Provided by: libproc-daemon-perl_0.14-2_all 
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:
work_dir
Defines the path to the working directory of your daemon. Defaults to "/".
setuid Sets the real user identifier ($<) and the effective user identifier ($>) for
the daemon process using "POSIX::setuid( ... )", in case you want to run your
daemon under a different user from the parent. Obviously the first user must
have the rights to switch to the new user otherwise it will stay the same. It
is helpful to define the argument "setuid" if you start your script at boot
time by init with the superuser, but wants the daemon to run under a normal
user account.
child_STDIN
Defines the path to STDIN for your daemon. Defaults to "/dev/null". Default
Mode is '<' (read). You can define other Mode the same way as you do using
Perls "open" in a two-argument form.
child_STDOUT
Defines the path where the output of your daemon will go. Defaults to
"/dev/null". Default Mode is '+>' (write/read). You can define other Mode the
same way as you do using Perls "open" in a two-argument form.
child_STDERR
Defines the path where the error output of your daemon will go. Defaults to
"/dev/null". Default Mode is '+>' (write/read). You can define other Mode the
same way as you do using Perls "open" in a two-argument form, see example
below.
dont_close_fh
If you define it, it must be an arrayref with file handles you want to
preserve from the parent into the child (daemon). This may be the case if you
have code below a "__DATA__" token in your script or module called by "use" or
"require".
dont_close_fh => [ 'main::DATA', 'PackageName::DATA', $my_filehandle, ... ],
You can add any kind of file handle to the array (expression in single quotes
or a scalar variable), including 'STDIN', 'STDOUT' and 'STDERR'. Logically the
path settings from above ("child_STDIN", ...) will be ignored in this case.
DISCLAIMER: Using this argument may not detach your daemon fully from the
parent! Use it at your own risk.
dont_close_fd
Same function and disclaimer as "dont_close_fh", but instead of file handles
you write the numeric file descriptors inside the arrayref.
pid_file
Defines the path to a file (owned by the parent user) where the PID of the
daemon process will be stored. Defaults to "undef" (= write no file).
exec_command
Scalar or arrayref with system command(s) that will be executed by the daemon
via Perls "exec PROGRAM_LIST". In this case the child will never return to the
parents process!
Example:
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' ],
);
In this example:
• the PID of the daemon will be returned to $daemon in the parent process and a
pid-file will be created at "/working/daemon/directory/pid.txt".
• STDOUT will be open with Mode '+>' (write/read) to
"/path/to/daemon/output.file" and STDERR will be open to
"/working/daemon/directory/debug.txt" with Mode '+>>' (write/read opened for
appending).
• the script "/home/my_script.pl" will be executed by "perl" and run as daemon.
Therefore the child process will never return to this parent script.
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:
• "undef", in this case it tries to get the PID to check out of the object
reference settings.
• a PID number to check.
• the path to a file containing the PID to check.
• the command line entry of the running program to check. This requires
Proc::ProcessTable to be installed.
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.
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:
• Detlef Pilzecker, http://search.cpan.org/~deti/, http://www.secure-sip-server.net/
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).
SEE ALSO
perl(1), POSIX, Proc::ProcessTable
COPYRIGHT
This module is Copyright (C) 1997-2011 by Earl Hood and Detlef Pilzecker.
All Rights Reserved.
This module is free software. It may be used, redistributed and/or modified under the same
terms as Perl itself.