Provided by: libproc-daemon-perl_0.23-2_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 ($>) for the daemon
process using "POSIX::setuid( ... )", in case you want to run your daemon under a different
user from the parent. Obviously the first user must have the rights to switch to the new user
otherwise it will stay the same. It is helpful to define the argument "setuid" if you start
your script at boot time by init with the superuser, but wants the daemon to run under a
normal user account.
setgid Sets the real group identifier ($() 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)