Obtaining and Installing

A full installation of CASA including custom python environment is available as a Linux (.tar) or Mac (.dmg) file from our Downloads page (http://casa.nrao.edu/casa_obtaining.shtml)

The CASA 6.x series is also available as modular packages, giving users the flexibility to build CASA tools and tasks in their own Python environment. This includes the casatools, casatasks, and casampi modules, allowing for core data processing capabilities in parallel.

The CASA 5 and 6 versions in each release share the same C++ source code producing equivalent scientific output.  Both versions are intended to be nearly identical in functionality and output and thus share the same documentation found here. 

CASA 5 will be supported alongside CASA 6 for three release cycles (6.0/5.6, 6.1/5.7, and 6.2/5.8). CASA 5.8 will be the last CASA 5 release.


Full Installation of CASA 5 and 6

On Linux: 

  1. Download the .tar file and place it in a work directory (e.g. ~/casa)
  2. From a Linux terminal window, expand the casa-xyz.tar.gz (CASA 6.1)  or casa-release-xyz.tar.gz (CASA 5.7) file:

    $ tar -xvf casa-xyz.tar.xz

  3. Start CASA

    $ ./casa-xyz/bin/casa

  4. The one caveat is that CASA on Linux currently will not run if the Security-Enhanced Linux option of the linux operating system is set to enforcing. For the non-root install to work, SElinux must be set to disabled or permissive (in /etc/selinux/config) or you must run (as root):

    setsebool -P allow_execheap=1

     Otherwise, you will encounter errors like:

    error while loading shared libraries: /opt/casa/casa-20.0.5653-001/lib/liblapack.so.3.1.1: cannot restore segment prot after reloc: Permission denied

The non-root installation is thought to work on a wide variety of linux platforms. Check the list of operating systems here for the officially supported OSs. Other platforms may work, too, but we do not regularly test those.  An unofficial Knowledge Base article on installing CASA on Ubuntu or Debian can be found here.


On Macintosh:

  1. Download the .dmg disk image file
  2. Double click on the disk image file (if your browser does not automatically open it).
  3. Drag the CASA application to the Applications folder of your hard disk.
  4. Eject the CASA disk image.
  5. Double click the CASA application to run it for the first time. If the OS does not allow you to install apps from non-Apple sources, please Change the settings in "System Preferences-> Security & Privacy -> General" and "Allow applications downloaded from: Mac App store and identified developers".
  6. Optional: Create symbolic links to the CASA version and its executables (Administrator privileges are required), which will allow you to run casa, casaviewer, casaplotms, etc. from any terminal command line. To do so, run 


WARNING: By default, python 3.6 (and earlier versions of python 3) include the current working directory in the python path at startup. Any script in that directory with the same name as a standard python module or a CASA module will be detected and used by python instead of the code that is delivered with CASA. Protections have been included for files called "new.py" and "pickle.py", but other scripts may cause problems with the CASA startup. For example, do not include a file named runpy.py in the working directory.

WARNING: Several tasks have not yet been migrated into the CASA 6.1, but remain available in CASA 5.7. These are:

  • plotcal (GUI based)
  • interactive mode of flagdata (GUI based)
  • clean (soon to be deprecated)
  • deconvolve
  • apparentsens
  • caltabconvert
  • msuvbin
  • uvcontsub3
  • viewer (which is now imview)



Modular Installation of CASA 6

Pip wheels for casatools and casatasks are available as Python 3 modules from the public PyPI server casa-pip.nrao.edu. This allows simple installation and import in to standard Python 3.6 environments. The casatools wheel is necessarily a binary wheel so there may be some compatibility issues for some time as we work toward making wheels available for important Python configurations. Initially, we are targeting Python 3.6 as provided by RedHat for our wheel production, with RH6 and RH7 as official supported platforms. We have had some success on other Linux-based platforms as well, but we do not recommend the use of Conda until compatibility with Conda is better understood. The modular pip-wheel version is also not yet supported for Mac OSX, so for now we recommed Mac users to use the tarfile distribution.

The following prerequisites must be present on the host machine before installing CASA:

  1. Python 3.6
  2. libgfortran3 (yum or apt-get install)

Installation instructions are as follows (from a Linux terminal window):

$ python3.6 -m venv casa6

$ source casa6/bin/activate

(casa6) $ pip install --index-url https://casa-pip.nrao.edu/repository/pypi-casa-release/simple casatools

(casa6) $ pip install --index-url https://casa-pip.nrao.edu/repository/pypi-casa-release/simple casatasks

By default, pip will install the latest released version of the casatools and casatasks modules. An earlier released version of the pip wheels can be installed by adding the version number to the casatools and casatasks, e.g., casatools== Adding casatools== (i.e., without version number) to the pip install command will list all available version numbers in the terminal. 


Start CASA and sanity check:

(casa6) $ python

Python 3.6.9 (default, Nov 7 2019, 10:44:02)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import casatasks
>>> help(casatasks)

To exit the python venv, type deactivate from the terminal.  However, the rest of this documentation assumes the venv is active (to reactivate, type source casa6/bin/activate)

The use of python3 venv is a simple built-in method of containerizing the pip install such that multiple versions of CASA 6.x can be kept on a single machine in different environments. In addition, CASA is built and tested using standard (python 3.6) libraries which can be replicated with a fresh venv, keeping the libraries needed for CASA isolated from other libraries which may already be installed on your machine.

With the pip installation, CASA may be used in a standard Pythonic manner. For example, CASA tasks can be invoked using “import”, while CASA tools first need to be instantiated:

>>> import casatasks
>>> from casatasks import listobs
>>> listobs(vis='filename.ms')

>>> import casatools
>>> from casatools import ms
>>> MS=casatools.ms()
>>> MS.open('filename.ms')

Examples can be found in this Jupyter Notebook.


WARNING: The pip-wheel modules for CASAviewer and CASAplotms, as well as other GUIs, are unvalidated. They are included in the full tar-file distribution, and we recommend to use of the tar-file for these GUIs. We also recommend to use the tar-file for add-on ALMA tools/tasks, such as wvrgcal. Additional testing is being performed to ensure that the pip-wheels for the GUIs and add-on ALMA tools/tasks can be reliably offered as stand-alone modules in a subsequent CASA 6 release.

WARNING: The pip-wheel version is intended for manual data processing, and is not yet officially endorsed by ALMA or VLA. Currently, pipelines are included in -and tested only for- all-inclusive monolithic CASA distributions. 


Parallel Processing Installation

The casampi package provides the task-level MPI parallelization infrastructure of CASA.  The casatasks module detects when casampi is available and enables the parallel processing capabilities of CASA. Advanced users may also access the casampi package directly to build new or custom parallelization schemes.

The full installation of CASA includes the MPI package and no further action is necessary. 

For the modular installation of individual packages in to a standard python environment, ensure that openmpi is installed on the host machine (RHEL: yum install openmpi-devel, Ubuntu: apt-get install libopenmpi-dev), then perform the following commands(from the venv in a Linux terminal after the previous installation of casatools and casatasks):

NRAO systems only: contact the helpdesk to install casa-toolset-3, then run the command following command: export PATH=/opt/casa/03/bin:$PATH

(casa6) $ pip install wheel

(casa6) $ pip install --index-url https://casa-pip.nrao.edu/repository/pypi-casa-release/simple casampi

Sanity check (from Linux terminal):

(casa6) $ echo "from casampi.MPIEnvironment import MPIEnvironment; print('working?', MPIEnvironment.is_mpi_enabled)" > test.py

(casa6) $ mpirun -q -n 2 python test.py

observe two instances of "working? True"


Jupyter Notebooks and Google Colab

Jupyter notebooks are ideally suited for code tutorials, exploration, and collaborative development. Together with Google Colaboratory, which hosts Jupyter notebooks on free virtual hardware in the cloud, the door is opened to powerful new ways of developing and sharing software. CASA 6 casatools and casatasks modules are compatible with the Google Colab environment.  The CASA team is working towards making additional modules compatible in the future as well as introducing new Jupyter-based CASAguide tutorials.

An example of a Jupyter notebook that explains installation and usage of CASA 6 is available here.


CASA Tool Names

From the CASA 6 command line, the tools can be listed with 'toolhelp( )'  and the tasks can be listed with 'taskhelp( )'. In CASA 5, the tools had a certain name when imported from the casac module, and another name when used from the CASA 5 command line. In addition, one instance of each tool was pre-constructed and available for the user at the command line. The table below lists the tool naming in CASA 5 and CASA 6. In CASA 6, all of the CASA 5 names (e.g. imtool, im, etc.) are available for the user at the CASA 5 command line, but otherwise, the CASA 6/casac names are used by default. It is easy to import the CASA 6 tool with whatever name you like with:

>>> from casatools import imager as imtool

CASA 6/casac CASA 5/Class/Ctor CASA 5 instance
imager imtool im
calibrater cbtool


ms mstool


quanta qatool qa
table tbtool tb
agentflagger aftool af
measures metool me
image iatool ia
imagepol potool po
simulator smtool sm
componentlist cltool cl
coordsys cstool cs
regionmanager rgtool rg
spectralline sltool sl
vpmanager vptool vp
msmetadata msmdtool msmd
functional fntool fn
imagemetadata imdtool imd
atmosphere attool at
calanalysis catool


mstransformer mttool mt
singledishms sdmstool sdms