I'M NOT SHOUTING!

The Caps Lock key is an evil remnant of the hardware implemented typewriter. Today it appears to be mostly used for SHOUTING in the seedier sections of the net, like the comments on certain YouTube videos. Less said the better.

I want to use it for a third Control key like civilized people.

According to keyboard(5), the file to fiddle with might be /etc/default/keyboard 

The way I found that out is by using the man command for keyboard, like this:

pi@raspberrypi ~ $ man keyboard

The (5) indicates that keyboard is in section 5 of the Unix manuals and describes a file format (this convention goes way back to the early 1970s). The sections are

       1   Executable programs or shell commands
       2   System calls (functions provided by the kernel)
       3   Library calls (functions within program libraries)
       4   Special files (usually found in /dev)
       5   File formats and conventions eg /etc/passwd
       6   Games
       7   Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7)
       8   System administration commands (usually only for root)
       9   Kernel routines [Non standard]

In the examples of keyboard(5) we see that we can add "ctrl:nocaps" to XKBOPTIONS.

But first we make a backup:

pi@raspberrypi ~ $ cd /etc/default/
pi@raspberrypi /etc/default $ sudo cp keyboard keyboard.orig

Then we edit the file keyboard :

pi@raspberrypi /etc/default $ sudo vi keyboard

and change it to read (in part):

XKBOPTIONS="terminate:ctrl_alt_bksp,ctrl:nocaps"

The we reboot:

pi@raspberrypi ~ $ sudo reboot

Happy Happy Joy Joy! The Caps Lock is gone! It even works when I launch X and start an LXTerminal. Wonderful.