U-Boot allows you to configure console activation at boot.

Go to General setup > Console settings in your configuration tool of choice and define the following configuration variables:

  • CONSOLE_DISABLE: This setting disables the U-Boot input and output consoles and performs a silent boot into Linux. You can then choose whether to optionally enable the console in one of two exclusive methods:

    • CONSOLE_ENABLE_GPIO: Use this setting to enable the console when the selected GPIO is high at boot.

      • CONSOLE_ENABLE_GPIO_NR: Use an integer to identify the GPIO pin.

    • CONSOLE_ENABLE_PASSPHRASE: Use this setting to enable the console when the correct passphrase is used at boot time.

      • CONSOLE_ENABLE_PASSPHRASE_KEY: This is the SHA-256 hash of the passphrase in binary form. You can generate it using the following command:

        $ echo -n "mypassphrase" | sha256sum
788006caf535441ad49e2747bb0edd0203f38a74caacf7c337fc1a9ecfa99cd8  -

See Secure console modes for further details.