How to use the command "df" (with examples)

The “df” command provides an overview of the filesystem disk space usage on a Linux system. It is a useful command for monitoring disk usage and identifying any potential storage issues. This article will illustrate several use cases of the “df” command and provide explanations for each argument used.

Use case 1: Display all filesystems and their disk usage

Code:

df

Motivation: Running the “df” command without any arguments will display information about all mounted filesystems and their respective disk space usage. This is useful for getting a general overview of the disk usage on the system and identifying if any filesystems are running out of space.

Explanation: In this use case, no arguments are provided to the “df” command. It will automatically display the filesystem, total size, used space, available space, percentage of usage, and mount point for each mounted filesystem.

Example output:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/sda1       1024000  316428    707572  31% /
tmpfs            409600       4    409596   1% /dev/shm
/dev/sdb1       2048000 1648032    399968  81% /mnt/data

Use case 2: Display all filesystems and their disk usage in human-readable form

Code:

df -h

Motivation: The “-h” option is used to display the disk usage in a human-readable form, making it easier to interpret the sizes. Instead of displaying the usage in kilobytes (KB), it will display in megabytes (MB) or gigabytes (GB) depending on the size.

Explanation: In this use case, the “-h” option is added to the “df” command. This option modifies the output to display the disk usage in a human-readable format. For example, sizes will be displayed as “100M” for 100 megabytes or “2G” for 2 gigabytes.

Example output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       1000M  309M  691M  31% /
tmpfs            400M    4K  400M   1% /dev/shm
/dev/sdb1       2000M 1610M  390M  81% /mnt/data

Use case 3: Display the filesystem and its disk usage containing the given file or directory

Code:

df path/to/file_or_directory

Motivation: This use case is useful when you want to determine the filesystem where a particular file or directory resides. By specifying the path to the file or directory, the “df” command will display the filesystem and its associated disk usage.

Explanation: In this use case, the “df” command is used with the path argument to a specific file or directory. The command will display the filesystem on which the file or directory is located and provide the disk usage information for that particular filesystem.

Example output:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/sda1       1024000  316428    707572  31% /

Use case 4: Display statistics on the number of free inodes

Code:

df -i

Motivation: Inodes are data structures used to store metadata for files and directories on a filesystem. The “-i” option in the “df” command allows you to display statistics on the number of free inodes available on each filesystem. This is useful for monitoring the number of available inodes and determining if a filesystem is running out.

Explanation: In this use case, the “-i” option is used with the “df” command. This option modifies the output to display statistics on the number of free inodes available on each filesystem. It will show the total number of inodes, the number of used inodes, the number of free inodes, and the percentage of inodes used.

Example output:

Filesystem       Inodes  IUsed    IFree IUse% Mounted on
/dev/sda1         65536  16384    49152   25% /
tmpfs            102400      4   102396    1% /dev/shm
/dev/sdb1        131072  52480    78592   40% /mnt/data

Use case 5: Display filesystems but exclude the specified types

Code:

df -x squashfs -x tmpfs

Motivation: Sometimes you may want to exclude certain types of filesystems from the output of the “df” command. This use case demonstrates how to exclude “squashfs” and “tmpfs” filesystems from the output.

Explanation: In this use case, the “-x” option is used twice with the “df” command, followed by the filesystem types to exclude. “squashfs” and “tmpfs” filesystems will be excluded from the output. This can be useful if you want to focus only on specific types of filesystems or exclude certain types from the output.

Example output:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/sda1       1024000  316428    707572  31% /
/dev/sdb1       2048000 1648032    399968  81% /mnt/data

Conclusion:

The “df” command is a versatile tool for displaying filesystem disk space usage on a Linux system. It provides valuable information about mounted filesystems, their disk usage, and the number of free inodes. By utilizing the different options and arguments available with the “df” command, you can effectively monitor disk usage and identify any potential storage issues.