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#!/bin/bash
#
# Alternate Access Tunnel for Remote Hosts
#
# Opens an SSH connection to a central aggregation host and forwards the local
# SSH port over that connection. This allows remote connections to the server
# from the central aggregation host. In the absence of true OOB recovery
# systems this mechanism provides some OOB recovery capability provided the
# entire internet connection is not down.
#
KEY=/root/.ssh/phonehome.id_rsa
CRONTAB=/var/spool/cron/crontabs/root
CRON_ENTRY="*/5 * * * * /root/phonehome.sh"
# Alt host hedges against DNS being down if the default DNS server is on the
# wrong side of a collapsed ssh tunnel
#
# Grab only answers starting with numbers since we're trying to resolve the IP
# itself not the hostname (in the absence of normal DNS). Grab the first numeric
# answer in the case of multiple records
HOST_IP=$(dig +short @8.8.8.8 phonehome.crute.me | awk '/^[0-9]+/ { print $0; exit; }')
function start_autossh {
autossh -f \
-gNxCT \
-l phonehome -p 4321 $1 \
-i $KEY \
-R $REMOTE_PORT:localhost:22
}
if [ ! -f /etc/default/phonehome ]; then
echo "echo 'REMOTE_PORT=1234' > /etc/default/phonehome"
exit 1
else
source /etc/default/phonehome
fi
if ! grep 'phonehome.sh' $CRONTAB 2>&1 > /dev/null; then
echo "Not in crontab, adding"
echo "$CRON_ENTRY" >> $CRONTAB
else
if ! grep -F "$CRON_ENTRY" $CRONTAB 2>&1 > /dev/null; then
echo "In crontab but not correct, fixing"
sed -i '/phonehome.sh/d' $CRONTAB
echo "$CRON_ENTRY" >> $CRONTAB
fi
fi
if ! pgrep autossh > /dev/null; then
start_autossh $HOST_IP
fi
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