即使守护进程正在运行，Docker也无法连接到Docker守护进程

Docker工作得很好，然后突然开始说它无法连接到Docker Daemon。 在检查之后，我发现Docker Daemon实际上正在运行。 我也可以访问在Docker上运行的所有服务。

docker version （或任何与守护进程交谈的命令）给了我这个：

 username@docker-host:~$ docker version Client: Version: 17.03.1-ce API version: 1.27 Go version: go1.7.5 Git commit: c6d412e Built: Mon Mar 27 17:14:09 2017 OS/Arch: linux/amd64 Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? 

当我运行systemctl status docker ，它显示这个：

 username@docker-host:~$ systemctl status docker ● docker.service - Docker Application Container Engine Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled) Active: active (running) since <TIME_REDACTED>; 21min ago Docs: https://docs.docker.com Main PID: 890 (dockerd) Tasks: 168 Memory: 136.8M CPU: 5.974s CGroup: /system.slice/docker.service ├─ 890 /usr/bin/dockerd -H fd:// ├─ 982 docker-containerd -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --metrics-interval=0 --start-timeout 2m --state-dir /var/run/docker/libcontainerd/containerd --shim docker-c ├─1336 /usr/bin/docker-proxy -proto tcp -host-ip 0.0.0.0 -host-port 3276 -container-ip 172.19.0.3 -container-port 80 ├─1352 /usr/bin/docker-proxy -proto tcp -host-ip 0.0.0.0 -host-port 3307 -container-ip 172.19.0.4 -container-port 3306 ├─1364 docker-containerd-shim d73155f7c78f407cc5b46a6f1efd995114b08084e04bf367aaed78320e1e7b19 /var/run/docker/libcontainerd/d73155f7c78f407cc5b46a6f1efd995114b08084e04bf367aaed78320e1e7b19 docker ├─1374 docker-containerd-shim dfdf4377d1036078ad47984d670dee163e6c6c49f3305e69acb9b3b25bfffc2d /var/run/docker/libcontainerd/dfdf4377d1036078ad47984d670dee163e6c6c49f3305e69acb9b3b25bfffc2d docker ├─1387 docker-containerd-shim cd8f62c7b880ca3ed7ad8de84de2da05b3940c3370693e1c2eae50ddf77f324b /var/run/docker/libcontainerd/cd8f62c7b880ca3ed7ad8de84de2da05b3940c3370693e1c2eae50ddf77f324b docker ├─1400 docker-containerd-shim 53a66e76be1cfe6e88e372d18d7f4f4cbee4d157273e9a43077624b247dcf222 /var/run/docker/libcontainerd/53a66e76be1cfe6e88e372d18d7f4f4cbee4d157273e9a43077624b247dcf222 docker ├─1416 docker-containerd-shim 2f2662cacb28eb74a1da10249b9a7128648f8d47f8496a3e7791a0ddcd1c6c16 /var/run/docker/libcontainerd/2f2662cacb28eb74a1da10249b9a7128648f8d47f8496a3e7791a0ddcd1c6c16 docker ├─1636 /usr/bin/docker-proxy -proto tcp -host-ip 0.0.0.0 -host-port 8923 -container-ip 172.18.0.2 -container-port 8080 ├─1638 /usr/bin/docker-proxy -proto tcp -host-ip 0.0.0.0 -host-port 3306 -container-ip 172.17.0.2 -container-port 3306 ├─1663 /usr/bin/docker-proxy -proto tcp -host-ip 0.0.0.0 -host-port 8080 -container-ip 172.17.0.3 -container-port 8080 ├─1699 docker-containerd-shim d404befa2ee9522c4670836e786b2817fbe3c8636efdad4e04f624b264bb942c /var/run/docker/libcontainerd/d404befa2ee9522c4670836e786b2817fbe3c8636efdad4e04f624b264bb942c docker ├─1709 docker-containerd-shim 4ab25629ef1fd51111e901efb1c02b268a7fdbbda600cb39b7489a19789f0c20 /var/run/docker/libcontainerd/4ab25629ef1fd51111e901efb1c02b268a7fdbbda600cb39b7489a19789f0c20 docker └─1750 docker-containerd-shim 8eaef2b677c7907d156a0c98e6c028667cea902f31b65d73f8f45532cf2d0771 /var/run/docker/libcontainerd/8eaef2b677c7907d156a0c98e6c028667cea902f31b65d73f8f45532cf2d0771 docker <TIME_REDACTED> docker-host dockerd[890]: time="<TIME_REDACTED>" level=info msg="Firewalld running: false" <TIME_REDACTED> docker-host dockerd[890]: time="<TIME_REDACTED>" level=info msg="Firewalld running: false" <TIME_REDACTED> docker-host dockerd[890]: time="<TIME_REDACTED>" level=info msg="Firewalld running: false" <TIME_REDACTED> docker-host dockerd[890]: time="<TIME_REDACTED>" level=info msg="Firewalld running: false" <TIME_REDACTED> docker-host dockerd[890]: time="<TIME_REDACTED>" level=info msg="Firewalld running: false" <TIME_REDACTED> docker-host dockerd[890]: time="<TIME_REDACTED>" level=info msg="Loading containers: done." <TIME_REDACTED> docker-host dockerd[890]: time="<TIME_REDACTED>" level=info msg="Daemon has completed initialization" <TIME_REDACTED> docker-host dockerd[890]: time="<TIME_REDACTED>" level=info msg="Docker daemon" commit=c6d412e graphdriver=aufs version=17.03.1-ce <TIME_REDACTED> docker-host dockerd[890]: time="<TIME_REDACTED>" level=info msg="API listen on /var/run/docker.sock" <TIME_REDACTED> docker-host systemd[1]: Started Docker Application Container Engine. 

Docker守护进程肯定正在运行。 我试图把自己添加到docker组，作为sudo运行，然后重新启动。 没有一个帮助。

我正在Ubuntu 16.04服务器上运行docker docker-ce 17.03.1。