Crontab Tutorial: Schedule Tasks on Linux (Beginner Guide)

Quick Answer: crontab -e opens your cron jobs. Add a line like 0 2 * /opt/backup.sh to run backup.sh at 2 AM daily. Format: minute hour day-of-month month day-of-week command. Use our Crontab Explainer to translate any expression.

What is Crontab?

Crontab is Linux's built-in task scheduler. It runs commands automatically at specified times — backups at midnight, log cleanup every week, health checks every 5 minutes.

Every user has their own crontab. Root has a separate one for system tasks.

Basic Commands

# Edit your cron jobs
crontab -e

# List your cron jobs
crontab -l

# Remove all your cron jobs (careful!)
crontab -r

# Edit root's crontab
sudo crontab -e

# Edit another user's crontab
sudo crontab -u www-data -e

Cron Syntax

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

Symbol	Meaning	Example
`*`	Every	`*` = every minute
`*/N`	Every N	`/5 *` = every 5 minutes
`N`	At exactly N	`0 2 *` = at 2:00 AM
`N,M`	At N and M	`0,30` = at :00 and :30
`N-M`	Range N to M	`0 9-17 *` = every hour 9 AM to 5 PM

Common Examples

Time-Based

# Every minute
* * * * * /opt/scripts/check.sh

# Every 5 minutes
*/5 * * * * /opt/scripts/monitor.sh

# Every 15 minutes
*/15 * * * * /opt/scripts/sync.sh

# Every hour (at minute 0)
0 * * * * /opt/scripts/hourly.sh

# Every day at midnight
0 0 * * * /opt/scripts/daily.sh

# Every day at 2:30 AM
30 2 * * * /opt/scripts/backup.sh

# Every Monday at 9 AM
0 9 * * 1 /opt/scripts/weekly-report.sh

# Every weekday at 9 AM
0 9 * * 1-5 /opt/scripts/workday.sh

# First day of every month at midnight
0 0 1 * * /opt/scripts/monthly.sh

# Every 6 hours
0 */6 * * * /opt/scripts/periodic.sh

# Twice a day (8 AM and 8 PM)
0 8,20 * * * /opt/scripts/twice-daily.sh

Real-World Tasks

# Backup database every night at 2 AM
0 2 * * * mysqldump -u root mydb | gzip > /backups/db-$(date +\%Y\%m\%d).sql.gz

# Clean old log files every Sunday at 3 AM
0 3 * * 0 find /var/log -name "*.log" -mtime +30 -delete

# Renew SSL certificates (twice daily, Let's Encrypt recommends)
0 0,12 * * * certbot renew --quiet

# Check disk space, email alert if >90%
*/30 * * * * df -h / | awk 'NR==2{if($5+0>90) print}' | mail -s "Disk Alert" [email protected]

# Restart a service every night (if it has memory leaks)
0 4 * * * systemctl restart myapp

# Pull latest code and restart (auto-deploy)
*/10 * * * * cd /opt/myapp && git pull && systemctl restart myapp

# Sync files to backup server
0 1 * * * rsync -avz /data/ backup-server:/backups/data/

Logging Cron Output

By default, cron output goes to your system mail. Better options:

# Log output to a file
0 2 * * * /opt/backup.sh >> /var/log/backup.log 2>&1

# Discard output (silent)
0 2 * * * /opt/backup.sh > /dev/null 2>&1

# Log only errors
0 2 * * * /opt/backup.sh >> /var/log/backup.log 2>> /var/log/backup-errors.log

The 2>&1 redirects stderr to the same place as stdout.

Important Rules

Use Full Paths

Cron runs with a minimal environment. Always use full paths:

# Bad (might not find the command)
0 2 * * * backup.sh

# Good
0 2 * * * /opt/scripts/backup.sh

# Or set PATH at the top of crontab
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
0 2 * * * backup.sh

Escape Percent Signs

In crontab, % has special meaning (newline). Escape it with \%:

# Bad
0 2 * * * echo "Today is $(date +%Y-%m-%d)"

# Good
0 2 * * * echo "Today is $(date +\%Y-\%m-\%d)"

Make Scripts Executable

chmod +x /opt/scripts/backup.sh

Add a Shebang

Your scripts should start with:

#!/bin/bash

System-Wide Cron

Besides user crontabs, Linux has system cron directories:

Location	Schedule
`/etc/cron.d/`	Custom schedules (like crontab format)
`/etc/cron.daily/`	Runs once per day
`/etc/cron.weekly/`	Runs once per week
`/etc/cron.monthly/`	Runs once per month
`/etc/cron.hourly/`	Runs once per hour

Drop a script into any of these directories and it runs automatically:

# Run daily
sudo cp myscript.sh /etc/cron.daily/
sudo chmod +x /etc/cron.daily/myscript.sh

Troubleshooting

Problem	Fix
Cron job not running	Check `crontab -l` — is it there? Check syntax
Runs but nothing happens	Add logging: `>> /tmp/cron.log 2>&1`
Command not found	Use full paths: `/usr/bin/python3` not `python3`
Script works manually but not in cron	Environment differs — set PATH in crontab
Runs at wrong time	Check server timezone: `timedatectl`
Permission denied	`chmod +x script.sh` and check file ownership

# Check if cron service is running
systemctl status cron

# Check cron logs
grep CRON /var/log/syslog | tail -20

# Check your timezone
timedatectl

Cron vs systemd Timers

	Cron	systemd Timer
Simplicity	Simple one-liner	Requires two files
Logging	Manual	Built into journalctl
Dependencies	None	Can depend on other services
Missed runs	Skipped	Can catch up (Persistent=true)
Best for	Simple scheduled tasks	Complex service scheduling

For most tasks, cron is fine. Use systemd timers for services that need dependency management.

Shorthand Schedules

Shortcut	Equivalent	When
`@reboot`	--	Once at startup
`@yearly`	`0 0 1 1 *`	January 1st
`@monthly`	`0 0 1`	First of month
`@weekly`	`0 0 0`	Every Sunday
`@daily`	`0 0 *`	Every midnight
`@hourly`	`0`	Every hour

@reboot /opt/scripts/startup.sh
@daily /opt/backup.sh >> /var/log/backup.log 2>&1

Related Tools

Crontab Explainer — translate cron expressions to English
Cron Generator — build cron expressions visually