Debian Menu System
Chapter 6 The internals of the menu package

6.1 The update-menus program

On startup, update-menus checks the file /var/run/update-menus.pid and the pid in it. If there's an update-menus process with that pid it kills it. If /var/lib/dpkg/lock exists, it forks to background and returns control to dpkg. The background process checks the /var/lib/dpkg/lock file approx. every second until the file's gone.

After that, update-menus reads the menu-entry-files in the following directories:/etc/menu /usr/lib/menu /usr/lib/menu/default (if a user runs update-menus, it will add ~/.menu to the front of that list). For every menu entry line in each file it checks if the corresponding package is installed (works on file bases for old syntax menu entry files). The menu entries of all "installed" packages are added together in one big buffer that is kept in memory (exception: executable menu entry files are executed, and stdout is placed in the buffer).

Once it's read all menu entry files, update-menus starts all executable scripts in /etc/menu-methods/, hands the scripts the previously created buffer via stdin. (If update-menus is ran by a user, it will first try to run the scripts in ~/.menu-methods, and only if that directory doesn't exist, it will run the scripts in /etc/menu-methods).

Note that as an aid to debugging, one can create a simple script like

     #!/bin/sh
     cat > /tmp/menu-stdout

and then view the file /tmp/menu-stdout to see exactly what update-menus handed the menu-methods on their stdin.

This may also be usefull for people writing /etc/menu-method/* scripts: Running update-menus every time you changed something in the script may be quite time-consuming. So, it's much easier to install the above script in /etc/menu-methods/, run update-menus once, and then run

       /etc/menu-methods/mymethod < /tmp/menu-stdin

(and, if that also takes too long, just try editing /tmp/menu-stdin, and removing 90% or so of all entries)

6.2 The install-menu program

The files /etc/menu-methods/$wm are executable config files that start with the line

       #!/usr/sbin/install-menu

and thus start that program, handing it the configuration file for the specific window manager in the first command line argument. This configuration consists of:

1. the compatibility mode ("menu-1" or "menu-2").
2. where the various files should be stored/read.
3. what "needs" are supported, and what wrapper files should be used for each "type".

See /usr/doc/menu/examples/ of the menu package for more comments.

Options to install-menu:

       -v              be verbose
       -d              Produce loads of debugging output

Some window managers don't support an `include' like statement in their system.*rc files (like m4 or cpp preprocessing), they cannot read the menudefs.hook file generated by install-menu from their system.*rc config file. To still be able to use them, install-menu will copy the file $path/$examplercfile to $path/$rcfile (with $examplercfile and $rcfile