With the recent glibc from 7.3 debuging threaded apps doesn't work. I get: [New Thread 2049 (LWP 3394)] Can't attach LWP 3402: Operation not permitted (gdb) I get this with both nautilus and mozilla. I tried backing down gdb, glibc and the kernel to 7.2-ent and 7.2-errata versions, and it the only thing that seems to break is when i use the 7.3 glibc (I tried 2.2.5-30).
http://sources.redhat.com/ml/libc-hacker/2002-04/msg00037.html
Fixed in glibc-2.2.5-32.