通过命令行查看docker服务是否已启动的方法如下：
查看docker的运行状态
systemctl status docker
输出如下：
[root@izr86o15kikb3az /]# systemctl status docker
● docker.service - Docker Application Container Engine
Loaded: loaded (/usr/lib/systemd/system/docker.service; enabled; vendor preset: disabled)
Active: active (running) since Thu 2019-10-24 16:05:01 CST; 29s ago
Docs: https://docs.docker.com
Main PID: 6485 (dockerd)
Tasks: 9
Memory: 111.3M
CGroup: /system.slice/docker.service
└─6485 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
Oct 24 16:05:01 izr86o15kikb3az dockerd[6485]: time="2019-10-24T16:05:01.127523857+08:00" level=info msg="ccResolverWrapper...e=grpc
Oct 24 16:05:01 izr86o15kikb3az dockerd[6485]: time="2019-10-24T16:05:01.127533900+08:00" level=info msg="ClientConn switch...e=grpc
Oct 24 16:05:01 izr86o15kikb3az dockerd[6485]: time="2019-10-24T16:05:01.218871071+08:00" level=info msg="[graphdriver] usi...rlay2"
Oct 24 16:05:01 izr86o15kikb3az dockerd[6485]: time="2019-10-24T16:05:01.233949835+08:00" level=info msg="Loading container...tart."
Oct 24 16:05:01 izr86o15kikb3az dockerd[6485]: time="2019-10-24T16:05:01.631635629+08:00" level=info msg="Default bridge (d...dress"
Oct 24 16:05:01 izr86o15kikb3az dockerd[6485]: time="2019-10-24T16:05:01.764941881+08:00" level=info msg="Loading containers: done."
Oct 24 16:05:01 izr86o15kikb3az dockerd[6485]: time="2019-10-24T16:05:01.775134383+08:00" level=info msg="Docker daemon" co...9.03.4
Oct 24 16:05:01 izr86o15kikb3az dockerd[6485]: time="2019-10-24T16:05:01.775613028+08:00" level=info msg="Daemon has comple...ation"
Oct 24 16:05:01 izr86o15kikb3az systemd[1]: Started Docker Application Container Engine.
Oct 24 16:05:01 izr86o15kikb3az dockerd[6485]: time="2019-10-24T16:05:01.815780672+08:00" level=info msg="API listen on /va....sock"
Hint: Some lines were ellipsized, use -l to show in full.扩展：
启动docker
systemctl start docker
关闭docker
systemctl stop docker
推荐教程：docker教程
