The authors take a practical approach and use short code snippets to illustrate how to use system calls. I highly recommend adding this book to your UNIX library if you want to learn UNIX system ...

Unlike the TELNET sign-on process, the UNIX spawner program allows sign ons to a UNIX system without scripts. In most cases, you should run the UNIX spawner using the root privilege in order to start ...

For example, the program may expect an "int" to be 4 bytes, but the system where it's being compiled might have 2 or 8 byte ints instead.