# Notes for saving disk space when building LAMMPS from source

LAMMPS is a large software project with a large number of source files,
extensive documentation, and a large collection of example files. When
downloading LAMMPS by cloning the [git repository from
GitHub](https://github.com/lammps/lammps)\_ this will by default also
download the entire commit history since September 2006. Compiling
LAMMPS will add the storage requirements of the compiled object files
and libraries to the tally.

In a user account on an HPC cluster with filesystem quotas or in other
environments with restricted disk space capacity it may be needed to
reduce the storage requirements. Here are some suggestions:

-   Create a so-called shallow repository by cloning only the last
    commit instead of the full project history by using
    `git clone git@github.com:lammps/lammps --depth=1 --branch=develop`.
    This reduces the downloaded size to about half. With `--depth=1` it
    is not possible to check out different versions/branches of LAMMPS,
    using `--depth=1000` will make multiple recent versions available at
    little extra storage needs (the entire git history had nearly 30,000
    commits in fall 2021).
-   Download a tar archive from either the [download section on the
    LAMMPS homepage](https://www.lammps.org/download.html)\_ or from the
    [LAMMPS releases page on
    GitHub](https://github.com/lammps/lammps/releases)\_ these will not
    contain the git history at all.
-   Build LAMMPS without the debug flag (remove `-g` from the machine
    makefile or use `-DCMAKE_BUILD_TYPE=Release`) or use the `strip`
    command on the LAMMPS executable when no more debugging would be
    needed. The strip command may also be applied to the LAMMPS shared
    library. The static library may be deleted entirely.
-   Delete compiled object files and libraries after copying the LAMMPS
    executable to a permanent location. When using the traditional build
    process, one may use `make clean-<machine>` or `make clean-all` to
    delete object files in the src folder. For CMake based builds, one
    may use `make clean` or just delete the entire build folder.
-   The folders containing the documentation tree (doc), the examples
    (examples) are not needed to build and run LAMMPS and can be safely
    deleted. Some files in the potentials folder are large and may be
    deleted, if not needed. The largest of those files (occupying about
    120 MBytes combined) will only be downloaded on demand, when the
    corresponding package is installed.
-   When using the CMake build procedure, the compilation can be done on
    a (local) scratch storage that will not count toward the quota. A
    local scratch file system may offer the additional benefit of
    speeding up creating object files and linking with libraries
    compared to a networked file system. Also with CMake (and unlike
    with the traditional make) it is possible to compile LAMMPS
    executables with different settings and packages included from the
    same source tree since all the configuration information is stored
    in the build folder. So it is not necessary to have multiple copies
    of LAMMPS.