Migration FAQ

Why Migrate from CircleCI 1.0 to 2.0?

  • CircleCI 2.0 includes a significant rewrite of container utilization to run more jobs faster and to prevent available containers from sitting idle.
  • In 2.0, Jobs are broken into Steps. Compose these Steps within a Job at your discretion, giving you greater flexibility to run your build the way you want.
  • 2.0 Jobs support almost all public Docker images and custom images with your own dependencies specified.

Can I try CircleCI 2.0 while still using 1.0?

Yep! If you’re not ready to fully commit to 2.0, you can easily try it while still building on 1.0:

Create a new branch and add 2.0 configuration as described in the 2.0 Project Tutorial. When you push the branch with 2.0 configuration, your project will build on CircleCI 2.0. All other branches will continue building on CircleCI 1.0.

If you’d like to completely revert to 1.0 configuration, simply replace .circleci/config.yml with a 1.0 circle.yml file.

What operating systems does CircleCI 2.0 support?

  • Linux: CircleCI is flexible enough that you should be able to build most applications that run on Linux. These do not have to be web applications!

  • Android: Refer to Android Language Guide for instructions.

  • iOS: Building iOS apps is not yet supported on CircleCI 2.0. Please refer to our documentation for Getting Started with iOS on 1.0 until 2.0 support is available.

  • Windows: We do not yet support building and testing Windows applications.

Why is the 2.0 build not working?

In CircleCI 2.0, the first image listed in the .circleci/config.yml file is where the build runs. If you are trying to figure out why the new 2.0 build is not working it may be that the build runs on the first image specified in the list. The first image in the list is used for the primary container.

How do I migrate from Jenkins to CircleCI 2.0?

Start with the Hello World doc, then add steps: to duplicate your project exactly as it is in Jenkins, for example:

  - run: "Add any bash command you want here"
  - run:
      command: |
        echo "Arbitrary multi-line bash"
        echo "Probably copy-pasted from 'Execute Shell' on Jenkins"

Does CircleCI 2.0 run inference commands?

CircleCI 2.0 does not infer from your project and is moving toward a model of smart defaults with a configuration builder interface to assist with configuring all jobs in the config.yml file.

Can I use CircleCI 2.0 without creating base images?

Yes, you can use one of ours! For now, but this image may be deprecated in a future release.

The circleci/build-image:ubuntu-14.04-XL-922-9410082 image has the same content as the Ubuntu Trusty 14.04 image our web app uses. Just know that the image is fairly large (around 17.5 GB uncompressed), so it’s less ideal for local testing.

The image defaults to running actions as the ubuntu user and is designed to work with network services provided by Docker Compose.

Here’s a list of languages and tools included in the image.

How do Docker image names work? Where do they come from?

CircleCI 2.0 currently supports pulling (and pushing with Docker Engine) Docker images from Docker Hub. For official images, you can pull by simply specifying the name of the image and a tag:


For public images on Docker Hub, you can pull the image by prefixing the account or team username:


Can I use the latest tag when specifying image versions?

It is best practice not to use the latest tag for specifying image versions. For more context, refer to the Avoid Mutable Tags section of Writing Jobs with Steps.

How can I set the timezone in Docker images?

You can set the timezone in Docker images with the TZ environment variable. In your .circleci/config.yml, it would look like:

A sample .circleci/config.yml with a defined TZ variable would look like this:

version: 2
      - image: your/primary-image:version
      - image: mysql:5.7
           TZ: "/usr/share/zoneinfo/America/Los_Angeles"
    working_directory: ~/your-dir
      TZ: "/usr/share/zoneinfo/America/Los_Angeles"

In this example, the timezone is set for both the primary image and an additional mySQL image.

A full list of available timezone options is available on Wikipedia.


Can I use the API with Workflows?

Not yet, but we are working on that functionality.

Can I use the Auto-cancel feature with Workflows?

Not yet, but we are working on that functionality.

Can I use Workflows with CircleCI 1.0?

This feature only exists on CircleCI 2.0. In order to use Workflows, you must first be building on CircleCI 2.0.

Can I use Workflows with CircleCI Enterprise?

Workflows will soon be available in CircleCI Enterprise as part of our roll-out of or 2.0 system for Enterprise. Contact your account manager if you’d like to get on the list for early previews.

How many jobs can I run at one time?

The number of containers in your plan determines the number of jobs that may be run at one time. For example, if you have ten workflow jobs ready to run, but only five containers in your plan, only five jobs will run. Using Workflow config you can run multiple jobs at once or sequentially. You can fan-out (run multiple jobs at once) or fan-in (wait for all the jobs to complete before executing the dependent job).

Do you plan to add the ability to launch jobs on both Linux and Mac environments in the same workflow?

Yes, we are currently working on that functionality.

Is it possible to split the config.yml into different files?

Splitting config.yml into multiple files is not yet supported.

Can I build only the jobs that changed?


Can I build fork PR’s using Workflows?

We do not support fork PR’s yet.