Update docs

docs/busybox_header.pod

@@ -14,42 +14,67 @@ BusyBox - The Swiss Army Knife of Embedded Linux
 
 BusyBox combines tiny versions of many common UNIX utilities into a single
 small executable. It provides minimalist replacements for most of the utilities
-you usually find in fileutils, shellutils, findutils, textutils, grep, gzip,
-tar, etc.  BusyBox provides a fairly complete POSIX environment for any small
-or embedded system.  The utilities in BusyBox generally have fewer options than
-their full-featured GNU cousins; however, the options that are included provide
-the expected functionality and behave very much like their GNU counterparts.
+you usually find in GNU coreutils, util-linux, etc. The utilities in BusyBox
+generally have fewer options than their full-featured GNU cousins; however, the
+options that are included provide the expected functionality and behave very
+much like their GNU counterparts. BusyBox provides a fairly complete POSIX
+environment for any small or embedded system.
 
 BusyBox has been written with size-optimization and limited resources in mind.
 It is also extremely modular so you can easily include or exclude commands (or
-features) at compile time.  This makes it easy to customize your embedded
-systems.  To create a working system, just add a kernel, a shell (such as ash),
-and an editor (such as elvis-tiny or ae).
+features) at compile time. This makes it easy to customize your embedded
+systems. To create a working system, just add /dev, /etc, and a Linux kernel.
+
+BusyBox is extremely configurable.  This allows you to include only the
+components you need, thereby reducing binary size. Run 'make config' or 'make
+menuconfig' for select the functionality that you wish to enable.  The run
+'make' to compile BusyBox using your configuration.
+
+After the compile has finished, you should use 'make install' to install
+BusyBox.  This will install the '/bin/busybox' binary, and will also create
+symlinks pointing to the '/bin/busybox' binary for each utility that you
+compile into BusyBox.  By default, 'make install' will place these symlinks
+into the './_install' directory, unless you have defined 'PREFIX', thereby
+specifying some alternative location (i.e., 'make PREFIX=/tmp/foo install').
+If you wish to install using hardlinks, rather than the default of using
+symlinks, you can use 'make PREFIX=/tmp/foo install-hardlinks' instead.
 
 =head1 USAGE
 
-When you create a link to BusyBox for the function you wish to use, when BusyBox
-is called using that link it will behave as if the command itself has been invoked.
-
-For example, entering
-
-	ln -s ./BusyBox ls
-	./ls
-
-will cause BusyBox to behave as 'ls' (if the 'ls' command has been compiled
-into BusyBox).
+BusyBox is a multi-call binary.  A multi-call binary is an executable program
+that performs the same job as more than one utility program.  That means there
+is just a single BusyBox binary, but that single binary acts like a large
+number of utilities.  This allows BusyBox to be smaller since all the built-in
+utility programs (we call them applets) can share code for many common operations.
 
 You can also invoke BusyBox by issuing the command as an argument on the
 command line.  For example, entering
 
-	./BusyBox ls
+	/bin/busybox ls
 
 will also cause BusyBox to behave as 'ls'.
 
+Of course, adding '/bin/busybox' into every command would be painful.  So most
+people will invoke BusyBox using links to the BusyBox binary.
+
+For example, entering
+
+	ln -s /bin/busybox ls
+	./ls
+
+will cause BusyBox to behave as 'ls' (if the 'ls' command has been compiled
+into BusyBox).  Generally speaking, you should never need to make all these
+links yourself, as the BusyBox build system will do this for you when you run
+the 'make install' command.
+
+If you invoke BusyBox with no arguments, it will provide you with a list of the
+applets that have been compiled into your BusyBox binary.
+
 =head1 COMMON OPTIONS
 
-Most BusyBox commands support the B<-h> option to provide a
-terse runtime description of their behavior.
+Most BusyBox commands support the B<--help> argument to provide a terse runtime
+description of their behavior.  If the CONFIG_FEATURE_VERBOSE_USAGE option has
+been enabled, more detailed usage information will also be available.
 
 =head1 COMMANDS
 
@@ -80,4 +105,26 @@ Currently defined functions include:
 
 =over 4
 
+=head1 LIBC NSS
+
+GNU Libc (glibc) uses the Name Service Switch (NSS) to configure the behavior
+of the C library for the local environment, and to configure how it reads
+system data, such as passwords and group information.  This is implemented
+using an /etc/nsswitch.conf configuration file, and using one or more of the
+/lib/libnss_* libraries.  BusyBox tries to avoid using any libc calls that make
+use of NSS.  Some applets, such as login and su, will use libc functions that
+usually require NSS.
+
+If you enable CONFIG_USE_BB_PWD_GRP, BusyBox will use internal functions to
+directly access the /etc/passwd, /etc/group, and /etc/shadow files without
+using NSS.  This may allow you to run your system without the need for
+installing any of the NSS configuration files and libraries.
+
+When used with glibc, the BusyBox 'networking' applets will similarly require
+that you install at least some of the glibc NSS stuff (in particular,
+/etc/nsswitch.conf, /lib/libnss_dns*, /lib/libnss_files*, and /lib/libresolv*).
+
+Shameless Plug: As an alternative one could use a C library such as uClibc.  In
+addition to making your system significantly smaller, uClibc does not need or
+use any NSS support files or libraries.