procexec/orphan.c

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

This file is not printed in the book; it is the solution to Exercise 26-1 (page 562).

The source code file is copyright 2022, 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

   Demonstrate how a child becomes orphaned (and adopted by init(1))
   when its parent exits.

   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 "tlpi_hdr.h"
int
main(int argc, char *argv[])
{
    pid_t ppid, ppidOrig;

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

    ppidOrig = getpid();

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

    case 0:             /* Child */
        while ((ppid = getppid()) == ppidOrig) {   /* Loop until orphaned */
            printf("Child running (parent PID=%ld)\n", (long) ppid);
            sleep(1);
        }
        printf("Child is orphaned (parent PID=%ld)\n", (long) ppid);
        exit(EXIT_SUCCESS);

    default:            /* Parent */
        printf("Parent (PID=%ld) sleeping\n", (long) getpid());
        sleep(3);                           /* Give child a chance to start */
        printf("Parent exiting\n");
        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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