4. Floppies, Hard Disks, and the Like

4.1 Managing Devices

You have never thought about it, but the DOS command FORMAT A: does a lot more work than it seems. In fact, when you issue the command FORMAT it will: 1) physically format the disk; 2) create the A:\ directory (= create a filesystem); 3) make the disk available to the user (= mount the disk).

These three steps are addressed separately under Linux. You can use floppies in MS-DOS format, though other formats are available and are better---the MS-DOS format won't let you use long filenames. Here is how to prepare a disk (you'll need to start a session as root):

• To format a standard 1.44 meg floppy disk (A:):

  # fdformat /dev/fd0H1440
  

• To create a filesystem:

  # mkfs -t ext2 -c /dev/fd0H1440
  

  To create an MS-DOS filesystem, use msdos instead of ext2. Before using the disk, you must mount it.
• To mount the disk:

  # mount -t ext2 /dev/fd0 /mnt
  

  or

  # mount -t msdos /dev/fd0 /mnt
  

  Now you can address the files in the floppy. When you've finished, before extracting the disk you must unmount it.
• To unmount the disk:

  # umount /mnt
  

Now you can extract the disk. Obviously, you have to fdformat and mkfs only unformatted disks, not previously used ones. If you want to use drive B:, refer to fd1H1440 and fd1 instead of fd0H1440 and fd0 in the examples above.

All you used to do with A: or B: is now done using /mnt instead. Examples:

DOS                                     Linux
---------------------------------------------------------------------

C:\GUIDO>DIR A:                         $ ls /mnt
C:\GUIDO>COPY A:*.*                     $ cp /mnt/* /docs/temp
C:\GUIDO>COPY *.ZIP A:                  $ cp *.zip /mnt/zip
C:\GUIDO>A:                             $ cd /mnt
A:>_                                    /mnt/$ _

If you don't like this mounting/unmounting thing, use the mtools suite: it's a set of commands that are perfectly equivalent to their DOS counterpart, but start with an `m': i.e., mformat, mdir, mdel, and so on. They can even preserve long file names, but not file permissions. Use these commands as you'd use the DOS commands and rest in peace.

Needless to say, what holds for floppies also holds for other devices; for instance, you may want to mount another hard disk or a CD-ROM drive. Here's how to mount the CD-ROM:

# mount -t iso9660 /dev/cdrom /mnt

This was the ``official'' way to mount your disks, but there's a trick in store. Since it's a bit of a nuisance having to be root to mount a floppy or a CD-ROM, every user can be allowed to mount them this way:

• as root, do the following:

  ~# mkdir /mnt/a: ; mkdir /mnt/a ; mkdir /mnt/cdrom
  ~# chmod 777 /mnt/a* /mnt/cd*
  ~# # make sure that the CD-ROM device is right
  ~# chmod 666 /dev/hdb ; chmod 666 /dev/fd*
  

• add in /etc/fstab the following lines:

  /dev/cdrom      /mnt/cdrom  iso9660 ro,user,noauto          0       0
  /dev/fd0        /mnt/a:     msdos   user,noauto             0       0
  /dev/fd0        /mnt/a      ext2    user,noauto             0       0
  

Now, to mount a DOS floppy, an ext2 floppy, and a CD-ROM:

$ mount /mnt/a:
$ mount /mnt/a
$ mount /mnt/cdrom

/mnt/a, /mnt/a:, and /mnt/cdrom can now be accessed by every user. Remember that allowing everyone to mount disks this way is a gaping security hole, if you care.

4.2 Backing Up

Now that you know how to handle floppies etc., a couple of lines to see how to do your backup. There are several packages to help you, but the very least you can do for a multi-volume backup is (as root):

# tar -M -cvf /dev/fd0H1440 dir_to_backup/

Make sure to have a formatted floppy in the drive, and several more ready. To restore your stuff, insert the first floppy in the drive and do:

# tar -M -xpvf /dev/fd0H1440