The df command in Linux is used to display the amount of disk space available and used on the file systems. It shows the available and used space on mounted filesystems, helping users monitor disk usage.

Basic Syntax:

df [options] [filesystem]

Commonly Used Options:

• -h: Human-readable format (displays sizes in KB, MB, GB, etc.).
• -T: Show the filesystem type.
• -a: Include all file systems, even ones that are 0 bytes in size.
• -t <type>: Show only filesystems of the specified type.
• -l: Show only local filesystems (exclude network-mounted file systems).
• -i: Show inode information (useful for checking inode usage).

Basic Usage:

df

Example Output:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/sda1        1024000   512000   512000  50% /
/dev/sdb1        2048000   1024000  1024000  50% /mnt/data
tmpfs            1024000        1000  1023000   1% /run

Explanation of Output:

• Filesystem: The name of the filesystem or device (e.g., /dev/sda1, /dev/sdb1, tmpfs).
• 1K-blocks: The total size of the filesystem in 1K blocks.
• Used: The amount of space used on the filesystem.
• Available: The amount of available space left on the filesystem.
• Use%: The percentage of used space on the filesystem.
• Mounted on: The mount point (directory where the filesystem is mounted) in the system (e.g., /, /mnt/data).

Example with -h (Human-readable format):

df -h

Sample Output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       1000M  500M  500M  50% /
/dev/sdb1       2000M 1000M 1000M  50% /mnt/data
tmpfs            1000M  1M   999M   1% /run

• The output is now in human-readable format (MB, GB) instead of 1K blocks, making it easier to understand the disk usage.

Example with -T (Filesystem type):

df -T

Sample Output:

Filesystem     Type      1K-blocks    Used Available Use% Mounted on
/dev/sda1      ext4       1024000   512000   512000  50% /
/dev/sdb1      ext4       2048000   1024000  1024000  50% /mnt/data
tmpfs          tmpfs       1024000        1000  1023000   1% /run

• The -T option shows the type of each filesystem (e.g., ext4, tmpfs).

Example with -i (Inode information):

df -i

Sample Output:

Filesystem     Inodes  IUsed   IFree IUse% Mounted on
/dev/sda1       256000  1024   254976    1% /
/dev/sdb1       512000  2048   509952    1% /mnt/data
tmpfs           256000     20   255980    1% /run

• Inodes: Filesystem inodes represent individual files and directories.
• IUsed: Number of inodes in use.
• IFree: Number of free inodes available.
• IUse%: Percentage of used inodes on the filesystem.

Example with -a (Include all filesystems):

df -a

Sample Output:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/sda1        1024000   512000   512000  50% /
/dev/sdb1        2048000   1024000  1024000  50% /mnt/data
tmpfs            1024000        1000  1023000   1% /run
/dev/sr0          700000  700000      0  100% /mnt/cdrom

• The -a option includes all filesystems, including the CD-ROM (/dev/sr0), even if their space is fully used (100%).

Example with -t <type> (Filter by filesystem type):

df -t ext4

Sample Output:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/sda1        1024000   512000   512000  50% /
/dev/sdb1        2048000   1024000  1024000  50% /mnt/data

• The -t ext4 option filters the output to show only filesystems of type ext4.

Example with -l (Local filesystems only):

df -l

Sample Output:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/sda1        1024000   512000   512000  50% /
/dev/sdb1        2048000   1024000  1024000  50% /mnt/data

• The -l option filters out network-mounted file systems (such as NFS, CIFS, etc.) and only shows local filesystems.

Conclusion:

The df command provides an overview of disk space usage, which is essential for monitoring storage on a Linux system. By using options like -h, -T, -i, and others, you can customize the output to get more detailed information or to filter specific types of filesystems. It's a very useful tool for ensuring you have enough disk space and for troubleshooting disk space issues.