remove reliance on privileged containers

[ccraddock]

docker2singularity must run in a privileged containers due to its use of /dev/loop0 (and possibly other reasons). This makes it impossible to run in circleCI, which explicitly runs its containers without privileges. It would be awesome if a workaround could be found to remove the need on privilege so that we can do singularity deployments from circleCI.

[chrisgorgo]

It might be worth trying if 2.2 does not rely on /dev/loop0 (especially when using tgz image format).

BTW Travis allows running docker with --privilege flag. I have successfully done singularity conversions with it. The main drawback is that Travis provides less disk space and have shorter timeout cutoffs than circle.

[vsoch]

@ccraddock is this still an issue for you? Note that you can pull a docker container directly to singularity, without sudo:

singularity pull docker://godlovedc/lolcow
Creating empty 495MiB image file: ./lolcow.img
Formatting image with ext3 file system
Image is done: ./lolcow.img
...

and for your own wellbeing, please run the image after you pull it :)

[vsoch]

I'm closing here, as Singularity can pull from docker without priviledges (and this issue is also very old!) @ccraddock please let us know if you need any further help!