The installation of OpenWrt is device specific. A detailed procedure should be found in the wiki-page for your device. See Table of Hardware for available ones. If your device is not listed, read on… Definitely have a look at the Flash Layout.
If your attempt to install OpenWrt fails, generic.debrick could help you.
This Howto is VERY generic. You cannot just use it, but you have to adapt values and other stuff to your hardware. Look at the supported hardware page for your device-specific documentation.
Generally, you have three options:
Option_1:install OpenWrt onto the router's non-volatile memory: this page
Option_2:install OpenWrt into the RAM:
There are four ways to install OpenWrt on a device:
Open the WebUI of the OEM firmware with your web browser and install the OpenWrt factory firmware image file using the "Firmware Upgrade" option. Done.
NOTE: Sometimes the OEM firmware will only allow you to flash your device with a specific firmware file. If that is the case, you will not be able to install OpenWrt using this method. However, for some devices the build bots prepare tagged builds such that they are compliant with the firmwares from the manufacturer. This should be documented on the device specific page for your model.
Most, if not all bootloaders provide built-in functionality for this purpose. Some use a TFTP-client, others a TFTP-server, others a FTP-client, some an FTP-server, some a web server and some use the XMODEM-protocol.
Before proceeding you need to determine the following:
Once you know all of the above parameters, you may proceed.
NOTES: Sometimes even the bootloader prevents you from flashing a non-OEM firmware.
If you have a short time window, the connection between your computer and device needs to be established quickly. To make this as quick possible, you can disable auto-negotiation on your NIC and/or disable media sensing.
This step shows you howto upload a new ramdisk image to the device. The existing firmware on the flash remains unchanged! You require a working serial cable to do the ramdisk upload.
./wndr3700 openwrt-ar71xx-uImage-lzma.bin openwrt-fixed.out
setenv ipaddr 192.168.0.1 setenv serverip 192.168.0.10 setenv bootargs 'board=WNDR3700' tftpboot 80800000 openwrt-fixed.out bootm(if you forget the bootargs piece below, the board will boot and look normal, but it won't be able to bring up any of the network interfaces!)
Concrete examples: wnr2000, …
Don't forget to consult the other Generic Basic Howtos for OpenWrt
This checklist cannot and does not completely cover all the ways you can install OpenWrt.