Linux Filesystem Hierarchy

umount /dev/hda2
$
umount /usr
$
See the man page for further instructions on how to use the command. It is imperative that you always
unmount a mounted floppy. Don't just pop the floppy out of the drive! Because of disk caching, the data is not
Linux Filesystem Hierarchy
Chapter 1. Linux Filesystem Hierarchy
54

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necessarily written to the floppy until you unmount it, so removing the floppy from the drive too early might
cause the contents to become garbled. If you only read from the floppy, this is not very likely, but if you write,
even accidentally, the result may be catastrophic.
Mounting and unmounting requires super user privileges, i.e., only root can do it. The reason for this is that if
any user can mount a floppy on any directory, then it is rather easy to create a floppy with, say, a Trojan horse
disguised as 
/bin/sh
, or any other often used program. However, it is often necessary to allow users to use
floppies, and there are several ways to do this:
Give the users the root password. This is obviously bad security, but is the easiest solution. It works
well if there is no need for security anyway, which is the case on many non−networked, personal
systems.
• 
Use a program such as sudo to allow users to use mount. This is still bad security, but doesn't directly
give super user privileges to everyone. [1]
• 
Make the users use mtools, a package for manipulating MS−DOS filesystems, without mounting
them. This works well if MS−DOS floppies are all that is needed, but is rather awkward otherwise.
• 
List the floppy devices and their allowable mount points together with the suitable options in
/etc/fstab
.
• 
The last alternative can be implemented by adding a line like the following to the 
/etc/fstab
 file:
  /dev/fd0 /floppy
  msdos user,noauto 0 0
The columns are: device file to mount, directory to mount on, filesystem type, options, backup frequency
(used by dump), and fsck pass number (to specify the order in which filesystems should be checked upon
boot; 0 means no check).
The 
noauto
 option stops this mount to be done automatically when the system is started (i.e., it stops mount
−a
 from mounting it). The 
user
 option allows any user to mount the filesystem, and, because of security
reasons, disallows execution of programs (normal or setuid) and interpretation of device files from the
mounted filesystem. After this, any user can mount a floppy with an msdos filesystem with the following
command:
$