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INTERFACES(5)                              File formats                             INTERFACES(5)

NAME
       /etc/network/interfaces - network interface configuration for ifup and ifdown

DESCRIPTION
       /etc/network/interfaces  contains  network  interface  configuration  information  for the
       ifup(8) and ifdown(8) commands.  This is where you configure how your system is  connected
       to the network.

       Lines  starting  with  `#'  are ignored. Note that end-of-line comments are NOT supported,
       comments must be on a line of their own.

       A line may be extended across multiple lines by making the last character a backslash.

       The file consists of zero or more  "iface",  "mapping",  "auto",  "allow-",  "source"  and
       "source-directory" stanzas. Here is an example:

       auto eth0
       allow-hotplug eth1

       source interfaces.d/machine-dependent

       source-directory interfaces.d

       iface eth0 inet dhcp

       iface eth0 inet6 auto

       mapping eth1
            script /usr/local/sbin/map-scheme
            map HOME eth0-home
            map WORK eth0-work

       iface eth1-home inet static
            address 192.168.1.2/24
            gateway 192.168.1.1
            up flush-mail

       iface eth1-work inet dhcp

       Lines  beginning  with  the word "auto" are used to identify the physical interfaces to be
       brought up when ifup is run with the -a option.  (This option is used by the  system  boot
       scripts.)  Physical interface names should follow the word "auto" on the same line.  There
       can be multiple "auto" stanzas.  ifup brings the named interfaces up in the order listed.

       Lines beginning with "allow-" are used to identify interfaces that should  be  brought  up
       automatically  by  various  subsytems.  This  may  be  done  using a command such as "ifup
       --allow=hotplug eth0 eth1", which will only bring up eth0 or eth1 if it is  listed  in  an
       "allow-hotplug" line. Note that "allow-auto" and "auto" are synonyms.

       Lines  beginning  with  "no-auto-down"  are used to identify interfaces that should not be
       brought down by the command "ifdown -a". Its main use is  to  prevent  an  interface  from
       being  brought  down  during system shutdown time, for example if the root filesystem is a
       network filesystem and the interface should stay up until the very end. Note that you  can
       still bring down the interface by specifying the interface name explicitly.

       Lines  beginning  with  "no-scripts"  are used to identify interfaces for which scripts in
       /etc/network/if-*.d/ should not be run when those interfaces are brought up or down.

       Lines beginning with "source" are used to include stanzas from other files, so  configura‐
       tion can be split into many files. The word "source" is followed by the path of file to be
       sourced. Shell wildcards can be used.  (See wordexp(3) for details.)

       Similarly, "source-directory" keyword is used to source multiple files  at  once,  without
       specifying  them  individually or using shell globs. Additionally, when "source-directory"
       is used, names of the files  are  checked  to  match  the  following  regular  expression:
       ^[a-zA-Z0-9_-]+$.  In  other  words,  the  names must consist entirely of ASCII upper- and
       lower-case letters, ASCII digits, ASCII  underscores,  and  ASCII  minus-hyphens.  In  the
       directory path, shell wildcards may be used as well.

       When  sourcing  files or directories, if a path doesn't have a leading slash, it's consid‐
       ered relative to the directory containing the file in which the keyword is placed. In  the
       example  above,  if  the file is located at /etc/network/interfaces, paths to the included
       files are understood to be under /etc/network.

       Currently, "source-directory" isn't supported by network-manager and guessnet.

       By default, on a freshly installed Debian system, the interfaces file includes a  line  to
       source files in the /etc/network/interfaces.d directory.

       Stanzas  beginning  with  the word "mapping" are used to determine how a logical interface
       name is chosen for a physical interface that is to be brought up.  The  first  line  of  a
       mapping  stanza consists of the word "mapping" followed by a pattern in shell glob syntax.
       Each mapping stanza must contain a script definition.  The named script is  run  with  the
       physical interface name as its argument and with the contents of all following "map" lines
       (without the leading "map") in the stanza provided to it on its standard input. The script
       must  print  a  string  on  its  standard  output before exiting. See /usr/share/doc/ifup‐
       down/examples for examples of what the script must print.

       Mapping a name consists of searching the remaining mapping patterns and running the script
       corresponding  to  the  first  match; the script outputs the name to which the original is
       mapped.

       ifup is normally given a physical interface name as its first non-option  argument.   ifup
       also uses this name as the initial logical name for the interface unless it is accompanied
       by a  suffix of the form =LOGICAL, in which case ifup chooses LOGICAL as the initial logi‐
       cal  name for the interface.  It then maps this name, possibly more than once according to
       successive mapping specifications,  until  no  further  mappings  are  possible.   If  the
       resulting  name  is the name of some defined logical interface then ifup attempts to bring
       up the physical interface as that logical interface.  Otherwise ifup exits with an error.

       Stanzas defining logical interfaces start with a line consisting of the word "iface"  fol‐
       lowed  by  the  name  of  the logical interface.  In simple configurations without mapping
       stanzas this name should simply be the name of the physical interface to which it is to be
       applied.   (The  default  mapping  script is, in effect, the echo command.)  The interface
       name is followed by the name of the address family that the interface uses.  This will  be
       "inet"  for  TCP/IP networking, but there is also some support for IPX networking ("ipx"),
       and IPv6 networking ("inet6").  Following that is the name of the method used to configure
       the interface.

       Additional  options  can  be  given  on subsequent lines in the stanza.  Which options are
       available depends on the family and method, as described below.  Additional options can be
       made  available  by  other Debian packages.  For example, the wireless-tools package makes
       available a number of options prefixed with "wireless-" which can be used to configure the
       interface using iwconfig(8).  (See wireless(7) for details.)

       Options are usually indented for clarity (as in the example above) but are not required to
       be.

       Multiple "iface" stanzas can be given for the same interface, in which  case  all  of  the
       configured  addresses and options for that interface will be applied when bringing up that
       interface.  This is useful to configure both IPv4 and IPv6 addresses on the same interface
       (although  if no inet6 stanza is present, the kernel will normally still perform stateless
       address autoconfiguration if there is an IPv6 route advertisement daemon on the  network).
       It  can  also  be used to configure multiple addresses of the same type on a single inter‐
       face.

INTERFACE TEMPLATES
       It is possible to define interface definition templates and extend them using the inherits
       keyword:

       iface ethernet inet static
            mtu 1500
            hwaddress 11:22:33:44:55:66

       iface eth0 inet static inherits ethernet
            address 192.168.1.2/24

       This may be useful to separate link-level settings shared by multiple interfaces from, for
       example, IP address settings specific to every interface.

VLAN AND BRIDGE INTERFACES
       To ease the configuration of VLAN interfaces, interfaces having .  (full  stop  character)
       in  the name are configured as 802.1q tagged virtual LAN interface. For example, interface
       eth0.1 is a virtual interface having eth0 as physical link, with VLAN ID 1.

       For compatibility with bridge-utils package, if bridge_ports  option  is  specified,  VLAN
       interface configuration is not performed.

IFACE OPTIONS
       The  following "command" options are available for every family and method.  Each of these
       options can be given multiple times in a single stanza, in which  case  the  commands  are
       executed in the order in which they appear in the stanza.  (You can ensure a command never
       fails by suffixing them with "|| true".)

       pre-up command
              Run command before bringing the interface up.  If  this  command  fails  then  ifup
              aborts,  refraining  from marking the interface as configured, prints an error mes‐
              sage, and exits with status 0.  This behavior may change in the future.

       up command

       post-up command
              Run command after bringing the interface up.   If  this  command  fails  then  ifup
              aborts,  refraining  from  marking  the interface as configured (even though it has
              really been configured), prints an error message, and exits with  status  0.   This
              behavior may change in the future.

       down command

       pre-down command
              Run  command  before  taking the interface down.  If this command fails then ifdown
              aborts, marks the interface as deconfigured (even though it  has  not  really  been
              deconfigured), and exits with status 0.  This behavior may change in the future.

       post-down command
              Run  command  after  taking  the interface down.  If this command fails then ifdown
              aborts, marks the interface as deconfigured, and exits with status 0.  This  behav‐
              ior may change in the future.

       There   exists   for   each   of   the  above  mentioned  options  a  directory  /etc/net‐
       work/if-

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