Linux df Command

last modified February 25, 2025

The df command in Linux is used to display disk space usage for file systems. It provides information about the total, used, and available space on mounted file systems. This tutorial covers basic and advanced usage of df with practical examples.

df is commonly used for monitoring disk space, identifying full file systems, and managing storage resources.

Basic Usage

This checks disk usage across all mounts.

df

The df command lists all mounted file systems in a table with columns: Filesystem, 1K-blocks, Used, Available, Use%, and Mounted on. Output is in 1KB blocks by default, showing raw numbers. For example, it might list /dev/sda1 with its usage stats. Use mount to see all mounts beforehand. If a file system is full, Use% nears 100%.

Display in Human-Readable Format

This shows disk usage in easy units.

df -h

The -h (human-readable) option converts sizes to units like MB, GB, or TB, making it easier to interpret than raw blocks. For instance, 1.2G is clearer than 1234567 blocks. It’s the go-to option for quick checks. Combine with watch df -h to refresh every 2 seconds. Sizes adjust dynamically based on magnitude.

Display Specific File System

This checks usage for the root partition.

df /dev/sda1

The df command targets /dev/sda1, showing only its usage stats. You can use a device (e.g., /dev/sdb2) or mount point (e.g., /). Useful for focusing on a specific disk. Run lsblk or df -h to find device names. If unmounted, it shows nothing unless specified via a file system path.

Display Inode Usage

This monitors inode availability.

df -i

The -i (inodes) option lists total, used, and free inodes per file system instead of space. Inodes track file metadata; running out prevents new files, even with free space. For example, /dev/sda1 might show "IUsed: 5000, IFree: 10000". Critical for directories with many small files. Check with ls -li to see inode numbers in a directory.

Exclude Specific File System Types

This filters out temporary file systems.

df -x tmpfs -x devtmpfs

The -x option excludes tmpfs (RAM-based) and devtmpfs (device files) from the output, focusing on physical storage. Multiple -x flags stack. Run df -T first to identify types (e.g., ext4). Useful for ignoring virtual mounts like /dev or /run. Output still shows blocks unless -h is added.

Display File System Type

This identifies file system formats.

df -T

The -T (type) option adds a "Type" column, e.g., ext4, ntfs, or btrfs, to the output. Helps distinguish between local disks and network mounts (e.g., nfs). Combine with -h (df -hT) for readability. Use lsblk -f for a similar view with device details. Essential for troubleshooting file system-specific issues.

Advanced: Display Total Disk Space

This sums up usage across all mounts.

df -h --total

The --total option appends a "total" row summing Used, Available, and Use% across all listed file systems. With -h, it’s in readable units (e.g., "Total: 500G used, 1T available"). Ignores excluded types if -x is used. Perfect for an overall storage snapshot. Compare with du -sh / for directory-specific totals, noting root access might be needed.

Example: Filter by Mount Point

This checks space on a specific mount.

df -h /home

The df -h /home command shows usage for the file system mounted at /home, like /dev/sdb1 if partitioned separately. Unlike /dev/sda1, it uses the mount point, not device name. Handy for user directories or external drives. Run mount | grep /home to confirm the mount. Output is human-readable, showing GB or TB as needed.

Example: Sort Output by Usage

This ranks file systems by usage percentage.

df -h | sort -k5 -r

This pipes df -h output to sort, ordering by the 5th column (Use%, e.g., "95%") in reverse (-r)—highest first. Identifies fullest file systems quickly. The header might sort incorrectly; use df -h | tail -n +2 | sort -k5 -r to skip it. Add head to limit results. Useful for spotting space hogs on busy servers.

Example: Check Space with Threshold

This flags nearly full file systems.

df -h | awk '$5+0 >= 90 {print $0}'

This uses awk to filter df -h output, printing lines where Use% (column 5) is 90% or higher. The +0 strips the "%" for numeric comparison. For example, /dev/sda1 100G 95G 5G 95% / would appear. Adjust the threshold (e.g., 80) as needed. Pipe to mail -s "Disk Full" admin@example.com for alerts. Monitors critical storage levels.

Best Practices for df

• Use -h for Readability: Always use -h for human-readable output.
• Monitor Inodes: Use -i to monitor inode usage, especially on systems with many small files.
• Exclude Unnecessary File Systems: Use -x to exclude temporary or virtual file systems.
• Check Specific File Systems: Use df with a specific file system path for targeted monitoring.

Source

GNU df Manual

In this article, we have explored various examples of using the df command for monitoring disk space usage, including human-readable output, inode usage, and excluding specific file systems.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

List all Linux tutorials.