Cron & Task Scheduling (Cron/Systemd Timers/At)
Stop cron jobs from overlapping and killing your CPU
🧩 The Challenge
Ever had a backup script that took longer than expected to run, only to have a second instance trigger and turn your server into a space heater? I’ve spent more than one late night cleaning up after lock files that didn’t actually lock.
đź’ˇ The Fix
Use flock to wrap your cron commands so they only run one instance at a time. It’s the easiest way to ensure the new job waits for the old one to finish or just gives up gracefully.
* * * * * flock -n /tmp/my-script.lock /usr/local/bin/my-script.sh⚙️ Why It Works
This utility manages a file lock on a specific file descriptor, meaning if the lock is already held by another process, the new one hits the exit signal immediately. By using the -n flag, you tell the script to bail out rather than sitting around and clogging up the process table.
🚀 Pro-Tip: Use a dedicated directory like /run/lock for these instead of /tmp so a random reboot or cleanup script doesn’t delete your lock file.
Linux Tips & Tricks | © ngelinux.com | 10/10/2026