Re: Writing a Perl Daemon

[cees]

Using Proc::PID_File and Proc::Daemon should get you most of the way there. Here is a chopped down version of a daemon script that I use, complete with logging. Hope it is a helpful starting point.

#!/usr/bin/perl

use strict;
use warnings;

use constant LOG_DIR    => '/var/log/mydaemon';
use constant LOG_FILE   => 'mydaemon.log';
use constant PIDDIR     => LOG_DIR;

use Proc::PID_File;
use Proc::Daemon;
use Log::Dispatch;
use Log::Dispatch::File;
use Date::Format;
use File::Spec;

sub dienice ($);

#
# fork and background process
#
our $ME = $0; $ME =~ s|.*/||;
our $PIDFILE = PIDDIR."/$ME.pid";
startDaemon();

#
# Setup a logging agent
#
our $HOSTNAME = `hostname`;
chomp $HOSTNAME;
my $log = new Log::Dispatch(
      callbacks => sub { my %h=@_; return Date::Format::time2str('%B %
+e %T', time)." ".$HOSTNAME." $0\[$$]: ".$h{message}."\n"; }
);
$log->add( Log::Dispatch::File->new( name      => 'file1',
                                     min_level => 'warning',
                                     mode      => 'append',
                                     filename  => File::Spec->catfile(
+LOG_DIR, LOG_FILE),
                                   )
);
$log->warning("Starting Processing:  ".time());


#
# Setup signal handlers so that we have time to cleanup before shuttin
+g down
#
my $keep_going = 1;
$SIG{HUP}  = sub { $log->warning("Caught SIGHUP:  exiting gracefully")
+; $keep_going = 0; };
$SIG{INT}  = sub { $log->warning("Caught SIGINT:  exiting gracefully")
+; $keep_going = 0; };
$SIG{QUIT} = sub { $log->warning("Caught SIGQUIT:  exiting gracefully"
+); $keep_going = 0; };
#$SIG{TERM} = sub { $log->warning("Caught SIGTERM:  exiting gracefully
+"); $keep_going = 0; };


#
# enter main loop
#
while ($keep_going) {

        # do something useful here


}

#
# Mark a clean exit in the log
#
$log->warning("Stopping Processing:  ".time());


#
# startDaemon
#
# Fork and detach from the parent process
#
sub startDaemon {

  #
  # Fork and detach from the parent process
  #
#  eval { close DATA; }; # having __END__ will trigger __DATA__ to ope
+n and should be closed
  eval { Proc::Daemon::Init; };
  if ($@) {
    dienice("Unable to start daemon:  $@");
  }

  #
  # Get a PID file
  #
  dienice("Already running!") if hold_pid_file($PIDFILE);
}

#
# dienice
#
# write die messages to the log before die'ing
#
sub dienice ($) {
  my ($package, $filename, $line) = caller;
  $log->critical("$_[0] at line $line in $filename");
  die $_[0];
}