I want to install python 2.7 as a conda environment.
conda create -n python2 python=2.7 anaconda
Collecting package metadata (current_repodata.json): done
Solving environment: failed with repodata from current_repodata.json, will retry with next repodata source.
Collecting package metadata (repodata.json): done
Solving environment:
it's been running for the last 12 hours.
The anaconda package is a metapackage, meaning it tells conda to install other packages. It will install hundreds of packages, and it turns out this can stress conda. One typically does not need all of the packages in the anaconda metapackage -- it is often better to install only the packages one requires.
Try to create an environment without anaconda and instead specify only the packages you need.
conda create -n python2 python=2.7
If all that is actually needed is Python 2.7 environment (not full Anaconda distribution), then see @jakub's answer. However, Conda is perfectly capable of creating an Anaconda distribution environment with Python 2.7, and it should not take 12+ hours to solve.
The extremely long solve is almost certainly aggravated by your channel priorities. An "Anaconda" distribution should source most - if not all - of its software from the anaconda channel (part of defaults channel). However, most users eventually add conda-forge into their global channels and give it higher or equal priority (e.g., channel_priority: flexible). When this is the case, Conda will spend a bunch of time trying to satisfy the packages specified within the anaconda metapackage with the latest versions from conda-forge, and that's what tends to bog things down.
If you want a faster Anaconda install, then install only from Anaconda
conda create -n anaconda27 --override-channels -c defaults python=2.7 anaconda
Everything in the anaconda metapackage was originally intended to be sourced from the anaconda channel, so this shouldn't be so unreasonable.
Note that if you have conda-forge prioritized globally, this will be an issue every time you install in this environment (so remember to override channels).
Another option is Mamba. It's a faster (compiled) drop-in alternative to the conda CLI functionality. It seems to both solve faster and less prone to mutate unrelated packages when requesting changes - but that's just my anecdotal experience.
# install it in your *base* env (only need this once)
conda install -n base conda-forge::mamba
# use it like you would `conda`
mamba create -n python2 python=2.7 anaconda