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I've been using 18.04, along with GNOME for a while now. It took a while to get used to it after being so used to Unity, but now I really don't enjoy Unity. The only feature I enjoy from it, is removable drives in the dock. Anyway: I can't log in suddenly, unless I use the gear to select Unity, or some odd thing called AfterStep. And when I say suddenly, I mean: one night I can log in, the next morning I can't.
And I really don't want an answer telling me to just use Unity, because I don't want to. My problem is that I can't use GNOME. I've seen things about gdm3 being broken, but I don't know whether or not that applies.
Another big thing to note is that, I can log in to another (seldom used) administrator account I created about a month ago, using the Ubuntu login (GNOME), and it works fine. Assuming the reason I can't log in to my main account is a settings problem is there any way I can just copy over these GNOME settings from the user account that works?
And to clarify, when I say can't log in, I mean I am stuck in a log in loop where after entering my password and waiting a minute, it just kicks me back to the login screen.
And finally, I have tried many combinations of uninstalling, and reinstalling gdm3, and lightdm, to no avail obviously.
EDIT: Addressing the possible duplicate of Ubuntu gets stuck in a login loop
This was actually the first or second post I found, and I followed the steps in the accepted answer, however it did not fix my problem. One thing of note to me, is that all the files mentioned already had the proper owners.
EDIT 2: I tried many of the non-accepted answers, for an hour or two, and none of them worked, however I did get my login working again.
I'm still not 100% on what caused the issue, but I decided since it was still very new, that I would try to see if I could uninstall recently installed packages. I found on Google that I could use things like
history | grep " install " and
grep " install " /var/log/dpkg.log to see recently installed packages and recently run commands with the string "install" in them. I started uninstalling pretty much everything that was installed in the last 5 days, restarted my computer, and it worked. So while I haven't nailed down exactly what caused the issue, I can at least report the issue as fixed.