Managing channels#

Conda channels are the locations where packages are stored. They serve as the base for hosting and managing packages. Conda packages are downloaded from remote channels, which are URLs to directories containing conda packages. The conda command searches a default set of channels and packages are automatically downloaded and updated from the default channel. Read more about conda channels and the various terms of service for their use.

Different channels can have the same package, so conda must handle these channel collisions.

There will be no channel collisions if you use only the defaults channel. There will also be no channel collisions if all of the channels you use only contain packages that do not exist in any of the other channels in your list. The way conda resolves these collisions matters only when you have multiple channels in your channel list that host the same package.

By default, conda prefers packages from a higher priority channel over any version from a lower priority channel. Therefore, you can put channels at the bottom of your channel list to provide additional packages that are not in the default channels. However, it is not recommended to mix channels in a single environment.

Conda collects all of the packages with the same name across all listed channels and processes them as follows:

Sorts packages from highest to lowest channel priority.
Sorts tied packages---packages with the same channel priority---from highest to lowest version number. For example, if channelA contains NumPy 1.12.0 and 1.13.1, NumPy 1.13.1 will be sorted higher.
Sorts still-tied packages---packages with the same channel priority and same version---from highest to lowest build number. For example, if channelA contains both NumPy 1.12.0 build 1 and build 2, build 2 is sorted first. Any packages in channelB would be sorted below those in channelA.
Installs the first package on the sorted list that satisfies the installation specifications.

Essentially, the order goes: channelA::numpy-1.13_1 > channelA::numpy-1.12.1_1 > channelA::numpy-1.12.1_0 > channelB::numpy-1.13_1

Note

If strict channel priority is turned on then channelB::numpy-1.13_1 isn't included in the list at all.

To make conda install the newest version of a package in any listed channel:

Add channel_priority: disabled to your .condarc file.

OR

Run the equivalent command:

conda config --set channel_priority disabled

Conda then sorts as follows:

Sorts the package list from highest to lowest version number.
Sorts tied packages from highest to lowest channel priority.
Sorts tied packages from highest to lowest build number.

Because build numbers from different channels are not comparable, build number still comes after channel priority.

The following command adds the channel "new_channel" to the top of the channel list, making it the highest priority:

conda config --add channels new_channel

Conda has an equivalent command:

conda config --prepend channels new_channel

Conda also has a command that adds the new channel to the bottom of the channel list, making it the lowest priority:

conda config --append channels new_channel

Channel configuration best practices#

To avoid channel conflicts and ensure environment reproducibility, we recommend the following approach:

Use a single channel as your default. Configure either defaults or conda-forge in your .condarc, but not both. Mixing these channels in your global configuration can result in mixed-channel environments with incompatible packages and can introduce hard-to-debug dependency conflicts.
Install from a specific channel with a single command when needed. If you need a package from a channel that isn't in your global config, you can target that channel with a single command using the options below. Note that mixing packages from different channels in this way might result in dependency issues if the channels are not fully compatible.
- The --channel flag installs the named package and all its dependencies from the specified channel. Add --override-channels to ignore any channels configured in your .condarc, using only the specified channel.
```
conda install --channel conda-forge --override-channels numpy
```
- The <channel>::<package> syntax installs only the named package from the specified channel, with dependencies resolved from your configured channels.
  
  Warning
  
  If the channel you specify and your configured channels are not fully compatible, this approach can result in binary incompatibilities that can cause hard-to-debug runtime errors, also known as "ABI incompatibility".
```
conda install conda-forge::numpy
```
Use strict channel priority only if you must mix channels. If your workflow requires both defaults and conda-forge in your channel list, set your channel priority to strict to reduce the risk of incompatible mixed-channel environments:
```
conda config --set channel_priority strict
```
Warning

Strict channel priority can make some environments unsatisfiable. It also prevents fallback to lower-priority channels when a package with the same name exists in a higher-priority channel. This includes channels that supply packages not available as conda packages.