Preventing to Bash script from running in parallel or overlap using cron

Question

If i have the following entries in my cron table:

00 03 * * * /java_prog1.sh 
00 5 * * * /java_prog2.sh

The first job usually takes around 30 m

Answer 1

The creation of directories is atomic, so you could add this in both scripts:

lock_dir=/tmp/name_of_lock_directory
if ! mkdir "$lock_dir"; then
    echo "Cannot run $0: lock directory $lock_dir exists" >&2
    exit 1
fi
cleanup () { rm -r "$lock_dir"; }
trap cleanup EXIT
# if you want, you can add the running pid to a file in the lock directory
echo $$ > "$lock_dir/pid"