Linux and Unix ifup and ifdown command
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...
ifdown [-nv] [--no-act] [--verbose] [-i FILE|--interfaces=FILE] [--allow CLASS] -a|IFACE...
|-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.|
|--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 for more information about the mapping feature.|
|-V, --version||Show copyright and version information.|
|-v, --verbose||Show commands as they are executed.|
Bring up all the interfaces defined with auto in /etc/network/interfaces
Bring up interface eth0
Bring down all interfaces that are currently up.