---------- Forwarded message ---------- From: Errin Larsen <[EMAIL PROTECTED]> Date: Thu, 23 Sep 2004 16:30:21 -0500 Subject: Re: Daemon that starts other Daemons To: Wiggins d Anconia <[EMAIL PROTECTED]>
Hi again, Ok ... so with some research and playi^H^H^H^H^Htesting I've found the answer to what's really been bothering me. If I fork(), I get the PID of the resulting child. However, if THAT child runs and external command, how do I get the (now grand)child's PID. The answer I was looking for was a deeper understanding of exec(). by fork()ing a child and having that child run exec(), the exec()ed command will have the SAME process ID as the original child. In actuality, the exec()ed command is NOT a grandchild, but has taken over the original child's process and all it's environment (STDIN, STDOUT, %ENV, etc.). That's what I needed to know! Now, if I just collect and keep the child's PID, when I run the exec() I'll have the PID of whatever command was exec()ed. Also, with some experimenting, the setsid() doesn't NEED the original parent to die to work, it just needs the child to be forked before it runs setsid(). In other words, if you try to run setsid() BEFORE you fork the child (in an attempt to give both the child and the parent the same session and group ID, perhaps) it will fail. If you instead have the child run setsid() after it is fork()ed, it will run fine, whether the parent is dead or not! YAY!! On Thu, 23 Sep 2004 13:30:08 -0600, Wiggins d Anconia <[EMAIL PROTECTED]> wrote: > > > > On Thu, 23 Sep 2004 11:23:16 -0500, Errin Larsen > <[EMAIL PROTECTED]> wrote: > > > Hi perl-people, > > > > <<SNIP>> > > > > > So, my question is, how do I implement this code WITHOUT the parent > > > process dieing? > > > > > > --Errin > > > > > <<SNIP>> Thanks for the help, Wiggins. I agree this would all be easier if I just went a grabbed a module, but for (probably strange) reasons I'd rather not go into, I want to do this from scratch. Also, this has been extremely helpful in teaching me what's going on with the backticks, system(), fork() and exec() functions. This process has really helped me along with my Perl education. Also, I realized that the ORIGINAL parent needs to die (So as to disassociate the daemons from the calling terminal/process), but I was looking for a daemon that would run, start other servers, and that hang around monitoring them. I think we're talking about the same thing here, just I didn't explain it will originally. Now, I just need to implement some code to dump a file with PIDs into /var/run! Thanks for the suggestions/help and I'll get working on it now! --Errin -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] <http://learn.perl.org/> <http://learn.perl.org/first-response>
