Cron & Task Scheduling (Cron/Systemd Timers/At)

Avoid Cron Overlap with Flock

🧩 The Challenge

Cron jobs that take a long time to complete can overlap if they are triggered again before the previous instance finishes. This leads to resource exhaustion and race conditions where multiple processes try to modify the same data.

💡 The Fix

Use the flock utility to ensure that only one instance of a specific task script runs at any given time by locking a file.

* * * * * /usr/bin/flock -n /tmp/my_task.lock /usr/local/bin/my_long_running_script.sh

⚙️ Why It Works

The flock command checks for a lock file and exits immediately if it is held by another process, preventing concurrent execution of your script.

🚀 Pro-Tip: Use the -w option with flock to specify a timeout in seconds if you want the task to wait briefly rather than failing immediately.

Linux Tips & Tricks | © ngelinux.com | 7/5/2026