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Proc::Daemon(3) |
User Contributed Perl Documentation |
Proc::Daemon(3) |
Proc::Daemon - Run Perl program(s) as a daemon process.
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( ... );
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!
- 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 ($>) for the daemon
process using "POSIX::setuid( ... )", in
case you want to run your daemon under an other user than the parent.
Obviously the first user must have the rights to switch to the new user
otherwise it will stay the same. It is helpful to define the argument
"setuid" if you start your script at
boot time by init with the superuser, but wants the daemon to run under a
normal user account.
- setgid
- Sets the real group identifier ($() 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.
- 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".
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.
"Proc::Daemon::init" is still available for
backwards capability.
Proc::Daemon is now taint safe (assuming it is not passed any
tainted parameters).
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/
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.
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).
<https://github.com/akreal/Proc-Daemon>
perl(1), POSIX, Proc::ProcessTable
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.
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