nagios-plugins/config_test/child_test.c

// Base code taken from http://www-h.eng.cam.ac.uk/help/tpl/unix/fork.html
// Fix for redhat suggested by Ptere Pramberger, peter@pramberger.at
#include <unistd.h>
#include <sys/wait.h>
#include <stdio.h>
#include <sys/types.h>
#include <signal.h>
void popen_sigchld_handler (int);
int childtermd;

int main(){
 char str[1024];
 int pipefd[2];
 pid_t pid;
 int status, died;

        if (signal (SIGCHLD, popen_sigchld_handler) == SIG_ERR) {
                printf ("Cannot catch SIGCHLD\n");
		_exit(-1);
        }

  pipe (pipefd);
  switch(pid=fork()){
   case -1: 
	    printf("can't fork\n");
            _exit(-1);
   
   case 0 : // this is the code the child runs 
            close(1);      // close stdout
            // pipefd[1] is for writing to the pipe. We want the output
            // that used to go to the standard output (file descriptor 1)
            // to be written to the pipe. The following command does this,
            // creating a new file descripter 1 (the lowest available) 
            // that writes where pipefd[1] goes.
            dup (pipefd[1]); // points pipefd at file descriptor
            // the child isn't going to read from the pipe, so
            // pipefd[0] can be closed
            close (pipefd[0]);

	    //These are the commands to run, with success commented. dig and nslookup only problems
            //execl ("/bin/date","date",0);			// 100%
	    //execl ("/bin/cat", "cat", "/etc/hosts", 0); 	// 100%
	    //execl ("/usr/bin/dig", "dig", "redhat.com", 0);	// 69%
	    //execl("/bin/sleep", "sleep", "1", 0);		// 100%
            execl ("/usr/bin/nslookup","nslookup","redhat.com",0); // 90% (after 100 tests), 40% (after 10 tests)
            //execl ("/bin/ping","ping","-c","1","localhost",0);	// 100%
            //execl ("/bin/ping","ping","-c","1","192.168.10.32",0);	// 100%
	    _exit(0);

   default: // this is the code the parent runs 

            close(0); // close stdin
            // Set file descriptor 0 (stdin) to read from the pipe
            dup (pipefd[0]);
            // the parent isn't going to write to the pipe
            close (pipefd[1]);
            // Now read from the pipe
            fgets(str, 1023, stdin);
            //printf("1st line output is %s\n", str);

	    //while (!childtermd);  // Uncomment this line to fix

            died= wait(&status);
	    //printf("died=%d status=%d\n", died, status);
	    if (died > 0) _exit(0);
	    else          _exit(1);
   }
}

void
popen_sigchld_handler (int signo)
{
        if (signo == SIGCHLD) {
                //printf("Caught sigchld\n");
                childtermd = 1;
        }
}