Not KDE but might be similar: For the MATE desktop it is mate-screensaver-command --inhibit. I would expect something similar for KDE.
There is kde-inhibit --screenSaver <command> provided by KDE.
But these days, I would just recommend everyone to use systemd-inhibit --what=idle --why=<because> --who=<myself> <command> instead. Works across desktops and does the same thing.
What should I put in the <command> part?
Anything that runs as long as you want the block to be. Usually sleep is a good one, use sleep infinity if you want the blocker to never go away until the systemd-inhibit process is killed manually.
Aaaah, that's probably what Plasma is doing.
Would yes command work ?
Presumably, but it prints "y" to the program output as fast as your CPU allows it, so that's probably not a very efficient way to do it.
I don't know if this fits your use case (you didn't describe what you want to achieve in detail), but commands that can possible help if the screen did lock (or turn off):
loginctl unlock-screenkscreen-doctor --dpms onWasn't that. I want to keep the screen on. No sleep, no lockscreen, no blackscreen, etc.
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