cd ~
mkdir rtlinux
cd rtlinux
wget ftp://ftp.kernel.org/pub/linux/kernel/v3.x/linux-3.18.13.tar.xz 
wget https://www.kernel.org/pub/linux/kernel/projects/rt/3.18/patch-3.18.13-rt9.patch.gz
tar -xpf linux-3.18.13.tar.xz
gunzip patch-3.18.13-rt9.patch.gz
cp patch-3.18.13-rt9.patch linux-3.18.13
cd linux-3.18.13
cat patch-3.18.13-rt9.patch | patch -p1
sudo apt-get install libqt4-dev
make xconfig
make
sudo make modules_install
sudo make install