How should I disable beep permanently? I know xset b off can do this, but what's the corresponding option in xorg.conf? Or any other way to do this?
Turn off beep of Xorg
xorg;x11;bell
There are a few ways that you could achieve this permanently:You could add xset b off to your launch programs (if you are using startx or similar, this will be ~/.xinitrc, otherwise for GNOME/KDE/etc, use your startup programs application)You could blacklist the module responsible for controlling the PC speaker (and thus also the PC beep), by adding blacklist pcspkr to a file called /etc/modprobe.d/99-nobeep.conf (or similar if your system is not Linux)If your system supports it, you could use your audio system to mute the PC beep (ALSA, PulseAudio, OSS, et al)I do not believe that there is an option for this in xorg.conf.