system command not working after connection with cgi breaks

advait has asked for the wisdom of the Perl Monks concerning the following question:

Hi All, I take the data from user and tell the user that result will be emailed.
On the server side I process the data . For processing I have made a small perl script which breaks the data into multiple small segments and process them in using system command

$command ="nice R --slave --args $DirName $SubDirName < read_parameter
+s_by_file_batch.R ";
system($command);
[download]

System calls R till the main cgi script is alive. I can see cgi as defunctional using top. Once cgi dies system command doesnt gets executed
Last few lines of main cgi script are

    $cmd = "perl /var/www/cgi-bin/vcgi/ProcessFiles_test.pl $UploadDir
+ $DirName $TotFiles &";
    system ($cmd);
    fork && exit;
[download]

Can anyone please suggest how to overcome this situation thank you

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Re: system command not working after connection with cgi breaks by pc88mxer (Vicar) on Jun 23, 2008 at 17:57 UTC
Try these two things: 1. Remove the `fork && exit` at the end of your script - you don't need it. 2. On all of your `system()` commands, redirect STDOUT to a file or `/dev/null`. This especially is important for commands executed in the background like the last one you perform just before exiting. Without #2, the server will never finish sending the response to your browser, and this might be causing your browser to time-out the connection which might have something to do with your problem.	[reply] [d/l] [select]
Re^2: system command not working after connection with cgi breaks by advait (Beadle) on Jun 23, 2008 at 18:04 UTC
Thank you for the reply. I have removed fork and exit and I am using close(STDOUT) still not working...facing same problem	[reply]
Re^3: system command not working after connection with cgi breaks by pc88mxer (Vicar) on Jun 23, 2008 at 19:42 UTC
To elaborate, you should append `" >/dev/null"` to your system command strings (but in the last case insert it before the `&`). Here's some basics on I/O redirection: Standard Input and Output Redirection	[reply] [d/l] [select]
Re^3: system command not working after connection with cgi breaks by dwm042 (Priest) on Jun 23, 2008 at 18:24 UTC
You're still having problems because you didn't do what you were asked to do. pc88mixer asked you to redirect stdout in the system call to something else, like /dev/null, so that the output was not 'attached' to the cgi process. Closing stdout in the perl script isn't the same thing.	[reply]
Re: system command not working after connection with cgi breaks by psini (Deacon) on Jun 23, 2008 at 17:30 UTC
I'm not sure if what you find is a standard behavior and if it's possible avoiding it but, in a similar situation, I resolved the problem executing a `at now ...` command instead of forking. It's a hack, but it works. Careful with that hash Eugene.	[reply] [d/l]
Re^2: system command not working after connection with cgi breaks by advait (Beadle) on Jun 23, 2008 at 17:52 UTC
can you please elaborate on at now command	[reply]
Re^3: system command not working after connection with cgi breaks by psini (Deacon) on Jun 23, 2008 at 18:08 UTC
You make a `system` call to the `at` unix command (see man at). In our context, if you execute `at now <"your_command"` the at command returns immediately, so you can terminate your cgi script but the command "your_command" is executed in another process that is not a child of your process, but of cron deamon. Actually `at` schedules a single execution of your_command via crond. Careful with that hash Eugene.	[reply] [d/l] [select]