Linux crunchbang 3.2.0-4-686-pae #1 SMP Debian 3.2.35-2 i686 GNU/Linux
PR_SET_PTRACER (since Linux 3.4) This is only meaningful when the Yama LSM is enabled and in mode 1 ("restricted ptrace", visible via /proc/sys/kernel/yama/ptrace_scope). When a "ptracer process ID" is passed in arg2, the caller is declaring that the ptracer process can ptrace(2) the calling process as if it were a direct process ancestor. Each PR_SET_PTRACER operation replaces the previous "ptracer process ID". Employing PR_SET_PTRACER with arg2 set to 0 clears the caller's "ptracer process ID". If arg2 is PR_SET_PTRACER_ANY, the ptrace restrictions introduced by Yama are effectively disabled for the calling process. For further information, see the kernel source file Documentation/security/Yama.txt.
Seems like you need a more recent kernel for that.