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<TITLE>The Answer Guy 51: Removing an OS</TITLE>
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<H4>"The Linux Gazette...<I>making Linux just a little more fun!</I>"</H4>
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<H1><A NAME="answer">
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<font color="#B03060">The Answer Guy</font>
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<H4>By James T. Dennis,
<a href="mailto:linux-questions-only@ssc.com">linux-questions-only@ssc.com</a><BR>
LinuxCare,
<A HREF="http://www.linuxcare.com/">http://www.linuxcare.com/</A>
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<H3 align="left"><img src="../../gx/dennis/qbubble.gif"
height="50" width="60" alt="(?) " border="0"
>Removing an OS</H3>
<p><strong>From Paully0529 on Sun, 30 Jan 2000
</strong></p>
<!-- ::
Removing an OS
~~~~~~~~~~~~~~
:: -->
<P><STRONG>
I recently received a laptop which has <A HREF="http://www.redhat.com/">Red Hat</A> 5.1 installed on it. I would
like to remove this OS but have no idea what the login password is.
Is there any way around this?
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
You don't need a user/account password to remove any
operating system. So long as you can control the boot
sequence of the system (i.e. boot from floppy or CD)
then you can boot up into something that will wipe out
all that nasty stuff that you don't want on your new
laptop's hard disk.
</BLOCKQUOTE>
<BLOCKQUOTE>
There are also ways for you do force a password change
on a Linux box. I've described it several times
--- but the basic sequence is something like this:
</BLOCKQUOTE>
<BLOCKQUOTE>
At the LILO: prompt type:
</BLOCKQUOTE>
<BLOCKQUOTE><BlockQuote><code>
linux init=/bin/sh rw
</code></BlockQuote></BLOCKQUOTE>
<BLOCKQUOTE>
... this will boot the system using the "linux" LILO
stanza, and force the kernel to bypass the normal
bootup process (by loading a command shell instead of
the usual init process). It will also force the kernel
to mount it's "root" filesystem in "read/write" mode.
</BLOCKQUOTE>
<BLOCKQUOTE>
You can then type:
</BLOCKQUOTE>
<BLOCKQUOTE><BlockQuote><code>
mount /usr
</code></BlockQuote></BLOCKQUOTE>
<BLOCKQUOTE>
... which might not be necessary, and thus might
give a (harmless) error message.
</BLOCKQUOTE>
<BLOCKQUOTE>
Then type:
</BLOCKQUOTE>
<BLOCKQUOTE><BlockQuote><code>
/usr/bin/passwd
</code></BlockQuote></BLOCKQUOTE>
<BLOCKQUOTE>
... and provide a new password (which you'll need to
repeat twice).
</BLOCKQUOTE>
<BLOCKQUOTE>
Next you can type the following commands (ignoring
some possible, harmless warnings and errors):
</BLOCKQUOTE>
<BLOCKQUOTE><BlockQuote><pre>
sync
umount /usr
mount -o remount,ro /
exec /sbin/init 6
</pre></BlockQuote></BLOCKQUOTE>
<BLOCKQUOTE>
Of course those directions are for people who want
to take over a Linux system and preserve the
programs, configuration and data on it. In your case
you could do something more like the following at the
LILO prompt:
</BLOCKQUOTE>
<BLOCKQUOTE><BlockQuote><code>
linux init=/bin/sh rw
</code></BlockQuote></BLOCKQUOTE>
<BLOCKQUOTE>
... and when you get a shell prompt just use:
</BLOCKQUOTE>
<BLOCKQUOTE><BlockQuote><code>
dd if=/dev/zero of=/dev/hda
</code></BlockQuote></BLOCKQUOTE>
<BLOCKQUOTE>
... (assuming that Linux is on your primary IDE drive).
</BLOCKQUOTE>
<BLOCKQUOTE>
NOTE: This last command example will WIPE OUT EVERYTHING
ON YOUR PRIMARY IDE DRIVE! It will scribble strings
of binary zeros (ASCII NUL characters) all over the
drive wiping out everything. Don't use this unless that's
really what you want to do!
</BLOCKQUOTE>
<BLOCKQUOTE>
(Note: one some systems you might have to use some
other "stanza" name other than "linux" --- hit a
[Tab] key at the LILO prompt to see a list of options).
</BLOCKQUOTE>
<BLOCKQUOTE>
SysAdmins Note: If you want to prevent users from
doing these sorts of things to their desktop systems
(as a matter of policy for example) then you can set
up a LILO password and mark the system as "restricted"
in the <TT>/etc/lilo.conf</TT> file.
</BLOCKQUOTE>
<BLOCKQUOTE>
Of course this by itself will not be much "protection" --
you'll also have to mark the file as not readable by users
other than root, restrict root access to the system, change
the CMOS boot sequence to prevent booting from floppies, CD
discs and other removable media, and set a CMOS/NVRAM
password to prevent the users from changing the boot
sequences back. On top of all that you'll have to pick a
brand of PC/BIOS that doesn't have any known "backdoor" CMOS
passwords and you'll have to lock the cases so that the
users can't open them up to short the battery to clock chip
leads, or otherwise reset the CMOS registers to their
factory state. Those are all hardware security limitations
of PCs, Macintosh and many of the other workstations. They
are not OS specific issues.
</BLOCKQUOTE>
<BLOCKQUOTE>
With most operating systems, you can boot up off their
installation media and readily wipe out whatever happens
to be sitting on the system by simply answer some silly
install program warning. (Early versions of MS-DOS were
pretty stupid in that they would refuse to remove or
overwrite "foreign" or "unknown" partitions in FDISK
regardless of a users wishes. I don't know if they
ever fixed that. I haven't installed any MS operating
system on anything for several years).
</BLOCKQUOTE>
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<P> <hr> <P>
<H5 align="center"><a href="http://www.linuxgazette.com/copying.html"
>Copyright &copy;</a> 2000, James T. Dennis
<BR>Published in <I>The Linux Gazette</I> Issue 51 March 2000</H5>
<H6 ALIGN="center">HTML transformation by
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