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How to Check Disk Space in Linux

The two commands that answer "how full is my disk" and "what is using all the space" — df and du — plus how to find the biggest directories fast.

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The short version: df -h shows free space per filesystem · du -sh /path shows how much a directory uses · find the biggest dirs with du -h --max-depth=1 / | sort -h · check inode exhaustion with df -i.

df: how full is each filesystem

df ("disk free") reports used and available space per mounted filesystem. The -h flag makes it human-readable, which is the difference between 490162316 and 468G.

Filesystem usage, human-readable
df -h

# A single filesystem or path
df -h /home

# Show the filesystem type too
df -hT

# Inode usage — the check for 'full' disks that have free space
df -i
The columns of df -h
ColumnMeaning
Filesystemthe device or pseudo-device mounted at that point
Size / Used / Availtotal, used and available space
Use%percentage used — the number to watch
Mounted onwhere the filesystem lives in the tree

du: what is using the space

Once df tells you a filesystem is nearly full, du ("disk usage") finds what is using it. It sums directory contents recursively, so run it on the narrowest path you can — scanning / counts every file on the system.

Directory sizes, from a single folder to the whole tree
# Size of one directory, summarized (not a per-file list)
du -sh /var/log

# Size of every item in the current directory
du -sh *

# Largest subdirectories, one level deep, sorted biggest-first
du -h --max-depth=1 /var 2>/dev/null | sort -h

# Top-level directories of the whole system, sorted
du -x -h --max-depth=1 / 2>/dev/null | sort -h

Use -x (stay on one filesystem) when scanning /, otherwise du descends into every mounted filesystem and the numbers stop making sense. Redirect errors to /dev/null so permission-denied warnings do not drown the useful output.

Find the biggest files, not just directories

The largest files anywhere under a path
# The 20 largest files under /var, biggest last
find /var -type f -printf '%s %p\n' 2>/dev/null | sort -n | tail -20

# Human-readable version
find /var -type f -exec du -h {} + 2>/dev/null | sort -h | tail -20

The first form is fast because it uses the file's recorded size directly; the second is human-readable but slower because it stats every file. On a busy production box, prefer the -printf form.

When df says full but there is space

Two classic gotchas produce this. First, inodes: a filesystem can run out of directory entries before it runs out of bytes — millions of tiny files, common with mail queues, cache dirs and session stores. df -i shows inode use; if IUse% is 100% while space remains, that is your answer.

Second, deleted-but-open files: on Linux, a process holding a deleted file open keeps its space allocated until the process exits. The space is used but invisible to du.

Find processes holding deleted files open
# Show deleted files still held open (the 'deleted' marker)
sudo lsof +L1

# The top consumers by size
sudo lsof +L1 | awk '{print $1, $7}' | sort -k2 -nr | head

Restarting the owning process releases the space. This is the single most common reason a server shows a full disk that a reboot "mysteriously" fixes.

Frequently asked questions

What is the difference between df and du?

df reports free space per mounted filesystem, from the filesystem metadata. du sums the size of files and directories you point it at. They answer different questions: df says how full the disk is, du says what is using it.

Why do df and du disagree about used space?

Because they count differently: du sees only files it can read and misses deleted-but-open files, while df reports allocation from the filesystem. A large df/du gap usually means a process is holding a deleted file open — find it with lsof +L1 and restart the process.

What is an inode and why does running out matter?

An inode is the metadata record for a file or directory. A filesystem has a fixed number, so millions of tiny files can exhaust inodes before exhausting bytes. Check with df -i; if IUse% is 100%, delete files even though space looks available.

Is there an interactive way to explore disk usage?

Yes — ncdu is a terminal-based, interactive disk-usage viewer you can navigate with arrow keys and delete from directly. Install it (apt install ncdu or dnf install ncdu) and run ncdu /path when you need to drill down quickly.