CODEWITHSUNDEEP
objective-ccmacos
Waqar
Waqar

Reputation: 105

Reading physical drives in Mac OS X

In the code given below:

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/disk.h>

int main(int argc, char **argv)
{
    int fd = open("/dev/disk0", O_RDONLY, 0);

    ...
}

fd has -1 for physical hard drives but it works fine for a USB/flash drive. Why is this happening?

Upvotes: 3

Views: 994

Answers (1)

Brendan Shanks
Brendan Shanks

Reputation: 3236

This is almost certainly a permissions issue. Giving ordinary users any access to raw disks is a security hole (the user could circumvent all file permissions and read anything they want on the disk), so no OS gives raw disk access to normal users.

In the example below, disk0 is my internal hard drive and disk3 is a USB flash drive. In OS X, even "administrators" aren't part of the operator group that would allow raw disk access to fixed hard drives.

pip$ ls -ltr /dev/disk*
brw-r----- 1 root operator 14, 3 Dec 12 10:14 /dev/disk0s3
brw-r----- 1 root operator 14, 2 Dec 12 10:14 /dev/disk0s2
brw-r----- 1 root operator 14, 1 Dec 12 10:14 /dev/disk0s1
brw-r----- 1 root operator 14, 0 Dec 12 10:14 /dev/disk0
br--r----- 1 root operator 14, 4 Dec 14 15:15 /dev/disk1
brw-r----- 1 root operator 14, 7 Dec 14 15:15 /dev/disk2s2
br--r----- 1 root operator 14, 6 Dec 14 15:15 /dev/disk2s1
brw-r----- 1 root operator 14, 5 Dec 14 15:15 /dev/disk2
brw-r----- 1 pip operator 14, 9 Dec 14 15:18 /dev/disk3s1
brw-r----- 1 pip operator 14, 8 Dec 14 15:18 /dev/disk3

If your app really needs raw disk access you'll either need to run it as root with sudo, add yourself to the operator group, or use the OS X APIs for privilege escalation.

Upvotes: 2

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