All files accessible in a Unix system are arranged in one big tree, the file hierarchy, rooted at /. These files can be spread out over several devices. The mount command serves to attach the file system found
on some device to the big file tree. Conversely, the umount(8) command will detach it again.
The standard form of the mount command, is
mount -t type device dir
This tells the kernel to attach the file system found on device (which is of type type) at the directory dir. The previous contents (if any) and owner and mode of dir become invisible, and as long as this file
system remains mounted, the pathname dir refers to the root of the file system on device.