Creating a boot theme

This section explains how you can create your own boot script theme.

Section “The boot scripts anatomy” already explained that a theme is a single script file. In fact, if you really want, you can create a theme that spreads through multiple files (but this is not necessarily a good idea). The point here is that one file is enough. This file implements a five functions: ThemeInit, ThemeFinish, ThemeBefore ThemeAfter, and ThemeFile.

So, if you want to create a boot theme for GoboLinux, all you have to do is to create a script file like /Programs/BootScripts/*<version>*/Themes/MyVeryOwnBootTheme that implements those functions (and optionally something in the script body) with all the bells and whistles you want.

Subtopics:

1. Implementing a boot theme
2. Testing a boot theme

Implementing a boot theme

This section describes how each of the obligatory theme functions must be implemented.

ThemeInit

This, as the name implies, is the standard location to perform initializations. Below is an example on how you can use the standard $PREVLEVEL variable (from the Sysvinit init program) to echo some message when system initializes or goes down.

if [ "$PREVLEVEL" = "N" ]
  then
    echo "GoboLinux is initializing..."
  else
    echo "GoboLinux is going down..."
fi

ThemeFile

GoboLinux boot scripts work by processing a sequence of files (again, check section “Customizing the initialization” for more details). Before starting to process each of these files, the boot scripts core will call ThemeFile passing as the first (and only) parameter the name of the file that is starting to be processed. Needless to say, you are not obligated to give feedback on what file is being processed (the “Hat” theme, example, does nothing in its implementation of ThemeFile.

A very simple example implementation of ThemeFile follows.

function ThemeFile() {
  echo "Entering file '$1'..."
}

ThemeBefore and ThemeAfter

These functions wrap the execution of commands. ThemeBefore runs before a program is executed and ThemeAfter, as expected, afterwards.

ThemeBefore is given two parameters: an identifier and a message. The identifier is a numeric id so you can match calls to ThemeBefore and ThemeAfter. Likewise, ThemeAfter is given two parameters, the identifier and a numeric result code, indicating success (zero) or failure (other values).

If your theme supports only sequential booting (ie, does not use Fork and Wait to parallelize the execution of the boot tasks), you can ignore the identifier – most themes do, as sequential boots are more common and that makes the themes simpler. On parallel boot, however, programs can end in a different order than they were started; with some escape code trickery, one can represent graphically the intrincacies of parallel booting (the CheckList theme is an attempt at that).

Here’s a quick example of ThemeBefore and ThemeAfter:

function ThemeBefore() {
  shift # ignore id
  echo -n "===> $@... "
}
function ThemeAfter() {
  if [ "$2" -eq 0 ]
    then echo "{SUCCESS}"
    else echo "{ERROR}"
  fi
}

ThemeFinish

The ThemeFinish function is called as the last step in a runlevel switch (after everything else was done). Hence, this is the place to add any finalization code. A common task performed by ThemeFinish is writing to the issue file, whose contents are displayed on the screen just before the login prompt. The issue file name is passed as the first (and only) ThemeFinish parameter.

The following example shows a sample ThemeFinish implementation that just writes an issue file that clears the screen.

function ThemeFinish() {
    clear > $1
    echo "Welcome!!" >> $1
}

Testing a boot theme

Fortunately you don’t have to reboot your computer to test every feature you add to your boot theme. The TestBootTheme script is your friend. Just run it passing your boot script name as a parameter:

TestBootTheme MyVeryOwnBootTheme

This will simulate a boot procedure with lots of things getting executed. Some of them will be quiet, some will echo a lot of text, some will succeed, some will fail… Just press enter when it ends up at the “login” prompt to finish. If you don’t give it a Theme name, it will output the list of available Themes from /Programs/BootScripts/Current/Themes/ instead.

Of course, this script is also useful to see how the various boot themes are, so that you can choose which one is your favorite.