[lug] Re: linux

[J. Wayde Allen]

On Tue, 19 Jun 2001, Dhruva B. Reddy wrote:

> So basically, as long as you have physical access to the machine,
> there is a way to reset the root password?

If you have physical access to a machine, there is an awful lot you can do
with a screwdriver and some time.

Remember that you don't have a root password when you install Linux for
the first time.  You have to set it once you've got the system installed.  
The way many (all?) of the install packages work is to load a simple Linux
kernel, and create a RAM disk that contains a small file system with the
utilities needed to manipulate and build the target Linux file system on
your hard drive.  The CDROM based versions may skip the RAM disk, and
simply mount a file system directly from the CDROM.  This is also the
basic idea behind the various "rescue" disks available.  If you use one of
these rescue disks, and/or load your installation disk and break out of
the install program, you should then have command line access to the root
file system commands.  That should allow you to manualy mount and
manipulate file systems.  Check the man page for the mount command.  If
you mount the /root partition from your disk, then you should have root
access to any of the files it contains, and should be able to modify
/etc/passwd as needed.

> Sounds scary.

It is just another level in the security puzzle.  Also, if you lock things
down too tightly you'd have to throw the box away and buy another if you
forgot the root password for instance.

> Is it possible to do this remotely?

I'd say very unlikely.  To do what I'm suggesting you have to be able
to shutdown the installed Linux kernel and boot the rescue kernel.  That
typically means you have to pull the power plug to kill the installed
version.  It also means you need to load the rescue kernel into the system
somehow.  Either via a floppy or CDROM that is inserted into the
drive.  This might also mean you'd need to change some of the BIOS
settings to get the correct disk to boot.  These are all things that are
kind of difficult to do remotely.

- Wayde
  (wallen at lug.boulder.co.us)