Mounting USB flash disk under ONIE to upgrade SONiC failed

1. Verify if the USB flash disk format is FAT32. If it's not FAT32, the upgrade file might not be readable, resulting in an upgrade failure.

Solution: Format and convert the USB flash disk format to FAT32, copy the files again, and attempt the upgrade.

2. Ensure the USB flash disk isn't mounted in the /mnt directory. As there are native files in the /mnt directory of the ONIE system, mounting the USB flash disk would overwrite them, leading to an upgrade failure.

Solution: Mount the USB flash disk to the /usb directory, or access the ONIE interface and utilize the Install OS method.