提示的错误信息为：
Updates successful. Rebuilding in 5 seconds.
Building app
Device "docker0" does not exist.
Cannot connect to the docker daemon - verify it is running and you have access
[root@vps-8b254e4b discourse]# docker daemon - verify
docker: 'daemon' is not a docker command.
See 'docker --help'
问题和解决
这是因为 Docker 虽然已经安装了，但是还没有运行。
运行命令：
systemctl start docker
来启动 Docker