How to Check Disk Usage with df -h

What this is

This guide explains how to check disk usage on Linux with df -h and interpret the result.

What it is for

• Prevent outages caused by a full disk
• Find which filesystem is running out of space

Prerequisites

• SSH access

Step-by-step

Step 1) Run df -h

df -h

What it does: Shows disk usage for mounted filesystems in human-readable units.

Expected output: Columns like Size, Used, Avail, Use%, Mounted on.

Step 2) Focus on the root filesystem

Look for the line mounted on /.

Warning threshold: If Use% is above 85–90%, plan cleanup soon; near 100% can break services.

Step 3) Identify what is filling the disk

sudo du -xh / --max-depth=2 2>/dev/null | sort -h | tail -n 20

Expected output: Largest directories.

Warnings & notes

• Some filesystems (tmpfs) are RAM-based; they are normal.
• Cleanup should be careful: deleting logs or database files can cause issues.

Final verification

df -h

Conclusion

df -h is your first “health check” for disk space. Use it regularly to avoid downtime.