U-Boot makes use of the so-called environment variables to define various aspects of the target functionality. The U-Boot environment is stored in the SD Card memory and is persistent across power or reset cycles. Parameters defined by the U-boot environment variables include: target IP address, target MAC address, location in RAM where a Linux bootable image will be loaded, and many others.
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In various use case scenarios, it may be needed to read or update U-Boot environment variables from Linux. Probably, the most obvious scenario would be when a remote target is accessible only through an Ethernet or WiFi link and no access to the serial console is available. In that scenario, it is impossible to get access to the U-Boot serial line command monitor, however the target still can be connected to over a telnet or ssh link providing access to the Linux shell interface. This application note explains how to read and update U-Boot environment variables from Linux.
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