Net::OpenSSH with fork

brp4h has asked for the wisdom of the Perl Monks concerning the following question:

I'm having trouble using the system call of the Net::OpenSSH module from a child process. After I fork, the child successfully creates a new SSH object, but then when I try this code the program dies:

$ssh->system({stdin_data => $sas_string},
                  "cat >$rmt_dir/$rmt_file")
        or die "unable to write file: " . $ssh->error;
[download]

and the error is unable to write file: child process 14947 does not exists: No child processes Is there something I should know that could be causing this? It works fine without the fork.

Comment on Net::OpenSSH with fork Select or Download Code

Replies are listed 'Best First'.
Re: Net::OpenSSH with fork by ikegami (Patriarch) on Jan 26, 2010 at 18:36 UTC
Does that child have a `$SIG{CHLD}` handler? Just guessing here, but it could interfere.	[reply] [d/l]
Re^2: Net::OpenSSH with fork by brp4h (Acolyte) on Jan 26, 2010 at 18:42 UTC
Yep, that was it. Thank you!	[reply]
Re: Net::OpenSSH with fork by salva (Canon) on Jan 26, 2010 at 23:01 UTC
I (the module author) am considering solving that inside the module: Other `system` implementations (i.e. NetBSD) call sigprocmask(2) to disable delivering of CHLD signals inside the function, but I am not sure how portable that approach is. Does anybody have any experience using `POSIX::sigprocmask()` across different Unix/Linux OSs? BTW, Perl builtins (`system` and `qx()`) do nothing to handle that case and also fail when $SIG{CHLD} is set to 'IGNORE' or to some funny handler reaping children. update: at least on Linux, blocking `SIGCHLD` with sigprocmask(2) is not enough when the `SA_NOCLDWAIT` flag (aka `$SIG{CHLD}='IGNORE'`) is set. The OS continues to reap dead children and `waitpid` fails.	[reply] [d/l] [select]