This is psem/psem_create.c (Listing 53-1, page 1092), 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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/* psem_create.c

   Create a POSIX named semaphore.

   Usage as shown in usageError().

   On Linux, named semaphores are supported with kernel 2.6 or later, and
   a glibc that provides the NPTL threading implementation.
#include <semaphore.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "tlpi_hdr.h"
static void
usageError(const char *progName)
    fprintf(stderr, "Usage: %s [-cx] name [octal-perms [value]]\n", progName);
    fprintf(stderr, "    -c   Create semaphore (O_CREAT)\n");
    fprintf(stderr, "    -x   Create exclusively (O_EXCL)\n");
main(int argc, char *argv[])
    int flags, opt;
    mode_t perms;
    unsigned int value;
    sem_t *sem;

    flags = 0;
    while ((opt = getopt(argc, argv, "cx")) != -1) {
        switch (opt) {
        case 'c':   flags |= O_CREAT;           break;
        case 'x':   flags |= O_EXCL;            break;
        default:    usageError(argv[0]);

    if (optind >= argc)

    /* Default permissions are rw-------; default semaphore initialization
       value is 0 */

    perms = (argc <= optind + 1) ? (S_IRUSR | S_IWUSR) :
                getInt(argv[optind + 1], GN_BASE_8, "octal-perms");
    value = (argc <= optind + 2) ? 0 : getInt(argv[optind + 2], 0, "value");

    sem = sem_open(argv[optind], flags, perms, value);
    if (sem == SEM_FAILED)



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