Repository is not signed in docker build

Question

I have the following Dockerfile that uses the latest Ubuntu image pulled from dockerhub:

FROM ubuntu:latest  
RUN apt-get update  && apt-get install -y           


        

Answer 1

Since Docker api v1.25+ ( released: Nov 18, 2019 )

Running command below fixed problem for me:

docker system prune --force

The --force flag stands for non interactive prune.

Answer 2

I tried again later and it worked.

From https://github.com/docker-library/php/issues/898#issuecomment-539234070:

That usually means the mirror is having issues (possibly partially out of date; i.e. not completely synced from other mirrors) and often clears itself up.