In the following code sample the database connection cannot be started until after Proc::Background::Init because DBI connections do not survive forks. The fork has to happen before the potentially fatal register_process() because you wouldn't want to write the wrong pid to the process list. This leaves you with no way to report a fatal exit to the console that just started the application.

exit main( @ARGV );

sub main
{
    eval
    {
        Sys::Syslog::openlog( $SYSLOG_IDENT, '', $SYSLOG_FACILITY );
        1;
    }
    or Carp::croak( $@ );
 
    Proc::Background::Init();

    db_start(); # <- The database connection cannot be established

    ...
}

sub db_start
{
    return if $::DBH;
    main::log_debug( "DBI->connect" ) if $::DEBUG;
    $::DBH = DBI->connect
        ( $::DBI_DSN,
          $::DBI_USER,
          $::DBI_PASS,
          { RaiseError => 1,
            PrintError => 0,
            AutoCommit => 1 } )
        or main::log_emerg( 'emerg', "Error connecting to database: $D
+BI::errstr" );

    # Potentially fatal - if the process is already running that would
+ violate the table's constraint system.
    $::DBH->do( "SELECT register_process( ?, ? )",
                undef,
                File::Basename::basename( $0 ),
                $$ );
    
    return 1;
}
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