在CentOS 7 上使用yum安装docker后，无法启动，报：
# service docker start
Redirecting to /bin/systemctl start docker.service
Job for docker.service failed because the control process exited with error code. See "systemctl status docker.service" and "journalctl -xe" for details.
通过# systemctl status docker.service 命令查看日志，有如下错误：（关键是高亮的那一句）
● docker.service - Docker Application Container Engine
Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)
Active: failed (Result: exit-code) since Thu 2018-03-22 11:01:13 EDT; 4s ago
Docs: http://docs.docker.com
Process: 2948 ExecStart=/usr/bin/dockerd-current --add-runtime docker-runc=/usr/libexec/docker/docker-runc-current --default-runtime=docker-runc --exec-opt native.cgroupdriver=systemd --userland-proxy-path=/usr/libexec/docker/docker-proxy-current --seccomp-profile=/etc/docker/seccomp.json $OPTIONS $DOCKER_STORAGE_OPTIONS $DOCKER_NETWORK_OPTIONS $ADD_REGISTRY $BLOCK_REGISTRY $INSECURE_REGISTRY $REGISTRIES (code=exited, status=1/FAILURE)
Main PID: 2948 (code=exited, status=1/FAILURE)
Mar 22 11:01:12 localhost.localdomain systemd[1]: Starting Docker Application Container Engine...
Mar 22 11:01:12 localhost.localdomain dockerd-current[2948]: time="2018-03-22T11:01:12.114129701-04:00" level=warning msg="could not change g...found"
Mar 22 11:01:12 localhost.localdomain dockerd-current[2948]: time="2018-03-22T11:01:12.118546683-04:00" level=info msg="libcontainerd: new co... 2953"
Mar 22 11:01:13 localhost.localdomain dockerd-current[2948]: Error starting daemon: SELinux is not supported with the overlay2 graph driver on this kernel. Either boot into a newer kernel or disable selinux in docker (--selinux-enabled=false)
Mar 22 11:01:13 localhost.localdomain systemd[1]: docker.service: main process exited, code=exited, status=1/FAILURE
Mar 22 11:01:13 localhost.localdomain systemd[1]: Failed to start Docker Application Container Engine.
Mar 22 11:01:13 localhost.localdomain systemd[1]: Unit docker.service entered failed state.
Mar 22 11:01:13 localhost.localdomain systemd[1]: docker.service failed.
Hint: Some lines were ellipsized, use -l to show in full.
Solutions:
根据加粗亮红色字体的错误日志可以看出，此linux的内核中的SELinux不支持 overlay2 graph driver ，解决办法有两种，要么启动一个新内核，要么就在docker里禁用selinux，--selinux-enabled=false
重新编辑docker配置文件：
# vim /etc/sysconfig/docker
# /etc/sysconfig/docker
# Modify these options if you want to change the way the docker daemon runs
OPTIONS='--selinux-enabled=false --log-driver=journald --signature-verification=false'
if [ -z "${DOCKER_CERT_PATH}" ]; then
DOCKER_CERT_PATH=/etc/docker
fi
如上改为紫色部分--selinux-enabled=false后保存，注意false后面有一个空格，改完之后重启docker，就可以正常使用了！