configure_x-session-manager

$ sudo update-alternatives --config x-session-manager
There is only one alternative in link group x-session-manager (providing /usr/bin/x-session-manager): /usr/bin/gnome-session
Nothing to configure.
$ sudo update-alternatives --install $(which x-session-manager) x-session-manager $(which dwm) 20
$ sudo update-alternatives --list x-session-manager
/usr/bin/gnome-session
/usr/local/bin/dwm
$ sudo update-alternatives --config x-session-manager
There are 2 choices for the alternative x-session-manager (providing /usr/bin/x-session-manager).

  Selection    Path                    Priority   Status
------------------------------------------------------------
* 0            /usr/bin/gnome-session   50        auto mode
  1            /usr/bin/gnome-session   50        manual mode
  2            /usr/local/bin/dwm       20        manual mode

Press <enter> to keep the current choice[*], or type selection number: 2
update-alternatives: using /usr/local/bin/dwm to provide /usr/bin/x-session-manager (x-session-manager) in manual mode
 
$ less /usr/bin/x-session-manager