Need to create a orphan process in perl - ruby

Question

HI I am trying to execute a code by forking a child process.
I have ruby code a.rb in which i use system call
system("perl abc.pl -subroutine='a' -command='b' -status='c' -logfile='d' -start_datetime='e'")
now in abc.pl i am doing this
my $pid = fork;
if (!$pid) {
print "[INFO] in the child process \n ";
print "[INFO] forking worked, child process id: ($$) \n";
while (1) {
if ( -d "$ENV{OUT_HOME}" ) {
print "[INFO] $ENV{OUT_HOME} is available now to write $seq \n";
open(my $FH,'>',"$ENV{OUT_HOME}/SEQ") or die "cannot open file to write $seq into $ENV{OUT_HOME}/SEQ";
print $FH "$seq";
close $FH;
print "[INFO] exiting from forked child process id: ($$) \n";
exit; # exit the while loop
}
else {
sleep (2);
}
}
} else {
print "[INFO] I am parent Process exiting from here \n";
exit;
}
Now with this i am trying to get child process which is not dependent on parent process (here it is abc.pl) When i run the script, it does the system command which is running perl script and i see the perl script in process tree. But i keeps hanging there. I am not sure on why system command doesn't terminate after parent is done? any suggestions or comments appreciated.

Answer 1

You need to create a new POSIX session for your newly-independent forked process.
Try this (assuming that the environment variable OUT_HOME has been set to a folder before calling perl):
my $pid = fork;
if (!$pid) {
print "[INFO] in the child process \n ";
print "[INFO] forking worked, child process id: ($$) \n";
require POSIX;
POSIX::setsid();
while (1) {
if ( -d "$ENV{OUT_HOME}" ) {
print "[INFO] $ENV{OUT_HOME} is available now to write $seq \n";
open(my $FH,'>',"$ENV{OUT_HOME}/SEQ") or die "cannot open file to write $seq into $ENV{OUT_HOME}/SEQ";
print $FH "$seq";
close $FH;
print "[INFO] exiting from forked child process id: ($$) \n";
exit; # exit the while loop
}
else {
sleep (2);
}
}
} else {
print "[INFO] I am parent Process exiting from here \n";
exit;
}

Answer 2

This is addressed in perlfaq8:
How do I fork a daemon process?
If by daemon process you mean one that's detached (disassociated from its tty), then the following process is reported to work on most Unixish systems. Non-Unix users should check their Your_OS::Process module for other solutions.
Open /dev/tty and use the TIOCNOTTY ioctl on it. See tty(1) for details. Or better yet, you can just use the POSIX::setsid() function, so you don't have to worry about process groups.
Change directory to /
Reopen STDIN, STDOUT, and STDERR so they're not connected to the old tty.
Background yourself like this:
fork && exit;
The Proc::Daemon module, available from CPAN, provides a function to perform these actions for you.
As the FAQ states, the Proc::Daemon module can simplify this for you, although this is just one of several modules available for this task.