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.