Proc::Daemon(3pm) User Contributed Perl Documentation Proc::Daemon(3pm)
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 ($>) for the daemon process using
"POSIX::setuid( ... )", in case you want to run your daemon
under a different user from the parent. Obviously the first
user must have the rights to switch to the new user
otherwise it will stay the same. It is helpful to define
the argument "setuid" if you start your script at boot time
by init with the superuser, but wants the daemon to run
under a normal user account.
setgid Sets the real group identifier ($() and the effective group
identifier ($)) for the daemon process using
"POSXI::setgid( ... )", just like "setuid". As with
"setuid", the first user must have the rights to switch to
the new group, otherwise the group id will not be changed.
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).
file_umask
Defines umask for "pid_file", "child_STDIN", "child_STDOUT"
and "child_STDERR" files. Defaults to 066 (other users may
not modify or read the files).
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.
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.
perl v5.34.0 2022-06-17 Proc::Daemon(3pm)
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