ifup - bring a network interface up

ifdown - take a network interface down

ifup [-nv] [--no-act] [--verbose] [-i FILE|--interfaces=FILE] [--allow CLASS] -a|IFACE...

ifup -h|--help

ifup -V|--version

ifdown [-nv] [--no-act] [--verbose] [-i FILE|--interfaces=FILE] [--allow CLASS] -a|IFACE...

The ifup and ifdown commands may be used to configure (or, respectively, deconfigure) network interfaces based on interface definitions in the file /etc/network/interfaces.

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. If given to ifdown, affect 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.

-h, --help

Show summary of options.

--allow=CLASS

Only allow interfaces listed in an allow-CLASS line in /etc/network/interfaces to be acted upon.

-i FILE, --interfaces=FILE

Read interface definitions from FILE instead of from /etc/network/interfaces.

-n, --no-act

Don't configure any interfaces or run any "up" or "down" commands.

--no-mappings

Don't run any mappings. See interfaces(5) for more information about the mapping feature.

-V, --version

Show copyright and version information.

-v, --verbose

Show commands as they are executed.

ifup -a

Bring up all the interfaces defined with auto in /etc/network/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.

ifup and ifdown are actually the same program called by different names.

The program does not configure network interfaces directly; it runs low level utilities such as ifconfig and route to do its dirty work.

/etc/network/interfaces

definitions of network interfaces See interfaces(5) for more information.

/var/run/network/ifstate

current state of network interfaces

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 /var/run/network/ifstate must be writable for ifup or ifdown to work properly. On Ubuntu the /var/run location is a temporary filesystem which is always writable and thrown away on shutdown. You can also 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 result of hardware being removed. To automate the configuration of network interfaces you need to install other packages such as hotplug(8) or ifplugd(8).

The ifupdown suite was written by Anthony Towns <aj@azure.humbug.org.au>.

interfaces(5), ifconfig(8).