The //**df**// command in Linux and Unix-like systems is used to display information about the file system disk space usage. It shows the total amount of space available, used space, and free space on all file systems, including the file system type, mount points, and other details.

Here is the basic syntax for the **df** command:

<code>
df [options] [filesystem]</code>
filesystem is the name of the file system you want to check the disk space usage.

Here are some examples of the **df** command:

1. To display the disk space usage of all file systems
<code>
$ df</code>

2. To display the disk space usage of a specific file system
<code>
$ df /dev/sda1</code>

3. To display the disk space usage in human-readable format
<code>
$ df -h</code>
Note: The **-h** option is used to display the disk space usage in human-readable format.

4. To display the inodes usage of all file systems
<code>
$ df -i</code>
Note: The **-i** option is used to display the inodes usage of all file systems

5. To display the disk space usage of a specific file system and its subdirectories
<code>
$ df -ah /</code>
Note: The **-a** option is used to display the disk space usage of all file systems including the ones with 0 blocks, **-h** option is used to display the disk space usage in human-readable format

The **df** command is useful for checking the disk space usage on the file system, it allows you to identify the total amount of space available, used space, and free space on all file systems, including the file system type, mount points, and other details. This command is useful to monitor the disk space usage, identify the file systems that are running out of space, and take appropriate action to free up space. Additionally, the **df** command can be used in conjunction with other commands like **[[unix_commands:du|du]]** to further investigate the disk space usage of specific directories or files.