= Step 0: Checkout and Compile the Kernel =

In the preparation phase, we checkout and compile the repositories needed to get started with working with LITMUS^RT^.

First, obtain a copy of the LITMUS^RT^ kernel.
{{{
$ git clone http://www.litmus-rt.org/src/litmus-rt.git
Cloning into litmus-rt...                                                                                                                                                                                       
$ cd litmus-rt/                                                                                                                                                               
$ ls
COPYING  Documentation  Kconfig      Makefile  REPORTING-BUGS  block   drivers   fs       init  kernel  litmus  net      scripts   sound  usr
CREDITS  Kbuild         MAINTAINERS  README    arch            crypto  firmware  include  ipc   lib     mm      samples  security  tools  virt
}}}

Next, obtain a working kernel configuration. For this tutorial, we are going to use the default KVM configuration.

{{{
$ wget http://www.litmus-rt.org/releases/2014.2/x86_64-config                                                                                                       
[...]
2014-06-12 15:52:49 (8.31 MB/s) - "x86_64-config" saved [65001/65001]
$ cp x86_64-config .config
}}}

Compile the kernel. On x86, the kernel build target is `bzImage`. Note that we do not compile modules for the default KVM configuration because all necessary drivers are statically compiled into the kernel image.

{{{
$ make -j16 bzImage
[...]
  CC      arch/x86/boot/compressed/cmdline.o
  CC      arch/x86/boot/compressed/early_serial_console.o
  OBJCOPY arch/x86/boot/compressed/vmlinux.bin
  HOSTCC  arch/x86/boot/compressed/mkpiggy
  GZIP    arch/x86/boot/compressed/vmlinux.bin.gz
  MKPIGGY arch/x86/boot/compressed/piggy.S
  AS      arch/x86/boot/compressed/piggy.o
  LD      arch/x86/boot/compressed/vmlinux
  ZOFFSET arch/x86/boot/zoffset.h
  OBJCOPY arch/x86/boot/vmlinux.bin
  AS      arch/x86/boot/header.o
  LD      arch/x86/boot/setup.elf
  OBJCOPY arch/x86/boot/setup.bin
  BUILD   arch/x86/boot/bzImage
Root device is (8, 1)
Setup is 14908 bytes (padded to 15360 bytes).
System is 3334 kB
CRC 3e3102d9
Kernel: arch/x86/boot/bzImage is ready  (#1)
}}}

(The exact numbers don't matter and will differ depending the configuration, the current version of LITMUS^RT^, your compiler version, etc.)

Next, obtain a copy of liblitmus, the corresponding userspace library
{{{
$ git clone http://www.litmus-rt.org/src/liblitmus.git
Cloning into liblitmus...
$ cd liblitmus/
$ ls
INSTALL  Makefile  README  arch  bin  inc  include  setsched  showsched  src  tests
}}}

You can run `make doc` to get browsable documentation in `docs/`.

Finally, compile `liblitmus`. Note that this must occur ''after'' checking out the kernel since the `liblitmus` build system pulls some headers out of the kernel repository.

{{{
$ make
cp ../litmus-rt/include/litmus/rt_param.h include/litmus/rt_param.h
[...]
gcc -o runtests -m64  core_api.o fdso.o locks.o pcp.o runner.o   -L. -llitmus 
}}}

We are now ready to start hacking LITMUS^RT^.

On to the [[../Step1|next step]].