To customize this, create your own in your home directory. Name it
.xinitrc, make sure it is an executable script, and
– TLDP - The X Window User HOWTO - Running X
Customization is done by a
.xinitrc file in
~; if present,
/etc/X11/xinit/xinitrc doesn't load.
The above TLDP HOWTO suggests that there is
.xclients for situations without
The order of loading the files works like this:
Startx typically runs without command line arguments, but command line arguments will override its normal behavior described below. It gets client arguments from one of:
.xinitrc in the user's home directory, if the file exists.
/etc/X11/xinit/xinitrc if the above file doesn't exist.
/usr/X11R6/lib/X11/xinit/xinitrc by default if the above two files don't exist.
– How Linux X works
As the quote reveals;
startx decides this, which is a shell script that can be customized.