Check_MK Werk 5971: docker_node_disk_usage: Fix "No JSON object could be decoded" exception with older docker versions

ID: 5971 Title: docker_node_disk_usage: Fix "No JSON object could be decoded" exception with older docker versions Component: Checks & agents Level: 1 Class: Bug fix Version: 1.6.0i1 When the new agent is executed on a docker nodes that does not yet support the "docker system df" command with the "--format" parameter, then the check crashed. The agent has now been fixed to not transport the error message to the Check_MK server.