Implementing a boot theme

Joel Roth edited this page Apr 30, 2017 · 5 revisions

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 
    } 
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