Hi again Monks.

Well, depending on your definition, what I am writing may not be a daemon. However, what I want is for my script to be running in the background and for it to be unique in the process list.

I came across some behaviour that I do not understand, and am seeking clarification.

  • Why is the PID not being written to the file until after the script is HUPped?
  • How can I get it to write the PID into the file, so that I can check it externally?
    The point being that a third party script (or process) can run which checks that the PID in the file matches that in the process list. Pretend, if you will, that I am overly paranoid and must be assured that there is only ever one of these scripts running. :) 
    #!perl -w
use strict;
use Fcntl qw(LOCK_EX LOCK_NB);

my $PID_FILE    = '/tmp/_pid_file';
my $TASK        = 'test_script';
my $EVENT_DELAY = 30 ;
my $DEBUG       = 'YES';


eval { main( @ARGV ) };
error( $@ ) if $@;

# --------------------------------------------------------------------
+----------
sub main
{
    my $start_mess = "===== Starting $TASK";
    $start_mess   .= " (@_)" if @_;
    $start_mess   .= " =====";
    error( $start_mess );

    open( HIGHLANDER, ">>$PID_FILE") or die( "Cannot write to $PID_FIL
+E: $!" );
    {
    my $count = 0;
    {
        flock HIGHLANDER, LOCK_EX | LOCK_NB and last;
        sleep 1;
        redo if ++$count < 3;
        error( "Script is already running." );
            die( "Startup failed, PID file locked." );
        }
     }
     print HIGHLANDER $$;

    my $stopped;
    local $SIG{HUP} = sub { $stopped = 1 };

    while( not $stopped )
    {
    error( "DEBUG: Script Running" ) if $DEBUG;
    sleep $EVENT_DELAY;
    }

    my $finish_mess = "===== Stopping $TASK =====";
    error( $finish_mess );

    close HIGHLANDER;
}

# --------------------------------------------------------------------
+----------
sub error{ print "$TASK -> WARN: @_\n" }

    [download]
    Please bear in mind that the code has been altered somewhat to work for this particular snippet.

    <a href="http://www.graq.co.uk">Graq</a>

    In reply to Writing to flock files in a daemon by graq

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