Qt Ubuntu 12.10 error ptrace: Operation not permitted

While trying to debug for the first time I got this error:

ptrace: Operation not permitted.

Could not attach to the process. Make sure no other debugger traces this process.
Check the settings of
/proc/sys/kernel/yama/ptrace_scope
For more details, see /etc/sysctl.d/10-ptrace.conf


Solution:

On Ubuntu versions after 10.10 you'll run into this in more related applications, such as QtCreator. It is a security feature of Ubuntu that prevent the debugger to attach to processes not owned by him.
This is filed as a  bug #3509 against QtCreator . To work around this issue, do this:
temporary solution (won't survive a reboot):

 echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope

In a file  /etc/sysctl.d/10-ptrace.conf  (should already exist), change the value of kernel.yama.ptrace_scope  to  0  and then reload the configuration:  sudo sysctl -p .
I'm explicitly posting the temporary solution, as you probably don't want to keep this feature disabled on a regular machine for security reasons.
 
Ref:  http://askubuntu.com/questions/244336/receiving-error-while-trying-to-debug-in-qtproject