Mutex, Singleton, Only one instance of bash script running at a time

mutex_test.sh

#!/bin/bash

# Credit: https://unix.stackexchange.com/a/479309

singleton(){
    # get absolute path to the script itself
    script=`realpath $0`
    # open bash script using file descriptor 6
    exec 6< "$script"
    # lock file descriptor 6 OR show error message if script is already running
    flock -n 6 || { echo "ERROR: script is already running" && exit 1; }
}

singleton

# Your code goes here
# Known limitations: 
# Doesn't lock across users
# Doesn't lock if the script is copied to multiple places

echo "Running $@"
sleep 10