Accessing U-Boot Environment from Userspace

The 4Kopen board uses U-Boot as the bootloader. Using the u-boot-tools package, you can inspect and modify the U-Boot environment from within userspace.

apt install u-boot-tools

You'll also need to setup the configuration, put only the following in /etc/fw_env.config:

# MTD device name     Device offset    Env. size    Flash sector size
/dev/mtd0             0xC0000          0x4000       0x10000

Once setup, you can use fw_printenv to confirm that it is operating correctly:

fourkopen@4kopen:~ $ sudo fw_printenv
bootcmd=run load_mac;echo Looking for uenv.txt on sdcard;if mmc rescan && fatload mmc 0:1 0x98000000 uenv.txt; then setenv bootdev mmc; run load_env; boot; echo *** Boot from MMC failed... ***; fi; echo Looking for uenv.txt on usb 0:1; if usb start && usb storage && fatload usb 0:1 0x98000000 uenv.txt; then setenv bootdev usb; run load_env; boot; echo *** Boot from USB failed... ***; fi; echo Starting a default system; display_splash error; run error; sf probe; sf read 0x98000000 0x100000 766a00; bootm 0x98000000; reset;
error=run ledt; run ledt; run ledt; run ledt; run ledt;
ledt=led green on;sleep 1;led green off;sleep 1;
load_env=env import -t 0x98000000 ${filesize}
load_mac=sf probe; sf read 0x97000000 0xD0000 1B;env import -t 0x97000000 1B;

If you see a warning about CRC issues, or "using default environment", then something is probably not configured correctly. For example:

Warning: Bad CRC, using default environment

NOTE: Do NOT use fw_setenv if fw_printenv gives any warnings, as you likely have an error with your configuration and risk corrupting the flash, and potentially rendering the board unusable.

NOTE: Incorrect use of the fw_setenv utility can render your board unusable - be careful.


  • Print whole environment:
    • fw_printenv
  • Print specific environment variable:
    • fw_printenv ${NAME}
  • Clear (delete) environment variable
    • fw_setenv ${NAME}
  • Set environment variable:
    • fw_setenv ${NAME} ${VALUE}