by ypan » Sun, 03 Dec 2000 04:00:00
i tested fork like this:
if ((pid = fork()) == 0) {
if (r=execl("./myserv", "myserv", argv[1], (char*)NULL));
cerr<<"err"<<endl;
}
the program "myserv <port_number>" is a tcp socket listener.
question:
how can i redirect the output of myserv to /dev/null in an execl()?
and, how can i get the return value of myserv, i mean, not execl()?
and, how to kill the spawned myserv in parent process?
thanks a lot!
by ypan » Sun, 03 Dec 2000 04:00:00
if ((pid = fork()) == 0) {
if ((r=execl("./myserv", "myserv", argv[1], (char*)NULL)) < 0)
cerr<<"err"<<endl;
}
by NOWIES » Sun, 03 Dec 2000 04:00:00
>i tested fork like this:
> if ((pid = fork()) == 0) {
> if (r=execl("./myserv", "myserv", argv[1], (char*)NULL));
> cerr<<"err"<<endl;
> }
>the program "myserv <port_number>" is a tcp socket listener.
>question:
>how can i redirect the output of myserv to /dev/null in an execl()?
I heard (I'm not alse not sure) wait(...) waits for child being ended andQuote:>and, how can i get the return value of myserv, i mean, not execl()?
kill(SIGKILL,pid);Quote:>and, how to kill the spawned myserv in parent process?
NOWIESZ
by Axel Wei » Tue, 05 Dec 2000 04:00:00
> i tested fork like this:
> if ((pid = fork()) == 0) {
> if (r=execl("./myserv", "myserv", argv[1], (char*)NULL));
> cerr<<"err"<<endl;
> }
> the program "myserv <port_number>" is a tcp socket listener.
> question:
> how can i redirect the output of myserv to /dev/null in an execl()?
The return value of 'myserv' can be obtained, only _after_ 'myserv' hasQuote:> and, how can i get the return value of myserv, i mean, not execl()?
int pid, ret=0;Quote:> and, how to kill the spawned myserv in parent process?
else{Quote:}
Hope I could help youQuote:}
--
Humboldt-Universit?t zu Berlin, Institut fr Informatik
Axel Wei?
Rudower Chaussee 25, 12489 Berlin
Postanschrift: Unter den Linden 6, 10099 Berlin
Telefon: + 49(30) 2093 3050 FAX : + 49(30) 2093 3045
by Scott Neugrosch » Tue, 05 Dec 2000 04:00:00
> Hallo, Ypang
> > i tested fork like this:
> > if ((pid = fork()) == 0) {
> > if (r=execl("./myserv", "myserv", argv[1], (char*)NULL));
> > cerr<<"err"<<endl;
> > }
> > the program "myserv <port_number>" is a tcp socket listener.
> > question:
> > how can i redirect the output of myserv to /dev/null in an execl()?
> The simplest way is to (temporarily) redirect the output in your parent
> process, _before_ you fork. If you like, you then can reset the output
> channel of the parent process.
> > and, how can i get the return value of myserv, i mean, not execl()?
> The return value of 'myserv' can be obtained, only _after_ 'myserv' has
> been terminated. Every parent process has to organize to wait for it's
> children after their termination -- otherwise you will have some
> 'zombies', in worst case until your next reboot! Wait(pid) will deliver
> the return value.
> > and, how to kill the spawned myserv in parent process?
> int pid, ret=0;
> if ((pid=fork()) == 0){
> /* child process */
> }
> else{
> /* parent process */
> ...
> kill(SIGTERM, pid);
> if (waitpid(pid, &ret, NULL) == pid){
> /* ret contains the return value */
> }
> }
if ((pid = fork()) == 0) {
close(1);
// note -- only redirecting stdout so that we can still send stuff to
stderr/cerr
open("/dev/null",O_WRONLY);
if (r = execl(...)) ...
//...Quote:}
Scott
by Karl Keusge » Thu, 07 Dec 2000 04:00:00
Hi,Quote:> i tested fork like this:
> if ((pid = fork()) == 0) {
> if (r=execl("./myserv", "myserv", argv[1], (char*)NULL));
> cerr<<"err"<<endl;
> }
> the program "myserv <port_number>" is a tcp socket listener.
> question: how can i redirect the output of myserv to /dev/null in an
> execl()? and, how can i get the return value of myserv, i mean, not
> execl()? and, how to kill the spawned myserv in parent process?
> thanks a lot!
run this small program, it answers your questions.
/* small demo-programm which daemonizes itself and */
/* starts one child process. The stdout of the Child- */
/* process is redirected to /dev/null */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <signal.h>
#include <wait.h>
int daemon_child(int param1 )
{
long i = 0;
int fd_null = open ("/dev/null", O_WRONLY);
printf ("\n child process %d started\n redirect stdout NOW! \n\n",
getpid());
fflush(stdout);
/* doin some errhanfding, or not */
/* close the old stdout */
close (STDOUT_FILENO);
/* redirect it to fd_null */
dup2( fd_null, STDOUT_FILENO);
/* close it, cause after dup it's not used anymore */
close (fd_null);
/* do some output */
while (1)
{
printf("%d\n", i);
fflush (stdout);
}
return 0;
int main (int argc, char** argv, char** env)Quote:}
if (!fork())
{
/* set process leader ID */
setsid();
/* daemonize it, nice */
if (!(PID=fork()))
{
/* start child's workin' function */
exit(daemon_child(20));
}
else
{
/* kill child-process after 10 seconds */
fprintf (stderr, "parent process %d is daemonized and
got one child, PID: %d\n", getpid(), PID );
fflush(stderr);
sleep (10);
fprintf (stderr, "parent process %d is goin' to kill
child %d\n", getpid(), PID );
kill(PID, SIGKILL);
/*wait for killed processes, otherwise you get a zomby*/
/*may use waitpid if you got more than one child */
wait(&status);
fflush (stderr);
sleep (10);
fprintf (stderr, "daemonized parent process %d exits
itself\n", getpid());
fflush (stderr);
}
}
else
{
exit (0);
}
return 0;
Quote:}
Hi,
I hope this is a simple question, in the following code I make a child and
parent process, but what I want to do is create one parent and an arbitrary
number, n of child processes. Okay so I thought a for loop from 0 to n-1 but
I'm unsure how to do it, how would I prevent getting n child AND n parent
processes, when I want just the one parent process. Also, will the child
processes be distinguishable, as I want to be able to use the execlp()
command to call a different function for each child process (or the same
function with different parameters for each child).
Many thanks to anyone who can help with this.
Philip.
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
main()
{
pid_t pid;
int rv;
pid = fork();
if ( pid == -1 )
perror("fork"); /* something went wrong */
exit(1); /* parent exits */
}
if ( pid == 0 )
{
printf(" CHILD: This is the child process!\n");
printf(" CHILD: My PID is %d\n", getpid());
printf(" CHILD: My parent's PID is %d\n", getppid());
printf(" CHILD: Enter my exit status (make it small): ");
scanf(" %d", &rv);
printf(" CHILD: I'm outta here!\n");
exit(rv);
}
else
{
printf("PARENT: This is the parent process!\n");
printf("PARENT: My PID is %d\n", getpid());
printf("PARENT: My child's PID is %d\n", pid);
printf("PARENT: I'm now waiting for my child to exit()...\n");
wait(&rv);
printf("PARENT: My child's exit status is: %d\n",
WEXITSTATUS(rv));
printf("PARENT: I'm outta here!\n");
}
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