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A template to write a quick daemon as a bash script
#!/bin/sh
# This is a skeleton of a bash daemon. To use for yourself, just set the
# daemonName variable and then enter in the commands to run in the doCommands
# function. Modify the variables just below to fit your preference.
daemonName="DAEMON-NAME"
pidDir="."
pidFile="$pidDir/$daemonName.pid"
pidFile="$daemonName.pid"
logDir="."
# To use a dated log file.
# logFile="$logDir/$daemonName-"`date +"%Y-%m-%d"`".log"
# To use a regular log file.
logFile="$logDir/$daemonName.log"
# Log maxsize in KB
logMaxSize=1024 # 1mb
runInterval=60 # In seconds
doCommands() {
# This is where you put all the commands for the daemon.
echo "Running commands."
}
################################################################################
# Below is the skeleton functionality of the daemon.
################################################################################
myPid=`echo $$`
setupDaemon() {
# Make sure that the directories work.
if [ ! -d "$pidDir" ]; then
mkdir "$pidDir"
fi
if [ ! -d "$logDir" ]; then
mkdir "$logDir"
fi
if [ ! -f "$logFile" ]; then
touch "$logFile"
else
# Check to see if we need to rotate the logs.
size=$((`ls -l "$logFile" | cut -d " " -f 8`/1024))
if [[ $size -gt $logMaxSize ]]; then
mv $logFile "$logFile.old"
touch "$logFile"
fi
fi
}
startDaemon() {
# Start the daemon.
setupDaemon # Make sure the directories are there.
if [[ `checkDaemon` = 1 ]]; then
echo " * \033[31;5;148mError\033[39m: $daemonName is already running."
exit 1
fi
echo " * Starting $daemonName with PID: $myPid."
echo "$myPid" > "$pidFile"
log '*** '`date +"%Y-%m-%d"`": Starting up $daemonName."
# Start the loop.
loop
}
stopDaemon() {
# Stop the daemon.
if [[ `checkDaemon` -eq 0 ]]; then
echo " * \033[31;5;148mError\033[39m: $daemonName is not running."
exit 1
fi
echo " * Stopping $daemonName"
log '*** '`date +"%Y-%m-%d"`": $daemonName stopped."
if [[ ! -z `cat $pidFile` ]]; then
kill -9 `cat "$pidFile"` &> /dev/null
fi
}
statusDaemon() {
# Query and return whether the daemon is running.
if [[ `checkDaemon` -eq 1 ]]; then
echo " * $daemonName is running."
else
echo " * $daemonName isn't running."
fi
exit 0
}
restartDaemon() {
# Restart the daemon.
if [[ `checkDaemon` = 0 ]]; then
# Can't restart it if it isn't running.
echo "$daemonName isn't running."
exit 1
fi
stopDaemon
startDaemon
}
checkDaemon() {
# Check to see if the daemon is running.
# This is a different function than statusDaemon
# so that we can use it other functions.
if [ -z "$oldPid" ]; then
return 0
elif [[ `ps aux | grep "$oldPid" | grep -v grep` > /dev/null ]]; then
if [ -f "$pidFile" ]; then
if [[ `cat "$pidFile"` = "$oldPid" ]]; then
# Daemon is running.
# echo 1
return 1
else
# Daemon isn't running.
return 0
fi
fi
elif [[ `ps aux | grep "$daemonName" | grep -v grep | grep -v "$myPid" | grep -v "0:00.00"` > /dev/null ]]; then
# Daemon is running but without the correct PID. Restart it.
log '*** '`date +"%Y-%m-%d"`": $daemonName running with invalid PID; restarting."
restartDaemon
return 1
else
# Daemon not running.
return 0
fi
return 1
}
loop() {
# This is the loop.
now=`date +%s`
if [ -z $last ]; then
last=`date +%s`
fi
# Do everything you need the daemon to do.
doCommands
# Check to see how long we actually need to sleep for. If we want this to run
# once a minute and it's taken more than a minute, then we should just run it
# anyway.
last=`date +%s`
# Set the sleep interval
if [[ ! $((now-last+runInterval+1)) -lt $((runInterval)) ]]; then
sleep $((now-last+runInterval))
fi
# Startover
loop
}
log() {
# Generic log function.
echo "$1" >> "$logFile"
}
################################################################################
# Parse the command.
################################################################################
if [ -f "$pidFile" ]; then
oldPid=`cat "$pidFile"`
fi
checkDaemon
case "$1" in
start)
startDaemon
;;
stop)
stopDaemon
;;
status)
statusDaemon
;;
restart)
restartDaemon
;;
*)
echo "\033[31;5;148mError\033[39m: usage $0 { start | stop | restart | status }"
exit 1
esac
exit 0
@ghost

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@ghost ghost commented Dec 19, 2017

Thanks / Nice!
On Ubuntu systems /bin/sh points to dash. Dash complains about the double-brackets tests. One way to fix this, is to make sure the script starts with #!/bin/bash to make sure the bash shell is used.
...also, line 11 should be removed.

@chris-towles

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@chris-towles chris-towles commented May 25, 2018

Some of the content got messed up. like echo "\033[31;5;148mError\033[39m: usage $0 { start | stop | restart | status }"

The original at https://github.com/shawnrice/alfred-cron/blob/master/alfred-cron.sh isn't messed up for anyone looking.

@Wyatts

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@Wyatts Wyatts commented Jul 25, 2018

This is a nice idea, but it doesn't work for arbitrarily long-running tasks because of the recursion.

@avonjo

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@avonjo avonjo commented Sep 5, 2019

The recursive loop will segfault after some time. Better do a regular infinite loop inside the loop function.

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