Bash Script PID file locking with extra care trying to avoid simultaneous runs using a random backoff

bash_pid.sh

#!/bin/bash -
set -e
scriptname=$(basename $0)
pidfile="/tmp/${scriptname}.pid"
if [ -d /var/run ] && [ -w /var/run ]; then
  pidfile="/var/run/${scriptname}.pid"
fi

if [ -f $pidfile ]; then
  pid=$(cat $pidfile)
  # lets try to avoid simultaneous start by random backoff
  random=$(od -A n -t d -N 1 /dev/random); random=$(( 1 + $random % 6 ))
  running=1
  ps -eo pid,command | grep "^$pid.*${scriptname}" > /dev/null 2>&1 || running=0
  if [ $running -eq 0 ]; then
    echo $$ > $pidfile
    sleep $random
  fi
  pid=$(cat $pidfile)
  if [ $$ -ne $pid ]; then
    running=1
    ps -eo pid,command | grep "^$pid.*${scriptname}" > /dev/null 2>&1 || running=0
    if [ $running -eq 1 ]; then
      echo "[PID $$]: ${scriptname} already running with pid ${pid}. Exiting."
      exit 1
    fi
  fi
fi
echo $$ > $pidfile
if [ $? -ne 0 ]; then
    echo "Could not create PID file ${pid}"
    exit 1
fi

### main script ###
echo Main [$$]
while [ 1 -eq 1 ]; do
        sleep 20;
done