(Working) Screenlock for Linux

Hello I've been searching for a good, working screenlock for linux, but all the apps I find are for win. KDE's screenlock is simply bugged here, I can never unlock it. I have seen this happening with other people and no one had a solution for this problem, so, I assume it must be a bug on kdesktop_lock. A desktop screenlock seems so trivial to implement, why are there so few versions for linux? I have tried xlock too and followed the command line instructions, but it didn't really lock the screen. Anyone knows a good screenlock for linux?