SHMAT() permission denied

Asked May 14 '14 at 12:36

Active May 14 '14 at 16:51

Viewed 1,361 times

I have just started using shared memory. I cannot attach file which I created using shm_open() (shmat()) returns permission denied.Later I will attatch the shm in another process which I will create using fork exec, but I cannot get shmat() to work. It works if I use sudo to execute the program. How can I set the permissions for sharedMemory file. I tried creating the memory in a local folder but shm_open() does not allow it.

int shm_fd;

shm_fd = shm_open("mySharedMemory", O_CREAT | O_TRUNC, S_IRWXU | S_IRWXG);

if(shm_fd == -1)
{
    perror("p1");
    exit(1);
}

if( truncate("/run/shm/mySharedMemory", myFileSize) == -1 )
{
    perror("p1");
    exit(1);
}   

close(shm_fd);

key_t key;
int shmid;

key = ftok("/run/shm/mySharedMemory", 'A');
printf("\n%d\n",key);
shmid = shmget(key, 80, S_IWUSR | IPC_CREAT);

//char *ptr = shmat(shmid,NULL,0);
perror("p1");

exit(1);

edited May 14 '14 at 16:51

alk

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asked May 14 '14 at 12:36

user1821344

Are you running the program from /run/shm? If not, have you checked the permissions the file has been created under and which user you're running the program from? – Michael Di Felice May 14 '14 at 12:39
create `mySharedMemory` in local folder and try – gangadhars May 14 '14 at 12:40
why last line `perror("p1");` – gangadhars May 14 '14 at 12:41
it follow shmat() which I commented out – user1821344 May 14 '14 at 12:44
I can get it to work if I use the sudo command. Can shmget/shmopen be used to set the permissions of the shared memory file being created – user1821344 May 14 '14 at 12:47
@SGG how to create it in a local folder. shm_open does nothing if I give a path to a local folder. run/shm is the only place where I have been able to create the shm – user1821344 May 14 '14 at 13:56
You seem to be mixing POSIX and SysV SHM. You might like to read on this here: http://stackoverflow.com/q/21311080/694576 – alk May 14 '14 at 17:26
So there is no way I can change the permissions? Can this code only be run through the sudo command? – user1821344 May 15 '14 at 07:22
I found solution here: http://stackoverflow.com/a/30199902/1440299 – Ishayahu Jun 06 '16 at 19:55

SHMAT() permission denied

0 Answers0