Enabling other users to login from the xscreensaver lockscreen in Lubuntu 20.10

If Lubuntu 20.10 suspends to RAM, xscreensaver displays a lockscreen with login window when the system resumes. However, LXQt and SDDM currently do not provide a ‘Switch User’ option, so, if you are not the currently logged-in user and you do not know that user’s password, you will be stuck on the xscreensaver lockscreen. If you click on ‘New Login’ in the xscreensaver window, a message similar to the following is displayed and there is no way for a different user to login:

xscreensaver: 19:01:52: could not execute "gdmflexiserver": No such file or directory

To get around this problem so that other users can login, create the file /usr/local/bin/gdmflexiserver containing the following two lines:

#!/bin/bash
who | awk '!/root/{ cmd="/usr/bin/pkill -KILL -u " $1; system(cmd)}'

Make it executable:

$ sudo chmod +x /usr/local/bin/gdmflexiserver

Now, when the xscreensaver login window appears, if you do not know the currently logged-in user’s password you can click on the ‘New Login’ button instead and the SDDM greeter screen will be displayed so that another user can login. Note that clicking on ‘New Login’ will lose all the open windows and any running applications in the current user’s session, but at least a different user will not be prevented from logging-in and using the machine if the original user is not available to login then logout from his/her session. Of course, if the current user is still available, he/she can simply unlock the current session as usual via the xscreensaver lockscreen window.