How to Schedule Tasks with Cron in Linux automation

What is Cron?

Cron is a time-based job scheduler in Linux. It allows users and administrators to schedule commands or scripts to run at specific times or intervals.

Editing the Crontab

# open user’s crontab
crontab -e

# list current cron jobs
crontab -l

Each line in a crontab represents one job.

Cron Syntax

* * * * * command_to_run
│ │ │ │ │
│ │ │ │ └─ Day of week (0-6, Sun=0)
│ │ │ └─── Month (1-12)
│ │ └───── Day of month (1-31)
│ └─────── Hour (0-23)
└───────── Minute (0-59)

Example: Run a script at 2:30 AM daily:

30 2 * * * /home/user/backup.sh

Examples of Cron Jobs

• System update daily at midnight:
  0 0 * * * sudo apt update && sudo apt upgrade -y
• Clean /tmp every week:
  0 3 * * 0 rm -rf /tmp/*
• Run a script every 15 minutes:
  */15 * * * * /home/user/script.sh

Viewing Cron Logs

On most systems, cron activity is logged to /var/log/syslog or /var/log/cron:

# Debian/Ubuntu
grep CRON /var/log/syslog

# CentOS/AlmaLinux
sudo cat /var/log/cron

Alternative: systemd Timers

Modern Linux distributions also support systemd timers, which can replace cron for more advanced scheduling:

systemctl list-timers