.\" -*- nroff -*- .\" macros .de EX \" Begin Example . IP . ft CW . nf . ne \\$1 .. .de EE \" End Example . ft P . fi . PP .. .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. .SH EXAMPLE The following example configures two network interfaces: eth0 is brought up at boot, and uses DHCP for IPv4 and SLAAC for IPv6, whereas eth1 is brought up whenever the network hardware is detected, and is configured with static IPv4 and IPv6 addresses. .EX auto eth0 allow-hotplug eth1 iface eth0 inet dhcp iface eth0 inet6 auto iface eth1 inet static address 192.168.1.2/24 gateway 192.168.1.1 iface eth1 inet6 static address fec0:0:0:1::2/64 gateway fec0:0:0:1::1 .EE .SH FILE FORMAT 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. These will be described in more detail in the following sections. .SH INTERFACE SELECTION 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 also used by the system boot scripts, so interfaces marked "auto" are brought up at boot time.) 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. (Interfaces marked "allow-hotplug" are brought up when udev detects them. This can either be during boot if the interface is already present, or at a later time, for example when plugging in a USB network card. Please note that this does not have anything to do with detecting a network cable being plugged in.) .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. .SH INCLUDING OTHER FILES 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. .SH MAPPINGS 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. .SH INTERFACE DEFINITIONS 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.) A list of packages providing additional options is mentioned in the section "OPTIONS PROVIDED BY OTHER PACKAGE". .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 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. .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