Upgrading from 23.05.5 to 25.12.3 on ZyXEL GS1900-8

dabbes · May 6, 2026, 6:37pm

Hello!

I want to upgrade to the current version 25.12.3 from 23.05.5.

root@OpenWrt:/tmp# sysupgrade -v /tmp/openwrt-25.12.3-realtek-rtl838x-zyxel_gs19
00-8-a1-squashfs-sysupgrade.bin
Wed May  6 18:29:18 UTC 2026 upgrade: The device is supported, but this image is incompatible for sysupgrade based on the image version (1.0->2.0).
Wed May  6 18:29:18 UTC 2026 upgrade: Dual firmware paritition merged due to size constraints. Upgrade requires a new factory install. Regular sysupgrade is not possible.
Image check failed.
root@OpenWrt:

What does (1.0->2.0) mean in this case?

What does upgrade: “Dual firmware paritition merged due to size constraints.” mean?

Is it possible and reasonable to install the new firmware to the 2nd partition to be able to boot the old one?

kind regards

efahl · May 6, 2026, 6:46pm

No, you lose dual partitions when you upgrade. Details here

github.com/openwrt/openwrt

realtek: merge Zyxel GS1900 firmware partitions

committed 10:09AM - 22 Dec 24 UTC

svanheule

+8 -12

The dual-boot partition layout for the Zyxel GS1900 switches results in 6.9MB fo…r both kernel and rootfs. Depending on the package selection, this may already leave no space for the user overlay. Merge the two firmware partitions, effectively dropping dual boot support with OpenWrt. This results in a firmware partition of 13.9MB, which should leave some room for the future. To maintain install capabilites on new devices, an image is required that still fits inside the original partition. The initramfs is used as factory install image, so ensure this meets the old size constraints. The factory image can be flashed via the same procedure as vendor images when reverting to stock, can be installed from stock, or can be launched via tftpboot. Link: https://github.com/openwrt/openwrt/issues/16439 Link: https://github.com/openwrt/openwrt/pull/16442 Tested-by: Stijn Segers <foss@volatilesystems.org> Signed-off-by: Sander Vanheule <sander@svanheule.net>

dabbes · May 6, 2026, 7:06pm

ok, but in case the new FW does not boot, it is bricked. How should I
handle the testing in that case?

efahl · May 6, 2026, 8:05pm

Probably serial or tftp recovery... I would ask on those issue threads linked in the PR, or find one of the realtek threads here on the forum.

slh · May 8, 2026, 6:34am

Three Philips head screws and a 3.3V usb2serial adapter with 2.54mm DuPont wires (header prepoluted, marked but rather unconventionally) is all what separates you from booting an initramfs image. Compared to most other devices, this is easy and relatively safe. Read the device page, it's pretty verbose.

andyboeh · May 8, 2026, 8:18am

It's a rather easy process, I did it a few times and it never failed.

Steps:

Flash 25.12 initramfs image via sysupgrade, do not keep settings
Once in initramfs, flash the standard 25.12 sysupgrade image, do not keep settings

OpenWrt 25.12.x is installed. In case something goes wrong, you can still open the device and attach serial console, but it's usually not required for this upgrade.