Use the OpenWRT ImageBuilder to build a firmware that automatically formats and moves extroot to any (!) inserted storage device
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It's a script to build a customized OpenWRT firmware image on a Linux x86_64 host (basic familiarity with OpenWRT is assumed).

If the generated image is flashed on a device it will try to automatically set up extroot on any (!) storage device plugged into the USB port (/dev/sda). Keep in mind that this will erase any inserted storage device while the router is in the initial setup phase! Unfortunately there's little that can be done at that point to ask the user for confirmation.


So that e.g. customers can buy a router on their own, flash our custom firmware, plug in a pendrive, and manage their SIP (telephony) node from our webapp.

I've extracted the generic parts from the above mentioned auto-provision project because I thought it's useful enough for making it public.



To build it, issue the following command: ./ architecture variant device-profile, e.g.:

  • ./ ar71xx generic tl-wr1043nd-v2

Results will be under build/openwrt-imagebuilder-${release}-${architecture}-${variant}.Linux-x86_64/bin/.

To see a list of available targets, run make info in the ImageBuilder dir.

If you want to change which OpenWRT version is used, then edit the relevant variable(s) in

Setup stages

Blinking leds show which phase the extroot setup scripts are in. Consult the sources for details:

Stage 1: setup extroot

When the custom firmware first boots, the autoprovision script will wait for anything (!) in /dev/sda to show up (that is >= 512M), then erase it and set up a swap, an extroot, and a datafilesystem (for the remaining space), and then reboot.

Stage 2: download and install some packages from the internet

Once it booted into the new extroot, it will continuously attempt to install some OpenWRT packages until an internet connection is set up on the router (either by using ssh or the web UI (LuCI)).


After flashing the firmware the router will have the standard IP address.

By default the root passwd is not set, so the router will start telnet with no password. If you want to set up a password, then edit the stage 2 script:

If a password is set, then telnet is disabled by OpenWRT and SSH will listen using the keys specified in authorized_keys.

Once connected, you can read the log with logread -f.


This is more of a template than something standalone. You most probably want to customize this script here and there; search for CUSTOMIZE for places of interest.

Most importantly, set up a password and maybe an ssh key.

At the time of writing it only supports a few ar71xx routers out of the box, but it's easy to extend it.

Tested with

OpenWRT 17.01.4 on a TP-Link WR-1043nd-v2.


Which file should I flash?

You should consult the OpenWRT documentation. The produced firmware files should be somewhere around build/openwrt-imagebuilder-17.01.4-ar71xx-generic.Linux-x86_64/bin/ar71xx.

In short:

  • You need a file with the name -factory.bin or -sysupgrade.bin. The former is to be used when you first install OpenWRT, the latter is when you upgrade an already installed OpenWRT.

  • You must carefully pick the proper firmware file for your hardware version! I advise you to look up the wiki page for your hardware on the OpenWRT wiki, because most of them have a table of the released hardware versions with comments on their status (sometimes new hardware revisions are only supported by the latest OpenWRT, which is not released yet).

Help! The build has finished but there's no firmware file!

If the build doesn't yield a firmware file (*-factory.bin and/or *-sysupgrade.bin): when there's not enough space in the flash memory of the target device to install everything then the OpenWRT ImageBuilder prints a hardly visible error into its flow of output and silently continues. Look into and try to remove some packages that you can live without.