To set up your environment for using a particular (set of) software package(s), you can use the modules that are provided centrally.
On the Tier-2 of UGent, interacting with the modules is done via Lmod (since August 2016), using the module command or the handy shortcut command ml.

Quick introduction

A very quick introduction to Lmod. Below you will find more details and examples.

  • ml lists the currently loaded modules, and is equivalent with module list
  • ml GCC/4.9.3 loads the GCC/4.9.3 module, and is equivalent with module load GCC/4.9.3
  • ml -GCC unloads the currently loaded GCC module, and is equivalent with module unload GCC
  • ml av gcc prints the currently available modules that match gcc (case-insensitively), and is equivalent with module avail GCC
  • ml show GCC/4.9.3 prints more information about the GCC/4.9.3 module, and is equivalent with module show GCC
  • ml spider gcc searches (case-insensitive) for gcc in all available modules over all clusters
  • ml spider GCC/4.9.3 show all information about the module GCC/4.9.3 and on which clusters it can be loaded.
  • ml save mycollection stores the currently loaded modules to a collection
  • ml restore mycollection restores a previously stored collection of modules

Module commands: using module (or ml)

Listing loaded modules: module list (or ml)

To get an overview of the currently loaded modules, use module list or ml (without specifying extra arguments).

In a default environment, you should see a single cluster module loaded:

$ ml
Currently Loaded Modules:
  1) cluster/delcatty (S)
   S:  Module is Sticky, requires --force to unload or purge

(for more details on sticky modules, see the section on ml purge)

Searching for available modules: module avail (or ml av) and ml spider

Printing all available modules: module avail (or ml av)

To get an overview of all available modules, you can use module avail or simply ml av:

$ ml av
----------------------------- /apps/gent/CO7/haswell-ib/modules/all -----------------------------
   ABAQUS/6.12.1-linux-x86_64           libXext/1.3.3-intel-2016a                  (D)
   ABAQUS/6.14.1-linux-x86_64    (D)    libXfixes/5.0.1-gimkl-2.11.5
   ADF/2014.02                          libXfixes/5.0.1-intel-2015a
   ...                                  ...

In the current module naming scheme, each module name consists of two parts:

  • the part before the first /, corresponding to the software name; and
  • the remainder, corresponding to the software version, the compiler toolchain that was used to install the software, and a possible version suffix

For example, the module name matplotlib/1.5.1-intel-2016a-Python-2.7.11 will set up the environment for using matplotlib version 1.5.1, which was installed using the intel/2016a compiler toolchain; the version suffix -Python-2.7.11 indicates it was installed for Python version 2.7.11.

The (D) indicates that this particular version of the module is the default, but we strongly recommend to not rely on this as the default can change at any point. Usuall, the default will point to the latest version available.

Searching for modules: ml spider

The (Lmod-specific) spider subcommand lets you search for modules across all clusters.

If you just provide a software name, for example gcc, it prints on overview of all available modules for GCC.

$ ml spider gcc
     Other possible modules matches:
  To find other possible module matches do:
      module -r spider '.*GCC.*'
  For detailed information about a specific "GCC" module (including how to load the modules) use the module's full name.
  For example:
     $ module spider GCC/4.9.3

Note that spider is case-insensitive.

If you use spider on a full module name like GCC/4.9.3-2.25 it will tell on which cluster(s) that module available:

$ ml spider GCC/4.9.3-2.25
  GCC: GCC/4.9.3-2.25
     Other possible modules matches:
    You will need to load all module(s) on any one of the lines below before the "GCC/4.9.3-2.25" module
    is available to load.
       The GNU Compiler Collection includes front ends for C, C++, Objective-C, Fortran, Java, and Ada,
       as well as libraries for these languages (libstdc++, libgcj,...). - Homepage:
  To find other possible module matches do:
      module -r spider '.*GCC/4.9.3-2.25.*'

This tells you that the module named GCC/4.9.3-2.25 is available on the clusters delcatty, golett, phanpy, raichu and swalot. It also tells you what the module contains and a URL to the homepage of the software.

Available modules for a particular software package: module avail <name> (or ml av <name>)

To check which modules are available for a particular software package, you can provide the software name to ml av.

For example, to check which versions of IPython are available:

$ ml av ipython
----------------------------- /apps/gent/CO7/haswell-ib/modules/all -----------------------------
IPython/3.2.3-intel-2015b-Python-2.7.10    IPython/3.2.3-intel-2016a-Python-2.7.11 (D)

Note that the specified software name is treated case-insensitively.

Lmod does a partial match on the module name, so sometimes you need to use / to indicate the end of the software name you are interested in:

$ ml av GCC/
----------------------------- /apps/gent/CO7/haswell-ib/modules/all -----------------------------
GCC/4.9.2    GCC/4.9.3-binutils-2.25    GCC/4.9.3    GCC/4.9.3-2.25    GCC/5.3.0    GCC/6.1.0-2.25 (D)

Inspecting a module using module show (or ml show)

To see how a module would change the environment, use module show or ml show:

$ ml show matplotlib/1.5.1-intel-2016a-Python-2.7.11
----------------------------- /apps/gent/CO7/haswell-ib/modules/all -----------------------------
whatis("Description: matplotlib is a python 2D plotting library which produces publication quality figures in a variety of 
hardcopy formats and interactive environments across platforms. matplotlib can be used in python scripts, the python 
and ipython shell, web application servers, and six graphical user interface toolkits. - Homepage: ")
help([[ matplotlib is a python 2D plotting library which produces publication quality figures in a variety of
 hardcopy formats and interactive environments across platforms. matplotlib can be used in python scripts, the python
 and ipython shell, web application servers, and six graphical user interface toolkits. - Homepage:

Note that both the direct changes to the environment as well as other modules that will be loaded are shown.

If you're not sure what all of this means: don't worry, you don't have to know; just load the module and try using the software.

Loading modules: module load <modname(s)> (or ml <modname(s)>)

To effectively apply the changes to the environment that are specified by a module, use module load or ml and specify the name of the module.

For example, to set up your environment to use matplotlib:

$ ml matplotlib/1.5.1-intel-2016a-Python-2.7.11
$ ml
Currently Loaded Modules:
  1) cluster/delcatty                                    (S)  12) zlib/1.2.8-intel-2016a
  2) GCCcore/4.9.3                                          13) libreadline/6.3-intel-2016a
  3) binutils/2.25-GCCcore-4.9.3                            14) ncurses/6.0-intel-2016a
  4) icc/2016.1.150-GCC-4.9.3-2.25                          15) Tcl/8.6.4-intel-2016a
  5) ifort/2016.1.150-GCC-4.9.3-2.25                        16) SQLite/3.9.2-intel-2016a
  6) iccifort/2016.1.150-GCC-4.9.3-2.25                     17) Tk/8.6.4-intel-2016a-no-X11
  7) impi/      18) GMP/6.1.0-intel-2016a
  8) iimpi/8.1.5-GCC-4.9.3-2.25                             19) Python/2.7.11-intel-2016a
  9) imkl/             20) freetype/2.6.2-intel-2016a
 10) intel/2016a                                            21) libpng/1.6.21-intel-2016a
 11) bzip2/1.0.6-intel-2016a                                22) matplotlib/1.5.1-intel-2016a-Python-2.7.11

Note that even though we only loaded a single module, the output of ml shows that a whole bunch of modules were loaded, which are required dependencies for matplotlib, including both the compiler toolchain that was used to install matplotlib (i.e. intel/2016a, and its dependencies) and the module providing the Python installation for which matplotlib was installed (i.e. Python/2.7.11-intel-2016a).

Conflicting modules

It is important to note that only modules that are compatible with each other can be loaded together. In particular, modules must be installed either with the same toolchain as the modules that are already loaded, or with a compatible (sub)toolchain.

For example, once you have loaded one or more modules that were installed with the intel/2016a toolchain, all other modules that you load should have been installed with the same toolchain.

In addition, only one single version of each software package can be loaded at a particular time. For example, once you have the Python/2.7.11-intel-2016a module loaded, you can not load a different version of Python in the same session/job script; neither directly, nor indirectly as a dependency of another module you want to load.

See also the topic "module conflicts" in the list of key differences with the previously used module system.

Unloading modules: module unload <modname(s)> (or ml -<modname(s)>)

To revert the changes to the environment that were made by a particular module, you can use module unload or ml -<modname>.

For example:

$ ml
Currently Loaded Modules:
  1) cluster/golett (S)
$ which gcc
$ ml GCC/4.9.3
$ ml
Currently Loaded Modules:
  1) cluster/golett (S)   2) GCC/4.9.3
$ which gcc
$ ml -GCC/4.9.3
$ ml
Currently Loaded Modules:
  1) cluster/golett (S)
$ which gcc

Resetting by unloading all modules: ml purge (module purge)

To reset your environment back to a clean state, you can use module purge or ml purge:

$ ml
Currently Loaded Modules:
  1) cluster/delcatty                                    (S)  11) bzip2/1.0.6-intel-2016a
  2) GCCcore/4.9.3                                          12) zlib/1.2.8-intel-2016a
  3) binutils/2.25-GCCcore-4.9.3                            13) libreadline/6.3-intel-2016a
  4) icc/2016.1.150-GCC-4.9.3-2.25                          14) ncurses/6.0-intel-2016a
  5) ifort/2016.1.150-GCC-4.9.3-2.25                        15) Tcl/8.6.4-intel-2016a
  6) iccifort/2016.1.150-GCC-4.9.3-2.25                     16) SQLite/3.9.2-intel-2016a
  7) impi/      17) Tk/8.6.4-intel-2016a-no-X11
  8) iimpi/8.1.5-GCC-4.9.3-2.25                             18) GMP/6.1.0-intel-2016a
  9) imkl/             19) Python/2.7.11-intel-2016a
 10) intel/2016a
$ ml purge
The following modules were not unloaded:
   (Use "module --force purge" to unload all):
  1) cluster/delcatty
[15:21:20] vsc40023@node2626:~ $ ml
Currently Loaded Modules:
  1) cluster/delcatty (S)

Note that the cluster will always remain loaded, since it defines some important environment variables that point to the location of centrally installed software/modules, and others that are required for submitting jobs and interfacing with the cluster resource manager ( qsub, qstat, ...).

As such, you should not (re)load the cluster module anymore after running ml purge. See also the topic on the purge command in the list of key differences with the previously used module implementation.

Module collections: ml save, ml restore

If you have a set of modules that you need to load often, you can save these in a collection (only works with Lmod).

First, load all the modules you need, for example:

ml HDF5/1.8.16-intel-2016a GSL/2.1-intel-2016a Python/2.7.11-intel-2016a

Now store them in a collection using ml save:

$ ml save my-collection

Later, for example in a job script, you can reload all these modules with ml restore:

$ ml restore my-collection

With ml savelist you can get a list of all saved collections:

$ ml savelist
Named collection list:
  1) my-collection
  2) my-other-collection

To inspect a collection, use ml describe.

To remove a module collection, remove the corresponding entry in $HOME/.lmod.d.

Lmod vs Tcl-based environment modules

In August 2016, we switched to Lmod as a modules tool, a modern alternative to the outdated & no longer actively maintained Tcl-based environment modules tool.

Consult the Lmod documentation web site for more information.


  • significantly more responsive module commands, in particular module avail
  • a better and easier to use interface (e.g. case-insensitive avail, the ml command, etc.)
  • additional useful features, like defining & restoring module collections
  • drop-in replacement for Tcl-based environment modules (existing Tcl module files do not need to be modified to work)
  • module files can be written in either Tcl or Lua syntax (and both types of modules can be mixed together)

Key differences

The switch to Lmod should be mostly transparent, i.e. you should not have to change your existing job scripts.

Existing module commands should keep working as they were before the switch to Lmod.

However, there are a couple of minor differences between Lmod & the old modules tool you should be aware of:

  • module conflicts are strictly enforced
  • module purge does not unload the cluster module
  • modulecmd is not available anymore (only relevant for EasyBuild)

See below for more detailed information.

Module conflicts are strictly enforced

Conflicting modules can no longer be loaded together.

Lmod has been configured to report an error if any module conflict occurs (as opposed to the default behaviour which is to unload the conflicting module and replace it with the one being loaded).

Although it seemed like the old modules did allow for conflicting modules to be loaded together, this was highly discouraged already since it usually resulted in a broken environment. Lmod will ensure no changes are made to your existing environment if a module that conflicts with an already module is loaded.

If you do try to load conflicting modules, you will run into an error message like:

$ module load Python/2.7.11-intel-2016a
$ module load Python/3.5.1-intel-2016a 
Lmod has detected the following error:  Your site prevents the automatic swapping of modules with same name.
You must explicitly unload the loaded version of "Python" before you can load the new one. Use swap (or an unload
followed by a load) to do this:
   $ module swap Python  Python/3.5.1-intel-2016a
Alternatively, you can set the environment variable LMOD_DISABLE_SAME_NAME_AUTOSWAP to "no" to re-enable same name

Note that although Lmod suggests to unload or swap, we recommend to try and make sure you only load compatible modules together, and certainly not to define $LMOD_DISABLE_SAME_NAME_AUTOSWAP.

module purge does not unload the cluster module

Using module purge effectively resets your environment to a pristine working state, i.e. the cluster module stays loaded after the purge.
As such, it is no longer required to run module load cluster to restore your environment to a working state.

When you do run module load cluster when a cluster is already loaded, you will see the following warning message:

WARNING: 'module load cluster' has no effect when a 'cluster' module is already loaded.
For more information, please see

To change to another cluster, use module swap or ml swap; for example, to change your environment for the golett cluster, use ml swap cluster/golett.

If you are frequently see the warning above pop up, you may have something like this in your $VSC_HOME/.bashrc file:

. /etc/profile.d/
module load cluster

If you do, please remove that, and include this at the top of your ~/.bashrc file:

if [ -f /etc/bashrc ]; then
        . /etc/bashrc

modulecmd is not available anymore

The modulecmd command is not available anymore, and has been replacd by the lmod command.

This is only relevant for EasyBuild, which has be to configured to use Lmod as a modules tool, since by default it expects that modulecmd is readily available.
For example:


See the EasyBuild documentation for other ways of configuring EasyBuild to use Lmod.

You should not be using lmod directly in other circumstances, use either ml or module instead.

Questions or problems

In case of questions or problems, please do not hesitate to contact the HPC-UGent support team via