How things could be solved...

Exercise 4

Assignment 4.1

Executing mount answers my question.
Intuition (and also some senteces from assignment) tells you that virtual disks correspond to devices called /dev/ubda,ubdb,ubdc

Assignment 4.2

I'll try mount /dev/ubdc /mnt -o norock,ro, which mounts device to the /mnt directory. Well, and besides of that also few more command line switches.

Assignment 4.3

Append following line to /etc/fstab:

/dev/ubdc  /mnt/  iso9660   user,ro   0  0

This way every user can mount CD. If I wouldn't like this, I can also replace /mnt with some directory in /home/zahrada, where only vegetables (members of 'zelenina') can go:).
Well, and if I really wanted 'zelenina' to be the only group capable of that... it should be enough to revoke other permission to start program 'mount'.
That possible huuuuuge security hole won't happen, because option "user" implies another important options, as for example "nosuid" or "nodev".
Alternatively, I can set the option "group" (check the manual page to see what it does). In this case I need to make sure the device has the proper group set. It is not sufficient to set it once, because the setting will be forgotten after system restart. However, I can put the command for setting the group in a script that gets executed on system startup. A suitable candidate for this is the file /etc/rc.local.

Assignment 4.4

I'll have a look at device /dev/ubda, write down its majoc (98) and minor (0) number, and the only thing to do after that is mknod /home/zahrada/kombajn b 98 0.

Assignment 4.5

/dev/null is a black hole, which eats whatever I want, but I won't get anything back (ok, slight difference to black hole here). On the contrary, /dev/zero is huuuge (in short, infinite) pile of zeroes, which I can read. The difference between /dev/random and /dev/urandom is that the former gives us only gathered entropy... and until there's enough of it, we won't get any data.

Assignment 4.6

Executing mkfs -t ext2 /dev/ubdb solves all my problems.

Assignment 4.7 (extra)

This can be solved similarly to assignment 4.3, but the options will be different (and the mountpoint, given choice, as well):

/dev/ubdb  /mnt2  ext2  defaults   0  0

Assignment 4.8 (extra)

I'll try dd if=/dev/ubdb of=/home/zaloha and find out, that it really is the thing I was looking for.

Assignment 4.9 (extra)

Executing mount /home/zaloha /mnt -o loop,ro makes me feel lucky. :)