How to solve “ptrace operation not permitted” when trying to attach GDB to a process?

Question

I\'m trying to attach a program with gdb but it returns:

Attaching to process 29139
Could not attach to process. If your uid matches the ui

Answer 1

Jesup's answer is correct; it is due to Linux kernel hardening. In my case, I am using Docker Community for Mac, and in order to do change the flag I must enter the LinuxKit shell using justin cormack's nsenter (ref: https://www.bretfisher.com/docker-for-mac-commands-for-getting-into-local-docker-vm/ ).

docker run -it --rm --privileged --pid=host justincormack/nsenter1

/ # cat /etc/issue

Welcome to LinuxKit

                    ##         .
              ## ## ##        ==
           ## ## ## ## ##    ===
       /"""""""""""""""""\___/ ===
      {                       /  ===-
       \______ O           __/
         \    \         __/
          \____\_______/

/ # cat /proc/sys/kernel/yama/ptrace_scope

1

/ # echo 0 > /proc/sys/kernel/yama/ptrace_scope

/ # exit