How to read/write UEFI environment variables in application startup scripts for OTA dual-partition management?

[wangkaijing-work]

We're implementing an OTA update system with A/B partition scheme on Jetson Orin NX (NVIDIA BSP). Need to:

1. Use UEFI environment variables to track active partition (similar to Android's update_engine)
2. Access these variables from userspace during:
   Boot process (initramfs/early-boot scripts)
   Application runtime (update management service)

Specific questions:

1. What tools/APIs are recommended for UEFI variable access in Ubuntu userspace?
   efivar CLI tool usage examples
   Direct access via /sys/firmware/efi/efivars
   Programmatic access using libefivar
2. How to ensure persistence of modified variables across reboots?
3. What permissions/privileges are required (sudo vs. udev rules)?
4. Any Orin-specific limitations for UEFI variable storage?

[linh-nguyen-scaleaq]

Hi. I'm having the same question.

[bobm21]

Hi, UEFI on Orin NX records the active boot chain in the BootChainFwCurrent UEFI variable (0=A, 1=B). The NVIDIA BSP also provides the nvbootctrl utility which may be useful to you to manage the boot chain from the OS. See https://docs.nvidia.com/jetson/archives/r36.4/DeveloperGuide/SD/Bootloader/UpdateAndRedundancy.html#boot-control

Regarding your specific questions:

1. UEFI on Orin NX supports the UEFI runtime variable services which give the OS full runtime access to UEFI variables. Availability of the efivarfs in /sys/firmware/efi/efivars depends on your kernel and linux configuration, but is enabled by default in the NVIDIA BSP. You can use any OS-supported mechanism that results in the appropriate calls to the UEFI runtime services. Direct access via /sys/firmware/efi/efivars is often convenient to use in scripts.
2. Persistence of variables is controlled by the EFI_VARIABLE_NON_VOLATILE attribute bit defined in the UEFI spec (bit 0). See this page for accessing the attribute bits in the efivarfs: https://docs.kernel.org/filesystems/efivarfs.html
3. Permission requirements to read and write efivarfs are determined by the OS, but root access is usually required to write.
4. There are no Orin-specific limitations on UEFI variables, but total UEFI variable storage space is limited by the QSPI flash partition configuration.