Realtime priority not enabled w/ realtime module (or bad log message)

[rob+mythtv.org@…]

I have the realtime module loaded with rights granted to a group the user mythtv runs as. However, I find the following message in my mythfrontend logs

Realtime priority would require SUID as root

It worked with svn head from several months ago.

[danielk]

The error message is no longer correct for modern Linux setups.

[sandeen-mythtv@…]

I have the same issue, and a bit more info:

2006-12-19 19:42:05.497 user: 500 effective user: 0 before privileged thread 2006-12-19 19:42:05.514 user: 500 effective user: 0 after privileged thread 2006-12-19 19:42:05.514 user: 500 effective user: 500 run_priv_thread

for some reason the created pthread has the real UID instead of the EUID.

A very quick testcase sorta like this:

printf("main: uid %d euid %d\n", getuid(), geteuid()); rc = pthread_create(&thread_id, NULL, thread_main, NULL);

and in the new thread:

printf("thread: uid %d euid %d\n", getuid(), geteuid());

seems to work:

main: uid 500 euid 0 thread: uid 500 euid 0

Odd...

[sandeen-mythtv@…]

Oh should have checked this first :)

It's the main thread dropping privs that does it - the sub-thread inherits the privs when the main thread drops it.

If the main thread does this:

rc = pthread_create(&thread_id, NULL, thread_main, NULL); sleep(2); setuid(getuid()); sleep(2);

and the sub-thread does this:

printf("thread: uid %d euid %d\n", getuid(), geteuid()); sleep(3); printf("thread: uid %d euid %d\n", getuid(), geteuid());

then I get:

main: uid 500 euid 0 thread: uid 500 euid 0 thread: uid 500 euid 500

guess I need to read up on how pthreads work... not sure you can use them this way?

[me again]

hmm FWIW using rlimits on FC6 works. Sorry, probably should not have put SUID related bugs into this rt module tracker... let me know if you'd like me to file a new bug on the SUID problem.

[danielk]

The message doesn't reflect current reality wrt enabling to real-time, but it still works... marking as won't fix without a ready to go patch.