After switching users, I can see the passwords in /dev/tty1

[Feu]

Basically I installed ubuntu 18.04.1 LTS on an old machine (on a blank SSD), and when I just when had finished the configuration installing just a few apps, I thought I had seen the admin's user password during Power Off (in the boot text screen that blinks) - as it's an old computer I could see this text blinking.

I didn't even use this machine.

After some tests, I found out that after performing these steps:
 - turning the machine on, logging into admin user
 - logging off the admin user
 - logging in a non admin user
 - logging off the non admin user
 - logging in back to the admin user

By running `sudo cat /dev/tty1` I could see everything which was typed in the login screen. And that is the content that appears during the power off text screen.

For more info, please see https://askubuntu.com/questions/1114802

The steps I can remember while setting up this machine were:
 - changing region to Portuguese (brazil) and configuring keyboard
 - installing Gweled, Pitivi, VLC, Spotify and SuperTuxKart through 'Ubuntu Software'
 - installing Google Chrome and Skype by downloading their deb packages from the official websites
 - uninstalled Thunderbird
 - updated everything

As you can see in the AskUbuntu question, I tried to simulate this by repeating these steps in a virtual machine, but was not able to reproduce it. One difference is that this is a HP Pavilion old laptop with all sorts of things on it, so many drivers may be needed which will not be present in the VM. I booted with 4.15.0-29-generic and it behaved the same. However, during the session booting with the 4.15.0.29 recovery mode, I could not detect that sympton!

Running:

sudo lsof /dev/tty1

prints two processes, systemd-l and gdm-wayla.

I installed again the same OS on a different machine and got all the updates installed - no external app installed this time. And I was able to reproduce the issue. I don't know why it doesn't happen in the VM, but it did happen on two different machines (on blank SSDs).

```
uname -a
Linux spider 4.15.0-45-generic #48-Ubuntu SMP Tue Jan 29 16:28:13 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
```

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gnome-screensaver (not installed)
ProcVersionSignature: Ubuntu 4.15.0-45.48-generic 4.15.18
Uname: Linux 4.15.0-45-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sat Feb 2 13:38:45 2019
InstallationDate: Installed on 2019-01-30 (2 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
SourcePackage: gnome-screensaver
Symptom: security
Title: Screen locking issue
UpgradeStatus: No upgrade log present (probably fresh install)

[Feu (feu)]

Based on the 'lsof' command, I suspect the issue might be related to GDM. Well, certainly it's not related to the screensaver.

[Daniel van Vugt (vanvugt)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. This particular bug has already been reported and is a duplicate of bug 1803993, so it is being marked as such. Please look at the other bug report to see if there is any missing information that you can provide, or to see if there is a workaround for the bug. Additionally, any further discussion regarding the bug should occur in the other report. Feel free to continue to report any other bugs you may find.