iOS mkfifo() operation not permitted

Question

I have the following code which I call from a Swift main program in Xcode and when running it in the Simulator in a virtual iPhone for example, it works. It creates /tmp/MYFIFO.

int32_t init_udpC(void) {

    static char *filename="/tmp/MYFIFO";

    umask(0);
    unlink(filename);
    if((mkfifo(filename, 0666)) == -1){
        perror("mkfifo");
        exit(2);
    }
    if((fd=open("/tmp/MYFIFO",O_RDWR|O_APPEND)) == -1) {
        perror("open");
        exit(2);
    }
    return fd;
}

Running it on the physical device the code fails with

mkfifo: Operation not permitted

I found this link https://stackoverflow.com/questions/5328398/what-are-the-directory-locations-that-are-writable-on-ios serving as a helpful source of information. — Krischu, Dec 27 '18 at 08:40

score 2 · Answer 1 · answered Dec 26 '18 at 19:27

2

It's because of iOS sandboxing. On iOS, your app isn't allowed to access /tmp/. It works in the simulator because you're running on macOS, where it's OK.

You need to use a path that's someplace where your app is allowed to access. One possibility is to replace the path with

const char *filename=[[NSTemporaryDirectory() stringByAppendingPathComponent:@"MYFIFO"] UTF8String];

There are other valid paths-- the key is that you have to be allowed to access the directory.

answered Dec 26 '18 at 19:27

Tom Harrington

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Thanks. NS (Cocoa) isn't always present. – Krischu Dec 27 '18 at 08:41
There are other ways to do it. The crucial detail is that you must be able to write to the director you use. – Tom Harrington Dec 27 '18 at 16:55

iOS mkfifo() operation not permitted

1 Answers1