check_host_shutdown

#!/bin/bash
# Dennis U.
# request@decstasy.de
#
# Script to shutdown local machine when a remote host is not available
# Check out the exception_present function!
#
# V 0.1 Initial release
# V 0.2 Added support for exceptions

### for debugging
if [[ "$1" = "--debug" ]]; then
        shift
        set -x
fi

### Vars
PATH=$PATH:/sbin
pidfile="/var/run/$(basename ${0}).pid"

declare -A shutdown
shutdown[delay]="5"
shutdown[initiate]="shutdown +${shutdown[delay]} 'Automatic shutdown triggered by $(basename ${0}) script'"
shutdown[abort]="shutdown -c 'Automatic shutdown aborted by $(basename ${0}) script'"

### Functions
manual() {
        cat <<EOF
Usage: $0 [IP ADDRESS]
This script will poweroff your machine when the remote host is not reachable for more than ${shutdown[delay]} minutes.

You can alter the delay and commands in the beginning of the script. For debugging use --debug as your first argument.
EOF
        _exit 0
}

_exit() {
        # $1 exit code
        # $2 optional output message
        if [[ ! -z "$2" ]]; then
                echo "$2" | logger -t check_host_shutdown
        fi
        rm $pidfile
        exit $1
}

exception_present() {
        # Return 0 exception found
        # Return 1 no exception present and go on
        ### No shutdown if we have established samba sessions
        #[[ $( lsof -iTCP -a -c smbd | grep -c 'ESTABLISHED' ) -ge 1 ]] && return 0
        ### No shutdown if Server has rsync processes
        #ps -C rsync >/dev/null 2>&1 && return 0
        ### Continue to host check
        return 1
}

initiate_shutdown() {
        eval ${shutdown[initiate]}
}

abort_shutdown() {
        eval ${shutdown[abort]}
        _exit 0 "Automatic shutdown aborted. The remote host is reachable again."
}

is_alive() {
        ping -nqc 1 -W 1 $1 >/dev/null 2>&1
}

check_host() {
        is_alive $1 && _exit 0 || initiate_shutdown
        echo "$1 is not alive. Shutdown in ${shutdown[delay]} minutes if it's not back online." | logger -t check_host_shutdown
        # Wait loop
        while true; do
                sleep 5
                is_alive $1 && abort_shutdown
        done
}

#########################################################
################## MAIN ###############################
#####################################################

### Check for execution (we dont want messy effects with multiple executions)
if [[ -r "$pidfile" ]]; then
        if kill -0 &>1 > /dev/null $(<"$pidfile"); then
                # Script is already running
                exit 0
        else
                rm "$pidfile"
        fi
fi
echo $$ > "$pidfile"

### Trap if script is aborted
trap abort_shutdown INT

### Check Args
[[ $# -ne 1 ]] && manual

### Check for valid ip
if ! grep -P '^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$' <<<$1 >/dev/null 2>&1; then
        _exit 1 "Your IP is not valid!"
fi

### Check for exceptions
if exception_present; then
        _exit 0
fi

### Action :)
check_host $1