How to monitor disk space and avoid running out

When the disk fills up, databases stop, logs stop writing and the site can go down. Prevention is simple.

1. Check space

df -h

2. Find what uses space

du -sh /var/* | sort -h
du -sh /home/* | sort -h

Frequent culprits: uncleaned logs, old backups, unused Docker images (see Docker cleanup).

3. Automatic alert at 85%

A simple script that runs in cron and warns you:

#!/bin/bash
USED=$(df / | awk 'NR==2 {print $5}' | tr -d '%')
if [ "$USED" -gt 85 ]; then
  echo "Disk at $USED% on $(hostname)" | mail -s "Disk alert" [email protected]
fi

0 * * * * /usr/local/bin/check-disk.sh

4. Free up space

• Configure log rotation, see logrotate.
• Move backups to a Backup Box.
• If it is still too little, move to a plan with a bigger disk.