Process Management and AutomationLesson 5.4

How to monitor and manage Bash script processes

ps and pgrep, kill and pkill, pidfile pattern, wait with timeout, process substitution, /proc filesystem, lsof for open files, monitoring script health with while loop

Finding and Managing Processes

Scripts that run as daemons or long-running tasks need a way to track and manage themselves.

# PID file pattern — track your script's process
PIDFILE="/var/run/myscript.pid"

# On start: write PID
echo $$ > "$PIDFILE"
trap "rm -f $PIDFILE" EXIT

# Check if another instance is running
if [[ -f "$PIDFILE" ]]; then
  old_pid=$(cat "$PIDFILE")
  if kill -0 "$old_pid" 2>/dev/null; then
    echo "Script already running (PID $old_pid)" >&2
    exit 1
  fi
  rm -f "$PIDFILE"  # stale PID file
fi

Finding Processes

# pgrep/pkill are cleaner than ps | grep
pgrep -f "myapp.sh"              # PIDs of matching processes
pkill -TERM -f "myapp.sh"        # send SIGTERM

# Check if a process is alive
if kill -0 "$pid" 2>/dev/null; then
  echo "Process $pid is running"
fi

Wait with Timeout

wait_for_process() {
  local pid=$1 timeout=$2 elapsed=0
  while kill -0 "$pid" 2>/dev/null; do
    if (( elapsed >= timeout )); then
      echo "Timeout waiting for PID $pid" >&2
      return 1
    fi
    sleep 1
    (( elapsed++ ))
  done
}

kill -0 PID doesn't send a signal — it just checks if the process exists. Exit code 0 = running, non-zero = not found.