# Start from scratch
cd /usr
sudo rm -fr obj src
sudo mkdir obj src

# Checkout sources
sudo svnlite checkout https://svn.FreeBSD.org/base/releng/10.3 /usr/src

# Backup /etc
cd /
sudo rm -fr etc.old
sudo cp -Rp etc etc.old

# Apply local patches (if any)
cd /usr/src/.../...
patch -p0 < /root/patches/.../patch.diff

# Compile a new world and kernel
cd /usr/src
less UPDATING
sudo make buildworld
sudo make buildkernel

# Optional: remove all -C flags from install to force installation of unmodified files
cd /usr/src/share/mk
sudo nano bsd.incs.mk
sudo nano bsd.lib.mk

# Install new kernel
cd /usr/src
sudo make installkernel

# Stop all services except sshd
sudo service stop ...

# Install new world
cd /usr/src
sudo mergemaster -p
sudo make installworld
sudo mergemaster -iF
sudo make delete-old

sudo reboot

cd /usr/src
sudo make delete-old-libs