Linksys WRT1900ACS

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The following instructions describe how to install Untangle's next-generation firmware on an Linksys WRT1900ACS router.

Linksys WRT1900ACS


Flashing aftermarket firmware on a router can void the factory warranty. Improperly flashing the firmware on a router can brick it.

Pre-flashed routers are sold via our partner FlashRouters


Please review the firmware FAQ found here


  • An Linksys WRT1900ACS router (link)
  • USB flash drive (link)
  • The Untangle firmware image (trx file contained in the zip available from Downloads)
  • The Untangle disk image (rootfs file contained in the zip available from Downloads)

The Basics

Unlike traditional firmware images (like DD-WRT, OpenWRT, Tomato) the Untangle firmware currently requires two images.

The Untangle firmware image will be flashed onto the router, like a traditional firmware or aftermarket firmware upgrade, and the Untangle disk image will be written to a USB memory stick and inserted into the router.

For storage a USB memory stick (or hard drive) is required. (example) The USB stick will hold the disk image

NOTE: Not all USB memory sticks are created equal. Many free USB memory sticks are very cheap quality and may suffer from data corruption or quick failure. We suggest buying a quality name-brand USB memory stick.


Creating the Untangle disk image

Follow the instructions for your O/S to write the disk image to the USB memory stick.

After writing the disk image insert the USB drive into the Linksys router on the USB2 port as shown in the diagram above.


  • Download and launch Rufus imaging utility
  • Insert the USB memory stick into the PC and select it under "Device." (be sure not to accidentally select the wrong drive!)
  • Next to "Create bootable disk using" select "DD Image" and hit the little disk icon to choose the rootfs file.
  • When choosing the file change the displayed files from *.iso to *.* and choose the downloaded rootfs file.
  • Click Start to write the image to the drive.

After completion insert the USB memory stick into the USB port labeled USB2 on your Linksys router.


  • Insert the USB memory stick into the PC.
  • Run 'dmesg' and determine the device name for the USB drive. (example: /dev/sdf)
  • Run 'sudo dd if=untangle.rootfs of=/dev/sdX bs=10M' (where X is the device name from above - be sure not to accidentally specify the wrong drive!)
  • Run 'sync'

Installing the Untangle firmware image

To install the firmware image upload the firmware image file to the router.

To do this:

  • Install the Linksys WRT1900ACS on the network.
    • Plug the yellow internet port into your ISP modem or internet connection
    • Optionally plug your wired device or PC into a blue LAN ethernet port.
  • Open a browser to the administration interface on the Linksys WRT1900ACS.
    • If this is a new router, connect the PC to an internal port and open a browser to
    • Either skip or complete the wizard
    • Login if required
  • Plug the imaged USB memory stick into the USB2 port on the router

This guide was created on Firmware Version -

  • Under Router Settings, click Connectivity.

  • Under the Firmware Update section, click Choose File.
  • Now select the Untangle firmware .trx file you wish to install
  • Click "Upload"

On older Firmware -

  • Click on Administration near the bottom on the left-hand menu
  • Click on Firmware on the top menu
  • Click browse and select the Untangle firmware .trx file you wish to install
  • Click "Upload"

At this point it will display a progress dialog that will never complete as it is expecting a newer Linksys firmware.

The router will automatically reboot when done and boot the new Untangle firmware. The first boot will take a while; grab a coffee and give it a few minutes to initialize!

Connecting to the Router

After the bootup process is complete, you can connect to the router with either a PC, laptop, tablet, smartphone, etc.

If you are using a wired device or PC connect your device to the LAN ethernet port (blue ports labeled 1-4), open a web browser and type If you do not see the setup wizard, restart your PC or device to ensure it gets a new address from the router and try again.

If you are using a wireless device connect to the UntangleLinksys or UntangleLinksys5 wireless network using a password of 12345678

Once connected open a browser (Safari/Chrome/etc) and type in

At this point the Setup Wizard should be visible.

Setup Wizard

The setup wizard will walk you through the initial configuration of your router. Simply follow the instructions in the wizard.

However, if you are connecting with a wireless device you will lose connection to your router when you change the wireless settings (SSID/encryption/password). If this happens simply reconnect to the wireless using the new settings and open the browser to and resume the setup wizard.


After the setup wizard is complete you will need to register and then you can configure Untangle. Refer to the Untangle documentation on how to use and configure Untangle.

Reverting to Stock Firmware

If you wish to uninstall Untangle and install another firmware follow these instructions.