General explanation:

  Upgrading without completely restarting the game is possible since
  svn revision 186 by doing an 'svn update' from the shell and then
  performing a 'warmboot' in the mud.

  Such upgrades take care of recompiling everything and migrating and
  converting objects and data where needed.

  Some more involved conversions only exist in specific revisions
  and when you are below such a specific revision, you need to upgrade
  to it first before upgrading to newer revisions.

  If you intend to start your mud from scratch after an upgrade, you
  don't need to worry about data and object conversion.

How it works:

  When you perform a warmboot, a number of steps are taken:

  - Recompile of the warmboot command

    This ensures that any checks and special procedures required for
    the revision you are upgrading to are known and handled by the
    warmboot command.

  - Check if upgrade is possible

  - Atomic recompile of critical objects

    Ensures that critical kernel objects are recompiled properly, will
    undo everything if a critical kernel object fails to compile.

  - Migration/conversion of kernel data and objects

  - Rebuilding remaining objects

  - Any remaining migration and conversion

Known mandatory revisions:

  222   : Conversion of user and player objects in preparation for a
          stack based security model.
  226   : cleanup compiler_d data.

  Note that revisions 223-225 contain a bug that prevents warmboot from working

  So, if you are currently using a revision before 222:

    $ svn -r222 update
    > warmboot

    $ svn -r226 update
    > warmboot

    $ svn update
    > warmboot

  Where $ indicates shell commands and > indicates mud commands.