parse interface configuration
Enable interface eth0
Enable all the interfaces defined with "auto" in /etc/network/interfaces
ifup [-nv] [--no-act] [--verbose] [-i FILE|--interfaces=FILE] [--state- dir=DIR] [--allow CLASS] -a|IFACE... ifup -h|--help ifup -V|--version ifdown [-nv] [--no-act] [--verbose] [-i FILE|--interfaces=FILE] [--state-dir=DIR] [--allow CLASS] -a|IFACE... ifquery [-nv] [--verbose] [-i FILE|--interfaces=FILE] [--state-dir=DIR] [--allow CLASS] IFACE... ifquery -l|--list [-nv] [--verbose] [-i FILE|--interfaces=FILE] [--state-dir=DIR] [--allow CLASS] [-a|IFACE...] ifquery --state [--state-dir=DIR] [--allow CLASS] [-a|IFACE...]
The ifup and ifdown commands may be used to configure (or, respec‐ tively, deconfigure) network interfaces based on interface definitions in the file /etc/network/interfaces. ifquery command may be used to parse interfaces configuration.
A summary of options is included below. -a, --all If given to ifup, affect all interfaces marked auto. Interfaces are brought up in the order in which they are defined in /etc/network/interfaces. Combined with --allow, acts on all in‐ terfaces of a specified class instead. If given to ifdown, af‐ fect all defined interfaces. Interfaces are brought down in the order in which they are currently listed in the state file. Only interfaces defined in /etc/network/interfaces will be brought down. --force Force configuration or deconfiguration of the interface. --ignore-errors If any of the commands of scripts fails, continue. -h, --help Show summary of options. --allow=CLASS Only allow interfaces listed in an allow-CLASS line in /etc/net‐ work/interfaces to be acted upon. -i FILE, --interfaces=FILE Read interface definitions from FILE instead of from /etc/net‐ work/interfaces. --state-dir=DIR Keep interface state in DIR instead of in /run/network. -X PATTERN, --exclude=PATTERN Exclude interfaces from the list of interfaces to operate on by the PATTERN. PATTERN uses a usual shell glob syntax. If shell wildcards are not used, it must match the exact interface name. This option may be specified multiple times resulting in more than one pattern being excluded. -o OPTION=VALUE Set OPTION to VALUE as though it were in /etc/network/inter‐ faces. -n, --no-act Don't configure any interfaces or run any "up" or "down" com‐ mands. --no-mappings Don't run any mappings. See interfaces(5) for more information about the mapping feature. --no-scripts Don't run any scripts under /etc/network/if-*.d/ --no-loopback Disable special handling of the loopback interface. By default, the loopback interface (lo on Linux) is predefined internally as an auto interface, so it's brought up on ifup -a automatically. In the case the loopback device is redefined by user, the inter‐ face is configured just once anyway. If, however, another inter‐ face is also defined as loopback, it's configured as usual. Specifying this option disables this behaviour, so the loopback interface won't be configured automatically. -V, --version Show copyright and version information. -v, --verbose Show commands as they are executed. -l, --list For ifquery, list all the interfaces which match the specified class. If no class specified, prints all the interfaces listed as auto. --state For ifquery, dump the state of the interfaces. When no inter‐ faces specified, lists all interfaces brought up together with logical interfaces assigned to them and exits with a status code indicating success. If one or more interfaces specified, display state of these interfaces only; successful code is returned if all of interfaces given as arguments are up. Otherwise, 0 is re‐ turned.
ifup -a Bring up all the interfaces defined with auto in /etc/net‐ work/interfaces ifup eth0 Bring up interface eth0 ifup eth0=home Bring up interface eth0 as logical interface home ifdown -a Bring down all interfaces that are currently up. ifquery -l Print names of all interfaces specified with the auto keyword. ifquery -l --allow=hotplug Print names of all interfaces specified with the allow-hotplug keyword. ifquery eth0 Display the interface options as specified in the ifupdown con‐ figuration. Each key-value pair is printed out on individual line using ": " as separator.
ifup, ifdown, and ifquery are actually the same program called by dif‐ ferent names. The program does not configure network interfaces directly; it runs low level utilities such as ip to do its dirty work. When invoked, ifdown checks if ifup is still running. In that case, SIGTERM is sent to ifup. During interface deconfiguration, ifdown ignores errors the same way as if --ignore-errors was specified.
/etc/network/interfaces definitions of network interfaces See interfaces(5) for more in‐ formation. /run/network/ifstate current state of network interfaces
Ifupdown uses per-interface locking to ensure that concurrent ifup and ifdown calls to the same interface are run in serial. However, calls to different interfaces will be able to run in parallel.
For ifup and ifdown, the exit status will be 0 if the given inter‐ face(s) have all been (de)configured successfully, 1 if there was any error. The result of these commands is idempotent; running ifup on an interface that is already up will result in an exit status of 0, and similarly running ifdown on an interface that is not up will also re‐ sult in an exit status of 0. ifquery will normally return with exit status 0 if an interface with a matching iface stanza, 1 if there is no matching stanza. ifquery --state will also return with exit status 1 if the given interface was known but was not up.
The program keeps records of whether network interfaces are up or down. Under exceptional circumstances these records can become inconsistent with the real states of the interfaces. For example, an interface that was brought up using ifup and later deconfigured using ifconfig will still be recorded as up. To fix this you can use the --force option to force ifup or ifdown to run configuration or deconfiguration commands despite what it considers the current state of the interface to be. The file /run/network/ifstate must be writable for ifup or ifdown to work properly. If that location is not writable (for example, because the root filesystem is mounted read-only for system recovery) then /run/network/ifstate should be made a symbolic link to a writable loca‐ tion. If that is not possible then you can use the --force option to run configuration or deconfiguration commands without updating the file. Note that the program does not run automatically: ifup alone does not bring up interfaces that appear as a result of hardware being installed and ifdown alone does not bring down interfaces that disappear as a re‐ sult of hardware being removed. To automate the configuration of net‐ work interfaces you need to install other packages such as udev(7) or ifplugd(8).
The ifupdown suite was created by Anthony Towns