keepalive.sh: send keepalive to remote server

This script is deployed on my odroid. It serves to keep track if the odroid has internet access and if it is alive. It uses simple keepalive sending via HTTPS protocol to a remote server. The remote server watches keepalive signals and will notify if they stop comming.

The scheme consists of 3 parts. First is on the client site (odroid), it handles keepalive sending. Other two are on the remote site (server), handling keepalive reception and processing. Following figure demonstrates component cooperation.

keepalive-send.sh:

#!/bin/bash
#
# krisko 2014
# Simple keepalive send, enable and disable script

enable(){
        curl -k "https://server.com/keepalive.php?keepalive=enable"
}

disable(){
        curl -k "https://server.com/keepalive.php?keepalive=disable"
}

alive(){
        curl -k "https://server.com/keepalive.php?keepalive=alive" &>/dev/null
}

rmnotified(){
        curl -k "https://server.com/keepalive.php?keepalive=rmnotified"
}

case "$1" in
        enable | disable | alive | rmnotified ) $1;;
        * ) echo "ERROR: unknown option"; exit 1;;
esac

exit 0

##################
# ChangeLog/TODO #
##################
# 1.0.0 2014-06-14 Genesis
##################

This script simply calls server.com url, where keepalive.php is listening for keepalive signals and handles to it a parameter (keepalive=alive). It is triggered with crontab (/usr/local/bin/keepalive-send.sh alive) each minute.

keepalive.php:

<?php
$keepalive=htmlspecialchars($_GET["keepalive"]);

if($keepalive=="help") {
        echo "Not allowed!\n";
        exit(1);
}

$output = shell_exec("/home/krisko/bin/keepalive.sh $keepalive");
echo "$output";
?>

This script simply calls keepalive.sh handling it the received parameter.
NOTE: you need to enable shell_exec in your php.ini

keepalive.sh:

#!/bin/bash
#
# krisko 2014
# simple keepalive checking script

alivefile="/tmp/krisko-keepalive"
notified="/tmp/krisko-notified"
MAXTIME=2
NOTIFYTIME=5
SUBJECT="KEEPALIVE Alert"
EMAILID="myemail@gmail.com"
URL="https://server.com/keepalive.php?keepalive="

help(){
cat << EOF
krisko 2014
Simple keepalive script
USAGE: $0 (OPTION)
OPTIONS:
    enable  enable keepalive checking
    disable disable keepalive checking
    alive   receive alive signal
    check   check keepalive timers
    rmnotified remove notified file (cannot be called directly from shell)
    refalive   refresh alive file state (cannot be called directly from shell)
EOF
}

callurl(){
        curl -k "$URL$1"
}

notify(){
        echo $@
    echo $@ | mail -s "$SUBJECT" $EMAILID
}

# wee need to call url because od apache permissions
rmnotified(){
        [ -f $notified ] && rm $notified
}

mknotified(){
        > $notified
}

refalive(){
        > $alivefile
}

enable(){
    > $alivefile
        callurl rmnotified
    notify "INFO: keeaplive check enabled"
}

disable(){
    echo ":" > $alivefile
    notify "INFO: keeaplive check disabled"
}

checknotify(){
    CHKNOTIFY=$(find $notified -cmin +$NOTIFYTIME 2>/dev/null)

    if [ ! -z $CHKNOTIFY ]; then
        callurl mknotified
        notify "ERROR: keepalive timeout";
    elif [ ! -f $notified ]; then
        callurl mknotified
        notify "ERROR: keepalive timeout";
    fi
}

alive(){
    [ $(cat $alivefile) ] && echo "DISABLED" || callurl refalive
}

check(){
    [ $(cat $alivefile) ] && echo "DISABLED" || {
    CHKFILE=$(find $alivefile -cmin +$MAXTIME 2>/dev/null)
    [ ! -z $CHKFILE ] && checknotify || { callurl rmnotified; echo OK; } 
    }
}

case "$1" in
    "enable" | "disable" | "alive" | "check" | "rmnotified" | "refalive" | "mknotified" )  "$1";;
    "help" ) help;;
    * )    echo "INFO: unknown parameter, use help for help"; exit 2;;
esac

exit 0

##################
# ChangeLog/TODO #
##################
# 1.0.0 2014-06-11 Genesis
# 1.0.1 2014-06-15 Added url handling functions
##################

This script will handle all necessary operation for keepalive signal handling. Notice the refalive function called from within the script. This is due to web server permissions when creating and removing temporary files.

keepalive.sh check:

*/2 * * * * /home/krisko/bin/keepalive.sh check &>/dev/null

This check is triggered with crontab each 2 minutes. It check whether the alivefile="/tmp/krisko-keepalive" was refreshed. If not, this means that the keepalive did not arive and an email notification is sent. Also another temporary file is created (notified="/tmp/krisko-notified") which will assure, that the next notification is sent after NOTIFYTIME period.
Practically, first notification is sent, when the keepalive did not arive after 2 minutes. Then each 6 minutes, an additional notification is sent. This can be adjusted with MAXTIME and NOTIFYTIME variables.