Man page 8 : ifup

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

R ifup 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.

R -a

    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.

R -h

    Show summary of options.

• --allow=CLASS
      Only allow interfaces listed in an allow-CLASSline in /etc/network/interfaces to be acted upon.
• -i FILE, --interfaces=FILE
      Read interface definitions from FILEinstead of from /etc/network/interfaces.

R -n

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

--no-mappings

    Don't run any mappings. See

R interfaces (5) for more information about the mapping feature.

R -V

    Show copyright and version information.

R -v

    Show commands as they are executed.

ifup -a

    Bring up all the interfaces defined with autoin /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.

R ifup are actually the same program called by different names.

The program does not configure network interfaces directly; it runs low level utilities such as

R ifconfig to do its dirty work.

• /etc/network/interfaces
      definitions of network interfaces See

R interfaces (5) for more information.

• /etc/network/run/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 /etc/network/run/ifstatemust 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 /etc/network/run/ifstateshould be made a symbolic link to a writable location. 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 result of hardware being removed. To automate the configuration of network interfaces you need to install other packages such as

R hotplug (8) or

R ifplugd (8).

The ifupdown suite was written by Anthony Towns <>.

R interfaces (5),

R ifconfig (8).