Just updated from 16.04 LTS to 18.04 LTS. New version of Ubuntu doesn't contain any power off button in both lockscreen and homescreen, obviously. Adding some gnome extensions couldn't help me either.
Please help me out. Thank you, guys.
Ask Ubuntu is a question and answer site for Ubuntu users and developers. It only takes a minute to sign up.Sign up to join this community
To get the familiar interface to Ubuntu 16.04 LTS in Ubuntu 18.04 LTS you need to sign in using the Unity interface. Do this right on the Sign In screen:
click the "gear" to select the Unity Desktop Environment (DE).
Now you will see the familiar "gear" on the top right of your screen where you can select "Lock Screen", "Log Out", "Suspend" and "Shutdown". If you press the power button you'll get your regular selector:
This video also shows how to activate the lock screen option which is disabled for some users.
Also of interest is some users are not getting a chance to select an action because system shuts down immediately: How to make Ubuntu 18.04 LTS ask for action when I press ACPI Power button/key on VirtualBox (now immediately shutdowns)?