(grub.info.gz) Preset Menu

 
 8 Embedding a configuration file into GRUB
 ******************************************
 
 GRUB supports a "preset menu" which is to be always loaded before
 starting. The preset menu feature is useful, for example, when your
 computer has no console but a serial cable. In this case, it is
 critical to set up the serial terminal as soon as possible, since you
 cannot see any message until the serial terminal begins to work. So it
 is good to run the commands `serial' ( serial) and `terminal'
 ( terminal) before anything else at the start-up time.
 
    How the preset menu works is slightly complicated:
 
   1. GRUB checks if the preset menu feature is used, and loads the
      preset menu, if available. This includes running commands and
      reading boot entries, like an ordinary configuration file.
 
   2. GRUB checks if the configuration file is available. Note that this
      check is performed *regardless of the existence of the preset
      menu*. The configuration file is loaded even if the preset menu was
      loaded.
 
   3. If the preset menu includes any boot entries, they are cleared when
      the configuration file is loaded. It doesn't matter whether the
      configuration file has any entries or no entry. The boot entries
      in the preset menu are used only when GRUB fails in loading the
      configuration file.
 
    To enable the preset menu feature, you must rebuild GRUB specifying a
 file to the configure script with the option `--enable-preset-menu'.
 The file has the same semantics as normal configuration files (
 Configuration).
 
    Another point you should take care is that the diskless support
 ( Diskless) diverts the preset menu. Diskless images embed a
 preset menu to execute the command `bootp' ( bootp)
 automatically, unless you specify your own preset menu to the configure
 script. This means that you must put commands to initialize a network in
 the preset menu yourself, because diskless images don't set it up
 implicitly, when you use the preset menu explicitly.
 
    Therefore, a typical preset menu used with diskless support would be
 like this:
 
      # Set up the serial terminal, first of all.
      serial --unit=0 --speed=19200
      terminal --timeout=0 serial
 
      # Initialize the network.
      dhcp
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