I have set a shortcut, <Super>l, to execute slock, which was /usr/bin/slock (and suid root), and all was fine and good.
Recently I have uninstalled slock, and changed the command to lock, which is ~/bin/lock (in path, not suid root but setcap CAP_DAC_READ_SEARCH+ep). executing lock in terminal, or as a panel plugin, works just fine, but the above shortcut just makes the monitor blink for a second.
I have then changed the command to ~/tst, which is a simple wraper:
~ $ cat tst.c
system("echo starting... > dbg");
int i = system("lock 2>> dbg");
FILE *fp = fopen("dbg", "a");
~/dbg is indeed created, and its content is:
~ $ cat dbg
How do I debug such an issue?
XFCE 4.10 on Arch Linux.
Never mind, the problem was with my application, it timed out too early.
Everything is working perfectly, and sorry for the noise.