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Automate with Cron

This guide explains how to automate tasks on your Linux VPS with cron.

What is Cron?​

Cron is a task scheduler built into Linux. It allows you to automatically run commands or scripts at defined intervals.

Cron Syntax​

┌───────────── minute (0 - 59)
│ ┌───────────── hour (0 - 23)
│ │ ┌───────────── day of month (1 - 31)
│ │ │ ┌───────────── month (1 - 12)
│ │ │ │ ┌───────────── day of week (0 - 6) (Sunday = 0)
│ │ │ │ │
* * * * * command to execute

Edit the crontab​

# Edit current user's tasks
crontab -e

# Edit root's tasks
sudo crontab -e

# View scheduled tasks
crontab -l

Common Examples​

Periodic Execution​

# Every minute
* * * * * /path/to/script.sh

# Every 5 minutes
*/5 * * * * /path/to/script.sh

# Every hour
0 * * * * /path/to/script.sh

# Every day at 3 AM
0 3 * * * /path/to/script.sh

# Every Monday at 8 AM
0 8 * * 1 /path/to/script.sh

# 1st of every month at midnight
0 0 1 * * /path/to/script.sh

Useful Shortcuts​

@reboot     # At server startup
@hourly     # Every hour (equivalent to 0 * * * *)
@daily      # Every day at midnight
@weekly     # Every Sunday at midnight
@monthly    # 1st of the month at midnight
@yearly     # January 1st at midnight

Practical Use Cases​

Automatic Database Backup​

# Create the backup script
nano /root/scripts/backup-db.sh
#!/bin/bash
DATE=$(date +%Y%m%d_%H%M%S)
BACKUP_DIR="/root/backups"

# Create folder if it doesn't exist
mkdir -p $BACKUP_DIR

# MySQL/MariaDB backup
mysqldump -u root -p'PASSWORD' my_database > $BACKUP_DIR/my_database_$DATE.sql

# Compress
gzip $BACKUP_DIR/my_database_$DATE.sql

# Delete backups older than 7 days
find $BACKUP_DIR -name "*.sql.gz" -mtime +7 -delete
# Make executable
chmod +x /root/scripts/backup-db.sh

# Add to cron (every day at 4 AM)
crontab -e
0 4 * * * /root/scripts/backup-db.sh

Automatic Service Restart​

# Restart Nginx every day at 5 AM
0 5 * * * systemctl restart nginx

# Restart a FiveM server every 6 hours
0 */6 * * * systemctl restart fivem

Automatic Log Cleanup​

# Delete logs older than 30 days
0 3 * * * find /var/log -name "*.log" -mtime +30 -delete

Automatic System Update​

# Security update every day at 2 AM
0 2 * * * apt update && apt upgrade -y

Disk Space Monitoring​

# Create the script
nano /root/scripts/check-disk.sh
#!/bin/bash
THRESHOLD=80
USAGE=$(df / | tail -1 | awk '{print $5}' | sed 's/%//')

if [ $USAGE -gt $THRESHOLD ]; then
    echo "Alert: Disk at ${USAGE}%" | mail -s "VPS Disk Alert" your@email.com
fi
# Check every hour
0 * * * * /root/scripts/check-disk.sh

Logs and Debugging​

Redirect Output​

# To a log file
0 3 * * * /root/scripts/backup.sh >> /var/log/backup.log 2>&1

# Ignore output
0 3 * * * /root/scripts/backup.sh > /dev/null 2>&1

# Receive by email (if mail is configured)
0 3 * * * /root/scripts/backup.sh

View Cron Logs​

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

# Or
journalctl -u cron

Environment Variables​

Add them at the top of your crontab:

SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
MAILTO=your@email.com

# Your tasks
0 3 * * * /root/scripts/backup.sh

Useful Tools​

Crontab Guru​

Use crontab.guru to verify your cron expressions.

Anacron​

For tasks that must run even if the server was down:

sudo apt install anacron
Tip

Always use absolute paths in your cron scripts, as the environment is different from your interactive session.