Bug 137757

This is indeed something we would like to clear up.  Ideally you
should never have to restart the X server, and your changes should
take effect immediately.  However it is a significant amount of work
to realize this, which will have to take place upstream in the X.org
forum (http://xorg.freedesktop.org).

The current behaviour is not a bug as such, more a limitation of the
X.org server architechture.  I'm changing the severity of the bug to
"enhancement".

Just to clarify:  The problem I was seeing is that sometimes even a logout-login (which 
does appear to restart X) was picking up the changes, and sometimes it wasn't.  The 
problem I'm reporting here is that there's some sort of weird inconsistency in the way it 
picks up new values.   (e.g. hidden caching?  not always restarting?)

So I would claim that this is not an enhancement but a real bug.  Meanwhile,I would be 
happy to file a separate enhancement request for dynamic changes (although I would 
imagine you already have one in the system) - let me know if you would like such a 
request entered as well.

The X server reads the config file exactly once during server
startup.  It parses the entire file, and sets internal variables,
etc.  Once that is done, the X server never looks at the config
file again during runtime ever.

If you make changes to the X server config file, you absolutely
must restart the X server in order for them to take effect, as
that is the only time that the X server looks at the config file.

Wether you reboot the entire system, or just restart the X server
itself, doesn't matter.  The important thing is that the running
X server process must terminate, and then a new X server process
must be restarted.  That can be done by quitting out of a
startx initiated session, and then re-running startx, or it
can be done by hitting CTRL-ALT-BACKSPACE to kill the server and
then restart it manually if you're not using gdm or something
else that restarts it automatically.

This is not a bug in the X server.  It is designed to read the
config file exactly once when the server starts, and never to
look at it again.

Having explained that however, I will agree with you completely
that it would be an excellent feature enhancement for the X server
to be able to re-read the config file at runtime on the fly some
day, and I believe that is an eventual goal of the X.Org project
to some day make the server capable of doing that.

It is not a simple hack to make the server re-read the config
file at runtime however, and so it will only occur once it has
been implemented by X.Org developers in the upstream official
X.Org source code repository and is an official feature in a
new X.Org release.

Any perceived inconsistency you appear to be seeing is not an
X server bug, but may perhaps be a misunderstanding for how
the system starts up and manages the X server.  If you make
changes to the X server config file and they do not take effect,
then the X server did not get killed and restarted.  You must
kill the X server first.  I'm not entirely sure, but I think
the display manager just reuses the same X server for multiple
logins and does not restart it by default.  I think that might
be a configureable option in gdm however.

Setting status to "NOTABUG" as per explanation above on how
the server reads the config file.  For the feature enhancement
of making the server read the config file at runtime, that
will happen upstream by X.org eventually, so I don't think there
is any real value in filing a separate bug report for it, as
it isn't that beneficial to track it in bugzilla IMHO.