What is the conda package manager?
Before CIAO 4.12, CIAO was installed using ciao-install (or, for the brave, manually). We can now install CIAO using the conda package manager. This is a separate mechanism to installing CIAO, and it must not be combined with the ciao-install script!
The conda package manager lets users create "software environments" each of which contain a set of pacakges, and to switch between these environments. When in one environment, the packages installed in the other environments are not available, which lets you avoid problems of conflicting versions or packages.
For CIAO, it lets you install CIAO - both the tools and the Python packages such as Sherpa - in such a way that you can also install many other Scientific Python packages, such as AstroPy, SciPy, and Pandas.
Support for conda was first added in CIAO 4.12 and there to be some teeting problems. One known issue (as of December 2020) is that the cfitsio package provided by CIAO clashes with that from AstroConda, and we currently recommend that people do not try to install CIAO and AstroConda packages into the same conda environment.
CIAO is provided via a separate "channel", called https://cxc.cfa.harvard.edu/conda/ciao, and please contact the CXC Helpdesk if you have problems with, or questions about, the conda installation that our documentation does not address.