After locking the screen (with a keystroke bound to
xlock -nice 8 -mode blank), I can unlock the screen as expected, but only within a few minutes.
After being locked overnight, when I hit a key (even Ctrl+Alt combos), the screen stays black with just a brief white flash across the middle of both monitors. The workaround is to ssh in from another host and restart X.
Some months ago, this happened every few weeks. By now it happens almost every morning.
How do I even start to diagnose this? What might I look for in log files? (The intermittency is particularly troubling.)
Failing that, is there an alternative to xlock aka xlockmore?
Hardware: 3-year-old HP minitower, GEForce 9800 GT, two Asus LCD monitors.
Software: Ubuntu 12.04.2 LTS. Window manager awesome-wm. NVidia driver 304.88. XLock version xlockmore-5.31.
It seems I am having the same problem though on a slightly different hardware (Intel graphics) and software (LXDE/Openbox on Ubuntu 12.04.2) but also dual-head setup (2 monitors). There is a bug report about xlock occasionally dying on dual-head setups that might be related. More importantly, though, linked in a comment to this bug MMlosh points out that xlockmore has been removed from unstable. It is not available anymore in recent versions of Ubuntu.
I suggest using alternatives such as xscreensaver or slock (which is part of the suckless-tools package).
I haven’t found how to diagnose why
xlock leaves the screen black.
But I find
xscreensaver to be a good workaround, after having given it several chances to commit the same error. (On Ubuntu, Gnome’s own screensaver may need disabling or uninstalling, even when using awesome-wm.)
I had a similar if not identical experience – killed and uninstalled gnome-screensaver and now xlock works fine again