# 3.2. Building JULES using FCM¶

FCM is a code management and build system developed by the Met Office with a particular focus on simplifying the process of building large Fortran programs. In this section, we will be using the build tool - FCM make.

As part of the build process, FCM make will analyse the dependencies of every Fortran file and automatically compile them in the correct order.

FCM make must be given a configuration file that it uses to determine how to build the source code. Extensive documentation on FCM make configuration files is available online.

Help pages for the FCM make command itself (rather than the configuration file) can be accessed using the command:

fcm help make


The FCM configuration file for building JULES is etc/fcm-make/make.cfg. This file uses the environment variables below to determine the compiler settings and NetCDF settings to use.

Running FCM make with this configuration file will create 4 new directories in your JULES root directory (i.e. the directory containing docs, src etc.):

.fcm-make
Used by FCM to store information about the build process.
extract
Contains a copy of the code that FCM will build.
preprocess
Contains the code after preprocessing but before compilation.
build
Contains the results of the compilation.

The JULES executable will be produced at build/bin/jules.exe.

## 3.2.1. Environment variables used when building JULES using FCM make¶

JULES_COMPILER

Used to select compiler specific settings.

Permitted value Purpose
gfortran Default. Use settings for the GNU Fortran compiler.
intel Use settings for the Intel Fortran compiler.
nag Use settings for the NAGWare compiler.
pgf Use settings for the Portland Group compiler.
JULES_BUILD

Used to select the type of build.

Permitted value Purpose
normal Default. Compile JULES normally.
debug Compile JULES with debug flags.
fast Compile JULES with optimisation flags for faster execution.
JULES_NETCDF

Indicates whether to use a dummy NetCDF library or a ‘real’ NetCDF library.

Permitted value Purpose
dummy Default. Use a dummy NetCDF library.
actual

Use a ‘real’ NetCDF library.

The NetCDF installation to use is specified using one of:

• JULES_NETCDF_PATH
• JULES_NETCDF_INC_PATH and JULES_NETCDF_LIB_PATH
JULES_NETCDF_PATH

Path to NetCDF installation.

This sets JULES_NETCDF_INC_PATH = $JULES_NETCDF_PATH/include and JULES_NETCDF_LIB_PATH =$JULES_NETCDF_PATH/lib. These can be overridden by setting the variables directly.

JULES_NETCDF_INC_PATH
Path to NetCDF include directory (i.e. directory containing netcdf.mod).
JULES_NETCDF_LIB_PATH
Path to NetCDF library directory (i.e. directory containing libnetcdff.a and libnetcdf.a).

## 3.2.2. Example FCM make commands¶

To create a normal JULES executable without NetCDF using the GFortran compiler (taking advantage of the default values for the environment variables):

fcm make -f etc/fcm-make/make.cfg


To create a fast JULES executable with NetCDF using the Intel compiler:

export JULES_COMPILER=intel
export JULES_BUILD=fast
export JULES_NETCDF=actual
export JULES_NETCDF_PATH=/usr/local/lib  # Replace this with the correct path
fcm make -f etc/fcm-make/make.cfg


## 3.2.3. Tips for effective use of FCM make (Unix-like systems only)¶

To check the current values of the environment variables JULES will use to build, use the command:

env | grep JULES


If you always use the same compilation options for JULES, consider adding the export lines to the .profile file in your \$HOME directory. Commands in the .profile file are automatically executed in any shell that you open, so defining environment variables there ensures your build environment remains consistent across shells and restarts of your computer. The definitions can still be overridden on the command line if required. For example, to always create a fast JULES executable with NetCDF using the Intel compiler (as above), add the following lines to your .profile:

export JULES_COMPILER=intel
export JULES_BUILD=fast
export JULES_NETCDF=actual
export JULES_NETCDF_PATH=/usr/local/lib


Then to build JULES with those settings, run:

fcm make -f etc/fcm-make/make.cfg


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