If you want to compile a custom FreeBSD kernel or rebuild world or be a developer for FreeBSD, you may want to download the source.
Download FreeBSD Source as follows.
Step 1 – Install Subversion
Install subversion from ports or as a package.
# cd /usr/ports/devel/subversion
# make install
# pkg_add -r subversion
Note: Don’t forget to run ‘rehash’ if after install your current shell cannot find svn.
Step 2 – Check Out FreeBSD Source
To download FreeBSD source, use subversion. You may want to use Release, Stable, or Current. Release doesn’t have any updates, so if you want patches since release, you are likely wanting to do Release Engineering.
svn checkout http://svn.freebsd.org/base/release/9.0.0/ /usr/src
svn checkout http://svn.freebsd.org/base/releng/9.0/ /usr/src
# svn checkout http://svn.freebsd.org/base/stable/9 /usr/src
# svn checkout http://svn.freebsd.org/base/head /usr/src
You now have FreeBSD source and you should be able to compile the kernel or the FreeBSD world.