BusyBox was developed by Bruce Perens in 1999 with the purpose of integrating available Linux tools in a single executable. It has been used with great success as a replacement for a great number of Linux command line utilities. Due to this, and the fact that it is able to fit inside small embedded Linux distributions, it has gained a lot of popularity in the embedded environment. It provides utilities from file interactions, such as cp, mkdir, touch, ls, and cat, as well as general utilities, such as dmesg, kill, fdisk, mount, umount, and many others.
Not only is it very easy to configure and compile, but it is also very easy to use. The fact that it is very modular and offers a high degree of configuration makes it the perfect choice to use. It may not include all the commands available in a full-blown Linux distribution available on your host PC, but the ones that it does are more than enough. Also, these commands are just simpler versions of the full-blown ones used...
