Mount Points

A

When we talk about mount points in Linux, we are referring to the location in the directory tree where a file system is attached to the operating system. A file system can be a local hard drive, a network share, or a removable storage device, and it needs to be attached to a mount point in order to be accessible.

Now, let's review each option:

A. Every existing directory can be used as a mount point. This statement is true. Any existing directory in the file system can be used as a mount point, as long as it is empty or doesn't have any data that will be overwritten by the mounted file system.

B. Only empty directories can be used as a mount point. This statement is partially true. While empty directories are a good option for mount points, directories that have data in them can also be used. However, any data within the directory will be hidden while the file system is mounted, and may not be accessible until the file system is unmounted.

C. Directories need to have the SetUID flag set to be used as a mount point. This statement is false. The SetUID flag is used to give a program the same permissions as the owner of the program. It has nothing to do with mount points, and is not required for a directory to be used as a mount point.

D. Files within a directory are deleted when the directory is used as a mount point. This statement is false. When a directory is used as a mount point, the files within the directory are not deleted. However, they will be hidden and inaccessible until the file system is unmounted.

In summary, option A is correct and options B, C, and D are incorrect.