Can't log in because I forgot my user name

Question

My friend had put Linux Mint 17.3 Cinnamon 64 bit on my computer. Well, I forgot the user name, so I did a search on the Net for "forgot username linux" and came here.

I got the suggestion to hit 'e' at the 1st item in GRUB which I did. The next part of the suggestion said to look for a line that started with KERNAL. Now here is where it gets interesting. I didn't find a line with KERNAL in it. However, I did find a line that started with LINUX.

The full unedited line reads:

linux        /vmlinuz-3.19.0-32-generic root=UUID=0c031f3a-81ae-4c33-06cc--c82a855736d1 ro  quiet splash $vt_handoff

The suggestion then said to look and edit splash quiet to single. Now if you notice above it says quiet splash instead of splash quiet. So I figured I would edit the quiet splash to single.

Now it's asking for a root password. Can anyone help? I suppose I'll need a Live CD.

Answer 1

Exactly what happens when you replace quiet splash or splash quiet (the order doesn't matter) by single depends on the distribution. Most distributions will ask for a root password.

If you don't remember the root password, or you just want to boot in the most minimal way, you can replace quiet splash (and $vt_handoff, for that matter) by init=/bin/bash. The line should look like

linux /vmlinuz-… root=… ro init=/bin/bash

The amount of whitespace between the parts doesn't matter, just leave at least one space wherever there was one before. The parts that I replaced by … above do matter, you must leave what was there before. Remove everything except for the leading word linux, the word after that, root=… and ro, and add init=/bin/bash.

When you boot, you'll get a bash command line, running as root. When you have physical access, the only security that could prevent you from getting in is encryption. (If your system has full-disk encryption, you will need to enter the encryption password.)

At this command line, run the following commands:

mount -o remount,rw /
mount /proc

Then you can view and modify the user database. The main user database file is /etc/passwd. It contains user names (for both physical users and system accounts), but passwords are in a different file /etc/shadow. Both files are human-readable up to a point. You cannot recover passwords though; if you've forgotten a password, all you can do is change it.

The following command lists accounts that have a password:

grep -v ':[*!]:' /etc/shadow

(Type it carefully, it's pretty sensitive to the exact punctuation.) The first part of each line, before the first : sign, is the username.

If you want to change the password for an account, run

passwd rob

where rob is the username.

Once you've noted the username and changed the password if desired, run

mount -o remount,ro /
reboot

Answer 2

Follow these steps:

1. boot from a live cd
2. open a terminal in the live environment
3. run command lsblk, you will get a list of drives and partitions. One of these should be the root partition in which you installed linux mint (sdxn, x being a letter, n being a number?).
4. mount the root partition on an empty directory
5. open etc/passwd file in the mounted partition. this should contain your username in one of the lines, you should be able to identify it.

Answer 3

http://www.microhowto.info/howto/reset_a_forgotten_root_password_using_a_live_distribution.html

That article seems to cover it well. Yes, you need a live cd.

In the article he gives you an alternate, and he notes, very risky method, of directly editing the password file. Follow his advice and do not try that.

it's not worth copying over verbatim his method, because it's well explained and complete, as well as being as verbose as necessary to do all the steps, with the code examples for each step.

It's not hard, just follow the directions closely.

Basically you boot into the live cd on the system you want to update, then you mount the root file system on the system to be updated, chroot to that mount point, then use passwd to change the password. It may sound intimidating, but really it's not. Note that some systems have /mnt, and others have /media, as defaults, just use which ever your live cd comes with when creating the mount directory, that does not matter at all, it's a just a path you are going to use when you chroot into the system you are trying to update the password on.

Many live cds, by the way, will give you root with this command (I think that's it, it's been a while, heh):

sudo su -

You will need to be root to do those actions on the live cd, so just check the live cd docs on how it allows the root user to login to the shell on the live cd.