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UPDATE [AM 17 Sept. 2025]: Issue has been solved!

(I might at some point post the entire process with screenshots and stuff... But anyway,)

In short;

After @Auth suggested to just copy the contents of the inaccessible user's homedir to a new user, I logged in with tempuser and fast recalled that said homedir was similarly inaccessible as such, as I had selected the option to encrypt home directory during installation, and thus the files within were to other users unreachable without first decrypting them.

I followed @just_another_person's [advice/instructions] until they stopped replying, then managed to successfully mount the home directory after running through the other steps of the guide they referenced ([see:34365607/19080549,34365607/19187230]). I then realised that maybe I could just reverse all the steps I had taken since the user was last accessible, ([see:34365607/19187230]) and regain full access to the user, so I formulated a list of commands to reverse the steps, ([see:34365607/19233599]) checked for flaws, couldn't really find any, and just tried running the commands.

Anyway, it worked, and I can now log in to the user again and access all the files!

Much thanks to everyone who commented, and thanks again to @Auth, @just_another_person, @Wolf_Munroe, @Fizz and again (again) to @just_another_person for continuing to reply for so long!

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Hi fediverse,

I'm hoping someone can give me some advice on an issue that means I can't access the main user account on my Linux Mint (Cinnamon) operating system.

Context:

I'm using a dual boot setup of windows and mint on my laptop. I use mint (or used to, when I could access my user) for pretty much anything that doesn't require things* only my windows instance has. (*things such as support for video games that support windows but not linux, for example)

When creating my main user account, I made a mistake in the username. It was irritating enough for me to want to change it, and as doing so seemed like it should have been fine, I settled upon three guides and ended up (mostly?) just following this one:

https://www.linuxuprising.com/2019/04/how-to-change-username-on-ubuntu-debian.html

I cant remember all of what happened anymore, but I have the following screenshots, along with the stuff I do remember.

(note: red blocks represent the new username, blue blocks represent the old username)

At the used-by-process error, I first tried following the guide precisely, then hoped that "PID" was Process ID, and that the guide expected me to put the ID that usermod stated after "PID", and tried doing that.

Idk if that fvcked something up...

Then I guess I fixed that somehow, idk if I did so by restarting and logging in only as tempuser, or if I had already done that and fixed it some other way.

Anyway I meant to run each line of the command separately to avoid stuff going wrong, but accidentally did both at once. I hoped it'd be fine anyway.

Then stuff happened I guess.

Anyway,

I cant remember much more but I know that I tried to log back in as my main user account and I found out that:

1. The username had been successfully changed.
2. I could not log into my main user account.

Inputting the correct username and password was successful, and acted like it was logging me in as usual. Then after the usual black screen, it just throws me back to the login window.

This still happens.

I ran some web searches, followed some advice. All that I could find of relevance was mostly just people saying to check how much disk space you have left - and to not keep timeshift snapshots on the same drive as your OS.

(this is one such post, which I'm pretty sure is the only one I found that I definitely recognise from the previous searching: https://www.reddit.com/r/linuxmint/comments/15revgg/cant_stay_logged_in_keeps_going_back_to_login/)

I did ctrl-alt-f1 and ran df -h, and deleted most of the timeshift snapshots I had (I think I had maybe 6 and deleted 4 or 5).

Here's the output of df -h that I think is from after I deleted the timeshifts:

Idk what to do, hope someone can advise.

(TL;DR: tried to change username on mint, now whenever I try to log in to the user it throws me back to the login window after the usual black screen. Hope this suffices for a summary...)

[(Edit [AM 06 Sept. 2025]: fixed typos, phrasing...)]

[(Edit [AM 17 Sept. 2025]: UPDATE [SOLVED])]