I ran the panic_action command-line as root on a running process - and get the ptrace just fine.
I read up on this on Google, and found that this would typically be a problem when using the "yama" security module, which I don't (there is no /proc/sys/kernel/yama subdir).
This is a very recent system, openSUSE 13.1 with current patchlevel. The kernel is the shipped SuSE-flavoured "default" kernel.
Before I dig into running a vanilla kernel to see if there's SUSE magic happening on their flavour - am I looking at the wrong place? Is this problem known and solved?
I had the yama problem on ubuntu, and poking the relevant file in the yama subdir solved it. But if you're not running yama... hmm. OK, someone reporting *exactly* the same problem back in 2008 on the GBD list. Here is the fix they helpfully posted: https://www.sourceware.org/ml/gdb/2008-01/msg00246.html Here's the original message: http://lists.gnu.org/archive/html/bug-gdb/2008-01/msg00002.html Googlefoo! Arran Cudbard-Bell <a.cudbardb@freeradius.org> FreeRADIUS Development Team FD31 3077 42EC 7FCD 32FE 5EE2 56CF 27F9 30A8 CAA2