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The "recovery image verify failed" error on Huawei S7721u devices occurs when the bootloader detects unauthorized system changes, corrupted updates, or incompatible recovery images, failing digital signature checks. Solutions involve forcing a stock firmware reinstallation via an SD card (dload method) or using the device's eRecovery mode to download and verify official software. For detailed, illustrated steps and recovery procedures, read the full article on akmr25.ru . How to Fix Huawei Recovery Image Verify Failed Error
This article is written for network engineers, embedded systems technicians, and advanced hobbyists dealing with Huawei enterprise ONT (Optical Network Terminal) devices.
The Ultimate Guide to Fixing "Huawei S7721U Recovery Image Verify Failed Repack" Introduction: The Bootloop Nightmare The Huawei S7721U is a rugged, industrial-grade GPON/EPON Optical Network Terminal (ONT), often deployed in FTTH (Fiber to the Home) scenarios, MDUs (Multi-Dwelling Units), and outdoor cabinets. It is renowned for its stability—until it isn't. One of the most terrifying errors an engineer can face on the serial console is: "Recovery image verify failed repack" This message signals a fatal checksum or signature mismatch during the bootloader’s integrity check. When this happens, the device refuses to boot the main firmware, drops into a recovery shell (often BusyBox), or enters an infinite reboot loop. Without intervention, the S7721U becomes a brick. But there is hope. This article dissects the anatomy of this error, explains why it happens, and provides a step-by-step forensic guide to repack a valid recovery image and flash it via UART or TFTP.
Part 1: Understanding the Error – What Does "Verify Failed Repack" Mean? 1.1 The Boot Chain of the S7721U To understand the error, you must understand the boot process: huawei s7721u recovery image verify failed repack
BootROM (Mask ROM): Immutable code on the SoC. It initializes DDR memory and loads the Primary Bootloader (UBoot from SPI NAND/NOR). Secondary Bootloader (UBoot): Checks the environment variables and loads the Linux kernel. Recovery Image: A compressed filesystem (SquashFS/UBIFS) containing a minimal Linux environment used for factory restores or emergency flashing. Main Firmware (System Image): The full OpenWRT-based or VxWorks-based operating system.
1.2 The "Repack" Context The keyword "repack" indicates that the device isn't using an official Huawei-signed image from the factory. Instead, someone (perhaps a developer or a third-party ISP) created a custom firmware image by:
Extracting the original s7721u_recovery.img . Modifying files (e.g., adding busybox tools, changing web UI assets). Re-compressing and re-flashing it. The "recovery image verify failed" error on Huawei
Huawei’s bootloader uses a proprietary digital signature (RSA-2048 or HMAC) appended to the image header. When you repack a modified image without updating the signature, the verification algorithm fails. 1.3 Common Causes
Corrupted NAND Flash: Bad blocks in the recovery partition ( mtd3 or mtd4 ). Incorrect CRC32 Checksum: The bootloader computes a checksum over the image; mismatched due to a bad flash write. Header Mismatch: The magic field (e.g., HUAWEI or 0x5A3C4F42 ) is missing or corrupted. Unsigned Custom Firmware: You flashed a third-party OpenWRT build that lacks Huawei's bootloader signature.
Part 2: Diagnosing the Failure Via Serial Console Before repacking, confirm the error. Connect to the S7721U using a USB-to-TTL adapter (115200 baud, 8N1). Example Boot Log of the Failure: U-Boot 2013.07 (Oct 12 2019 - 14:22:13) DRAM: 256 MiB NAND: SPI NAND 128 MiB Loading recovery image from mtd2... Verifying signature... !!!! Recovery image verify failed repack !!!! Starting recovery shell... BusyBox v1.23.2 (built-in) How to Fix Huawei Recovery Image Verify Failed
Key takeaways: The bootloader jumped to recovery mode but rejected the recovery.img 's signature. You are stuck in a limited shell. Commands to run in the recovery shell: # Check MTD partition layout cat /proc/mtd # Expected output: # mtd0: bootloader # mtd1: env # mtd2: recovery # mtd3: kernel # mtd4: rootfs Check the current image's header (if hexdump is available) hexdump -C /dev/mtd2 | head -n 20 Check for bad blocks flash_eraseall -j /dev/mtd2 # Dangerous, only for last resort
If you see I/O error or Invalid argument , the NAND has physical damage.