Creating a daemon using Perl

[Sahira]

I try to create a demon with proc:: daemon, but for now, I can not complete it. My script is launched, but I wanted to create a pid file containing the number of processes assigned by the system. Can you give an example to get to do that?

[absolute55]

There's certainly better but:

You can be "demonizing" your hand process, in which case you can do whatever you want with the pid by setsid (), starting from this example from perlipc :

use POSIX 'setsid';
 
sub daemonize {
  chdir '/' or die "Can't chdir to /: $!";
  open STDIN, '/dev/null' or die "Can't read /dev/null: $!";
  open STDOUT, '>/dev/null'
  or die "Can't write to /dev/null: $!";
  defined(my $pid = fork) or die "Can't fork: $!";
  exit if $pid;
  setsid or die "Can't start a new session: $!";
  open STDERR, '>&STDOUT' or die "Can't dup stdout: $!";
}

[MindSpace]

I do not find this solution robust. I think you are on Linux/Unix, then Proc:: Daemon is for the daemon and it works. It handles everything correctly.

Then, if you want to retrieve its pid, I recommend the Proc:: ProcessTableYou module that can read all the running processes on your server and using a regex, you can get your script running in daemon.

[Sahira]

Apparently it works this way:

# daemonize
my $pid_file = '/var/run/daemon.pid';
Proc::Daemon::Init;
open(PID,$pid_file);
my $pid = <PID>;
close PID;
if ($pid and kill 0 => $pid) { &set_log($log,"Pid present and reactive","info");  die;}
else {
        open(PID,"> $pid_file");
        print PID $$;
        close PID;
}

The problem is that when I run my script, I send a log to a file that is found in the pid file also (basically I have the pid monitor my log):

# declaration of the connection
my $server = IO::Socket::INET->new(
        Proto => 'tcp',
        LocalAddr => $serv_ip,
        LocalPort => $port,
        Listen => SOMAXCONN,
        Reuse => 1
);
 
die "Unable to start the server" unless $server;
&set_log($log,"Server $serv_name is ready to receive clients","info");

the set_log uses Log:: Handler:

sub set_log {
        my ($log,$logmsg,$level) = @_;
        $log->$level("$logmsg");
}

and the result in the pid file:

21233aoû 07 13:33:10 [INFO] Test Server is ready to receive clients

I'll try with setsid to see what happens, but it is a pity as Proc:Daemon done it all by himself.

[absolute55]

By hand, I'd like that (I'm not sure I was clear earlier).

use POSIX qw(setsid);
 
chdir '/'                 or die "Can't chdir to /: $!";
umask 0;
open STDIN, '/dev/null'   or die "Can't read /dev/null: $!";
open STDOUT, '>/dev/null' or die "Can't write to /dev/null: $!";
open STDERR, '>/dev/null' or die "Can't write to /dev/null: $!";
defined(my $pid = fork)   or die "Can't fork: $!";
exit if $pid;
$pid = setsid          or die "Can't start a new session: $!";
open my $fh, '>>', 'path/to/logfile' or die "Can't open log file:$!";
print $fh "$pid\n";
close $fh;
 
while(1) {
   # ...
}

In fact this is exactly what Proc:Daemon

perldoc -q daemon
 
       How do I fork a daemon process?
 
       If by daemon process you mean one that’s detached (disassociated from
       its tty), then the following process is reported to work on most
       Unixish systems. Non-Unix users should check their Your_OS::Process
       module for other solutions.
 
       ·   Open /dev/tty and use the TIOCNOTTY ioctl on it. See tty for
           details. Or better yet, you can just use the POSIX::setsid()
           function, so you don’t have to worry about process groups.
 
       ·   Change directory to /
 
       ·   Reopen STDIN, STDOUT, and STDERR so they’re not connected to the
           old tty.
 
       ·   Background yourself like this:
 
               fork && exit;
 
       The Proc::Daemon module, available from CPAN, provides a function to
       perform these actions for you.