Provided by: libparanoid-perl_2.07-1_all bug


       Paranoid::Process - Process Management Functions


       $Id: lib/Paranoid/, 2.07 2019/01/30 18:25:27 acorliss Exp $


         use Paranoid::Process qw(:all);

         $rv = daemonize();

         MAXCHILDREN = 100;

         $SIG{CHLD} = \&sigchld;
         $count = childrenCount();
         $rv = pfork();

         $uid = ptranslateUser("foo");
         $gid = ptranslateGroup("foo");
         $rv = switchUser($user, $group);

         $rv = pcapture($cmd, $crv, $out);

         installSIGH('INT', &sigint1):
         installSIGH('INT', &sigint2):
         installSIGH('INT', &sigint3):

         uninstallSIGH('INT', &sigint2);



       This module provides a few functions meant to make life easier when managing processes.
       The following export targets are provided:

         all               All functions within this module
         pfork             All child management functions
         signal            All signal dispatcher functions

       Only the functions switchUser and daemonize are currently exported by default.


       Setting this lvalue subroutine sets a limit to how many children will be forked at a time
       by pfork.  The default is zero, which allows unlimited children.  Once the limit is met
       pfork becomes a blocking call until a child exits so the new one can be spawned.

       NOTE: This limit on children is enforced on a per-process basis.  That means that while a
       process is limited to the max threshold, its children could also fork their own batch of
       children as well, up to whatever max is set in those processes.

         $count = childrenCount();

       This function returns the current number of children spawned by pfork.


       This function takes a reference to a subroutine.  If used the subroutine will be called
       every time a child exits and triggers sigchild.  That subroutine will be called with the
       child's PID and exit value as arguments.

         $SIG{CHLD} = \&sigchld;

         # Or, if using the signal dispatcher
         installSIGH('CHLD', &sigchld);

       This function decrements the child counter necessary for pfork's operation, as well as
       calling the user's signal handler with each child's PID and exit value.

           $rv = daemonize();

       This function forks a child who reopens all STD* filehandles on /dev/null and starts a new
       process group.  The parent exits cleanly.  If the fork fails for any reason it returns a
       false value.  The child will also change its directory to /.

         $rv = pfork();

       This function should be used in lieu of Perl's fork if you want to take advantage of a
       blocking fork call that respects the MAXCHILDREN limit.  Use of this function, however,
       also assumes the use of sigchld as the signal handler for SIGCHLD.

         $uid = ptranslateUser("foo");

       This function takes a username and returns the corresponding UID as returned by getpwent.
       If no match is found it returns undef.

         $gid = ptranslateGroup("foo");

       This function takes a group name and returns the corresponding GID as returned by
       getgrent.  If no match is found it returns undef.

         $rv = switchUser($user);
         $rv = switchUser($user, $group);

       This function can be fed one or two arguments, both either named user or group, or UID or
       GID.  Both user and group arguments are optional as long as one of them is defined.

         $rv = pcapture($cmd, $crv, $out);

       This function executes the passed shell command and returns one of the following three

         RV    Description
         -1    Command failed to execute or died with signal
          0    Command executed but exited with a non-0 RV
          1    Command executed and exited with a 0 RV

       The actual return value is populated in the passed scalar, while all command output
       (including STDERR) is stored in the next scalar.  Any errors executing the command will
       have the error string stored in Paranoid::ERROR.

       If the command exited cleanly it will automatically be bit shifted eight bits.

       NOTE: Unlike many other functions in this suite it is up to you to detaint the command
       passed to this function yourself.  There's simply no way for me to know ahead of time what
       kind of convoluted arguments you might be handing this call before system is called.
       Failing to detaint that argument will cause your script to exit under taint mode.

         installSIGH($signal, &subroutine);

       This installs another subroutine in the queue for the specified signal.  Subroutines are
       called in the order that they're added to the queue.  Adding a specific subroutine more
       than once is filtered out so each subroutine in the queue is unique.

         uninstallSIGH($signal, &subroutine);

       Removes a subroutine from the specified queue.


       Inserts the dispatcher for each signal with subroutines in the queue.


       Removes the dispatcher for each signal that's using the dispatcher.  The signal handler
       installed is what ever was set when this module's code was loaded and initialized.


       o   Carp

       o   Paranoid

       o   Paranoid::Debug

       o   POSIX


       This following example caps the number of children processes to three at a time:

         $SIG{CHLD}  = \&sigchld;
         MAXCHILDREN = 3;
         for (1 .. 5) {

           # Only the children execute the following block
           unless ($pid = pfork()) {
             # ....
             exit 0;

       You can also install a child-exit routine to be called by sigchld.  For instance, to track
       the children's history in the parent:

         sub recordChild ($$) {
           my ($cpid, $cexit) = @_;

           push(@chistory, [$cpid, $cexit]);

         for (1 .. 5) {
           unless ($pid = pfork()) {
             # ....
             exit $rv;

         # Prints the child process history
         foreach (@chistory) { print "PID: $$_[0] EXIT: $$_[1]\n" };


       On Solaris pcapture doesn't return a -1 for non-existant commands, but a 0.  On Linux this
       appears to work as intended.


       Arthur Corliss (


       This software is licensed under the same terms as Perl, itself.  Please see for more information.

       (c) 2005 - 2017, Arthur Corliss (