Issue with Docker on Digital Ocean plan. Would you like to attempt to recover space by cleaning docker images and containers in the system?(y/N)y docker: 'system' is not a docker command

[SMT]

I was getting the same error. The problem is fixed now. Pls visit the following topic.

Docker: 'system' is not a docker command. Unable to run ./launcher cleanup

Are you running a recent Docker, version 17.x ? You can add --skip-prereqs to ignore any checks too.