man/systemd.link.xml

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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 names with their values after equals sign
 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. Takes the special value
 496           <literal>off</literal> which disables Wake-on-LAN, or space separated list of the following
 497           words:</para>
 498
 499           <variablelist>
 500             <varlistentry>
 501               <term><option>phy</option></term>
 502               <listitem>
 503                 <para>Wake on PHY activity.</para>
 504               </listitem>
 505             </varlistentry>
 506             <varlistentry>
 507               <term><option>unicast</option></term>
 508               <listitem>
 509                 <para>Wake on unicast messages.</para>
 510               </listitem>
 511             </varlistentry>
 512             <varlistentry>
 513               <term><option>multicast</option></term>
 514               <listitem>
 515                 <para>Wake on multicast messages.</para>
 516               </listitem>
 517             </varlistentry>
 518             <varlistentry>
 519               <term><option>broadcast</option></term>
 520               <listitem>
 521                 <para>Wake on broadcast messages.</para>
 522               </listitem>
 523             </varlistentry>
 524             <varlistentry>
 525               <term><option>arp</option></term>
 526               <listitem>
 527                 <para>Wake on ARP.</para>
 528               </listitem>
 529             </varlistentry>
 530             <varlistentry>
 531               <term><option>magic</option></term>
 532               <listitem>
 533                 <para>Wake on receipt of a magic packet.
 534                 </para>
 535               </listitem>
 536             </varlistentry>
 537             <varlistentry>
 538               <term><option>secureon</option></term>
 539               <listitem>
 540                 <para>Enable secureon(tm) password for MagicPacket(tm).
 541                 </para>
 542               </listitem>
 543             </varlistentry>
 544           </variablelist>
 545
 546           <para>Defaults to unset, and the device's default will be used. This setting can be specified
 547           multiple times. If an empty string is assigned, then the all previous assignments are
 548           cleared.</para>
 549         </listitem>
 550       </varlistentry>
 551       <varlistentry>
 552         <term><varname>Port=</varname></term>
 553         <listitem>
 554           <para>The port option is used to select the device port. The
 555           supported values are:</para>
 556
 557           <variablelist>
 558             <varlistentry>
 559               <term><option>tp</option></term>
 560               <listitem>
 561                 <para>An Ethernet interface using Twisted-Pair cable as the medium.</para>
 562               </listitem>
 563             </varlistentry>
 564             <varlistentry>
 565               <term><option>aui</option></term>
 566               <listitem>
 567                 <para>Attachment Unit Interface (AUI). Normally used with hubs.
 568                 </para>
 569               </listitem>
 570             </varlistentry>
 571             <varlistentry>
 572               <term><option>bnc</option></term>
 573               <listitem>
 574                 <para>An Ethernet interface using BNC connectors and co-axial cable.</para>
 575               </listitem>
 576             </varlistentry>
 577             <varlistentry>
 578               <term><option>mii</option></term>
 579               <listitem>
 580                 <para>An Ethernet interface using a Media Independent Interface (MII).</para>
 581               </listitem>
 582             </varlistentry>
 583             <varlistentry>
 584               <term><option>fibre</option></term>
 585               <listitem>
 586                 <para>An Ethernet interface using Optical Fibre as the medium.</para>
 587               </listitem>
 588             </varlistentry>
 589           </variablelist>
 590         </listitem>
 591       </varlistentry>
 592       <varlistentry>
 593         <term><varname>Advertise=</varname></term>
 594         <listitem>
 595           <para>This sets what speeds and duplex modes of operation are advertised for auto-negotiation.
 596           This implies <literal>AutoNegotiation=yes</literal>. The supported values are:
 597
 598           <table>
 599             <title>Supported advertise values</title>
 600             <tgroup cols='3'>
 601               <colspec colname='Advertise' />
 602               <colspec colname='Speed' />
 603               <colspec colname='Duplex Mode' />
 604
 605               <thead><row>
 606                 <entry>Advertise</entry>
 607                 <entry>Speed (Mbps)</entry>
 608                 <entry>Duplex Mode</entry>
 609               </row></thead>
 610               <tbody>
 611                 <row><entry><option>10baset-half</option></entry>
 612                 <entry>10</entry><entry>half</entry></row>
 613
 614                 <row><entry><option>10baset-full</option></entry>
 615                 <entry>10</entry><entry>full</entry></row>
 616
 617                 <row><entry><option>100baset-half</option></entry>
 618                 <entry>100</entry><entry>half</entry></row>
 619
 620                 <row><entry><option>100baset-full</option></entry>
 621                 <entry>100</entry><entry>full</entry></row>
 622
 623                 <row><entry><option>1000baset-half</option></entry>
 624                 <entry>1000</entry><entry>half</entry></row>
 625
 626                 <row><entry><option>1000baset-full</option></entry>
 627                 <entry>1000</entry><entry>full</entry></row>
 628
 629                 <row><entry><option>10000baset-full</option></entry>
 630                 <entry>10000</entry><entry>full</entry></row>
 631
 632                 <row><entry><option>2500basex-full</option></entry>
 633                 <entry>2500</entry><entry>full</entry></row>
 634
 635                 <row><entry><option>1000basekx-full</option></entry>
 636                 <entry>1000</entry><entry>full</entry></row>
 637
 638                 <row><entry><option>10000basekx4-full</option></entry>
 639                 <entry>10000</entry><entry>full</entry></row>
 640
 641                 <row><entry><option>10000basekr-full</option></entry>
 642                 <entry>10000</entry><entry>full</entry></row>
 643
 644                 <row><entry><option>10000baser-fec</option></entry>
 645                 <entry>10000</entry><entry>full</entry></row>
 646
 647                 <row><entry><option>20000basemld2-full</option></entry>
 648                 <entry>20000</entry><entry>full</entry></row>
 649
 650                 <row><entry><option>20000basekr2-full</option></entry>
 651                 <entry>20000</entry><entry>full</entry></row>
 652               </tbody>
 653             </tgroup>
 654           </table>
 655
 656           By default this is unset, i.e. all possible modes will be advertised.
 657           This option may be specified more than once, in which case all specified speeds and modes are advertised.
 658           If the empty string is assigned to this option, the list is reset, and all prior assignments have no effect.
 659           </para>
 660         </listitem>
 661       </varlistentry>
 662       <varlistentry>
 663         <term><varname>ReceiveChecksumOffload=</varname></term>
 664         <listitem>
 665           <para>Takes a boolean. If set to true, hardware offload for checksumming of ingress
 666           network packets is enabled. When unset, the kernel's default will be used.</para>
 667         </listitem>
 668       </varlistentry>
 669       <varlistentry>
 670         <term><varname>TransmitChecksumOffload=</varname></term>
 671         <listitem>
 672           <para>Takes a boolean. If set to true, hardware offload for checksumming of egress
 673           network packets is enabled. When unset, the kernel's default will be used.</para>
 674         </listitem>
 675       </varlistentry>
 676       <varlistentry>
 677         <term><varname>TCPSegmentationOffload=</varname></term>
 678         <listitem>
 679           <para>Takes a boolean. If set to true, TCP Segmentation Offload (TSO) is enabled.
 680           When unset, the kernel's default will be used.</para>
 681         </listitem>
 682       </varlistentry>
 683        <varlistentry>
 684       <term><varname>TCP6SegmentationOffload=</varname></term>
 685         <listitem>
 686           <para>Takes a boolean. If set to true, TCP6 Segmentation Offload (tx-tcp6-segmentation) is enabled.
 687           When unset, the kernel's default will be used.</para>
 688         </listitem>
 689       </varlistentry>
 690       <varlistentry>
 691         <term><varname>GenericSegmentationOffload=</varname></term>
 692         <listitem>
 693           <para>Takes a boolean. If set to true, Generic Segmentation Offload (GSO) is enabled.
 694           When unset, the kernel's default will be used.</para>
 695         </listitem>
 696       </varlistentry>
 697       <varlistentry>
 698         <term><varname>GenericReceiveOffload=</varname></term>
 699         <listitem>
 700           <para>Takes a boolean. If set to true, Generic Receive Offload (GRO) is enabled.
 701           When unset, the kernel's default will be used.</para>
 702         </listitem>
 703       </varlistentry>
 704       <varlistentry>
 705         <term><varname>GenericReceiveOffloadHardware=</varname></term>
 706         <listitem>
 707           <para>Takes a boolean. If set to true, hardware accelerated Generic Receive Offload (GRO) is
 708           enabled. When unset, the kernel's default will be used.</para>
 709         </listitem>
 710       </varlistentry>
 711       <varlistentry>
 712         <term><varname>LargeReceiveOffload=</varname></term>
 713         <listitem>
 714           <para>Takes a boolean. If set to true, Large Receive Offload (LRO) is enabled.
 715           When unset, the kernel's default will be used.</para>
 716         </listitem>
 717       </varlistentry>
 718       <varlistentry>
 719         <term><varname>RxChannels=</varname></term>
 720         <term><varname>TxChannels=</varname></term>
 721         <term><varname>OtherChannels=</varname></term>
 722         <term><varname>CombinedChannels=</varname></term>
 723         <listitem>
 724           <para>Specifies the number of receive, transmit, other, or combined channels, respectively.
 725           Takes an unsigned integer in the range 1…4294967295 or <literal>max</literal>. If set to
 726           <literal>max</literal>, the advertised maximum value of the hardware will be used. When
 727           unset, the number will not be changed. Defaults to unset.</para>
 728         </listitem>
 729       </varlistentry>
 730       <varlistentry>
 731         <term><varname>RxBufferSize=</varname></term>
 732         <term><varname>RxMiniBufferSize=</varname></term>
 733         <term><varname>RxJumboBufferSize=</varname></term>
 734         <term><varname>TxBufferSize=</varname></term>
 735         <listitem>
 736           <para>Specifies the maximum number of pending packets in the NIC receive buffer, mini receive
 737           buffer, jumbo receive buffer, or transmit buffer, respectively. Takes an unsigned integer in
 738           the range 1…4294967295 or <literal>max</literal>. If set to <literal>max</literal>, the
 739           advertised maximum value of the hardware will be used. When unset, the number will not be
 740           changed. Defaults to unset.</para>
 741         </listitem>
 742       </varlistentry>
 743       <varlistentry>
 744         <term><varname>RxFlowControl=</varname></term>
 745         <listitem>
 746           <para>Takes a boolean. When set, enables receive flow control, also known as the ethernet
 747           receive PAUSE message (generate and send ethernet PAUSE frames). When unset, the kernel's
 748           default will be used.</para>
 749         </listitem>
 750       </varlistentry>
 751       <varlistentry>
 752         <term><varname>TxFlowControl=</varname></term>
 753         <listitem>
 754           <para>Takes a boolean. When set, enables transmit flow control, also known as the ethernet
 755           transmit PAUSE message (respond to received ethernet PAUSE frames). When unset, the kernel's
 756           default will be used.</para>
 757         </listitem>
 758       </varlistentry>
 759       <varlistentry>
 760         <term><varname>AutoNegotiationFlowControl=</varname></term>
 761         <listitem>
 762           <para>Takes a boolean. When set, auto negotiation enables the interface to exchange state
 763           advertisements with the connected peer so that the two devices can agree on the ethernet
 764           PAUSE configuration. When unset, the kernel's default will be used.</para>
 765         </listitem>
 766       </varlistentry>
 767       <varlistentry>
 768         <term><varname>GenericSegmentOffloadMaxBytes=</varname></term>
 769         <listitem>
 770           <para>Specifies the maximum size of a Generic Segment Offload (GSO) packet the
 771           device should accept. The usual suffixes K, M, G are supported and are
 772           understood to the base of 1024. An unsigned integer in the range 1…65536.
 773           Defaults to unset.</para>
 774         </listitem>
 775       </varlistentry>
 776       <varlistentry>
 777         <term><varname>GenericSegmentOffloadMaxSegments=</varname></term>
 778         <listitem>
 779           <para>Specifies the maximum number of Generic Segment Offload (GSO) segments the device should
 780           accept. An unsigned integer in the range 1…65535. Defaults to unset.</para>
 781         </listitem>
 782       </varlistentry>
 783       <varlistentry>
 784         <term><varname>UseAdaptiveRxCoalesce=</varname></term>
 785         <term><varname>UseAdaptiveTxCoalesce=</varname></term>
 786         <listitem>
 787           <para>Boolean properties that, when set, enable/disable adaptive Rx/Tx coalescing if the hardware
 788           supports it. When unset, the kernel's default will be used.</para>
 789         </listitem>
 790       </varlistentry>
 791       <varlistentry>
 792         <term><varname>RxCoalesceSec=</varname></term>
 793         <term><varname>RxCoalesceIrqSec=</varname></term>
 794         <term><varname>RxCoalesceLowSec=</varname></term>
 795         <term><varname>RxCoalesceHighSec=</varname></term>
 796         <term><varname>TxCoalesceSec=</varname></term>
 797         <term><varname>TxCoalesceIrqSec=</varname></term>
 798         <term><varname>TxCoalesceLowSec=</varname></term>
 799         <term><varname>TxCoalesceHighSec=</varname></term>
 800         <listitem>
 801           <para>These properties configure the delay before Rx/Tx interrupts are generated after a packet is
 802           sent/received. The <literal>Irq</literal> properties come into effect when the host is servicing an
 803           IRQ. The <literal>Low</literal> and <literal>High</literal> properties come into effect when the
 804           packet rate drops below the low packet rate threshold or exceeds the high packet rate threshold
 805           respectively if adaptive Rx/Tx coalescing is enabled. When unset, the kernel's defaults will be
 806           used.</para>
 807         </listitem>
 808       </varlistentry>
 809         <varlistentry>
 810         <term><varname>RxMaxCoalescedFrames=</varname></term>
 811         <term><varname>RxMaxCoalescedIrqFrames=</varname></term>
 812         <term><varname>RxMaxCoalescedLowFrames=</varname></term>
 813         <term><varname>RxMaxCoalescedHighFrames=</varname></term>
 814         <term><varname>TxMaxCoalescedFrames=</varname></term>
 815         <term><varname>TxMaxCoalescedIrqFrames=</varname></term>
 816         <term><varname>TxMaxCoalescedLowFrames=</varname></term>
 817         <term><varname>TxMaxCoalescedHighFrames=</varname></term>
 818         <listitem>
 819           <para>These properties configure the maximum number of frames that are sent/received before a Rx/Tx
 820           interrupt is generated. The <literal>Irq</literal> properties come into effect when the host is
 821           servicing an IRQ. The <literal>Low</literal> and <literal>High</literal> properties come into
 822           effect when the packet rate drops below the low packet rate threshold or exceeds the high packet
 823           rate threshold respectively if adaptive Rx/Tx coalescing is enabled. When unset, the kernel's
 824           defaults will be used.</para>
 825         </listitem>
 826       </varlistentry>
 827       <varlistentry>
 828         <term><varname>CoalescePacketRateLow=</varname></term>
 829         <term><varname>CoalescePacketRateHigh=</varname></term>
 830         <listitem>
 831           <para>These properties configure the low and high packet rate (expressed in packets per second)
 832           threshold respectively and are used to determine when the corresponding coalescing settings for low
 833           and high packet rates come into effect if adaptive Rx/Tx coalescing is enabled. If unset, the
 834           kernel's defaults will be used.</para>
 835         </listitem>
 836       </varlistentry>
 837       <varlistentry>
 838         <term><varname>CoalescePacketRateSampleIntervalSec=</varname></term>
 839         <listitem>
 840           <para>Configures how often to sample the packet rate used for adaptive Rx/Tx coalescing. This
 841           property cannot be zero. This lowest time granularity supported by this property is seconds.
 842           Partial seconds will be rounded up before being passed to the kernel. If unset, the kernel's
 843           default will be used.</para>
 844         </listitem>
 845       </varlistentry>
 846       <varlistentry>
 847         <term><varname>StatisticsBlockCoalesceSec=</varname></term>
 848         <listitem>
 849           <para>How long to delay driver in-memory statistics block updates. If the driver does not have an
 850           in-memory statistic block, this property is ignored. This property cannot be zero. If unset, the
 851           kernel's default will be used.</para>
 852         </listitem>
 853       </varlistentry>
 854
 855     </variablelist>
 856   </refsect1>
 857
 858   <refsect1>
 859     <title>Examples</title>
 860
 861     <example>
 862       <title>/usr/lib/systemd/network/99-default.link</title>
 863
 864       <para>The link file <filename>99-default.link</filename> that is
 865       shipped with systemd defines the default naming policy for
 866       links.</para>
 867
 868       <programlisting>[Link]
 869 NamePolicy=kernel database onboard slot path
 870 MACAddressPolicy=persistent</programlisting>
 871     </example>
 872
 873     <example>
 874       <title>/etc/systemd/network/10-dmz.link</title>
 875
 876       <para>This example assigns the fixed name <literal>dmz0</literal> to the interface with the MAC address
 877       00:a0:de:63:7a:e6:</para>
 878
 879       <programlisting>[Match]
 880 MACAddress=00:a0:de:63:7a:e6
 881
 882 [Link]
 883 Name=dmz0</programlisting>
 884
 885       <para><varname>NamePolicy=</varname> is not set, so <varname>Name=</varname> takes effect. We use the
 886       <literal>10-</literal> prefix to order this file early in the list. Note that it needs to be before
 887       <literal>99-link</literal>, i.e. it needs a numerical prefix, to have any effect at all.</para>
 888     </example>
 889
 890     <example>
 891       <title>Debugging <varname>NamePolicy=</varname> assignments</title>
 892
 893       <programlisting>$ sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/hub0
 894 …
 895 Parsed configuration file /usr/lib/systemd/network/99-default.link
 896 Parsed configuration file /etc/systemd/network/10-eth0.link
 897 ID_NET_DRIVER=cdc_ether
 898 Config file /etc/systemd/network/10-eth0.link applies to device hub0
 899 link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
 900 hub0: Device has name_assign_type=4
 901 Using default interface naming scheme 'v240'.
 902 hub0: Policies didn't yield a name, using specified Name=hub0.
 903 ID_NET_LINK_FILE=/etc/systemd/network/10-eth0.link
 904 ID_NET_NAME=hub0
 905 …</programlisting>
 906
 907      <para>Explicit <varname>Name=</varname> configuration wins in this case.</para>
 908
 909      <programlisting>sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/enp0s31f6
 910 …
 911 Parsed configuration file /usr/lib/systemd/network/99-default.link
 912 Parsed configuration file /etc/systemd/network/10-eth0.link
 913 Created link configuration context.
 914 ID_NET_DRIVER=e1000e
 915 Config file /usr/lib/systemd/network/99-default.link applies to device enp0s31f6
 916 link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
 917 enp0s31f6: Device has name_assign_type=4
 918 Using default interface naming scheme 'v240'.
 919 enp0s31f6: Policy *keep*: keeping existing userspace name
 920 enp0s31f6: Device has addr_assign_type=0
 921 enp0s31f6: MAC on the device already matches policy *persistent*
 922 ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
 923 …
 924 </programlisting>
 925
 926      <para>In this case, the interface was already renamed, so the <option>keep</option> policy specified as
 927      the first option in <filename index="false">99-default.link</filename> means that the existing name is
 928      preserved. If <option>keep</option> was removed, or if were in boot before the renaming has happened,
 929      we might get the following instead:</para>
 930
 931      <programlisting>enp0s31f6: Policy *path* yields "enp0s31f6".
 932 enp0s31f6: Device has addr_assign_type=0
 933 enp0s31f6: MAC on the device already matches policy *persistent*
 934 ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
 935 ID_NET_NAME=enp0s31f6
 936 …
 937 </programlisting>
 938
 939       <para>Please note that the details of output are subject to change.</para>
 940     </example>
 941
 942     <example>
 943       <title>/etc/systemd/network/10-internet.link</title>
 944
 945       <para>This example assigns the fixed name
 946       <literal>internet0</literal> to the interface with the device
 947       path <literal>pci-0000:00:1a.0-*</literal>:</para>
 948
 949       <programlisting>[Match]
 950 Path=pci-0000:00:1a.0-*
 951
 952 [Link]
 953 Name=internet0</programlisting>
 954     </example>
 955
 956     <example>
 957       <title>/etc/systemd/network/25-wireless.link</title>
 958
 959       <para>Here's an overly complex example that shows the use of a large number of [Match] and [Link] settings.</para>
 960
 961       <programlisting>[Match]
 962 MACAddress=12:34:56:78:9a:bc
 963 Driver=brcmsmac
 964 Path=pci-0000:02:00.0-*
 965 Type=wlan
 966 Virtualization=no
 967 Host=my-laptop
 968 Architecture=x86-64
 969
 970 [Link]
 971 Name=wireless0
 972 MTUBytes=1450
 973 BitsPerSecond=10M
 974 WakeOnLan=magic
 975 MACAddress=cb:a9:87:65:43:21</programlisting>
 976     </example>
 977   </refsect1>
 978
 979   <refsect1>
 980     <title>See Also</title>
 981     <para>
 982       <citerefentry>
 983         <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
 984       </citerefentry>,
 985       <citerefentry>
 986         <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
 987       </citerefentry>,
 988       <citerefentry>
 989         <refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum>
 990       </citerefentry>,
 991       <citerefentry>
 992         <refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum>
 993       </citerefentry>
 994     </para>
 995   </refsect1>
 996
 997 </refentry>