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App::Daemon 0.11
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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: /tmp/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. If the -X option is given, the
program is run in foreground mode for testing purposes.
stop
will find the daemon's PID in the pidfile and send it a kill signal.
It won't verify if this actually shut down the daemon or if it's
immune to the kill signal.
status
will print out diagnostics on what the status of the daemon is.
Typically, the output look like this:
Pid file: /tmp/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: /tmp/tt.pid
Pid in file: 14914
Running: no
Name match: 0
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
"/tmp/[appname].log".
-u as_user
User to run as if started as root. Defaults to 'nobody'.
-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
"/tmp/[appname].pid".
-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";
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
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.
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
Mike Schilli, cpan@perlmeister.com
COPYRIGHT AND LICENSE
Copyright (C) 2008 by Mike Schilli
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself, either Perl version 5.8.5 or, at
your option, any later version of Perl 5 you may have available.