Looking inside Mac OS X

Inside new Apple computers is an operating system referred to as Mac OS X. You might also hear Mac OS X referred to as Jaguar. Like Linux, OS X is a free UNIX-like operating system at its core. However, instead of using a Linux kernel, OS X is based on an open source project called Darwin (www.opendarwin.org).

Although Mac OS X and Linux are very different on the surface, there are many striking similarities. If you open a Terminal (shell) window on your Mac, you'll find that you can use many of the same basic commands that you can use from Linux. In addition, many of the same open source projects are included in both operating systems. These include:

Samba (Windows file/printer server)
Apache (Web server)
CUPS (Linux print service)
Sendmail (mail transport agent)
BIND (DNS server)

There are also a few differences:

OS X uses the tcsh shell instead of the bash shell (used in Linux) as the default. You set environment variables differently and use different source files (~/.tshrc, not ~/.bashrc).
Red Hat Linux is primarily covered under the General Public License, while OS X is covered by the Apple Public Source License (APSL). In August, 2003, APSL 2.0 was released (www.opensource.apple.com/apsl) and is now certified as a Free Software License from the Free Software Foundation.
Red Hat Linux uses the Linux kernel; Mac OS X is based on the FreeBSD kernel.
Most Linux configuration is done using Red Hat config windows, which often create text-based configuration files (mostly in the /etc directory) from command-line or GUI applications; Mac OS X stores the configuration file in its own NetInfo database, which is manipulated primarily by GUI tools as well as by the niutil command.
Red Hat Linux requires root permission for many administrative operations; OS X discourages overuse of the root login and encourages user accounts that are granted administrative privileges.

For the examples in this chapter, I used an iMac running Mac OS X 10.2.6. Because there were big improvements made between 10.1 and 10.2, I recommend that you upgrade your software if you are using the former. To see what version in installed on your Mac, open the Apple System Profiler from your Mac computer.