Disk space requirements and check

[WolfgangFahl]

Recently when running

docker run -it -p 8182:8182 janusgraph/janusgraph

on an Ubuntu 18.04 LTS machine i got th error message:

cp: error writing '/etc/opt/janusgraph/janusgraph.properties': No space left on device
cp: error writing '/etc/opt/janusgraph/gremlin-server.yaml': No space left on device
/usr/local/bin/docker-entrypoint.sh: line 59: echo: write error: No space left on device
/usr/local/bin/docker-entrypoint.sh: line 59: echo: write error: No space left on device
/usr/local/bin/docker-entrypoint.sh: line 59: echo: write error: No space left on device
/usr/local/bin/docker-entrypoint.sh: line 59: echo: write error: No space left on device
/usr/local/bin/docker-entrypoint.sh: line 59: echo: write error: No space left on device
/usr/local/bin/docker-entrypoint.sh: line 74: echo: write error: No space left on device
waiting for storage...

The reason was that the docker server environment was out of disk space.
It would be an improvement if there would be a hint on how much disk space is needed and a rudimentary check if a minimal amount of disk space is still available before proceesing.