Huawei S7721u 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.

DECIMAL HEXADECIMAL DESCRIPTION 0 0x0 U-Boot uImage header 64 0x40 LZMA compressed data 262144 0x40000 Squashfs filesystem Extract the SquashFS part: huawei s7721u recovery image verify failed repack

00000000 48 55 41 57 45 49 00 01 00 00 1c 20 00 00 00 10 |HUAWEI..... ....| The first 4 bytes ( HUAW or NAND ) define the image type. If you repack without preserving this, verification fails. 3.4 Mounting and Modifying the Recovery Image Use binwalk to find the SquashFS start offset: This message signals a fatal checksum or signature

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 DECIMAL HEXADECIMAL DESCRIPTION 0 0x0 U-Boot uImage header

This article is written for network engineers, embedded systems technicians, and advanced hobbyists dealing with Huawei enterprise ONT (Optical Network Terminal) devices. 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.

loadb 0x80800000 Use your terminal software (PuTTY/Tera Term) to send the file via XMODEM/CRC. Then write to NAND as above. If you have a shell but no network: