Read fails after tcpreplay with error: 0: Resource temporarily unavailabl

Question

I have a very simple script to run. It calls tcpreplay and then ask the user to type in something. Then the read will fail with read: read error: 0: Resource temporarily una

Answer 1

Apparently tcpreplay sets O_NONBLOCK on stdin and then doesn't remove it. I'd say it's a bug in tcpreplay. To work it around you can run tcpreplay with stdin redirected from /dev/null. Like this:

tcpreplay -i eth4 SMTP.pcap 

Addition: note that this tcpreplay behavior breaks non-interactive shells only.

Another addition: alternatively, if you really need tcpreplay to receive your input you can write a short program which resets O_NONBLOCK. Like this one (reset-nonblock.c):

#include 
#include 
#include 

int
main()
{
    if (fcntl(STDIN_FILENO, F_SETFL,
              fcntl(STDIN_FILENO, F_GETFL) & ~O_NONBLOCK) < 0) {
        perror(NULL);
        return 1;
    }
    return 0;
}

Make it with "make reset-nonblock", then put it in your PATH and use like this:

tcpreplay -i eth4 SMTP.pcap
reset-nonblock