CentOS

Dear all,
I use Centos 7 lastest update: Linux com.v1h 3.10.0-862.6.3.el7.x86_64 #1 SMP Tue Jun 26 16:32:21 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
but I don't use shortcut key that configured in Keyboard. Shortcut key default: super + L, I changed it to ctrl + alt + L but it not working.
I install gnome-screensaver but it not working. I feel desperate!!!

Thanks & Regards
Please help me!

I am so ashamed that I cannot lock my screen. Pressing Superkey+L won't work. I am on the latest CentOS 7 now. This is so strange.

A way is to just switch user (top right corner) where a login screen is displayed. At least it works as a lock screen for me now.
Gnome 3 is fully of fancy bells and whistles but i need the basic ones!

On MATE: system > preferences > hardware > KeyboardShortcuts then scroll down until you see Desktop > LockScreen and set it to (for example) F12.

If you're running Gnome, then I'm sure there must be something similar, use the above as a guide.

May be I miss it somehow. But I could not find a solution from the web either. Superkey+L is supposed to work but it did not so I have to live
with what it is.