procexec/make_zombie.c

This is procexec/make_zombie.c (Listing 26-4, page 554), an example from the book, The Linux Programming Interface.

The source code file is copyright 2024, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* make_zombie.c

   Demonstrate how a child process becomes a zombie in the interval between
   the time it exits, and the time its parent performs a wait (or exits, at
   which time it is adopted by init(8), which does a wait, thus releasing
   the zombie).
*/
#include <signal.h>
#include <libgen.h>             /* For basename() declaration */
#include "tlpi_hdr.h"

#define CMD_SIZE 200
int
main(int argc, char *argv[])
{
    char cmd[CMD_SIZE];
    pid_t childPid;

    setbuf(stdout, NULL);       /* Disable buffering of stdout */

    printf("Parent PID=%ld\n", (long) getpid());

    switch (childPid = fork()) {
    case -1:
        errExit("fork");

    case 0:     /* Child: immediately exits to become zombie */
        printf("Child (PID=%ld) exiting\n", (long) getpid());
        _exit(EXIT_SUCCESS);

    default:    /* Parent */
        sleep(3);               /* Give child a chance to start and exit */
        snprintf(cmd, CMD_SIZE, "ps | grep %s", basename(argv[0]));
        system(cmd);            /* View zombie child */

        /* Now send the "sure kill" signal to the zombie */

        if (kill(childPid, SIGKILL) == -1)
            errMsg("kill");
        sleep(3);               /* Give child a chance to react to signal */
        printf("After sending SIGKILL to zombie (PID=%ld):\n", (long) childPid);
        system(cmd);            /* View zombie child again */

        exit(EXIT_SUCCESS);
    }
}

 

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