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 uid of the target process, check the setting of /proc/sys/kernel/yama/ptrace_scope, or try again as the root user. For more details, see /etc/sysctl.d/10-ptrace.conf
ptrace: Operation not permitted.

gdb-debugger returns "Failed to attach to process, please check privileges and try again."

strace returns "attach: ptrace(PTRACE_ATTACH, ...): Operation not permitted"

I changed "kernel.yama.ptrace_scope" 1 to 0 and /proc/sys/kernel/yama/ptrace_scope 1 to 0 and tried set environment LD_PRELOAD=./ptrace.so with this:

#include <stdio.h>
int ptrace(int i, int j, int k, int l) {
    printf(" ptrace(%i, %i, %i, %i), returning -1\n", i, j, k, l);
    return 0;
}

But it still returns the same error. How can I attach it to debuggers?

Answer 1

If you are using Docker, you will probably need these options:

docker run --cap-add=SYS_PTRACE --security-opt seccomp=unconfined