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Re: password

El Jueves, 19 de Febrero de 1998 12:49, Robert Stevens escribió:
> I purchased a computer on ebay with Fedora core.  The Fedora  core boots
> up, but asks for a user name and password and I can't go any further.  The
> seller is not helpful.  Is there any way I can get past the user name and
> password.  This is a gateway computer.  The computer is useless to me as it
> is. Bob
If you've lost your root password, you might be able to recover it this way. 
However, some systems are protected with boot loader passwords that won't let 
you do that without THAT password. If the boot loader is password protected, 
you need to boot from other media - for newer systems, the install CD 
probably has the recovery tools for that ("linux rescue" for example).

But let's try it the easy way first. The first thing to try is to boot to 
single user mode. This MIGHT not work for you, because your system might be 
configured to still ask for a root password to get to single user mode. If 
that's the case, we'll use another trick that replaces init with /bin/bash.

First, try single user. If you don't see either a LILO or GRUB boot screen, 
try hitting CTRL-X to get one. If it's LILO, just type "linux single" and 
that should do it (assuming that "linux" is the lilo label). If GRUB, hit 
'e", then select the "kernel" line, hit "e" again, and add " single" (or just 
" 1") to the end of the line. Press ENTER, and then "b" to boot. (More modern 
grub uses "a" to append to the boot line)

You should get a fairly normal looking boot sequence except that it terminates 
a little early at a bash prompt. If you get a "Give root password for system 
maintenance", this isn't going to work, so see the "init" version below.

If you do get the prompt, the / filesystem may not be mounted rw (although 
"mount" may say it is). Do

mount -o remount,rw /

If that doesn't work (it might not), just type "mount" to find out where "/" 
is mounted. Let's say it is on /dev/sda2. You'd then type:

mount -o remount,rw /dev/sda2

If you can do this, just type "passwd" once you are in and change it to 
whatever you like. Or just edit /etc/shadow to remove the password field: 
move to just beyond the first ":" and remove everything up to the next ":". 
With vi, that would be "/:" to move to the first ":", space bar once, then 
"d/:" and ENTER. You'll get a warning about changing a read-only file; that's 
normal. Before you do this, /etc/shadow might look like:


and after, the first few lines should be:


You'll need to force the write: with vi, ":wq!". (If that still doesn't work, 
you needed to do the -o remount,rw, see above).

Another trick is to add "init=/bin/bash" (LILO "linux init=/bin/bash" or add 
it to the Grub "kernel" line). This will dump you to a bash prompt much 
earlier than single user mode, and a lot less has been initialized, mounted, 
etc. You'll definitely need the "-o remount,rw" here. Also note that other 
filesystems aren't mounted at all, so you may need to mount them manually if 
you need them. Look in /etc/fstab for the device names.

Keep this in mind if you have a Linux machine in a publically accessible 
place : without more protection, it's not usually hard to recover a lost root 
password, which means it's just as easy for someone to CHANGE it, or access 
root without your knowlege.

Another way to do this is to remove the password from /etc/shadow. Just in 
case you screw up, I'd copy it somewhere safe first.
You want to end up with the root line looking something like this:

# original line
# after editing

If you are having trouble with editing (you really do have to learn vi one of 
these days), you could just (after making a copy, of course) just

  echo  "root::12832:0:::::" > /mnt/etc/shadow 
or, if you were in single user mode
  echo  "root::12832:0:::::" > /etc/shadow 

and then fix things up when rebooted.

If using something like "linux rescue" or other boot media, if the recovery 
disk doesn't automatically mount your disk, you need to do it manually. This 
shouldn't be difficult unless you have an unusual disk controller. For 
example, a Compaq raid controller will probably be /dev/ida/c0d0. Find the 
partitions by using fdisk /dev/ida/c0d0 (just "p" and quit) and then mount 
what you need.

If all else fails, consider that you can pull this drive (or install another 
drive in this machine) and mount it from another running Linux. Then recover 
the root password as explained above. 
Hope this helps
Manuel Arostegui Ramirez.

Electronic Mail is not secure, may not be read every day, and should not
be used for urgent or sensitive issues.

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