Gfilui

I just installed 18.04 and created 2 users. Switching between users often causes the computer to freeze/hang. The only escape is the power switch.

What I am going to post here is a workaround:

Edit as root /etc/gdm3/PostSession/Default and add before exit 0:

sleep 0.9
pkill -SIGQUIT -f gnome-session-binary

It should look like this:

#!/bin/sh
sleep 0.9
pkill -SIGQUIT -f gnome-session-binary
exit 0

This will result in a dark screen flash without showing any text and will probably cause a restart on gdm. This means that switching users will not be available without exiting the session.

But might make your life a bit more bearable.

"/etc/gdm3/PostSession/Default" is executed as root at the end of each session (after logout).

Instead of what presented above, you could try with:

#!/bin/sh
pkill X && systemctl restart gdm
exit 0

I have the same problem. I rebuilt my PC a couple of times fearing I had a hard disk issue but I get the same intermittent login freeze with blank purple screen when I change user or logout and back in.

Not a good idea to power off.

I find I can wait a minute then hit Ctl Alt + F1, F2 and F3 a few times -- forget which order, I get back to the main login screen. When I then click on the user I was trying to login it tells me there was an authentication issue (the password given was correct).

I can then login normally. This avoids power off and the damage that can do. I've been searching to see if other users are affected. There are some similar reporting similar issues see Why does my ubuntu 18.04 get stuck on the 'purple' screen after logging in?