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.TH INTERFACES 5 "4 June 2016" "ifupdown" "File formats"
.SH NAME
/etc/network/interfaces \- network interface configuration for ifup and ifdown
.SH DESCRIPTION
/etc/network/interfaces contains network interface configuration
information for the
.BR ifup (8)
and
.BR ifdown (8)
commands.
This is where you configure how your system is connected to the network.
.P
Lines starting with `#' are ignored. Note that end-of-line comments are
NOT supported, comments must be on a line of their own.
.P
A line may be extended across multiple lines by making the last character
a backslash.
.P
The file consists of zero or more "iface", "mapping", "auto", "allow-",
"source" and "source-directory" stanzas. Here is an example:
.P
.EX
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
.EE
.P
Lines beginning with the word "auto" are used to identify the physical
interfaces to be brought up when
.B ifup
is run with the
.B \-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.
.B ifup
brings the named interfaces up in the order listed.
.P
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.
.P
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.
.P
Lines beginning with "no-scripts" are used to identify interfaces for which scripts in
.IR /etc/network/if\-*.d/
should not be run when those interfaces are brought up or down.
.P
Lines beginning with "source" are used to include stanzas from other files,
so configuration 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
.BR wordexp (3)
for details.)
.P
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: \fI^[a\-zA\-Z0\-9_\-]+$\fR. 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.
.P
When sourcing files or directories, if a path doesn't have a leading slash,
it's considered relative to the directory containing the file in which the
keyword is placed. In the example above, if the file is located at
.IR /etc/network/interfaces\fR,
paths to the included files are understood to be under
.IR /etc/network\fR.
.P
Currently, "source-directory" isn't supported by
.BR network-manager " and"
.BR guessnet .
.P
By default, on a freshly installed Debian system, the interfaces file includes a
line to source files in the
.IR /etc/network/interfaces.d
directory.
.P
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
.BR script
definition.  The named script is run with the physical interface name as
its argument and with the contents of all following "map" lines
(\fBwithout\fR 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
.IR /usr/share/doc/ifupdown/examples
for examples of what the script must print.
.P
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.
.P
.B ifup
is normally given a physical interface name as its first non\-option argument.
.B ifup
also uses this name as the initial logical name for the interface unless
it is accompanied by a  suffix of the form \fI=LOGICAL\fR, in which case
ifup chooses \fILOGICAL\fR as the initial logical 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
.B ifup
attempts to bring up the physical interface
as that logical interface.  Otherwise
.B ifup
exits with an error.
.P
Stanzas defining logical interfaces start with a line consisting of the
word "iface" followed 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
.B 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.
.P
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
.BR iwconfig (8) .
(See
.BR wireless (7)
for details.)
.P
Options are usually indented for clarity (as in the example above)
but are not required to be.
.P
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 interface.
.P
.SH INTERFACE TEMPLATES
It is possible to define interface definition templates and extend
them using the
.B inherits
keyword:
.P
.EX
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
.EE
.P
This may be useful to separate link-level settings shared by multiple
interfaces from, for example, IP address settings specific to every
interface.
.P
.SH VLAN AND BRIDGE INTERFACES
To ease the configuration of VLAN interfaces, interfaces having
.B .
(full stop character) in the name are configured as 802.1q tagged
virtual LAN interface. For example, interface
.B eth0.1
is a virtual interface having
.B eth0
as physical link, with VLAN ID 1.
.P
For compatibility with
.B bridge-utils
package, if
.B bridge_ports
option is specified, VLAN interface configuration is
.B not
performed.
.SH 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".)
.TP
.BI pre\-up " command"
Run
.I command
before bringing the interface up.
If this command fails then
.B ifup
aborts,
refraining from marking the interface as configured,
prints an error message,
and exits with status 0.
This behavior may change in the future.
.TP
.BI up " command"
.TP
.BI post\-up " command"
Run
.I command
after bringing the interface up.
If this command fails then
.B 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.
.TP
.BI down " command"
.TP
.BI pre\-down " command"
Run
.I command
before taking the interface down.
If this command fails then
.B 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.
.TP
.BI post\-down " command"
Run
.I command
after taking the interface down.
If this command fails then
.B ifdown
aborts,
marks the interface as deconfigured,
and exits with status 0.
This behavior may change in the future.
.TP
.BI description " name"
Alias interface by
.I name
.P
There exists for each of the above mentioned options a directory
.IR /etc/network/if\-\fB<option>\fI.d/
the scripts in which are run (with no arguments) using
.BR run\-parts (8)
after the option itself has been processed. Please note that as
.BI post\-up
and
.BI pre\-down
are aliases, no files in the corresponding directories are processed.
Please use
.IR if-up.d
and
.IR if-down.d
directories instead.
.P
All of these commands have access to the following environment variables.
.TP
.B IFACE
The physical name of the interface being processed, or "--all" (see below).
.TP
.B LOGICAL
The logical name of the interface being processed, or "auto" (see below).
.TP
.B ADDRFAM
The address family of the interface, or "meta" (see below).
.TP
.B METHOD
The method of the interface (e.g.,
.IR static ),
or "none" (see below).
.TP
.B MODE
.IR start " if run from ifup, " stop " if run from ifdown".
.TP
.B PHASE
As per MODE, but with finer granularity, distinguishing the
\fIpre-up\fR, \fIpost-up\fR, \fIpre-down\fR and \fIpost-down\fR phases.
.TP
.B VERBOSITY
Indicates whether \fB\-\-verbose\fR was used; set to 1 if so, 0 if not.
.TP
.B PATH
The command search path:
.I /usr/local/sbin:\%/usr/local/bin:\%/usr/sbin:\%/usr/bin:\%/sbin:\%/bin
.P
Additionally, all options given in an interface definition stanza are
exported to the environment in upper case with "IF_" prepended and with
hyphens converted to underscores and non\-alphanumeric characters discarded.
.P
When ifupdown is being called with the \fB\-\-all\fR option, before doing anything
to interfaces, if calls all the hook scripts (\fIpre-up\fR or \fIdown\fR) with
\fBIFACE\fR set to "\-\-all", \fBLOGICAL\fR set to the current value of \-\-allow
parameter (or "auto" if it's not set), \fBADDRFAM\fR="meta" and \fBMETHOD\fR="none".
After all the interfaces have been brought up or taken down, the appropriate scripts
(\fIup\fR or \fIpost-down\fR) are executed.
.SH OPTIONS PROVIDED BY OTHER PACKAGES
This manual page documents the configuration options provided by the ifupdown package.
However, other packages can make other options available for use in /etc/network/interfaces.
Here is a list of packages that provide such extensions:
.P
arping, avahi-autoipd, avahi-daemon, bind9, bridge-utils, clamav-freshclam, controlaula, epoptes-client, ethtool, guidedog, hostap-utils, hostapd, htpdate, ifenslave, ifmetric, ifupdown-extra, ifupdown-multi, ifupdown-scripts-zg2, initscripts, isatapd, linux-wlan-ng, lprng, macchanger, miredo, nslcd, ntpdate, openntpd, openresolv, openssh-server, openvpn, openvswitch-switch, postfix, resolvconf, sendmail-base, shorewall-init, slrn, slrnpull, tinc, ucarp, uml-utilities, uruk, vde2, vlan, vzctl, whereami, wide-dhcpv6-client, wireless-tools, wpasupplicant.
.P
Please consult the documentation of those packages for information about how they extend ifupdown.
##ADDRESSFAM##
.SH KNOWN BUGS/LIMITATIONS
The
.B ifup
and
.B ifdown
programs work with so-called "physical" interface names.
These names are assigned to hardware by the kernel.
Unfortunately it can happen that the kernel assigns different
physical interface names to the same hardware at different
times; for example, what was called "eth0" last time you booted
is now called "eth1" and vice versa.
This creates a problem if you want to configure the interfaces
appropriately.
A way to deal with this problem is to use mapping scripts that
choose logical interface names according to the properties of
the interface hardware.
See the
.B get-mac-address.sh
script in the examples directory for an example of such a mapping
script.  See also Debian bug #101728.
.SH AUTHOR
The ifupdown suite was written by Anthony Towns <aj@azure.humbug.org.au>.
This manpage was contributed by Joey Hess <joey@kitenet.net>.
.SH "SEE ALSO"
.BR ifup (8),
.BR ip (8),
.BR ifconfig (8),
.BR run\-parts (8),
.BR resolvconf (8).
.P
For advice on configuring this package read the
.B Network Configuration
chapter of the \fIDebian Reference\fR manual,
available at
\fIhttp://www.debian.org/doc/manuals/debian-reference/ch05.en.html\fR
or in the \fBdebian-reference-en\fR package.
.P
Examples of how to set up interfaces can be found in
.BR /usr/share/doc/ifupdown/examples/network-interfaces.gz .