df Command Cheat Sheet

df (disk free) displays the amount of available disk space for file systems on which the invoking user has appropriate read access. It is the primary tool for checking "Why is my server full?".

Synopsis

df [OPTION]... [FILE]...

Basic Usage

Check All Mounted Filesystems

df

Output (default is 1K blocks):

Filesystem     1K-blocks      Used Available Use% Mounted on
tmpfs             810660      2028    808632   1% /run
/dev/sda2      102687672  20456128  76983228  21% /

Human Readable Output (-h)

The most common way to use df. Shows sizes in KB, MB, GB.

df -h

Output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda2        98G   20G   74G  21% /

Powers of 1000 (-H)

Uses SI units (1kB = 1000 bytes) instead of IEC units (1KiB = 1024 bytes).

df -H

Filesystem Types

Show Filesystem Type (-T)

Displays an extra column with the filesystem type (ext4, xfs, btrfs, tmpfs, etc.).

df -Th

Include/Exclude Specific Types

Show only ext4 filesystems:

df -t ext4 -h

Exclude tmpfs (memory) and squashfs (loops) to see "real" physical disks:

df -x tmpfs -x squashfs -h

Inode Usage (-i)

Sometimes a disk is not full by size, but runs out of inodes (index nodes), usually due to millions of tiny files.

df -i

Output:

Filesystem       Inodes  IUsed    IFree IUse% Mounted on
/dev/sda2       6553600 250000  6303600    4% /

Specific Targets

Check Specific Mount Point

df -h /home

Check File's Partition

Pass a file path to see which partition holds it.

df -h /var/log/syslog

Detailed Options

Total (-total)

Adds a grand total line at the bottom.

df -h --total

Local Only (-l)

List only local filesystems (excludes NFS, SMB mounts).

df -hl

All Filesystems (-a)

Include dummy filesystems (proc, sysfs, debugfs) which are normally hidden (size 0).

df -a

Custom Output Format

Use --output to display specific fields.

df --output=source,pcent,target -h

Fields: source, fstype, itotal, iused, iavail, ipcent, size, used, avail, pcent, file, target.

Practical Examples

Find What's Filling Up Root

First check usage:

df -h /

sudo du -sh /var/* | sort -hr | head -n 5

Check External Drives

Usually mounted under /media or /mnt.

df -h | grep "^/dev/sd"

Monitoring Script

Simple one-liner to check if root partition is > 90% full.

df -h / | grep / | awk '{ print $5 }' | sed 's/%//g' | awk '$1 > 90 { print "Disk Critical" }'

Exit Status

Notes

• df reads data from the superblock of the filesystem, making it much faster than du (which walks the directory tree).
• If you delete a large file but df doesn't show released space, a running process might still hold the file open. Check with lsof +L1.