df

Updated

September 4, 2026

Overview

df reports filesystem disk space usage for mounted filesystems. First stop for “is the disk full?” before descending into per-directory du/dust/ncdu. It answers capacity questions at mount granularity, not “which folder is large?”.

Syntax

df [options] [file...]

When given a path, reports the filesystem containing that path.

Common Options

Option	Description
`-h`, `--human-readable`	Sizes in powers of 1024
`-H`	Powers of 1000
`-T`	Print filesystem type
`-i`	Inode usage instead of blocks
`-l`	Local filesystems only
`-P`	POSIX output format (stable columns)
`--output=FIELD_LIST`	Select columns (GNU)
`-t type` / `-x type`	Include / exclude filesystem type
`-a`	Include pseudo, duplicate, inaccessible

Examples with Explanations

Everyday overview

df -h
df -hT
df -h -x tmpfs -x devtmpfs

Inodes exhausted?

df -ih

Millions of tiny files can exhaust inodes while df -h still shows free blocks — common on mail spool or container image layers.

Specific path

df -h /var
df -h .
df -h /var/lib/docker

Shows the mount that holds that path (critical with bind mounts).

Portable scripting

df -P / | tail -1
df -P --output=target,pcent /var

JSON-ish via findmnt (often clearer)

findmnt -D
findmnt -no TARGET,FSTYPE,USE% /

Correlate devices

df -hT
lsblk -f
findmnt

Root reserved space

On ext*, ~5% may be reserved for root. Use% at 100% can still allow root writes; non-root fails earlier.

Understanding output

Field	Meaning
Filesystem	Device or source
Size / Used / Avail	Block capacity
Use%	Used / size (rounding applies)
Mounted on	Mountpoint
Type (`-T`)	ext4, xfs, btrfs, nfs, …

Notes / Pitfalls

tmpfs/overlay/snap noise hides real disks — filter with -x / -t / duf -only local.
NFS free space can reflect server quotas, not your expectation.
Btrfs/ZFS free space may need native tools for accurate “allocatable” views.
Deleted-but-open files still consume space until close (lsof + (deleted)).
Don’t parse human -h in scripts — use -P or --output bytes fields.

2026-relevant notes

Prefer duf interactively; keep df in scripts and alerts.
Container hosts: full /var/lib/containerd or docker roots are common; df the right mount.
Metrics: node exporters scrape the same ideas — alert on both block and inode %.

Additional Resources

man df