How to Check Disk Usage with df and du on Linux

In this tutorial, you'll learn about How to Check Disk Usage with df and du on Linux. We cover key concepts, practical examples, and best practices.

The Problem

Your Linux server is running out of disk space. Applications fail with No space left on device, log writes stop, and you need to find what is consuming the disk space quickly.

Quick Fix

Step 1: Check overall filesystem usage with df

Show disk usage for all mounted filesystems in human-readable format:

df -h

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        98G   82G   12G  88% /
/dev/sdb1       500G  300G  200G  60% /data

The Use% column shows how full each filesystem is.

Step 2: Show filesystem type and inode usage

Some filesystems have free space but run out of inodes:

df -hT
df -i

Step 3: Find the largest directories with du

Scan the root directory to find top-level disk consumers:

sudo du -sh /* | sort -rh | head -10

4.5G    /usr
3.2G    /var
2.1G    /home
1.8G    /opt

Step 4: Drill down into a specific directory

Find large subdirectories under /var:

sudo du -sh /var/* | sort -rh | head -10

2.0G    /var/log
800M    /var/lib
500M    /var/cache

Step 5: List the largest files in a directory

Find individual files over 100MB:

sudo find /var -type f -size +100M -exec ls -lh {} \; | sort -k5 -rh | head -10

-rw-r----- 1 root adm 1.2G Jun 24 10:00 /var/log/syslog.1
-rw-r--r-- 1 root root 800M Jun 23 00:00 /var/log/nginx/access.log

Step 6: Show disk usage of the current directory

Check how much space the current directory uses:

du -sh .

256M    .

Alternative Solutions

Use ncdu for interactive disk analysis

Navigate directories with a terminal UI:

ncdu /var

Use du with --exclude to skip large directories

Ignore mount points or known large paths:

du -sh /* --exclude=/proc --exclude=/sys --exclude=/snap 2>/dev/null

Common Mistakes to Avoid

Using df without -h. Raw byte counts are hard to read. -h shows sizes in human format (G, M, K).

Running du on the root filesystem without excluding mounts. /proc, /sys, and /snap are pseudo-filesystems that du will descend into. Use --exclude.

Not using sudo with du. Without root permissions, du skips directories it cannot read, giving an incomplete picture of disk usage.

Pro Tips

Use du --max-depth for targeted scans. Limit directory depth to speed up scans: du -h --max-depth=2 /var shows two levels of subdirectories.

Use df -i to check inode exhaustion. Full inodes prevent file creation even with free disk space. Check with df -i and clean up many small files.

Use ncdu for interactive exploration. The ncdu tool provides a navigable terminal interface for finding large directories quickly.

Prevention

• Set up log rotation with logrotate to prevent log files from filling the disk.
• Monitor disk usage with df -h and set alerts at 80% and 90% usage.
• Use ncdu for interactive disk usage analysis when dealing with complex directory structures.