Mac OS X Leopard - ARCAism

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CHAPTER 18 INTRODUCING DARWIN AND THE SHELL
The Darwin file system starts from root, which is symbolized by /. This is the highest level
of the file system, and is essentially the same as viewing your primary hard drive in the Finder. A
quick look in our root directory reveals the following items (the trailing / and @ symbols that follow
have special meaning: / indicates that the item is a directory [or folder] and @ indicates that
the item is a link [or alias]):
Applications/ System/ etc@ sbin/
Desktop DB Users/ home/ tmp@
Desktop DF Volumes/ mach_kernel usr/
Developer/ bin/ mach_kernel.ctfsys var@
Library/ cores/ net/
Network/ dev/ private/
As you can see, all the basic Finder folders—Applications, Library, System, Users, and
Developer (provided you’ve installed the Developer tools)—are there, along with a slew of other
items. Some of these are merely system files that are of little interest to most people. Table 18-2
shows some common directory paths and describes what sorts of files are located in them.
Table 18-2. Common Darwin Directories and Their Contents
Directory Path Contents
/bin The /bin directory contains the core user executables that are necessary for
the OS to function normally.
/etc (/private/etc) The /etc directory contains the primary configuration files for much of OS X
and its services.
/sbin The /sbin directory contains the core administrative executables necessary
for the OS to function normally.
/tmp (/private/tmp) The /tmp directory is where the OS and many services and applications store
data that is only used briefly and then discarded.
/usr The /usr directory is a metadirectory that contains a number of
subdirectories. Traditionally, these directories contain files that, while not
necessary for the basic functioning of the system, are still often necessary for
a system that functions the way one would expect it to. The truth is that
these days, while the system would technically function without these files,
most people would find it unusable. (Although it’s not exactly the same, the
/usr directory is to Darwin what the /Library folder is to Quartz.)
/usr/X11 (/usr/X11R6) X11 is UNIX’s traditional graphical interface. While it’s seldom used in Mac
OS X, some people may have uses for specific applications that rely on it.
This is an optional install when you install Leopard, but if it is installed, this
is where most of the parts of X11 live.
/usr/bin Like /bin, /usr/bin contains user-level command-line executables. Many of
the most common commands you will use are found in this directory.
/usr/libexec This directory contains a number of special executables. This includes files
that control tasks related to printing, networking, security, and the built-in
web server.
/usr/local This is yet another metadirectory. In the traditional UNIX way of doing things,
this is where one would install any add-ons to the system that didn’t come
with it by default. Many third-party additions will still install themselves here.
This directory doesn’t exist by default in Leopard, but it’s likely if you make
much use of Darwin, it will be created sooner or later.
/usr/sbin Like /sbin, this is a directory that contains administrative executables.