I am using linux mint codename rebecca with xface. I tried to follow a description how to start a window manager of once choice:created an empty .xinitrc file in my homefolderfilled the file with exec twmran command xinitbut all I got was a fatal error message and a message I did not understand:(EE)  Fatal server error: (EE) Server is already active for display 0    If this server is no longer running, remove /tmp/.X0-lock   and start  again. (EE)  (EE)  Please consult the The X.Org Foundation support  at http://wiki.x.org  for help.  (EE)Could you tell me what I did wrong or what I missed to do. 
How to start the twm manager on a system which already has a window manager ?
command line;window manager;twm;xinit