Objective 3: Control Filesystem Mounting and Unmounting
As discussed in Objective 1: Create Partitions and Filesystems, the Linux directory hierarchy is usually made up of multiple partitions, each joined to the root filesystem. Filesystems on removable media, such as CD-ROMs, USB flash drives, and floppy disks, are joined in the same way, but usually on a temporary basis. Each of these separate filesystems is mounted to the parent filesystem as a directory (or mount point) in the unified hierarchy.
Directories intended as mount points usually don’t contain files or other directories. Instead, they’re just empty directories created solely to mount a filesystem. If a directory that already contains files is used as a mount point, its files are obscured and unavailable until the filesystem is unmounted. Typical mount points include the directories /usr, /home, /var, and others.