/* bliako modified https://reverseengineering.stackexchange.com/a/1931
   for https://perlmonks.org/?node_id=3333;parent=1229102
   KILL it with SIGKILL (kill -9)
   29/01/2019
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ptrace.h>
#include <unistd.h>
#include <signal.h>

void intHandler(int sig) { printf("got signal %d\n", sig); }

int main(void){
	printf("my pid: %d\n", getpid());

	char *e;
	if( (e=getenv("TRACEME")) != NULL && (strcmp(e,"0")==0) ){
		printf("Will not be traced...\n");
		signal(SIGSTOP, intHandler);
		if (ptrace(PTRACE_TRACEME, 0, 1, 0) == -1) 
		{
			printf("don't trace me !!\n");
			return 1;
		}
	}
	// normal execution
	for(int i=0;;i++){
		printf("i=%d\n", i);
		sleep(1);
	}
	return 0;
}

##</code><code>##

gcc tracee.c -o tracee && TRACEME=0 tracee

strace -p <PID-from-traceed>

strace: attach: ptrace(PTRACE_SEIZE, 11091): Operation not permitted

##</code><code>##

TRACEME=1 tracee

strace -p <PID-from-tracee>