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Filename : ensureifup
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#!/bin/sh
# This script is useful to check wether an interface is up and,
# if not, it attempts to bring it back. This can be necessary
# if your ISP provider causes occasional outages.
# Some ISPs are known to termine connections when they reach
# 24 hours to "prevent abuse".
# Run this script through cron (every 5 minutes? your call)
# and ensure that ifstate is located where it is defined below.
#
# NOTE: This script is just provided as an example. If you want this
# feature you might be better off installing ifplugd which provides
# similar functionality (but more featureful) out of the box.

# TODO:
# Improve it so it can find out (eg from /run/network/ifstate)
# whether an interface was brought down
# unexpectedly, or if a clean "ifdown" was issued.

iface="$1"
ifstate=/usr/local/sbin/ifstate

if [ `$ifstate "$iface"` = DOWN ]
then
    logger -s "Trying to bring $iface back up..."
    ifdown "$iface"
    ifup "$iface"
    [ `$ifstate "$iface"` = UP ] && logger -s "$iface now up again"
fi

exit 0