Extroot Not Mounting on OpenWRT

Installing and Using OpenWrt
1

Hello everyone,

I’m experiencing an issue setting up extroot on my ZyXEL NBG6817 router running OpenWRT 23.05.3. Despite following the standard extroot configuration steps, the system fails to mount /overlay on my USB flash drive (/dev/sda1) after a reboot. Instead, it continues to use the internal memory (/dev/loop0), leaving me with limited space for additional software and configurations.

What I’ve Done So Far

  1. Formatted the USB Drive:

    • The USB flash drive (32GB) was formatted to ext4 using mkfs.ext4.
    • Verified the UUID using block info.

  2. Updated /etc/config/fstab:
    I configured the /etc/config/fstab file as follows:

    config 'global'
    option anon_swap       '0'
    option anon_mount      '0'
    option auto_swap       '1'
    option auto_mount      '1'
    option delay_root      '30'
    option check_fs        '1'

config 'mount'
    option target  '/overlay'
    option uuid    '<UUID-of-my-USB-drive>'
    option fstype  'ext4'
    option enabled '1'

  3. Copied Files to the USB Drive:
    Used the following commands to copy /overlay to the USB drive:

    mount /dev/sda1 /mnt
tar -C /overlay -cvf - . | tar -C /mnt -xvf -
umount /mnt

  4. Ensured Kernel Modules Are Loaded at Boot:

    • Verified that usb-storage, usb-storage-extras, and ext4 modules are installed.

    • Created symbolic links in /etc/modules-boot.d/ to ensure they load during boot:

      ln -s /etc/modules.d/usb-storage /etc/modules-boot.d/usb-storage
ln -s /etc/modules.d/usb-storage-extras /etc/modules-boot.d/usb-storage-extras
ln -s /etc/modules.d/30-fs-ext4 /etc/modules-boot.d/30-fs-ext4

  5. Checked for Errors:

    • Logs from logread and dmesg indicate that the USB drive is detected after the system attempts to mount /overlay.

    • Example:

      [7.370701] EXT4-fs (loop0): mounted filesystem with ordered data mode.
[8.493107] scsi 0:0:0:0: Direct-Access USB DISK 2.0
[8.497058] sd 0:0:0:0: [sda] Attached SCSI removable disk
[8.868114] mount_root: switching to ext4 overlay

The Problem

Despite following the steps, /overlay continues to mount on the internal memory (/dev/loop0) instead of the USB drive (/dev/sda1) after a reboot.

I suspect the issue might be:

  • USB initialization delay: The USB drive is detected too late during the boot process.
  • Missing initramfs support: Modules for usb-storage or ext4 might not be loading early enough.

System Details

  • Router Model: ZyXEL NBG6817 (Link to OpenWRT page)
  • Firmware Version: OpenWRT 23.05.3
  • USB Drive: 32GB, formatted to ext4.

What I Need Help With

  • Ensuring /overlay mounts on /dev/sda1 at boot.

If anyone has experience with extroot on this router model or similar setups, I’d greatly appreciate your insights or suggestions.

Thank you in advance!

2

How fid you fill 4GB builtin flash?

What is initramfs? What is it supposed to do?