title: Can Buildroot build the root filesystem without building the Linux kernel?
body: <p>I tried:</p>
  
  <pre><code>git checkout 2018.05
  make qemu_x86_64_defconfig
  make BR2_JLEVEL="$(nproc)" "$(pwd)/output/images/rootfs.ext2"
  </code></pre>
  
  <p>but it still built the kernel at:</p>
  
  <pre><code>output/images/bzImage
  </code></pre>
  
  <p>I want to do that because:</p>
  
  <ul>
  <li>I'm making a setup where you can pick between multiple different root filesystems, so I will need to build Linux kernel manually for the other root filesystems, and would not like Buildroot to waste time building it again</li>
  <li>I don't want to wait 5 seconds every time for Buildroot to parse 100 Makefile configs when I want to rebuild the kernel :-)</li>
  </ul>
  
  <p>I'm using <code>LINUX_OVERRIDE_SRCDIR</code> with Linux on a submodule, so Linux the headers should match the source I will use for the build.</p>
  
  <p>Is there a fundamental dependency between, say, glibc and the kernel build, or is it just a weird use case never catered for?</p>
  
  <p>Ah, I noticed now that any loadable kernel modules need to go on the rootfs and would require a kernel build, and that build does have some <code>.ko</code> in the rootfs.</p>