How to Set Up Cron Jobs on Linux Server

Cron is the standard Linux scheduler for running scripts and commands at fixed times — backups, cache clearing, certificate checks, and more. This guide shows how to use cron on your Hiddence server.

Cron syntax

Each line has five time fields followed by the command:

# ┌──────── minute (0-59)
# │ ┌────── hour (0-23)
# │ │ ┌──── day of month (1-31)
# │ │ │ ┌── month (1-12)
# │ │ │ │ ┌─ day of week (0-7, 0 and 7 = Sunday)
# │ │ │ │ │
# * * * * * command

# Every day at 3:00 AM:
0 3 * * * /usr/local/bin/backup.sh

# Every 15 minutes:
*/15 * * * * /usr/local/bin/check.sh

Edit crontab

Use crontab -e for the current user. For root tasks (most system jobs), use sudo:

# Edit your user crontab
crontab -e

# Edit root crontab
sudo crontab -e

# List current jobs
crontab -l
sudo crontab -l

Common examples

• 0 2 * * * — daily backup at 2:00 AM
• 0 */6 * * * — every 6 hours
• 0 0 * * 0 — every Sunday at midnight
• */5 * * * * — every 5 minutes (use carefully)
• @reboot /path/script.sh — run once after server reboot
• @daily /usr/bin/certbot renew --quiet — daily Certbot check

Logging and debugging

Redirect output to a log file so you know if a job failed:

0 3 * * * /usr/local/bin/backup.sh >> /var/log/backup-cron.log 2>&1

# View cron execution in system log:
grep CRON /var/log/syslog   # Ubuntu
grep CRON /var/log/cron      # CentOS

Tips

• Use absolute paths in cron commands
• Test scripts manually before adding to crontab
• Set MAILTO=your@email.com in crontab for error emails (if mail is configured)
• Prefer systemd timers for complex dependencies on modern systems
• Do not run heavy tasks every minute — it can overload the VPS