Summary for xv6 setup:

1. Sync down xv6 soure code

git clone git://github.com/mit-pdos/xv6-public.git

2. Make sure your gcc is ready, test using following command. If the gcc is not installed, install it.

objdump -i

sudo apt-get install -y build-essential gdb

sudo apt-get install gcc-multilib  (for 64-bit machine)

3. Build xv6-public source code

    Strictly follow below steps, or you might run into cases such as no bootable device

   cd parent/folder/of/xv6-public

   chmod -R 777 xv6-public

   cd xv6-public

   make clean

   make

   make qemu 

4. Make sure CPU virtualization support is enabled

    If you run into problems when issuing "make qemu", e.g. Could not access KVM kernel module. You can check if CPU virtualization is enabled, such as intel VT-X. This requires you enter BIOS settings when machine bootstraps.

   Refer   for more details.