U-Boot shell

The U-Boot shell is a powerful tool. It allows modification of the environment, as well as the ability to run commands directly. By default, there are two ways to enter the shell: Set the U-Boot jumper, or press and hold the Push Switch before applying power and hold it for 5 seconds. When entering the U-Boot shell, it will attempt to run a script on a USB mass storage device before finally dropping to the shell.

The reset switch is provided as a convenience, so U-Boot can be entered without having to open any kind of enclosure. It can also be disabled for security purposes. Even if the switch is disabled, the U-Boot shell can still be accessed by using the U-Boot jumper.

To disable the press-and-hold method of entering the U-Boot shell, use the following U-Boot commands:

env set rstuboot 0
env save

By setting the env var, rstuboot, to a 1, the push-and-hold method can be re-enabled.