This is procexec/t_vfork.c (Listing 24-4, page 524), 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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/* t_vfork.c

   Demonstrate the use of vfork() to create a child process.
#define _BSD_SOURCE     /* To get vfork() declaration from <unistd.h>
                           in case _XOPEN_SOURCE >= 700 */
#include "tlpi_hdr.h"
main(int argc, char *argv[])
    int istack = 222;

    switch (vfork()) {
    case -1:

    case 0:             /* Child executes first, in parent's memory space */
        sleep(3);                   /* Even if we sleep for a while,
                                       parent still is not scheduled */
        write(STDOUT_FILENO, "Child executing\n", 16);
        istack *= 3;                /* This change will be seen by parent */

    default:            /* Parent is blocked until child exits */
        write(STDOUT_FILENO, "Parent executing\n", 17);
        printf("istack=%d\n", istack);


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