry>,
 943       <citerefentry>
 944         <refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum>
 945       </citerefentry>
 946     </para>
 947   </refsect1>
 948
 949 </refentry>