Suppose you want to add a custom command to the GDM menu that will give you the opportunity to boot into other operating system such as Windoze. Just add the following options into the [customcommand] section of the GDM configuration file.

          [customcommand]
          CustomCommand0=/sbin/rebootwindoze;/usr/local/sbin/rebootwindoze
          CustomCommandLabel0=_Windoze
          CustomCommandLRLabel0=Reboot into _Windoze
          CustomCommandText0=Are you sure you want to restart the computer into Windoze?
          CustomCommandTooltip0=Restarts the computer into Windoze
          CustomCommandIsPersistent0=true
        

CustomCommand0 specifies two commands separated by a semicolon: /sbin/rebootwindoze and /usr/local/sbin/rebootwindoze. GDM will use the first valid command in the list. This allows different commands for different operating systems to be included.

Note, that besides being able to customise this option to reboot into different operating systems you can also use it to define your own custom behaviours that you wish to run from the GDM menu. Suppose you want to give users the opportunity to run system update scripts from the login screen. Add the following options into the [customcommand] section of your GDM configuration file.

          [customcommand]
          CustomCommand0=/sbin/updatesystem;/usr/local/sbin/updatesystem
          CustomCommandLabel0=_Update Me
          CustomCommandLRLabel0=Update the system
          CustomCommandText0=Are you sure you want to update the system software?
          CustomCommandTooltip0=Updates the system
          CustomCommandNoRestart0=true
        

Both custom commands could be defined as follows.

          [customcommand]
          CustomCommand0=/sbin/rebootwindoze;/usr/local/sbin/rebootwindoze
          CustomCommandLabel0=_Windoze
          CustomCommandLRLabel0=Reboot into _Windoze
          CustomCommandText0=Are you sure you want to restart the computer into Windoze?
          CustomCommandTooltip0=Restarts the computer into Windoze
          CustomCommandIsPersistent0=true
          
          CustomCommand1=/sbin/updatesystem;/usr/local/sbin/updatesystem
          CustomCommandLabel1=_Update Me
          CustomCommandLRLabel1=Update the system
          CustomCommandText1=Are you sure you want to update the system software?
          CustomCommandTooltip1=Updates the system
          CustomCommandNoRestart1=true
        

There can be up to 10 custom commands numbered 0-9.

          [customcommand]
          CustomCommand0=/sbin/rebootwindoze;/usr/local/sbin/rebootwindoze
          CustomCommandLabel0=_Windoze
          CustomCommandLRLabel0=Reboot into _Windoze
          CustomCommandText0=Are you sure you want to restart the computer into Windoze?
          CustomCommandTooltip0=Restarts the computer into Windoze
          CustomCommandIsPersistent0=true
          
          CustomCommand1=/sbin/updatesystem;/usr/local/sbin/updatesystem
          CustomCommandLabel1=_Update Me
          CustomCommandLRLabel1=Update the system
          CustomCommandText1=Are you sure you want to update the system software?
          CustomCommandTooltip1=Updates the system
          CustomCommandNoRestart1=true
          
          CustomCommand3=/sbin/do_something
          .
          .
          .
          
          CustomCommand4=/sbin/do_something_else
          .
          .
          .