The following URLs may be of interest to those running UNIX. The master copy of this page lives at https://darwinsys.com/openbsd/unix-resources.html.
I prefer to use OpenBSD. See, in particular:
My runners-up are Mac OS X and Solaris.
O'Reilly is the leading UNIX, MS-Windows, and Java technical publisher. Many good UNIX user, administrator and programmer books.
Unix Power Tools while somewhat dated, is a priceless set of recipes on how to do more with Unix or Linux.
Unix and Linux System Admin Handbook by Evi Naimeth et al - the best book for SysAdmins. Now in its fifth edition, so reasonably up-to-date.
The Open Group - Software developer guidelines (for scripts and for C programs!), www.opengroup.org/onlinepubs/007908799/xbd/utilconv.htm.
Legit "free" books onlineI know that there are sites where you can get many computer books without paying, but please bear in mind that many of those sites are pirating those books and that the authors are getting ripped off.
On the other hand, all the books below are legally and morally availalble for free; most have been placed under public licenses by the authors. Many of these are from O'Reilly.com's Open Books Project (I have at least one book available from there). This list will grow as time goes by; please feel free to submit additions.
Open Source - General
Unix - General
Unix - Programming
Unix - Batch Text Processing