In this blog, we will see how to compile and boot openwrt inside virtualbox. Before going into the steps, let me explain the problem i was trying to solve. I wanted to try out few modification in openwrt code and wanted to try it before flashing my TP-Link router. I also wanted to compile lighttpd with openwrt image. This was the motivation behind compiling/running openwrt inside virtualbox. I tried it with Virtual machine manager also and it works the same way. I am assuming that we have a copy of openwrt source code.

step#1 Make Menuconfig. Choose below settings in menuconfiuration.

We can choose any target system but its a good idea to choose x86 as it has better driver support with underlying virtualization technology.

Target System : x86 
Subtarget     : x86_64

As we are compiling it for virtual machine, target image needs to be vmdk or vdi. 

Target Image: Vmdk
Target Image: Vdi

If we choose default size for kernel and rootfs, we will not be able to edit / partitions on openwrt router, as firmware will eat all the space. To increase the size of above mentioned partitions, we will need to set these values in target image section

Kernel partition size in MB : 16
RootFS partition size in MB : 64 or 128

step#2 Execute make. In case any errors, check build.log. If you have multi core machine, you can distribute make job across available cores by specifying -j [no_of_cores].

sudo make V=s 2>&1 | tee build.log | grep -i error

step#3 After successful completion of above step, new firmware will be available under bin directory.

step#4 Open Virtualbox. Create a virtual machine with existing virtual hard drive.

This should give us a openwrt virtual machine. In the next blog, we will see how we can turn this virtual machine into router/bridge.