Planet Android

Extending Android’s shell with BusyBox

Posted by Admin February - 5 - 2010 - Friday

A vanilla android installation is a bare bones affair aimed solely at the mobile device. This comes at the initial expense of our development environment. This platform is only intended for only the smallest devices and so searching amongst ‘system/bin‘ reveals only a cherry picking of Linux system administrator staples, even the most common binaries such as ‘ls‘, ‘mv‘ and ‘rm‘ have been stripped of all but their essential options and recompiled. Installing third party tools on Android offers a range of additional productive tools and options for ease of development within the Android shell.

Android shell

Invoking the android emulator from within an IDE is the ideal setup but developers will find need to interact with the emulator through other means for scripting, integration testing and just practical reasons. The SDK tools are located in the tools directory and I’d recommend regular users of the sdk to add this directory to their shell’s export path.

I develop on a mac so I have added the android-sdk-mac_x86-1.0_r1/tools to my .profile but you could equally add it to your .bashrc or .kornrc within your user’s home area giving you convenient direct access to all of android’s development tools via the binary names such as $adb, $emulator or $ddms. If you are on a windows machine these variables would instead be set via your system settings -> environment variables.

With the tools on the shells $PATH, the emulator can now be invoked:

$emulator

Now to telnet to the running device image:

$adb shell

BusyBox

BusyBox is a single multicall binary that packages the functionality of many popular standard Unix tools. The aim of the BusyBox project is to keep the total package size overhead as small as possible by sharing commonly used gnu libC libraries via a single set of ELF headers and stripping down gnu’s libc so as only to provide the functions necessary to support Busybox and the other executables.

Side note – Standing up for GNU with legal action

Busybox author’s have gained a reputation for their commendable efforts to uphold the legal rights of the GNU public license as they have brought about court action as plaintiffs on a series of cases where they believed companies were not holding to the terms of GNU public license. Companies they have appealed against include Verizon, High-Gain Antennas and Xterasys. Most notably they are commonly credited with the first GNU public licence related court action against Monsoon Multimedia for their use of BusyBox within it’s HAVA streaming video software (Hava have since made their alterations available). So far all cases have been settled before they reached the court.

Installing busy box on Android

It is common place for developers to check out the source of BusyBox and compile a tailor made build with any preferred tools and options. There are others like myself who just use whatever they can find and I have settled with a build generously donated with the intent of android deployment by Ben Leslie available from both his site and the run buddy code wiki.

First aquire your build and then add it to the running android device like so:

$adb shell mkdir /data/busybox
$adb push busybox /data/busybox
$adb shell

Now within the android Emulator shell:

$cd /data/busybox
$chmod 775 busybox
$./busybox –install

Now you have installed BusyBox!

For ease of use I would add this to the shell’s $PATH

export PATH=/data/busybox:$PATH

Now invoking busybox will reveal all your new commands!

$busybox

Some highlights of this particular binary of BusyBox are:
chown, chgrp: change permission ownership.
awk, sed: languages to both process & transform text
grep: a text search utility
du: shows disk usage
vi: a shell based text editor
pidof: return the pid of a running process
less: text reader with back and forward nav
tail: trail the end of a file for activity
gunzip, gzip, tar, bzip2: archival compression software
clear: clear screen
crontab, crond: task scheduling
diff: compare files
httpd: a light webserver
telnet: basic TCP remote login
xargs: use the output of a command as the arguments for another
su: masquerade as another system user
wget: retrieves content from a web server
which: identifies the location of an executable
For info on these or any linux commands check the man pages online.

Have I missed any of your shell essentials? If you have any BusyBox builds for Android then we’d love to hear about how you are using them in your development environment.