secure booting of linux
 

While booting linux(From Linux boot floppy) if i type "Linux 1" at the boot prompt I can bcome the root .Plz tell me if there is any way to prevent this

hm...if you're the only user, you could try putting BIOS password protection on, if your BIOS supports the password to be asked when booting...but there are some problems with this, so I don't think this is the solution:

1) if the battery is removed for some time, protection won't work
2) you need to give this every time you boot - if the electricity gets cut off or your machine reboots for some reason, it won't get up without you
3) it's a harm for you :) I'd say you get fed up with it quite quickly..

Is there any way to solve this problem by changing Linux settings(software level)

The basic rule is that if anyone has physical access to your machine, there's little you can do except encrypt your important files.
Having said that though, you can (physically) disable the floppy (& CD_ROM) and put a password into LILO/GRUB.

If you are using LILO, there is a line in your lilo.conf that says prompt. If you comment that out, then you won't have any place to enter the linux 1 command. However, that isn't going to prevent someone from bringing their own boot disk or CD distro and booting from that. As chrism said, if someone has physical access to your machine, you have no security.