Infrastructure & Operations › Linux & Servers

Disk Space (df, du)

Finding what's filling up the disk.

Also known as: df, du, disk full, disk space

Two commands answer two different questions:

• df (disk free): how full is each filesystem?
• du (disk usage): how much space do these files and directories use?

df -h                      # -h = human readable (GB, MB)
# e.g.
# Filesystem  Size  Used Avail Use% Mounted on
# /dev/sda1    50G   47G  1.2G  98% /

du -sh /var/log            # -s summary, -h human readable
du -h --max-depth=1 /var | sort -h    # biggest subfolders of /var, largest last

Hunting for what filled the disk

Start with df -h to see which filesystem is nearly full, then drill down with du one level at a time, always staying on the full filesystem (du -x avoids crossing into other mounts):

sudo du -xh --max-depth=1 / | sort -h | tail

Repeat inside the largest directory until you find the culprit. Usual suspects: logs in /var/log (see log rotation), old Docker images and volumes, package caches, core dumps, and database files.

Two surprises

• Deleted but still using space. If a running process holds a file open, deleting it doesn’t free the space until the process closes it or restarts. df stays high while du can’t find anything.
• Running out of inodes. df -i shows inode usage. Millions of tiny files can exhaust inodes while plenty of space remains.

A full disk makes databases and applications fail in strange ways, so alert before it hits 100%. See system monitoring tools.