Window Managers: olwm, twm, fvwm and gnome

At the beginning of each X session, the system will start up the programs which are in either ~/.xinitrc or the system default file, which resides in /usr/local/x11/lib/xinit/xinitrc. This is true regardless of which window manager you use. If you look at the system default file, you'll notice that the line

exec olwm

appears near the end of the file. This is the line which determines which window manager you are running. Also note that the programs which are being started up (xterm, mailtool and xclock), all must be run in the background, as indicated by the trailing ampersands (&). To customize the file, copy it to ~/.xinitrc.

olwm

The default startup file for olwm is /usr/openwin/lib/openwin-init. Copy this file to ~/.openwin-init to make changes.

twm

The default startup file for twm is /usr/openwin/lib/X11/system.twmrc. Copy this file to ~/.twmrc to make changes.

fvwm

The default startup file for fvwm is /usr/local/x11/lib/fvwm/system.fvwmrc. Copy this file to ~/.fvwmrc to make changes.
More information: The Official FVWM Homepage

fvwm95

This is a variant of fvwm designed to be more familiar to users of a certain Windows-based operating system. The default startup file is /usr/local/x11/lib/fvwm95/system.fvwm95rc. Copy this to ~/.fvwm95rc to make changes
More information: The Official FVWM95 Homepage

gnome

The gnome desktop works a bit differently than the other window managers. Instead of a startup file, it remembers the applications you run, and restarts them each time you log in. So you don't need to worry about an rc file as you do with other window managers.

Simply create a .xinitrc file with the following line:

. /usr/local/gnome2/gnome2.xinitrc

More information: help gnome on an SCF computer

The .Xdefaults file

The system default .Xdefaults file is /usr/local/X11R6/lib/xinit/Xdefaults . To modify it, make a copy in ~/.Xdefaults.

Other Resources

Different Window Managers - compares several window managers, including some screen shots.
FAQ for comp.windows.x
Setting Resources, a brief introduction to the .Xdefaults file, including some samples.