A free Basic UNIX-training with muLinux

Access to Floppies

Under UNIX there are no drive letters as in DOS.

The system used to access floppies and hard disks originated at a time when personal computers had only one or two floppy-drives (A:, B:). Later hard disks where added
(C:, D:, ...).

This raises some questions:

• i.e., How can I manage more disks than the alphabet has letters?
• I want to save my data, where shall I put it, on which drive and in what directory? In Windows, drives are simply specified with letters instead of the descriptive terms common to Linux such as hda1, hda5, hdb1, etc.
• How can I add hard disks without changing the structure of my data?

Floppies have a secondary role in the Unix world. The Superuser can even deny access to floppies for the normal user. Unix was meant to work with multiple hard disks. Therefore the structure of the data needs to be independent of the drive space. Directories in Unix can be put on hard disks, floppies, and in RAM, while keeping the user's data unchanged. For example, the user data is always in the directory /home no matter what drive is used.

Mounting the floppy-drive

Most of the time there are already mountpoints for changing drives. Unfortunately the different Unix versions don't use a standardized mountpoint. Sometimes they are located in the directory /mnt In other versions the directory is /floppy. Under muLinux the directory is /a. You can make any directory as mountpoint and use the command mount plus an option such as /fd0 to access it.

The option for the mount command is the device name of the floppy drive. While looking at the directory structure, you find the directory /dev as place for device files. There, the devices are files. The first floppy drive, under DOS the A: drive, is written as the file /dev/fd0.

Remove the muLinux boot disk and insert a DOS floppy. To mount the floppy drive into the directory /a, you enter the following:

/# mount /dev/fd0 /a

muLinux automatically recognizes if this is a DOS or a Linux disk. Then you can display the contents of the disk:

/# ls /a

Before you can remove the disk from the drive, you must unmount it. For this you need the command umount with the name of the device and the mountpoint.

/# umount /a

To see what is mounted, just enter the command mount without options:

/# mount
/dev/ram0 on / type ext2 (rw)
/proc on /proc type proc (rw)
/dev/ram1 on /usr type ext2 (rw)
/dev/ram2 on /tmp type ext2 (rw)
/dev/fd0 on /a type umdos (rw)
/# _

You see RAM-disks (/dev/ram*) with the mountpoints /, /usr and /tmp. And the special directory /proc. you also see the type. The standard file system under Linux is ext2.

The bold line appears only because you have mounted a DOS disk. Using the command history (cursor up arrow) you can quickly select the needed command. You can then mount the floppy drive and try a few things.

/# mount /dev/fd0 /a
/# cd /a
/a# _

Now you are in the mounted floppy drive. Try creating a file with a very long name:

/a# mkdir abcdefghijklmnopqrstuvwxyz
/a# ls
abcdefgh
/a# _

Unix allows long file names unlike DOS with its 8 character limit. And another experiment:

/a# mkdir ABC
/a# ls
abc       abcdefgh
/a# _

DOS does not differentiate between Upper and Lower case as Unix does. The DOS floppy format is good for exchanging data with the DOS and Windows, but as storage space for Linux it isn't very useful.

To unmount the floppy again:

/a# umount /a
umount: /dev/fd0: device is busy
/a# _

Why is the device busy? Of course! The mount point /a is the parent directory. You change to the root directory and unmount:

/a# cd /
/# umount /a
/# _

Everything is fine again. But we are curious to see what /a contains now.

/# ls /a
total 0
/# _

Now /a is empty.

Formatting floppies

1. Low-Level-formatting with the command fdformat (floppy disk format).
2. Making the ext2 file system with the command mkfs.ext2. In other Unix versions this command is mkfs (make file system).

First format the floppy:

/# fdformat /dev/fd0H1440
Double-sided, 80 tracks, 18 sec/track. Total capacity 1440 kB.
Formatting ... done
Verifying ... done

Then make the file system:

/# mkfs.ext2 /dev/fd0H1440
...
...
Writing inode tables: done
Writing superblocks and file system accounting information: done
/# _

Remove the floppy from the drive and label it"muLinux-workdisk", then put it back into the drive again.

Now you can mount the disk and look at the contents. It should be empty except for a directory called lost+found. Files which where lost in the file system are saved in this directory.

Other floppy-formats

/# ls /dev/fd0*
0 /dev/fd0       0 /dev/fd0H1440     0 /dev/fd0h17220     0 /dev/fd0h1440    
/# _

There is also a floppy format of 1,722 MByte permitting us to format our floppies with a greater storage capacity. Be aware that these disks are not always readable under other Linux versions.

Checking the drive space

/# df
Filesystem         1024-blocks  Used Available Capacity Mounted on
/dev/ram0               1428    1284      144     90%   /
/dev/ram1               1884    1542      342     82%   /usr
/dev/ram2                987     368      568     39%   /tmp
/dev/fd0                1390      13     1305      1%   /a

/# df /dev/fd0
Filesystem         1024-blocks  Used Available Capacity Mounted on
/dev/fd0                1390      13     1305      1%   /a

Configuration of file systems and their Mountpoints

/# less /etc/fstab
...
/dev/fd0 /a auto defaults,noauto,rw 1 1
...

There is a line for each mounted file system. Here CDROM, floppy, and hard disk drives, are mounted automatically and and the permissions set for the normal user. The line above means that the floppy drive /dev/fd0 is mounted standard on the directory /a. This means that with the command mount /dev/fd0 /a you can skip the /dev/fd0. The auto makes an automatic recognition of the file system. DOS or ext2 floppies are recognized automatically.

The parameter defaults sets the following parameters on standard (as far as I understand). With a "normal" Linux (SuSE) the following line is used:

...
/dev/fd0 /a auto noauto,user,exec,sync 0 0
...

The floppy isn't mounted automatically (noauto) but can be mounted by normal users (user) and is synchronized after unmounting (sync). Programs and scripts can be executed from floppies (exec). This allows the installation program to be started from a floppy.