Пул периодических задач на сервере

/usr/bin/flock -x -w 0 /var/lock/my_events/event_name -c /path/to/your/script.sh

Usage:
 flock [-sxun][-w #] fd#
 flock [-sxon][-w #] file [-c] command...
 flock [-sxon][-w #] directory [-c] command...

Опции:
 -s  --shared     Get a shared lock
 -x  --exclusive  Get an exclusive lock
 -u  --unlock     Remove a lock
 -n  --nonblock   Fail rather than wait
 -w  --timeout    Wait for a limited amount of time
 -o  --close      Close file descriptor before running command
 -c  --command    Run a single command string through the shell
 -h  --help       Display this text
 -V  --version    Display version

#!/bin/bash

DEFAULT_LOCK="/tmp/.somelock"

lock() {
	LOCK=${1:-$DEFAULT_LOCK}
	lockfile -r 0 $LOCK 1>/dev/null 2>&1
	return $?
}

unlock() {
	LOCK=${1:-$DEFAULT_LOCK}
	[ -f $LOCK ] && rm -f $LOCK
	return $?
}

lock && echo "lock ok test"
lock || echo "lock not ok test"
unlock && echo "unlock ok test"
unlock || echo "unlock not ok test"

# $PARAM -- что-то уникальное для каждого из 4 запусков скрипта. Например:
# PARAM=`echo -n "$@" | openssl dgst -sha1 -binary | base64`
LOCK="${DEFAULT_LOCK}_${PARAM}"

if ! lock $LOCK ; then
	echo "Locked"
	exit 1
fi

# ваши действия

unlock $LOCK