Where can I obtain a list of UNIX system calls?

man 2 syscalls

Aside from that, you can look in /usr/include/sys/syscall.h (which on my system merely #includes /usr/include/bits/syscall.h). That's generated at libc build time from kernel syscall list.

You can also grep the Linux kernel source for SYSCALL_DEFINE. (I'm not a BSD expert, but I think the equivalent in FreeBSD is SYSCALL_MODULE)

Read The Fine Manual. For system calls, start with

man 2 intro

That's how I got started in UNIX. We didn't have no fancy internet back then ...

For the official, authoritative IEEE Std. 1003.1 / Single UNIX Specification (UNIX 2004) manpages, see:

• Single UNIX Specification (Open Group Base Specification Issue 6) / IEEE Std. 1003.1 ("POSIX")

A full list of functions (system interfaces) may be found under "System Interfaces" or at the link. I would also like to use this as an opportunity to plug my Development / Coding Search custom search engine, which includes and is heavily biased towards the Single UNIX Specification / IEEE Std. 1003.1. For example, a standard search for fopen, close, unix, etc. have promotions taken out to ensure that results from the authoritative documentation are at the very top. Adding "man" in front of a query heavily weights the result in favor of the IEEE Std. 1003.1 man page as in man find, man free, man inttypes.h, etc., although most queries should favor IEEE Std. 1003.1 even without adding "man" (if it isn't, type bad query and tell me).