blog.padowi.se

… why it is a good idea, nay a must, to keep a live cd around.

After a system upgrade earlier tonight I got a message about an new sudoers file (placed in /etc/sudoers.pacnew) that had been downloaded and wanted me to take a look at it.

So I made a couple of mistakes here:

1. I didn’t stop to think it through enough, which lead to…
2. I didn’t edit the new sudoers file first before moving it in place, but also…
3. I MOVED the original file to a backup spot, instead of COPYING it
4. Of course, none of this would have mattered, had I logged into the root account before doing stuff, instead of relying on sudo… for tampering with sudoers… I’m so smart! S-M-R-T.

So, instead of doing things the right way, i.e.:

$ sudo su
# cp /etc/sudoers /etc/sudoers.bak
# vim -p /etc/sudoers.pacnew /etc/sudoers.bak
# mv /etc/sudoers.pacnew /etc/sudoers

what I did was (NEVER EVER DO THIS!):

$ sudo mv /etc/sudoers /etc/sudoers.bak

The instant I hit enter, I got a sinking feeling, knowing I’d frakked up. Attempting to undo the damage

$ sudo mv /etc/sudoers.bak /etc/sudoers

only resulted in an error message:

sudo: can’t stat /etc/sudoers: No such file or directory
sudo: no valid sudoers sources found, quitting

There might have been a root password set, but if so I couldn’t for the life of me remember it. Great! What now?

I knew of course I could access the filesystem from a live-cd but I hadn’t actually needed to do this before, so I was unsure about how to proceed once in the live-session (I had a vague notion about having to fiddle with chroot, something I have not done much of) but as luck would have it, hesa was online and helped me out (no need for chroot, just mount the partition, move some files, unmount, restart.)

Upon booting into Knoppix it was a small matter of

1. remembering which of the disk, and partitions which housed the root-partition, and
2. mounting it:

$ sudo mount /dev/sdb3 /media/sdb3
$ cd /media/sdb3/etc/
$ sudo mv sudoers.bak sudoers
$ cd /
$ sudo umount /media/sdb3
$ sudo reboot

Now, this would have been the sane thing to do, and start over from inside Arch… but instead I moved sudoers.pacnew into sudoers, forgot to edit it, rebooted, realized my new mistake, rebooted again (a hassle, since sudo reboot wasn’t available), remounted sdb3, edited sudoers adding myself again, and finally rebooted. And all was well.

So now I know, first hand… Live-CDs FTW!

:wq

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Tags: /etc/sudoers, knoppix, live-cd, mount, sudo, umount

This entry was posted on Sunday, August 15th, 2010 at 03:13:00 and is filed under Documentation, English, GNU/Linux, Tools. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.