task_for_pid always returns (os/kern) failure on darwin in C

Question

For some reasons I cannot get anything to come out of task_for_pid() I can't find very much information but what I am trying to do it attach to another process and search its memory, but every time I try to use task_for_pid, I get the same (os/kern) failure error.

#include <stdio.h>
#include <mach/mach_traps.h>
#include <mach/mach_init.h>

int main(int argc, char* argv[])
{
mach_port_name_t task;
printf("%d\n", argv[1]);
int pid = atoi(argv[1]);
printf("%d\n%d\n", pid, current_task());
int error = task_for_pid(2055, 24269, &task);
printf("%x\n", task);
if (error)
{
printf("task_for_pid return error:\n %s\n", mach_error_string(error));
} else {
printf("Get the process %d's task port : %x\n", pid, task);
}
return 0;
}

Output looks like:

gcc -o test test.c;./test 24269
803206115
24269
2055
0
task_for_pid return error:
 (os/kern) failure

Any idea's as to why im not getting a task, ever? I am running it as root.

As Adam Rosenfield said, it does say in the header that it is obsolete, but if thats true, could I still compile and run it with an older version of the toolchain? or what has it been replaced with? does anyone know?

Answer 1

1. Are you sure you are running as root?
2. Are you sure the process 24269 is still running?

I have no problem running this code (with sudo) on Mac OS X 10.6.8 with any running process:

#include <stdio.h>
#include <stdlib.h>
#include <mach/mach_traps.h>
#include <mach/mach_init.h>
#include <mach/mach_error.h>

int main(int argc, char* argv[])
{
    task_t task;
    pid_t pid = argc >= 2 ? atoi(argv[1]) : 1;
    kern_return_t error = task_for_pid(current_task(), pid, &task);
    printf("%d -> %x [%d - %s]\n", pid, task, error, mach_error_string(error));
    return error;
}

For example, here is my result with pid 182 (Dock)

$ sudo ./task_for_pid 182
182 -> 413 [0 - (os/kern) successful]