Filesystem:/bin/su

Introduction
su is a command used for quickly switching between the root and mobile accounts on an iOS device. The root account gives you access to the entire filesystem and allows you to modify any file you wish. As this could be potentially dangerous, Apple has locked you out of the root account. To gain access to it, you must go through a process known as jailbreaking. You can find a list of all arguments and the proper syntax for 'su' at this link, but if you don't want to do that much reading, a basic highlight of the command is shown below.

Usage
su {user} {-c "command"}

Using the syntax above, if I were logged in as root and were to type 'su mobile -c "hi there"', the output would be the user mobile executing the command "echo hi there", which would just appear as the words "hi there" on the terminal screen. If "su" is launched by root, it does not ask for a password, but if it is launched by mobile, the terminal output is "Password:" and you need to put in the root password (by default it is "alpine" without the quotes).