CMake installation instructions

The CMake build system is used to build ECMWF software. The build process comprises two stages:

1. CMake runs some tests on the system and finds out if required software libraries and headers are available. It uses this information to create native build tools (e.g. Makefiles) for the current platform.
2. The actual build can take place, for example by typing 'make'.

Prerequisite

To install any ECMWF software package, CMake needs to be installed on your system. On most systems it will be already installed or this can be done through the standard package manager to install software. For further information to install CMake see

http://www.cmake.org/cmake/help/install.html

Directories

During a build with CMake there are three different directories involved: The source dir, the build dir and the install dir.

Of these, the source and build directories can be anywhere on the system. The installation directory is usually left at its default, which is /usr/local. Installing software here ensures that it is automatically available to users. It is possible to specify a different installation directory by adding -DCMAKE_INSTALL_PREFIX=/path/to/install/dir to the CMake command line.

Quick Build Example

Here is an example set of commands to set up and build a software package using default settings. More detail for a customised build is given below.

# unpack the source tarball into a temporary directory
mkdir -p /tmp/src
cd /tmp/src
tar xzvf software-version-Source.tar.gz

# configure and build in a separate directory
mkdir -p /tmp/build
cd /tmp/build
cmake /tmp/src/software-version-Source
make

On a machine with multiple cores, compilation will be faster by specifying the number of cores to be used simultaneously for the build, for example:

make -j8

If the make command fails, you can get more output by typing:

make VERBOSE=1

The software distribution will include a small set of tests which can help ensure that the build was successful. To start the tests, type:

ctest

As before if you have multiple cores, you can run the tests in parallel by:

ctest -j8

If the tests are successful, you can install the software:

make install

General CMake options

Various options can be passed to the CMake command. The following table gives an overview of some of the general options that can be used. Options are passed to the cmake command by prefixing them with -D, for example -DCMAKE_INSTALL_PREFIX=/path/to/dir.

CMAKE_INSTALL_PREFIX

CMAKE_BUILD_TYPE

CMAKE_CXX_FLAGS

CMAKE_C_FLAGS

CMAKE_Fortran_FLAGS

The C, C++ and Fortran compilers are chosen by CMake. This can be overwritten by setting the environment variables CC, CXX and F77, before the call to cmake, to set the preferred compiler. Further the variable CMAKE_CXX_FLAGS can be used to set compiler flags for optimisation or debugging. For example, using CMAKE_CXX_FLAGS="-O2 -mtune=native" sets options for better optimisation. 

Finding support libraries

If any support libraries are installed in non-default locations, CMake can be instructed where to find them by one of the following methods. First, the option CMAKE_PREFIX_PATH can be set to a colon-separated list of base directories where the libraries are installed, for example -DCMAKE_PREFIX_PATH=/path/where/my/sw/is/installed. CMake will check these directories for any package it requires. This method is therefore useful if many support libraries are installed into the same location.

Troubleshooting

Debugging configure failures

If CMake fails to configure your project, run with debug logging first:

cmake -DECBUILD_LOG_LEVEL=DEBUG [...] /path/to/source

This will output lots of diagnostic information (in blue) on discovery of dependencies and much more.