Raspberry Pi online course

Check Disk Space on Raspberry Pi with df

Learn how to use df on Raspberry Pi OS to check filesystem capacity, used space, available space, mounted partitions, and low-storage problems.

Available storage is important on a Raspberry Pi. Operating-system updates, package installations, logs, downloads, databases, and project files all need room on the storage device. When a filesystem becomes full, updates may fail, applications may be unable to write data, and services can behave unpredictably.

This lesson uses the df command from a Raspberry Pi OS terminal. You can work locally or connect through SSH. If you need a terminal introduction, see Terminal in Raspbian or access Raspbian remotely.

What Disk-Space Checks Tell You

A disk-space check measures storage on a filesystem. A filesystem is a formatted storage area organized for files and directories. It may occupy a whole device or only a partition, which is a logical section of a storage device.

Disk space is different from several related measurements:

• Filesystem capacity is the total storage available to that filesystem.
• Used space is storage currently occupied by files and filesystem data.
• Available space is the storage that remains usable for ordinary file creation.
• RAM usage describes working memory, not persistent SD-card, eMMC, or USB storage. A command such as free is used for memory checks.
• File or directory size describes how much space particular data consumes. The du command helps locate that data.

The df command answers “How much space is free on each filesystem?” It does not answer “Which directory is using the space?”

The df Command

df is the standard Linux utility for reporting disk-space usage for mounted filesystems. A filesystem is mounted when the operating system makes it accessible through a directory called a mount point. The main Raspberry Pi OS filesystem is normally mounted at /, called the root filesystem.

Run df without options to list mounted filesystems:

df

The default report uses the system's block-based units. A block is a unit used internally by filesystems and by some command-line reports, so the numbers may be less immediately understandable than megabytes or gigabytes.

Running df reports filesystem-level totals. It does not provide a directory-by-directory breakdown of the root filesystem.

Use Human-Readable Output with df -h

The -h option means human-readable. It scales values into convenient units such as K, M, G, and T:

df -h

Typical output looks similar to this:

Filesystem      Size  Used Avail Use% Mounted on
/dev/mmcblk0p2   29G   11G   17G  40% /
tmpfs            1.0G     0  1.0G   0% /dev/shm
/dev/mmcblk0p1  256M   62M  194M  25% /boot

The exact device names, sizes, filesystem entries, and boot mount point depend on your Raspberry Pi model, operating-system release, storage device, and configuration. Human-readable values are rounded for quick interpretation, so they may not add up exactly when compared manually.

Reading df Output

Each row represents a mounted filesystem or pseudo-filesystem. The root row, identified by the mount point /, is usually the most important row for general Raspberry Pi storage questions.

Important filesystem entries

Entries such as tmpfs, devtmpfs, and other system mounts can make the output look crowded. They do not represent SD-card capacity in the same way as the root filesystem row.

Check One Filesystem or Path

Pass a path to df when you want to identify the filesystem containing that path. This is useful when several partitions or mounts exist, because each filesystem has an independent capacity and available-space limit.

df -h /
df -h /home
df -h ~

df -h / reports the filesystem containing the operating-system root directory. df -h /home reports the filesystem containing the home-directory path. df -h ~ checks the current user's home directory; the shell expands ~ to that directory before running the command.

If /home is not a separate mount, its result will normally be the same filesystem as /. If you placed home directories on another partition or USB drive, it can report a different filesystem and different available space.

Check the boot filesystem

Some Raspberry Pi OS installations use a separate boot partition. Its mount location can differ between releases and setups. Common locations include /boot and a boot-related path below /boot, but do not assume one location applies to every system.

df -h /boot

If that path is not the boot mount point on your system, inspect the mounts with mount or findmnt, then run df -h against the path shown for the boot filesystem.

Useful df Options

What Low Disk Space Means

A filesystem close to full can cause failed updates, failed package installations, failed writes, application errors, incomplete downloads, and service or boot problems. These problems may appear before the displayed capacity reaches exactly 100 percent.

As a practical warning, investigate sustained usage above roughly 80–90 percent, especially on a small root filesystem. These are warning levels, not universal rules: a system's workload, database size, logging rate, and maintenance schedule determine how much free space it needs. Avoid waiting until a filesystem is completely full.

The Available value can be lower than a simple calculation of total size minus used size. Filesystem metadata, rounding, and blocks reserved for administrative use can account for differences. On some filesystems, reserved blocks help the system recover from a nearly full condition and may not be available to ordinary users. Treat Avail as the practical amount available to the current user.

When df Finds a Full Filesystem

Use df to identify which filesystem is full, then use du to estimate which directories and files consume space. These commands answer different questions:

• df reports capacity, used space, and available space for mounted filesystems.
• du estimates space used by directories and files.

For example, to inspect the current user's home directory:

du -sh ~

To list the largest top-level directories on the root filesystem without crossing into other mounted filesystems, run:

sudo du -xhd1 / 2>/dev/null | sort -h

The -x option keeps the scan on the same filesystem as /`. The -d1 option limits the report to one directory level, and sort -h sorts human-readable sizes. Permission errors are redirected away with 2>/dev/null.

df -h /

df -T -h

df -h /path/used/by/the/application

df -i

# List mounted filesystems
 df

# Use readable units
 df -h

# Check the root filesystem
 df -h /

# Check the current user's home filesystem
 df -h ~

# Show filesystem types
 df -T -h

# Check inode availability
 df -i

# Estimate home-directory usage
 du -sh ~