CPAN Module: Start an Application as a Daemon
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Daemon.pm
MANIFEST
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Makefile.PL
README

README

######################################################################
    App::Daemon 0.22
######################################################################

NAME
    App::Daemon - Start an Application as a Daemon

SYNOPSIS
         # Program:
       use App::Daemon qw( daemonize );
       daemonize();
       do_something_useful(); # your application

         # Then, in the shell: start application,
         # which returns immediately, but continues 
         # to run do_something_useful() in the background
       $ app start
       $

         # stop application
       $ app stop

         # start app in foreground (for testing)
       $ app -X

         # show if app is currently running
       $ app status

DESCRIPTION
    "App::Daemon" helps running an application as a daemon. The idea is that
    you prepend your script with the

        use App::Daemon qw( daemonize ); 
        daemonize();

    and 'daemonize' it that way. That means, that if you write

        use App::Daemon qw( daemonize ); 

        daemonize();
        sleep(10);

    you'll get a script that, when called from the command line, returns
    immediatly, but continues to run as a daemon for 10 seconds.

    Along with the common features offered by similar modules on CPAN, it

    *   supports logging with Log4perl: In background mode, it logs to a
        logfile. In foreground mode, log messages go directly to the screen.

    *   detects if another instance is already running and ends itself
        automatically in this case.

    *   shows with the 'status' command if an instance is already running
        and which PID it has:

            ./my-app status
            Pid file:    ./tt.pid
            Pid in file: 14914
            Running:     no
            Name match:  0

  Actions
    "App::Daemon" recognizes three different actions:

    my-app start
        will start up the daemon. "start" itself is optional, as this is the
        default action,

                $ ./my-app
                $

        will also run the 'start' action. By default, it will create a pid
        file and a log file in the current directory (named "my-app.pid" and
        "my-app.log". To change these locations, see the "-l" and "-p"
        options.

        If the -X option is given, the program is running in foreground mode
        for testing purposes:

                $ ./my-app -X
                ...

    stop
        will find the daemon's PID in the pidfile and send it a SIGTERM
        signal. It will verify $App::Daemon::kill_retries times if the
        process is still alive, with 1-second sleeps in between.

        To have App::Daemon send a different signal than SIGTERM (e.g.,
        SIGINT), set

            use POSIX;
            $App::Daemon::kill_sig = SIGINT;

        Note that his requires the numerial value (SIGINT via POSIX.pm), not
        a string like "SIGINT".

    status
        will print out diagnostics on what the status of the daemon is.
        Typically, the output looks like this:

            Pid file:    ./tt.pid
            Pid in file: 15562
            Running:     yes
            Name match:  1
                /usr/local/bin/perl -w test.pl

        This indicates that the pidfile says that the daemon has PID 15562
        and that a process with this PID is actually running at this moment.
        Also, a name grep on the process name in the process table results
        in 1 match, according to the output above.

        Note that the name match is unreliable, as it just looks for a
        command line that looks approximately like the script itself. So if
        the script is "test.pl", it will match lines like "perl -w test.pl"
        or "perl test.pl start", but unfortunately also lines like "vi
        test.pl".

        If the process is no longer running, the status output might look
        like this instead:

            Pid file:    ./tt.pid
            Pid in file: 14914
            Running:     no
            Name match:  0

        The status commands exit code complies with

            http://refspecs.freestandards.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/iniscrptact.html

        and returns

            0: if the process is up and running
            1: the process is dead but the pid file still exists
            3: the process is not running

        These constants are defined within App::Daemon to help writing test
        scripts:

            use constant LSB_OK               => 0;
            use constant LSB_DEAD_PID_EXISTS  => 1;
            use constant LSB_DEAD_LOCK_EXISTS => 2;
            use constant LSB_NOT_RUNNING      => 3;
            use constant LSB_UNKNOWN          => 4;
            use constant ALREADY_RUNNING      => 150;

  Command Line Options
    -X  Foreground mode. Log messages go to the screen.

    -l logfile
        Logfile to send Log4perl messages to in background mode. Defaults to
        "./[appname].log". Note that having a logfile in the current
        directory doesn't make sense except for testing environments, make
        sure to set this to somewhere within "/var/log" for production use.

    -u as_user
        User to run as if started as root. Defaults to 'nobody'.

    -g as_group
        Group to run as if started as root. Defaults to 'nogroup'.

    -l4p l4p.conf
        Path to Log4perl configuration file. Note that in this case the -v
        option will be ignored.

    -p pidfile
        Where to save the pid of the started process. Defaults to
        "./[appname].pid". Note that having a pidfile in the current
        directory doesn't make sense except for testing environments, make
        sure to set this to somewhere within "/var/run" for production use.

    -v  Increase default Log4perl verbosity from $INFO to $DEBUG. Note that
        this option will be ignored if Log4perl is initialized independently
        or if a user-provided Log4perl configuration file is used.

  Setting Parameters
    Instead of setting paramteters like the logfile, the pidfile etc. from
    the command line, you can directly manipulate App::Daemon's global
    variables:

        use App::Daemon qw(daemonize);

        $App::Daemon::logfile    = "mylog.log";
        $App::Daemon::pidfile    = "mypid.log";
        $App::Daemon::l4p_conf   = "myconf.l4p";
        $App::Daemon::background = 1;
        $App::Daemon::as_user    = "nobody";
        $App::Daemon::as_group   = "nogroup";

        use Log::Log4perl qw(:levels);
        $App::Daemon::loglevel   = $DEBUG;

        daemonize();

  Application-specific command line options
    If an application needs additional command line options, it can use
    whatever is not yet taken by App::Daemon, as described previously in the
    "Command Line Options" section.

    However, it needs to make sure to remove these additional options before
    calling daemonize(), or App::Daemon will complain. To do this, create an
    options hash %opts and store application-specific options in there while
    removing them from @ARGV:

        my %opts = ();

        for my $opt (qw(-k -P -U)) {
            my $v = App::Daemon::find_option( $opt, 1 );
            $opts{ $opt } = $v if defined $v;
        }

    After this, options "-k", "-P", and "-U" will have disappeared from
    @ARGV and can be checked in $opts{k}, $opts{P}, and $opts{U}.

  Gotchas
    Log File Permissions
        If the process is started as root but later drops permissions to a
        non-priviledged user for security purposes, it's important that
        logfiles are created with correct permissions.

        If they're created as root when the program starts, the
        non-priviledged user won't be able to write to them later (unless
        they're world-writable which is also undesirable because of security
        concerns).

        The best strategy to handle this case is to specify the
        non-priviledged user as the owner of the logfile in the Log4perl
        configuration:

            log4perl.logger = DEBUG, FileApp
            log4perl.appender.FileApp = Log::Log4perl::Appender::File
            log4perl.appender.FileApp.filename = /var/log/foo-app.log
            log4perl.appender.FileApp.owner    = nobody
            log4perl.appender.FileApp.layout   = PatternLayout
            log4perl.appender.FileApp.layout.ConversionPattern = %d %m%n

        This way, the process starts up as root, creates the logfile if it
        doesn't exist yet, and changes its owner to 'nobody'. Later, when
        the process assumes the identity of the user 'nobody', it will
        continue to write to the logfile without permission problems.

    Log4perl Categories
        Note that App::Daemon is logging messages in Log4perl's App::Daemon
        namespace. So, if you're running your own Log4perl configuration and
        define a root logger like

            log4perl.logger=DEBUG, appendername

        then App::Daemon's messages will bubble up to it and be visible in
        the output. If you don't want that, either use

            log4perl.logger.My.App=DEBUG, appendername

        to explicitly enable verbose logging in your application namespace
        (and not in App::Daemon's) or tone down App::Daemon's verbosity via

            log4perl.logger.App.Daemon=ERROR

        explicitly. If you want more details on basic Log4perl features,
        check out the Log::Log4perl manual page.

  Detach only
    If you want to create a daemon without the fancy command line parsing
    and PID file checking functions, use

        use App::Daemon qw(detach);
        detach();
        # ... some code here

    This will fork a child, terminate the parent and detach the child from
    the terminal. Issued from the command line, the program above will
    continue to run the code following the detach() call but return to the
    shell prompt immediately.

AUTHOR
        2008, Mike Schilli <cpan@perlmeister.com>

LICENSE
    Copyright 2008-2012 by Mike Schilli, all rights reserved. This program
    is free software, you can redistribute it and/or modify it under the
    same terms as Perl itself.