How to install OpenWrt on the Linksys WRT1900ACS Wireless Router

The Linksys WRT1900ACS is a good wireless router, but one of its best features is that it is supported by different open source firmwares including OpenWrt. So, if you’re like me and want to use this router with the OpenSource router firmware to unlock all of its power instead of the limited stock firmware, read this guide to learn how to install it. It’s not a hard process but I had several issues when I installed the firmware on my router so I’ve written in this guide all the solutions I had to apply. I hope they will help you too.

If you have previously installed DD-WRT on your Linksys WRT1900ACS router and want to switch to OpenWrt, read how to rollback to the stock firmware before installing OpenWrt.

If you have a different router and you want to check if it’s supported by OpenWrt, you can check it in the table of supported devices. On the other hand, if you want to buy a router to install OpenWrt, you can have a look at the ‘Ideal for OpenWrt’ table.

DISCLAIMER: Be aware that there is a potential risk of bricking your router while installing a non official firmware such as OpenWrt. Do it at your own risk. You assume all responsibility for anything you do and I will accept no responsibility for anything that could go wrong while trying to install OpenWrt on it, such as bricking your router.


Check your router version

It is essential that you confirm your Linksys WRT1900ACS router version (v1 or v2) before starting the process because firmwares are not compatible between hardware versions. The hardware version is located beside or beneath the model number and is labeled version, ver. or V. If there is no version number beside the model number on your Linksys product, the device is version 1. If you still have trouble finding your version number, see the complete article at Linksys Official Support site to learn more.


Download OpenWrt firmware

Now you must download the firmware image for your router from the Firmware downloads page of the OpenWrt Project. As a reference, the current Stable Release at the time I was writting this guide was version 18.06.4, wich was released on 1st July 2019.

Use the filter boxes to find the firmware for your router model and click on the ‘Firmware OpenWrt Install URL’ link. In my case was openwrt-18.06.4-mvebu-cortexa9-linksys-wrt1900acs-squashfs-factory.img.

Verify the downloaded firmware file

After downloading the firmware image you should verify, using a checksum tool, that the file you’ve just downloaded is correct so you will not brick your device by applying a faulty download. To do so first retrieve the reference checksum from the root folder of the url you used to download the firmware, in my case, and find the file you have downloaded. The checksum is the string in the column sha256sum. 4c2dfe16b427df50c2e7bd6753d82ea944bc0925c1cf25488ab42a1d9ba43839 in my case.

Next, use a checksum tool to generate the SHA 256 checksum of your downloaded file and compare it with the string from the previous page.

Only continue with flashing, if the firmware checksum of your download matches the checksum stated on the download site!

For more information about this process you can read the guide for verifying OpenWrt firmware binary in the OpenWrt project site.


Disconnect the Internet cable

Now that we have downloaded the OpenWrt firmware file we should disconnect the ethernet cable from the yellow Internet port on the back of your router. This will avoid errors when uploading the new firmware to the router such as the 'ErrorUnauthorized' that I had.


Do a factory reset

With your router connecter to power and turned on, press and hold the Reset button on the back of your router for 10 seconds until the power indicator flashes.


Update OpenWrt firmware

Login to the web admin interface

Connect your computer to the router using an ethernet cable and then open the IP address on a web browser.

Click on ‘Manual configuration‘.

Yo will see this ‘Internet connection is down’ message as expected. We have disconnected previously the ethernet cable from the yellow Internet port. Click on the Login button.

Type the router password ‘admin‘ and click on the Sign In button.

Upload the firmware

Navigate to the Connectivity section and locate the Router Firmware Update section on the right hand side.

Click on the Choose File button in the Manual section, select the firmware image that you downloaded from OpenWrt earlier (‘openwrt-18.06.4-mvebu-cortexa9-linksys-wrt1900acs-squashfs-factory.img‘) and then hit Start.

Click on Yes to continue.

Wait until the firmware installation is complete.

The firmware has been installed and the router will reboot automatically.


OpenWrt first login

Wait for the router to restart and visit the router administration page at the address on a web browser.

You’ll see a notification that the administrator’s root password is not set. For now just log in with the username of root and leave the password field empty.

Set up root password

Once you’ve logged in, you’ll see a page where you can set the root password. Root is the username of the administrative user in OpenWrt. Since this is an extremely powerful account, you must provide a strong password that you’ll remember.

Fill the ‘Password‘ and ‘Confirmation‘ fields and click on the ‘Save & Apply‘ button.

Set Timezone

It is a good idea to set your router’s timezone and local time on “System > System” so that there are no conflicts with future settings.

Turn On WiFi

When you install a fresh copy of OpenWrt on a router, the WiFi networks are disabled for security reasons. So let’s turn them on now so we can use the router wirelessly.
Go to the Wireless configuration page by selecting the “Network > Wireless” menu option at the top of the page.

The Wireless Overview page contains the information related to the physical radios in the router which handle Wi-Fi communication and the Wi-Fi networks associated with them. Click the ‘Edit‘ button on the wireless network you want to enable.

Select the correct country code where your OpenWrt router is installed in the ‘Country Code‘ field under the ‘Advanced Setting’ tab in the ‘Device Configuration’ section. This is important to ensure your OpenWrt device meets the legal regulations in your country.

If you wish, you can change the name of the wireless network (ESSID) or leave the default name ‘OpenWrt’. The name can be changed by modifying the value of the field ‘ESSID‘ under the ‘General Setup’ tab in the ‘Interface Configuration’ section.

Next we must set up the network security in the ‘Wireless Security‘ tab of the ‘Interface Configuration’ section.
Select an Encryption method (e.g. “WPA2-PSK”, recommended for home/small office networks).
Select a Cipher (“auto” is recommended).
Enter a Key, a secret phrase to connect to your WiFi network (with WPA2-PSK, the Key must be at least eight characters).

Finally click on the ‘Enable‘ button in the ‘General Setup’ tab of the ‘Device Configuration’ section.

Now your WiFi network is up and running and you can connect a device to your router wirelessly!


Some handy links

Amazon : Linksys WRT1900ACS Gigabit Wi-Fi Router

Linksys WRT1900ACS product page

OpenWrt Project
OpenWrt Project: Factory install: First-time installation on a device
OpenWrt Project: Verifying OpenWrt firmware binary
OpenWrt Project: Log into your Router Running OpenWrt
OpenWrt Project: Enabling a Wi-Fi access point on OpenWrt
OpenWrt Project: Linksys WRT1900ACS

How to install DD-WRT on the Linksys WRT1900ACS Wireless Router


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