Re: setpriority fails (even as root)

[Diego Nieto Cid]

Hi,

On Sat, Apr 11, 2026 at 06:15:42AM +0100, Michael Kelly wrote:
>
> Once I've completed the required change to adjtime() I can have a look at
> these too.
>

Sure, no worries, I'm not trying to push you. I'm just looking where I can help 
:)

The good news is that all that complex GLIBC code is probably not a problem.
I made a little reproduction program that calls task_priority directly and
the issue appears to be when GNU Mach is asked to change all threads.

    demo@debian:~/dev/tests$ sudo ./task_priority
    task_priority (5, 0) => 0 (0x0)
    task_priority (5, 1) => 5 (0x5)
    ./task_priority: error setting task priority: (os/kern) failure

I attach the test program source code.

Maybe the next step could be to add little test to the GNU Mach
test suite.

Thanks,
Diego

#include <error.h>
#include <mach/gnumach.h>
#include <mach/mach.h>
#include <stdio.h>

int main (int argc, char **argv)
{
  kern_return_t err;
  mach_port_t task = mach_task_self ();

  err = task_priority (task, 5, 0);
  if (err != KERN_SUCCESS)
    {
      printf ("task_priority (5, 0) => %d (0x%x)\n", err, err);
      error (1, err, "error setting task priority");
    }
  printf ("task_priority (5, 0) => %d (0x%x)\n", err, err);

  err = task_priority (task, 5, 1);
  if (err != KERN_SUCCESS)
    {
      printf ("task_priority (5, 1) => %d (0x%x)\n", err, err);
      error (1, err, "error setting task priority");
    }
  printf ("task_priority (5, 1) => %d (0x%x)\n", err, err);

  return 0;
}