Photo Slideshow on Screensaver on Ubuntu.

 My friend asked me whether he could run Slideshow of Photos on Screensaver. First I thought about Shotwell Photo Manager App. It has Desktop Slideshow option but it did not work on Lock screen.

Then I searched for good old xscreensaver utility and installed it as follows:

$ sudo apt install xscreensaver xscreensaver-gl-extra xscreensaver-data-extra

$ sudo apt remove gnome-screensaver

I added xscreensaver to Startup Applications

Then I opened Screensaver Preferences and selected GLSlideshow in Display Mode

 

 then selected Pictures Folder in Image Manipulation/Choose Random image

 and it works on reboot.