umount:tldr:867d9

The command "umount -a" is used to unmount all currently mounted file systems.

The "umount" command is primarily used to detach (or unmount) a previously mounted file system from the directory tree. When a file system is mounted, it becomes accessible and usable in the file system hierarchy, allowing you to read, write, and modify files. Unmounting is the process of making that file system no longer accessible.

In the command "umount -a", the "-a" option stands for "all" and is used to unmount all currently mounted file systems at once rather than unmounting them one by one.

This command is typically used in situations where you want to cleanly shutdown or restart a system, as it ensures that all file systems are unmounted before the system halts or restarts. Additionally, it can be used if you need to free up system resources or want to detach all file systems temporarily.