GCC Red Hat 4.8.5-39 上的 SEM_FAILED - 信号量

Question

This is simple shared memory program that I tried writing:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <sys/mman.h>
#include <getopt.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <errno.h>
#include <semaphore.h>
#include <fcntl.h>

#define SHM_NAME "/my_shm"
#define SEM_1 "/sem_1"
#define SEM_2 "/sem_2"
#define SEM_3 "/sem_3"
#define BUFFER_SIZE 10

typedef struct {
    int pred[8];
    int succ[8];
} fb_set;

struct sharedMemory{
    int rPos;
    int wPos;
    fb_set storage[BUFFER_SIZE];
    int done;
};

static struct sharedMemory *shared;

int main(int argc, char *argv[])
{
    int shmfd = shm_open(SHM_NAME, O_RDWR | O_CREAT, 0600);
    if (shmfd == -1){
       // exit
    }

    if (ftruncate(shmfd, sizeof(struct sharedMemory)) == -1){
        // exit
    }

    shared = mmap(NULL, sizeof(*shared), PROT_READ | PROT_WRITE, MAP_SHARED, shmfd, 0);
    if (shared == MAP_FAILED){
       // close resources
    }

    sem_t *sem_read = sem_open(SEM_1, O_CREAT | O_EXCL, 0600, 0);
    sem_t *sem_write = sem_open(SEM_2, O_CREAT | O_EXCL, 0600, BUFFER_SIZE);
    sem_t *sem_mutex = sem_open(SEM_3, O_CREAT | O_EXCL, 0600, 1);

    if (sem_read == SEM_FAILED){
        // close resources
    }
    if (sem_write == SEM_FAILED){
        // close resources
    }
    if(sem_mutex == SEM_FAILED){
        // close resources
    }
}

All semaphores are open correctly and the program compiles with:

gcc (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0

But when I try it on:

gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39)

I get SEM_FAILED on sem_t *sem_read = sem_open(SEM_1, O_CREAT | O_EXCL, 0600, 0); and errno is set to Permission denied .

Here is my Makefile:

CC = gcc 
DEFS = -D_DEFAULT_SOURCE -D_BSD_SOURCE -D_SVID_SOURCE -D_POSIX_SOURCE=200809L
CFLAGS = -std=c99 -pedantic -Wall -g $(DEFS)
supervisor: supervisor.o
    $(CC) $(CFLAGS) -o $@ $^ -lrt -pthread
supervisor.o : supervisor.c
    $(CC) $(CFLAGS) -c -o $@ $<
clean:
    rm -rf *.o supervisor

Can somebody explain me what I did wrong?

Answer 1

errno is set to Permission denied .

From shm_open() documentation :

[EACCES] The shared memory object exists and the permissions specified by oflag are denied, or the shared memory object does not exist and permission to create the shared memory object is denied, or O_TRUNC is specified and write permission is denied.