Init script to detect lost default network route and to restart network services to fix it. This script is useful when an unknown problem causes the default route to be lost (e.g. certain deployments of CentOS 7 and Fedora 20). Copy to /etc/init.d/route-repair and run "chkconfig route-repair on" and "service route-repair start".

route-repair.sh

#!/bin/sh
#
# chkconfig: 2345 15 85
# description: Maintains default route by restarting network
#
# This script (when run with the "run-loop" argument) checks if the
# default route is still present, and if not the network service is
# restarted.  The timestamp of when the failure was detected is
# logged.
#
# This script is also an init.d script that can be used to
# start the monitor process (i.e. it runs itself with the "run-loop"
# argument). To install and run:
#
#   # cp route-repair.sh /etc/init.d/route-repair
#   # chkconfig route-repair on
#   # service route-repair start
#   # service route-repair status
#
# Detected failures are written to the log file in /var/log/.
#
# This is a workaround for the problem with with CentOS 7 and Fedora 20
# running on the "QRIScloud" availability zone.
#
# Copyright (C) 2014, QCIF Ltd.
#----------------------------------------------------------------

# Seconds between checking
DELAY_BETWEEN_CHECKS=5

# Maximum delay between retrying repair if it failed
REPAIR_DELAY_MAX=$((5 * 60))

# Where to store the PID and log
PID_FILE=/var/run/`basename "$0" .sh`.pid
LOG_FILE=/var/log/`basename "$0" .sh`.log

PROG=`basename "$0"`

#----------------------------------------------------------------

has_default_route () {
    ip route show | grep '^default via' > /dev/null

    if [ $? -ne 0 ]; then
        return 1 # Default route is missing
    else
        return 0
    fi
}

check_and_fix () {
    if ! has_default_route; then
        # Default route is missing

        # Log it

        WHEN=`date "+%F %T"`
        echo "$WHEN: default route lost detected"

        # Attempt to repair it

        REPAIR_DELAY=1
        while true; do
           WHEN=`date "+%F %T"`

           # Restart network service

           systemctl restart network.service

            if has_default_route; then
                # Repair successful
                if [ $REPAIR_DELAY -ne 1 ]; then
                    # This was not the first attempt to repair it
                    echo "$WHEN: repair successful"
                fi
                return 0 # success
            else
                # Repair failed: wait before trying again

                if [ $REPAIR_DELAY -eq 1 ]; then
                    # First failure to repair
                    echo "$WHEN: repair failed"
                fi

                sleep $REPAIR_DELAY

                REPAIR_DELAY=$((REPAIR_DELAY * 2))
                if [ $REPAIR_DELAY -gt $REPAIR_DELAY_MAX ]; then
                    REPAIR_DELAY=$REPAIR_DELAY_MAX
                fi
            fi
        done
    fi
}
#----------------------------------------------------------------

if [ $# -ne 1 ]; then
    COMMAND=help
else
    COMMAND="$1"
fi

case "$COMMAND" in
    start)
        if [ -f "$PID_FILE" ]; then
            echo "$PROG: error: already running" >&2
            exit 1
        fi
        "$0" run-loop >> "$LOG_FILE" 2>&1 &
        echo $! > "$PID_FILE"
        ;;

    stop)
        if [ -f "$PID_FILE" ]; then
            PID=`cat "$PID_FILE"`
            if kill -0 $PID > /dev/null 2>&1; then
                kill `cat "$PID_FILE"` && rm "$PID_FILE"
            else
                rm "$PID_FILE"
            fi
        fi
        ;;

    restart)
        "$0" stop
        "$0" start
        ;;
        
    status)
        if [ -f "$PID_FILE" ]; then
            PID=`cat "$PID_FILE"`
            if kill -0 $PID > /dev/null 2>&1; then
                echo "$PROG: running"
		        exit 0
            else
                if kill -0 $PID 2>&1 | grep 'No such process' >/dev/null; then
                    echo "$PROG: stopped (process died)"
                elif kill -0 $PID 2>&1 | grep 'Operation not permitted' >/dev/null; then
                    echo "$PROG: insufficient permission: possibly running"
                else
                    echo "$PROG: possibly stopped"
                fi
                exit 1
            fi

        else
            echo "$PROG: stopped"
            exit 1
        fi
        ;;

    run-once)
        check_and_fix
        ;;

    run-loop)
        while true; do
            check_and_fix
            sleep $DELAY_BETWEEN_CHECKS
        done
        ;;

    help|--help|-h)
        echo "Usage: $PROG run-once|run-loop|start|stop|restart|status|help"
        ;;

    *)
        echo "Error: unknown command: $COMMAND (--help for help)" >&2
        exit 1
        ;;
esac

#EOF