crontab is a Linux command used to schedule commands or scripts to run automatically at fixed times or intervals. These scheduled tasks are called cron jobs and are executed by the cron daemon running in the background.
crontab is widely used for system maintenance, backups, log rotation, and automation tasks that must run without manual intervention.
crontab Command - Quick Cheat Sheet
| Task | crontab Command |
|---|---|
| Edit current user's cron jobs | crontab -e |
| List current user's cron jobs | crontab -l |
| Remove all cron jobs for current user | crontab -r |
| Remove cron jobs with confirmation | crontab -i -r |
| Edit cron jobs for another user | sudo crontab -u username -e |
| List cron jobs for another user | sudo crontab -u username -l |
| Remove cron jobs for another user | sudo crontab -u username -r |
| Install cron jobs from a file | crontab filename |
| Check cron service status | systemctl status cron |
| Run job every minute | * * * * * command |
| Run job every hour | 0 * * * * command |
| Run job daily at midnight | 0 0 * * * command |
| Run job weekly (Sunday midnight) | 0 0 * * 0 command |
| Run job monthly | 0 0 1 * * command |
This quick reference summarizes the most commonly used crontab command examples in Linux for scheduling and managing automated tasks.
How cron and crontab Work
Think of cron as the background scheduler and crontab as its schedule file.
time rules → cron service → command or script- cron runs continuously in the background
- crontab defines what task to run and when to run it
- Each line in crontab represents one scheduled job
This model helps understand why incorrect timing or paths cause cron jobs to fail silently.
Crontab File Locations and Access Control
Linux allows administrators to control who can use cron.
/etc/cron.allow
/etc/cron.deny- If
/etc/cron.allowexists, only listed users can use cron - If it does not exist, users not listed in
/etc/cron.denycan use cron - If neither file exists, only root is allowed to schedule cron jobs
This prevents unauthorized users from running background jobs.
Crontab Syntax and Time Format
Each cron job consists of five time fields followed by the command to execute.
MIN HOUR DOM MON DOW COMMAND| Field | Meaning | Allowed Values |
|---|---|---|
| MIN | Minute | 0–59 |
| HOUR | Hour | 0–23 |
| DOM | Day of Month | 1–31 |
| MON | Month | 1–12 or jan–dec |
| DOW | Day of Week | 0–6 or sun–sat |
Common patterns used in cron schedules:
*→ every value (every minute, hour, day),→ list (1,5,10)-→ range (1–5)
Understanding this format makes it easier to read and debug cron jobs.
Managing User Crontabs
Use the crontab command to view, edit, or manage scheduled jobs for a
user.
View current user’s cron jobs
crontab -lIf no cron jobs exist, cron explicitly reports that no crontab is configured for the user.
Edit current user’s cron jobs
crontab -eThis opens the user’s crontab file in the default editor, where jobs can be added, updated, or removed.
Each line represents one scheduled task.
Common Cron Scheduling Examples
These are the most frequently used cron schedules in real systems.
Run a job at a specific date and time
45 07 14 01 * cp -R /home/user/data /home/user/data_backupRuns once at 7:45 AM on January 14.
Run a job every day at a fixed time
0 20 * * * myscript.shRuns daily at 8:00 PM.
Run a job multiple times per day
0 7,21 * * * myscript.shRuns every day at 7 AM and 9 PM.
Run multiple commands in a single cron job
0 6 * * * script1.sh; script2.shCommands are executed sequentially in the same schedule.
Special Cron Time Strings (Shortcuts)
Cron provides predefined keywords for common schedules.
@yearly @monthly @weekly @daily @hourlyExample:
@daily myscript.shThese are easier to read and reduce syntax mistakes.
Run a job once per day
@daily backup.shIdeal for:
- Daily backups
- Log cleanup
- Health checks
Equivalent to:
0 0 * * *Run a job once per week
@weekly cleanup.shCommonly used for:
- Disk cleanup
- Weekly reports
- Maintenance tasks
Equivalent to:
0 0 * * 0Run a job once per month
@monthly billing.shUseful for:
- Monthly reports
- Billing or accounting scripts
- Data archival
Equivalent to:
0 0 1 * *Run a job once per year
@yearly archive.shSuitable for:
- Annual archiving
- License renewal checks
- Yearly audits
Equivalent to:
0 0 1 1 *Run a job every hour
@hourly sync.shGood for:
- Data synchronization
- Cache refresh jobs
- Monitoring scripts
Equivalent to:
0 * * * *Run a job at system startup
@reboot init_checks.shUseful for:
- Service validation after reboot
- Re-mounting network storage
- Recovery or initialization tasks
Note:
@rebootjobs run only when the cron service starts, not on every login.
Managing Other Users’ Crontabs (Root Only)
System administrators can manage cron jobs for other users using the
-u option. These commands require root privileges.
View another user’s crontab
sudo crontab -u username -lLists all cron jobs configured for the specified user.
Edit another user’s crontab
sudo crontab -u username -eOpens the user’s crontab in the editor for modification.
Remove another user’s crontab
sudo crontab -u username -rPrompt before removal:
sudo crontab -u username -i -rUse caution when removing crontabs, as all scheduled jobs for the user will be deleted.
Recommended logging pattern
* * * * * /path/script.sh >> /tmp/cron.log 2>&1This captures both standard output and errors, making troubleshooting much easier.
Frequently Asked Questions
1. What is crontab in Linux?
crontab is a Linux command used to create, edit, list, and remove cron jobs, which are scheduled tasks executed automatically at specified times.2. Where are crontab files stored?
User crontab files are stored under /var/spool/cron/crontabs and should only be edited using the crontab command.3. How do I check if a cron job is running?
You can verify cron execution by checking system logs such as /var/log/syslog or /var/log/cron depending on the distribution.4. Why is my cron job not running?
Common reasons include missing environment variables, incorrect paths, permission issues, or syntax errors in the crontab entry.Conclusion
The crontab command is a powerful and reliable tool for automating
tasks in Linux. By understanding cron syntax, scheduling patterns, and
common pitfalls, you can confidently schedule jobs that run in the
background without manual intervention.
From simple daily scripts to system maintenance and monitoring tasks, crontab remains an essential skill for Linux users and system administrators.
