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I am running Fedora 15 on a small server without grafical user interface (boots in text mode). So my server shows the text login screen on the attached tft. Systemd messages are logged to this tft by default (I have changend nothing). Last night logrotate was hanging forever and I figured out why: I accidentally hit the "Scroll Lock" key on the keyboard (or perhaps my cat, I don't know). I this state, systemctl hangs forever if you try to stop, start, restart or reload a service, I think because of the log messages to the console. And logrotate was hanging, because of the reload of a service (in my case httpd). After pressing "Scroll Lock" again, logrotate continued. Im am running systemd-26-4.fc15.i686.
Hmm, C-s/ScrollLock is a command to freeze the application on the console. If you press it, then that's what you get. That is the same with systemd and sysvinit and everything else and is expected behaviour. If you want to disallow freezing the apps which access the console then remove scrolllock/C-s from your keymap, but I don't think we should try to circumvent the explicit user request here (I don't even think there's a nice way how we even could). In short: I don't think there's anything we should or could fix here.