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 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

  Cover of The Linux Programming Interface
+/* 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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