Conda channels

The conda-build options -c CHANNEL or --channel CHANNEL configure additional channels to search for packages.

These are URLs searched in the order they are given (including file:// for local directories).

Then, the defaults or channels from .condarc are searched (unless --override-channels is given).

You can use 'defaults' to get the default packages for conda, and 'system' to get the system packages, which also takes .condarc into account.

You can also use any name and the .condarc channel_alias value will be prepended. The default channel_alias is http://conda.anaconda.org/.

The option --override-channels tells to not search default or .condarc channels. Requires the --channel or -c option.

Identical channel and package name problem

If the channel and package name are identical, it's possible to encounter a build problem if the short channel name is used.

Let's say your Anaconda.org username or an organization name is example. And suppose you created a package example, whose files' layout is similar to:

setup.py
conda/meta.yaml
example/

If your build depends on some other packages inside your channel, you will need to add -c example, however, the following code:

conda-build ./conda/ -c example

will fail with the following error message (the path will be different):

requests.exceptions.HTTPError: 404 Client Error: None for url:
file:///path/to/your/local/example/noarch/repodata.json
[...]
The remote server could not find the noarch directory for the requested channel with
url: file:///path/to/your/local/example/noarch/repodata.json
[...]
As of conda 4.3, a valid channel must contain a `noarch/repodata.json` and
associated `noarch/repodata.json.bz2` file, even if `noarch/repodata.json`
is empty. please request that the channel administrator create
`noarch/repodata.json` and associated `noarch/repodata.json.bz2` files.

This happens because conda-build will consider the directory ./example/ in your project as a channel. This is by design due to conda's CI servers, where the build path can be long, complicated, and not predictable prior to build.

There are several ways to resolve this issue.

1. Use the url of the desired channel:

   conda-build ./conda/ -c https://conda.anaconda.org/example/
   

2. Run the build from inside the conda recipe directory:

   cd conda
   conda-build . -c example
   

3. Use the label specification workaround:

conda-build ./conda/ -c example/label/main

which technically is the same as -c example, since main is the default label, but now it won't by mistake find a channel example/label/main on the local filesystem.