Linux cron tutorial – Scheduling Tasks in Linux with cron and at

Why Schedule Tasks?

• Run backups automatically.
• Clean logs or temporary files.
• Send reports at specific times.
• Restart services or scripts when needed.

Using cron for Repeated Jobs

cron runs jobs at specific intervals. Each user can have their own crontab.

Edit your crontab

crontab -e

Format: minute hour day month day-of-week command

# run every day at midnight
0 0 * * * /home/alex/backup.sh

# run every Monday at 6am
0 6 * * 1 /usr/bin/python3 /home/alex/report.py

# run every 5 minutes
*/5 * * * * /usr/local/bin/check.sh

List your cron jobs:

crontab -l

Special Cron Keywords

@reboot    run at startup
@hourly    run every hour
@daily     run once a day
@weekly    run once a week
@monthly   run once a month

Example: Run script at boot:

@reboot /usr/local/bin/startup.sh

Using at for One-Time Jobs

The at command runs jobs once at a specific time.

# run script at 10 PM tonight
at 10pm -f /home/alex/script.sh

# run tomorrow at 7:30 AM
echo "/home/alex/backup.sh" | at 7:30am tomorrow

List scheduled jobs:

atq

Remove a job:

atrm JOB_ID

Checking Logs

Cron logs can help you debug:

• Ubuntu/Debian: /var/log/syslog
• CentOS/AlmaLinux: /var/log/cron