namespaces/orphan.c

This is namespaces/orphan.c, an example to accompany the book, The Linux Programming Interface.

This file is not printed in the book; it demonstrates Linux features that are not described in the book (typically features that have appeared since the book was published).

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

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.

 

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  Cover of The Linux Programming Interface

Function list (Bold in this list means a function is not static)

/* orphan.c

   Copyright 2013, Michael Kerrisk
   Licensed under GNU General Public License v2 or later

   Demonstrate that a child becomes orphaned (and is adopted by init(1),
   whose PID is 1) when its parent exits.

   See https://lwn.net/Articles/532748/

   Change history:
   2019-02-15   Changes to allow for the fact that on systems with a modern
                init(1) (e.g., systemd), an orphaned child may be adopted
                by a "child subreaper" process whose PID is not 1.
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
    pid_t ppidOrig = getpid();

    pid_t pid = fork();
    if (pid == -1) {
        perror("fork");
        exit(EXIT_FAILURE);
    }

    if (pid != 0) {             /* Parent */
        printf("Parent (PID=%ld) created child with PID %ld\n",
                (long) getpid(), (long) pid);
        printf("Parent (PID=%ld; PPID=%ld) terminating\n",
                (long) getpid(), (long) getppid());
        exit(EXIT_SUCCESS);
    }

    /* Child falls through to here */

    do {
        usleep(100000);
    } while (getppid() == ppidOrig);            /* Am I an orphan yet? */

    printf("\nChild  (PID=%ld) now an orphan (parent PID=%ld)\n",
            (long) getpid(), (long) getppid());

    sleep(1);

    printf("Child  (PID=%ld) terminating\n", (long) getpid());
    exit(EXIT_SUCCESS);
}

 

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Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.

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