ifup − bring a network interface up
ifdown − take a network interface down
ifup [−nv] [−i FILE|−−interfaces=FILE] [−−no−act] [−−verbose] [−a|IFACE]...
ifdown [−nv] [−i FILE|−−interfaces=FILE] [−−no−act] [−−verbose] [−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.
−h, −−help
Show summary of options.
−V, −−version
Show copyright and version information.
−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 interfaces. Interfaces are brought down in the order in which they are currently listed in the state file.
−i FILE, −−interfaces FILE
Read interface definitions from FILE instead of from /etc/network/interfaces.
−v, −−verbose
Show commands as they are executed.
−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.
−−force
Force configuration or deconfiguration of the interface.
The ifup and ifdown programs don’t know much about configuring interfaces; they run low level utilities such as ifconfig and route to do their dirty work. One of the main advantages to using ifup and ifdown instead of calling the low level utilities directly is that ifup and ifdown allow you to keep all your interface specifications in a single easily parsable file.
/etc/network/interfaces
definitions of network interfaces See interfaces(5) for more information.
/etc/network/ifstate
current state of network interfaces
In some cases, the state maintained by ifup and ifdown in /etc/network/ifstate might be inconsistent with the actual state of the interfaces. If this happens, you might need to either modify the state file directly or manually configure/deconfigure interfaces using ifconfig(8) or ip(8).
The /etc/network/ifstate file must be writable. In particular, you will not be able to run ifup and ifdown if /etc/ is mounted read-only (for example, during a system recovery). A work-around for this issue (reported in Debian bug #84074) is to make /etc/network/ifstate a symbolic link to a writable location.
The ifup program itself does not automatically bring up interfaces that appear as a result of hardware being installed and ifdown does not automatically bring down interfaces that disappear as a result of hardware being removed. If you want to monitor interface state changes you might want to consider installing also hotplug(8) and ifplugd(8). Note that the improper use of ifupdown together with hotplug can result in deadlock between them as described in Debian bug #231197.
The ifupdown suite was written by Anthony Towns <aj [AT] azure.au>.