Exit code 13 from Perl’s system() command

perl

I am trying to call system commands from perl, using system().

That usually works fine, but when I don't start the perl script myself, but have a compiled C program run it using the C popen() function, then perl is not able to execute its system commands. Perl's system() then returns with exit code 13.

It works only if I use the backticks in Perl, instead of system. Does anyone know why?

Best Answer

It would help to see some of your code/output. Here's my guess at the root cause of your problem.

First, signal 13 equates to SIGPIPE, which in this case seems to indicates the perl process is attempting to write to a pipe (i.e. STDOUT/STDERR), but nothing is there to read it.

I tested a bit and my question is, are you handling the output from the the script within your C program? In my tests, simply processing the output of the perl script avoided the SIGPIPE error.

Signal 13 produced:

fp = popen("/home/chuckx/perl-test/perl.pl","r");
status = pclose(fp);

Signal 13 avoided:

fp = popen("/home/chuckx/perl-test/perl.pl","r");

do {} while (fgets(output,80,fp) != NULL);

status = pclose(fp);

Related Solutions

Java – Kill FINished sockets (using libpcap – tcpdump/tcpkill)

Looking at the source code for tcpkill, it uses libnet to generate a RST packet(s) to kill a given TCP connection. I'm not sure why it's not working (though verifying the PCAP version it was built against is a great place to start). You can also use tcpdump to look for the RST packets it should be sending out.

Regarding implementing the equivalent in Perl, I once had to do something sort of similar. Below is (untested!) code which might point you in the right direction.

use NetPacket::Ethernet;
use NetPacket::IP;
use NetPacket::TCP;
use Net::RawIP;

... (the rest of your script) ...

sub process_packet {
    my ($user_data,$header,$packet) = @_;

    my $ethernet_frame = NetPacket::Ethernet::strip($packet);
    my $ip_packet = NetPacket::IP->decode($ethernet_frame);
    my $tcp = NetPacket::TCP->decode($ip_packet->{data});

    my $reset_packet = new Net::RawIP;

    $reset_packet->set({
        ip => {
            saddr => $ip_packet->{dest_ip},
            daddr => $ip_packet->{src_ip}
        },
        tcp => {
            source => $tcp->{dest_port},
            dest => $tcp->{src_port}
        },
        rst => 1,
        seq => $ip->{acknum},
        data => 'access denied'
    });

    $reset_packet->send();
}

tcpkill is more refined in terms of attempting to figure out the correct sequence number, which is what the -1..9 flags are for. Have you tried using different values for that flag?

Linux – perl equivalent of sh -e

Look at the autodie core module. This replaces calls like open and fork with functions that die on failure. To get it to work with system, you need to import :all or :system, since the default does not do so.

use strict;   #always!
use warnings; #always!
use autodie qw(:system);

system('/bin/false'); #This will die
print "This will never be printed\n";

It's important to note that for autodie to work with system, you need the IPC::System::Simple module. Install it with CPAN, or on Ubuntu you can sudo apt-get install libipc-system-simple-perl.

Best Answer

Related Solutions

Java – Kill FINished sockets (using libpcap – tcpdump/tcpkill)

Linux – perl equivalent of sh -e

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