Singularity pull is the command that you would want to use to communicate with a container registry. The command does exactly as it says - there exists an image external to my host, and I want to pull it here. We currently support pull for both Docker and Singularity Hub images, and will review usage for both.

Singularity Hub

Singularity differs from Docker in that we serve entire images, as opposed to layers. This means that pulling a Singularity Hub means downloading the entire (compressed) container file, and then having it extract on your local machine. The basic command is the following:

singularity pull shub://vsoch/hello-world
Progress |===================================| 100.0% 
Done. Container is at: ./vsoch-hello-world-master.img

How do tags work?

On Singularity Hub, a tag coincide with a branch. So if you have a repo called vsoch/hello-world, by default the file called Singularity (your build recipe file) will be looked for in the base of the master branch. The command that we issued above would be equivalent to doing:

singularity pull shub://vsoch/hello-world:master

To enable other branches to build, they must be turned on in your collection (more details are available in the Singularity Hub docs). If you then put another Singularity file in a branch called development, you would pull it as follows:

singularity pull shub://vsoch/hello-world:development

The term latest in Singularity Hub will pull, across all of your branches, the most recent image. If development is more recent than master, it would be pulled, for example.

Image Names

As you can see, since we didn’t specify anything special, the default naming convention is to use the username, reponame, and the branch (tag). You have three options for changing this:

PULL OPTIONS:
    -n/--name   Specify a custom container name (first priority)
    -C/--commit Name container based on Github commit (second priority)
    -H/--hash   Name container based on file hash (second priority)

Custom Name

singularity pull --name meatballs.img shub://vsoch/hello-world
Progress |===================================| 100.0% 
Done. Container is at: ./meatballs.img

Name by commit

Each container build on Singularity Hub is associated with the Github commit of the repo that was used to build it. You can specify to name your container based on the commit with the --commit flag, if, for example, you want to match containers to their build files:

singularity pull --commit shub://vsoch/hello-world
Progress |===================================| 100.0% 
Done. Container is at: ./4187993b8b44cbfa51c7e38e6b527918fcdf0470.img

Name by hash

If you prefer the hash of the file itself, you can do that too.

singularity pull --hash shub://vsoch/hello-world
Progress |===================================| 100.0% 
Done. Container is at: ./4db5b0723cfd378e332fa4806dd79e31.img

Pull to different folder

For any of the above, if you want to specify a different folder for your image, you can define the variable SINGULARITY_PULLFOLDER. By default, we will first check if you have the SINGULARITY_CACHEDIR defined, and pull images there. If not, we look for SINGULARITY_PULLFOLDER. If neither of these are defined, the image is pulled to the present working directory, as we showed above. Here is an example of pulling to /tmp.

SINGULARITY_PULLFOLDER=/tmp
singularity pull shub://vsoch/hello-world
Progress |===================================| 100.0% 
Done. Container is at: /tmp/vsoch-hello-world-master.img

Pull by commit

You can also pull different versions of your container by using their commit id (version).

singularity pull shub://vsoch/hello-world@42e1f04ed80217895f8c960bdde6bef4d34fab59
Progress |===================================| 100.0%
Done. Container is at: ./vsoch-hello-world-master.img

In this example, the first build of this container will be pulled.

Docker

Docker pull is similar (on the surface) to a Singularity Hub pull, and we would do the following:

singularity pull docker://ubuntu
Initializing Singularity image subsystem
Opening image file: ubuntu.img
Creating 223MiB image
Binding image to loop
Creating file system within image
Image is done: ubuntu.img
Docker image path: index.docker.io/library/ubuntu:latest
Cache folder set to /home/vanessa/.singularity/docker
Importing: base Singularity environment
Importing: /home/vanessa/.singularity/docker/sha256:b6f892c0043b37bd1834a4a1b7d68fe6421c6acbc7e7e63a4527e1d379f92c1b.tar.gz
Importing: /home/vanessa/.singularity/docker/sha256:55010f332b047687e081a9639fac04918552c144bc2da4edb3422ce8efcc1fb1.tar.gz
Importing: /home/vanessa/.singularity/docker/sha256:2955fb827c947b782af190a759805d229cfebc75978dba2d01b4a59e6a333845.tar.gz
Importing: /home/vanessa/.singularity/docker/sha256:3deef3fcbd3072b45771bd0d192d4e5ff2b7310b99ea92bce062e01097953505.tar.gz
Importing: /home/vanessa/.singularity/docker/sha256:cf9722e506aada1109f5c00a9ba542a81c9e109606c01c81f5991b1f93de7b66.tar.gz
Importing: /home/vanessa/.singularity/metadata/sha256:fe44851d529f465f9aa107b32351c8a0a722fc0619a2a7c22b058084fac068a4.tar.gz
Done. Container is at: ubuntu.img

If you specify the tag, the image would be named accordingly (eg, ubuntu-latest.img). Did you notice that the output looks similar to if we did the following?

singularity create ubuntu.img
singularity import ubuntu.img docker://ubuntu

this is because the same logic is happening on the back end. Thus, the pull command with a docker uri also supports arguments --size and --name Here is how I would pull an ubuntu image, but make it bigger, and name it something else.

singularity pull --size 2000 --name jellybelly.img docker://ubuntu
Initializing Singularity image subsystem
Opening image file: jellybelly.img
Creating 2000MiB image
Binding image to loop
Creating file system within image
Image is done: jellybelly.img
Docker image path: index.docker.io/library/ubuntu:latest
Cache folder set to /home/vanessa/.singularity/docker
Importing: base Singularity environment
Importing: /home/vanessa/.singularity/docker/sha256:b6f892c0043b37bd1834a4a1b7d68fe6421c6acbc7e7e63a4527e1d379f92c1b.tar.gz
Importing: /home/vanessa/.singularity/docker/sha256:55010f332b047687e081a9639fac04918552c144bc2da4edb3422ce8efcc1fb1.tar.gz
Importing: /home/vanessa/.singularity/docker/sha256:2955fb827c947b782af190a759805d229cfebc75978dba2d01b4a59e6a333845.tar.gz
Importing: /home/vanessa/.singularity/docker/sha256:3deef3fcbd3072b45771bd0d192d4e5ff2b7310b99ea92bce062e01097953505.tar.gz
Importing: /home/vanessa/.singularity/docker/sha256:cf9722e506aada1109f5c00a9ba542a81c9e109606c01c81f5991b1f93de7b66.tar.gz
Importing: /home/vanessa/.singularity/metadata/sha256:fe44851d529f465f9aa107b32351c8a0a722fc0619a2a7c22b058084fac068a4.tar.gz
Done. Container is at: jellybelly.img