Use a virtual machine. Many of the operations in the problem sset use unsafe C functions and system calls. For this problem set, VirtualBox was used to run a lean installation of Debian, which is good enough for our purposes. VirtualBox is easy to use, even for novices (ahem), and ensures that any experiment that might end in disaster does not affect the integrity of the host system (in this case, Fedora 29).
/* stack1.c
* specially crafted to feed your brain by gera */
int main() {
int cookie;
char buf[80];
printf("buf: %08x cookie: %08x\n", &buf, &cookie);
gets(buf);
if (cookie == 0x41424344)
printf("you win!\n");
}When I looked at this problem at first, I had no idea what I was looking at. Reading this article was incredibly helpful.