Building:
=========

The BusyBox build process is similar to the Linux kernel build:

  make menuconfig     # This creates a file called ".config"
  make                # This creates the "busybox" executable
  make install        # or make CONFIG_PREFIX=/path/from/root install

The full list of configuration and install options is available by typing:

  make help

Quick Start:
============

The easy way to try out BusyBox for the first time, without having to install
it, is to enable all features and then use "standalone shell" mode with a
blank command $PATH.

To enable all features, use "make defconfig", which produces the largest
general-purpose configuration.  It's allyesconfig minus debugging options,
optional packaging choices, and a few special-purpose features requiring
extra configuration to use.  Then enable "standalone shell" feature:

  make defconfig
  make menuconfig
  # select Busybox Settings
  #   then General Configuration
  #     then exec prefers applets
  #   exit back to top level menu
  #   select Shells
  #     then Standalone shell
  #   exit back to top level menu
  # exit and save new configuration
  #   OR
  # use these commands to modify .config directly:
  sed -e 's/.*FEATURE_PREFER_APPLETS.*/CONFIG_FEATURE_PREFER_APPLETS=y/' -i .config
  sed -e 's/.*FEATURE_SH_STANDALONE.*/CONFIG_FEATURE_SH_STANDALONE=y/' -i .config
  make
  PATH= ./busybox ash

Standalone shell mode causes busybox's built-in command shell to run
any built-in busybox applets directly, without looking for external
programs by that name.  Supplying an empty command path (as above) means
the only commands busybox can find are the built-in ones.

Note that the standalone shell requires CONFIG_BUSYBOX_EXEC_PATH
to be set appropriately, depending on whether or not /proc/self/exe is
available or not. If you do not have /proc, then point that config option
to the location of your busybox binary, usually /bin/busybox.

Configuring Busybox:
====================

Busybox is optimized for size, but enabling the full set of functionality
still results in a fairly large executable -- more than 1 megabyte when
statically linked.  To save space, busybox can be configured with only the
set of applets needed for each environment.  The minimal configuration, with
all applets disabled, produces a 4k executable.  (It's useless, but very small.)

The manual configurator "make menuconfig" modifies the existing configuration.
(For systems without ncurses, try "make config" instead.) The two most
interesting starting configurations are "make allnoconfig" (to start with
everything disabled and add just what you need), and "make defconfig" (to
start with everything enabled and remove what you don't need).  If menuconfig
is run without an existing configuration, make defconfig will run first to
create a known starting point.

Other starting configurations (mostly used for testing purposes) include
"make allbareconfig" (enables all applets but disables all optional features),
"make allyesconfig" (enables absolutely everything including debug features),
and "make randconfig" (produce a random configuration).  The configs/ directory
contains a number of additional configuration files ending in _defconfig which
are useful in specific cases.  "make help" will list them.

Configuring BusyBox produces a file ".config", which can be saved for future
use.  Run "make oldconfig" to bring a .config file from an older version of
busybox up to date.

Installing Busybox:
===================

Busybox is a single executable that can behave like many different commands,
and BusyBox uses the name it was invoked under to determine the desired
behavior.  (Try "mv busybox ls" and then "./ls -l".)

Installing busybox consists of creating symlinks (or hardlinks) to the busybox
binary for each applet enabled in busybox, and making sure these symlinks are
in the shell's command $PATH.  Running "make install" creates these symlinks,
or "make install-hardlinks" creates hardlinks instead (useful on systems with
a limited number of inodes).  This install process uses the file
"busybox.links" (created by make), which contains the list of enabled applets
and the path at which to install them.

Installing links to busybox is not always necessary.  The special applet name
"busybox" (or with any optional suffix, such as "busybox-static") uses the
first argument to determine which applet to behave as, for example
"./busybox cat LICENSE".  (Running the busybox applet with no arguments gives
a list of all enabled applets.) The standalone shell can also call busybox
applets without links to busybox under other names in the filesystem.  You can
also configure a standalone install capability into the busybox base applet,
and then install such links at runtime with one of "busybox --install" (for
hardlinks) or "busybox --install -s" (for symlinks).

If you enabled the busybox shared library feature (libbusybox.so) and want
to run tests without installing, set your LD_LIBRARY_PATH accordingly when
running the executable:

  LD_LIBRARY_PATH=`pwd` ./busybox

Building out-of-tree:
=====================

By default, the BusyBox build puts its temporary files in the source tree.
Building from a read-only source tree, or building multiple configurations from
the same source directory, requires the ability to put the temporary files
somewhere else.

To build out of tree, cd to an empty directory and configure busybox from there:

  make KBUILD_SRC=/path/to/source -f /path/to/source/Makefile defconfig
  make
  make install

Alternately, use the O=$BUILDPATH option (with an absolute path) during the
configuration step, as in:

  make O=/some/empty/directory allyesconfig
  cd /some/empty/directory
  make
  make CONFIG_PREFIX=. install

More Information:
=================

Se also the busybox FAQ, under the questions "How can I get started using
BusyBox" and "How do I build a BusyBox-based system?"  The BusyBox FAQ is
available from http://www.busybox.net/FAQ.html