NAME¶

Proc::Daemon - Run Perl program(s) as a daemon process.

SYNOPSIS¶

    use Proc::Daemon;
    $daemon = Proc::Daemon->new(
        work_dir => '/my/daemon/directory',
        .....
    );
    $Kid_1_PID = $daemon->Init;
    unless ( $Kid_1_PID ) {
        # code executed only by the child ...
    }
    $Kid_2_PID = $daemon->Init( { 
                    work_dir     => '/other/daemon/directory',
                    exec_command => 'perl /home/my_script.pl',
                 } );
    $pid = $daemon->Status( ... );
    $stopped = $daemon->Kill_Daemon( ... );

DESCRIPTION¶

This module can be used by a Perl program to initialize itself as a daemon or to execute ("exec") a system command as daemon. You can also check the status of the daemon (alive or dead) and you can kill the daemon.

A daemon is a process that runs in the background with no controlling terminal. Generally servers (like FTP, HTTP and SIP servers) run as daemon processes. Do not make the mistake to think that a daemon is a server. ;-)

Proc::Daemon does the following:

1.

The script forks a child.

2.

The child changes the current working directory to the value of 'work_dir'.

3.

The child clears the file creation mask.

4.

The child becomes a session leader, which detaches the program from the controlling terminal.

5.

The child forks another child (the final daemon process). This prevents the potential of acquiring a controlling terminal at all and detaches the daemon completely from the first parent.

6.

The second child closes all open file descriptors (unless you define "dont_close_fh" and/or "dont_close_fd").

7.

The second child opens STDIN, STDOUT and STDERR to the location defined in the constructor ("new").

8.

The second child returns to the calling script, or the program defined in 'exec_command' is executed and the second child never returns.

9.

The first child transfers the PID of the second child (daemon) to the parent. Additionally the PID of the daemon process can be written into a file if 'pid_file' is defined. Then the first child exits.

10.

If the parent script is looking for a return value, then the PID(s) of the child/ren will be returned. Otherwise the parent will exit.

NOTE: Because of the second fork the daemon will not be a session-leader and therefore Signals will not be send to other members of his process group. If you need the functionality of a session-leader you may want to call POSIX::setsid() manually at your daemon.

INFO: Since "fork" is not performed the same way on Windows systems as on Linux, this module does not work with Windows. Patches appreciated!

CONSTRUCTOR¶

new ( %ARGS )

The constructor creates a new Proc::Daemon object based on the hash %ARGS. The following keys from %ARGS are used:

    my $daemon = Proc::Daemon->new(
        work_dir     => '/working/daemon/directory',
        child_STDOUT => '/path/to/daemon/output.file',
        child_STDERR => '+>>debug.txt',
        pid_file     => 'pid.txt',
        exec_command => 'perl /home/my_script.pl',
      # or:
      # exec_command => [ 'perl /home/my_script.pl', 'perl /home/my_other_script.pl' ],
    );

METHODS¶

Init( [ { %ARGS } ] )

Become a daemon.

If used for the first time after "new", you call "Init" with the object reference to start the daemon.

    $pid = $daemon->Init();
    

If you want to use the object reference created by "new" for other daemons, you write "Init( { %ARGS } )". %ARGS are the same as described in "new". Notice that you shouldn't call "Init()" without argument in this case, or the next daemon will execute and/or write in the same files as the first daemon. To prevent this use at least an empty anonymous hash here.

    $pid = $daemon->Init( {} );
    @pid = $daemon->Init( {
        work_dir     => '/other/daemon/directory',
        exec_command => [ 'perl /home/my_second_script.pl', 'perl /home/my_third_script.pl' ],
    } );
    

If you don't need the Proc::Daemon object reference in your script, you can also use the method without object reference:

    $pid = Proc::Daemon::Init();
    # or
    $pid = Proc::Daemon::Init( { %ARGS } );
    

"Init" returns the PID (scalar) of the daemon to the parent, or the PIDs (array) of the daemons created if "exec_command" has more then one program to execute. See examples above.

"Init" returns 0 to the child (daemon).

If you call the "Init" method in the context without looking for a return value (void context) the parent process will "exit" here like in earlier versions:

    Proc::Daemon::Init();
    

Status( [ $ARG ] )

This function checks the status of the process (daemon). Returns the PID number (alive) or 0 (dead).

$ARG can be a string with:

Kill_Daemon( [ $ARG [, SIGNAL] ] )

This function kills the Daemon process. Returns the number of processes successfully killed (which mostly is not the same as the PID number), or 0 if the process wasn't found.

$ARG is the same as of "Status()". SIGNAL is an optional signal name or number as required by Perls "kill" function and listed out by "kill -l" on your system. Default value is 9 ('KILL' = non-catchable, non-ignorable kill).

Fork

Is like the Perl built-in "fork", but it retries to fork over 30 seconds if necessary and if possible to fork at all. It returns the child PID to the parent process and 0 to the child process. If the fork is unsuccessful it "warn"s and returns "undef".

OTHER METHODS¶

Proc::Daemon also defines some other functions. See source code for more details:

OpenMax( [ $NUMBER ] )

Returns the maximum file descriptor number. If undetermined $NUMBER will be returned.

adjust_settings

Does some fixes/adjustments on the "new" settings together with "fix_filename".

fix_filename( $KEYNAME )

Prevents double use of same filename in different processes.

get_pid( [ $STRING ] )

Returns the wanted PID if it can be found.

get_pid_by_proc_table_attr( $ATTR, $MATCH )

Returns the wanted PID by looking into the process table, or "undef". Requires the "Proc::ProcessTable" module to be installed.

NOTES¶

"Proc::Daemon::init" is still available for backwards capability.

Proc::Daemon is now taint safe (assuming it is not passed any tainted parameters).

AUTHORS¶

Primary-maintainer and code writer until version 0.03:

•

Earl Hood, earl@earlhood.com, http://www.earlhood.com/

Co-maintainer and code writer since version 0.04 until version 0.14:

•

Detlef Pilzecker, http://search.cpan.org/~deti/, http://www.secure-sip-server.net/

Co-maintainer and code writer since version 0.15:

•

Pavel Denisov, http://search.cpan.org/~akreal/

CREDITS¶

Initial implementation of "Proc::Daemon" derived from the following sources:

• "Advanced Programming in the UNIX Environment" by W. Richard Stevens. Addison-Wesley, Copyright 1992.
• "UNIX Network Programming", Vol 1, by W. Richard Stevens. Prentice-Hall PTR, Copyright 1998.

PREREQUISITES¶

This module requires the "POSIX" module to be installed.

The "Proc::ProcessTable" module is not essentially required but it can be useful if it is installed (see above).

REPOSITORY¶

<https://github.com/akreal/Proc-Daemon>

SEE ALSO¶

perl(1), POSIX, Proc::ProcessTable

COPYRIGHT¶

This module is Copyright (C) 1997-2015 by Earl Hood, Detlef Pilzecker and Pavel Denisov.

All Rights Reserved.

This module is free software. It may be used, redistributed and/or modified under the same terms as Perl itself.