The C programming language, 2nd edition. Then if you are into BSD/Posix, Advanced Programming Unix environment. Here's a course on C programming for Unix, NetBSD actually. You can install NetBSD with ease. If not, head to sdf.org and try getting an user account. You can validate a basic account for cheap. But if you help the rest of the community with programming under Unix, you may get a validated account for free. Do the Unix programming that after TCPL 2nd Ed, BTW. https://stevens.netmeister.org/631/