错误信息：
Failed to restart docker.service: Unit docker.socket failed to load: No such file or directory
解决办法：(CentOS 7)
vi /lib/systemd/system/docker.socket
[Unit]Description=Docker Socket for the APIPartOf=docker.service[Socket]ListenStream=/var/run/docker.sockSocketMode=0660SocketUser=rootSocketGroup=docker[Install]WantedBy=sockets.target
接着运行命令：
systemctl unmask docker.servicesystemctl unmask docker.socketservice docker restart
即可。
CentOS 7:
错误信息：
msg="no sockets found via socket activation: make sure the service was started by systemd"
解决办法：
vi /lib/systemd/system/docker.service
[Unit]Description=Docker Application Container EngineDocumentation=https://docs.docker.comAfter=network.target[Service]Type=notify# the default is not to use systemd for cgroups because the delegate issues still# exists and systemd currently does not support the cgroup feature set required# for containers run by docker#ExecStart=/usr/bin/dockerd#ExecStart=/usr/bin/docker daemon --tlsverify --tlscacert=/root/openssl/ca.pem --tlscert=/root/openssl/server-cert.pem --tlskey=/root/openssl/server-key.pem --registry-mirror=http://3cda3ca9.m.daocloud.io -H tcp://0.0.0.0:2376#ExecStart=/usr/bin/docker daemon --registry-mirror=http://3cda3ca9.m.daocloud.io -H fd:// -H tcp://0.0.0.0:2375#ExecStart=/usr/bin/dockerd --registry-mirror=http://3cda3ca9.m.daocloud.ioExecStart=/usr/bin/dockerd --registry-mirror=http://3cda3ca9.m.daocloud.io -H unix:///var/run/docker.sock -H tcp://0.0.0.0:2375ExecReload=/bin/kill -s HUP $MAINPID# Having non-zero Limit*s causes performance problems due to accounting overhead# in the kernel. We recommend using cgroups to do container-local accounting.LimitNOFILE=infinityLimitNPROC=infinityLimitCORE=infinity# Uncomment TasksMax if your systemd version supports it.# Only systemd 226 and above support this version.#TasksMax=infinityTimeoutStartSec=0# set delegate yes so that systemd does not reset the cgroups of docker containersDelegate=yes# kill only the docker process, not all processes in the cgroupKillMode=process[Install]WantedBy=multi-user.target
systemctl daemon-reloadservice docker restart