Re: /etc/network/interfaces

[Joey Hess <joeyh@debian.org>]

Geoff Crompton wrote:
>   Just out of interest, has anyone found a useful script to use with the
>   map clause. When I fiddled with it, I found that the script has to
>   output to stdout the name of the config to use. My script ended up
>   being something like:
> 
>   #!/bin/sh
> 
>   echo "eth0-home"
>   #echo "eth0-work"
> 
>   And I would just edit it to change it. It seemed to me that it would
>   be difficult to write a script that dynamically worked out what
>   network you were in. Either that or it would have to interupt the boot
>   process to prompt the user for a location.
> 
>   What would a useful (for automation) script look like?

I don't do autodetection, but I find the following useful. If run with
-s it changes the scheme on the fly, rather like cardctl scheme does for
pcmcia.

#!/bin/sh -e
# /usr/local/bin/ifscheme

while [ ! -z "$1" ] ; do
	case "$1" in
		-s|--set)
			newscheme=$2
			shift
		;;
		-v|--verbose)
			verbose="-v"
		;;
		-*)
			echo "Usage: ifscheme [-v] [-s newscheme]" >&2
			exit 1
		;;
		*)
			iface=$1
		;;
	esac
	shift
done

if [ ! -z "$newscheme" ]; then
	if [ -e /etc/network/scheme ]; then
		oldscheme=$(cat /etc/network/scheme)
		if [ "$oldscheme" = "$newscheme" ]; then
			echo "Scheme unchanged."
			exit
		fi
	fi
	echo $newscheme > /etc/network/scheme
	echo "Scheme changed to $newscheme."

	if [ ! -z "$oldscheme" ] && [ -e /etc/network/ifstate ]; then
		for match in $(grep -- "-$oldscheme" /etc/network/ifstate | \
		               cut -d = -f 1); do
			printf "Reinitializing $match.."
			if ! ifdown $verbose $match || ! ifup $verbose $match ||
			   ! grep -q "$match-" /etc/network/ifstate; then
				echo "Failed!"
				echo $oldscheme > /etc/network/scheme
				printf "Going back to $oldscheme.."
				ifdown $verbose $match 2>/dev/null || true
				if ! ifup $verbose $match; then
					echo "Er, that failed too! Giving up."
				fi
				echo "done."
				exit 1
			fi
			echo "done."
		done
	fi
	exit 0
fi

if [ -z "$iface" ]; then
	if [ ! -e /etc/network/scheme ]; then
		echo "Scheme not set."
	else
		echo "Current scheme is $(cat /etc/network/scheme)."
	fi
	exit 0
fi

if [ ! -e /etc/network/scheme ]; then
	echo $iface
else
	echo $iface-$(cat /etc/network/scheme)
fi