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Where Is My Backtrace?


I noticed that lately, on Ubuntu 10.10, I dont get any! backtrace! anymore! Nothing! I ran e.g.

root [0] TObject *o = (TObject*)8764586
root [1] o->GetName() 

 *** Break *** segmentation violation
Root > .q

In the past I got a nice stacktrace showing what called what, and that I was supposed to send the crash to myself - and now?


Ubuntu's kernel hardening efforts are causing that:

$ cat /etc/sysctl.d/10-ptrace.conf
kernel.yama.ptrace_scope = 1

The temporary fix is

sudo bash -c "echo 0 > /proc/sys/kernel/yama/ptrace_scope"

, the proper one is to switch the flag in /etc/sysctl.d/10-ptrace.conf to 0.


Et voilà:

There was a crash (kSigSegmentationViolation).
This is the entire stack trace of all threads:
#0  0x00007fd0b6ef8dee in waitpid () from /lib/
#1  0x00007fd0b6e90a79 in ?? () from /lib/
#2  0x00007fd0b93ef9f0 in TUnixSystem::Exec (this=0x16dc9b0, shellcmd=0x1c024d8 "/mnt/ram/t/etc/ 32333 1>&2") at /build/root/srcram/core/unix/src/TUnixSystem.cxx:2010
#3  0x00007fd0b93f0387 in TUnixSystem::StackTrace (this=0x16dc9b0) at /build/root/srcram/core/unix/src/TUnixSystem.cxx:2237
#4  0x00007fd0b93edb23 in TUnixSystem::DispatchSignals (this=0x16dc9b0, sig=kSigSegmentationViolation) at /build/root/srcram/core/unix/src/TUnixSystem.cxx:1136
#5  0x00007fd0b93eb7d9 in SigHandler (sig=kSigSegmentationViolation) at /build/root/srcram/core/unix/src/TUnixSystem.cxx:357
#6  0x00007fd0b93f3aea in sighandler (sig=11) at /build/root/srcram/core/unix/src/TUnixSystem.cxx:3524
#8  0x00007fd0b9695aec in G__G__Base2_10_0_26 (result7=0x7fff593e15b0, funcname=0x18535e0 "", libp=0x7fff593d6b80, hash=0) at core/base/src/G__Base2.cxx:6687

Welcome back, dear stack frames!