Skip to content

Booting Turris Omnia over serial⚓︎


This howto is targeting really advanced users. Under normal circumstances you should never ever need this except if you reflashed your NOR (not easily accessible) with something that is not working. If your router works, do not attempt to reflash it.

Turris Omnia is using U-Boot to boot. That U-Boot is typically loaded from the beginning of the NOR memory and takes care of the rest of the booting process. If you try to flash it with a different U-Boot and your new U-Boot is corrupted, you’ll end up with an unbootable device. To fix that, there is an option to switch Omnia into a mode in which it will download U-Boot over serial line and boot it.


You’ll need a computer running Linux and a working serial cable connected to your Omnia. How to connect the serial cable is documented in another part of this documentation.


You will need the kwboot tool from the U-Boot tools package in v2022.04 or a newer version. You can install it via your Linux package manager (e.g. on Debian/Ubuntu via apt install u-boot-tools, on Fedora dnf install uboot-tools, on OpenSUSE zypper install u-boot-tools, …). Or you can get the binary for x86-64 CPU from our repository.


To use the binary from our repository, download it to your working directory and flag it as runnable:

chmod +x kwboot

Then, you can run it using ./kwboot as follows:

./kwboot -t -b uboot /dev/ttyUSB0


You will also need the latest U-Boot image and the latest rescue system image. You can find both in our GitLab. What you are interested in are two binary files there - rescue and uboot. You can use them to boot your Omnia over the serial line or to reflash the content of your NOR memory.


For the purpose of this tutorial, it is assumed that you have all the binaries in your current working directory and that your serial line is ttyUSB0.

  1. Disconnect your Omnia from power supply.
  2. Run the following command.

    kwboot -t -b uboot /dev/ttyUSB0
  3. Connect the power supply.

    kwboot will trigger the boot over serial mode of your Omnia automatically

  4. get ready to interrupt the booting process as described below


Close all other console connections to the router while booting. If you have another serial console open and attached to the /dev/ttyUSB0, the upload of the boot image will be very slow and will not be able to get uploaded in time.

If everything works well, you should see the U-Boot being transferred to your Omnia and once done, you’ll see U-Boot prompt and you can use that to recover your device.

Sometimes the kwboot command fails on the first try, but you can just run it again and again till it succeeds.

You may append additional argument -B 1500000 to increase transfer speed. The default speed is 115200 bauds/sec. Omnia supports speeds up to the 5200000 bauds/sec, but not all serial cables can handle such high speed modes.

Interrupting the booting process⚓︎

When you see the following message:

Hit any key to stop autoboot:

followed by a countdown from 3 to 0, do it. Now, you will get the U-Boot prompt as mentioned, introduced as =>.

NOR recovery⚓︎

Once you have U-Boot running, you can get various images, for example via an USB flash disk, tftp, serial console and write it to nor.


Do not forget to replace the [image] with the original file name (rescue or uboot) in the following commands.

Transfer via USB flash disk⚓︎

Copy an image (rescue or/and uboot file) to a FAT or EXT4 formatted USB flash disk, connect it to the Omnia USB port and run the following commands:

usb start
test -z "${loadaddr}" && setenv loadaddr 0x800000
load usb 0 ${loadaddr} [image]
usb stop

Transfer from TFTP server⚓︎

To download an image from TFTP server you need to get your network started, decide where to load it and load it. Assuming you have a TFTP server running on a computer with IP on a WAN network, the following U-Boot commands will get you a file named image into the RAM.

setenv autoload no
setenv serverip
test -z "${loadaddr}" && setenv loadaddr 0x800000
tftpboot ${loadaddr} [image]

Transfer via serial console⚓︎

Alternativelly, you can transfer the image over the serial console via the x-modem protocol. For this purpose you need the additional sx tool from the lrzsz package.

  1. Switch the U-Boot terminal from the command to the x-modem file transfer mode.

    test -z "${loadaddr}" && setenv loadaddr 0x800000
    loadx ${loadaddr}
  2. Disconnected from the U-Boot terminal.

    If using kwboot, press CTRL+\ followed by c.

  3. From the Linux console start x-modem file transfer for the file named image via sx tool.

    sh -c 'exec 0<>/dev/ttyUSB0 1>&0; sx [image]'
  4. After transfer finish, connect back to the U-Boot terminal.

    You can connect via kwboot by omitting -b option: kwboot -t /dev/ttyUSB0

Write image to NOR⚓︎

Now you have a file originally called image in the RAM on your router. To write to the NOR you have to know where it belongs.


Make sure you don’t mix an old U-Boot with the new rescue system or the new U-Boot with an old Turris OS, it might not work. Try to keep everything on the latest version if you are reflashing.

To reflash U-Boot, your image file on TFTP will be the uboot file from the Images section and you need to write it from the beginning of the NOR.

sf probe
sf update ${loadaddr} 0 ${filesize}

To recover the rescue system, your image file will be rescue from the Images section and you need to start writing it after the first megabyte that is reserved for U-Boot.

sf probe
sf update ${loadaddr} 0x00100000 ${filesize}

After that, you can call the reset command or hit the reset button and see your router booting again.

2024-03-15 2019-08-05