df:tldr:eff7d

The command "df" in Linux and UNIX systems stands for "disk free" and is used to display information about the amount of free disk space on a file system.

When you run the "df" command without any options or arguments, it will display information about all mounted file systems in a table format. The information includes the total size of the file system, the amount of used space, the available (free) space, the percentage of used and available space, and the mount point where the file system is located.

Here is an example output of the "df" command:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/sda1        2088456 1795484    193064  91% /
/dev/sdb1        5147496 2705640   2131856  56% /home
tmpfs             511176       4    511172   1% /dev/shm

From the output, you can see that there are three file systems listed:

• "/dev/sda1" with a total size of 2088456 kilobytes, used space of 1795484 kilobytes, available space of 193064 kilobytes, and it is mounted as the root ("/") directory.
• "/dev/sdb1" with a total size of 5147496 kilobytes, used space of 2705640 kilobytes, available space of 2131856 kilobytes, and it is mounted as the "/home" directory.
• "tmpfs" with a total size of 511176 kilobytes, used space of 4 kilobytes, available space of 511172 kilobytes, and it is mounted as the "/dev/shm" directory.

The "df" command can be useful to monitor the disk space usage on a system and ensure that enough space is available for storing files and running applications.