我是在Centos7里用 yum install docker安装的docker-1.8.2-7.el7，刚安装好时，是可以使用的，我还用 docker run -i -t ubuntu /bin/bash 下载了一个镜像下来，并且运行成功了。
后来重启了一次系统，就启动不了docker了，情况如下，请问怎么办？

[root@localhost /]# systemctl status docker.service -l
docker.service - Docker Application Container Engine
   Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled)
   Active: failed (Result: timeout) since Sat 2015-11-28 00:24:15 PST; 10min ago
     Docs: http://docs.docker.com
 Main PID: 13326
   CGroup: /system.slice/docker.service

Nov 28 00:23:15 localhost.localdomain docker[13326]: time="2015-11-28T00:23:15.965572881-08:00" level=info msg="Listening for HTTP on unix (/var/run/docker.sock)"
Nov 28 00:23:15 localhost.localdomain docker[13326]: time="2015-11-28T00:23:15.969942476-08:00" level=error msg="WARNING: No --storage-opt dm.thinpooldev specified, using loopback; this configuration is strongly discouraged for production use"
Nov 28 00:23:16 localhost.localdomain docker[13326]: time="2015-11-28T00:23:16.114079015-08:00" level=info msg="[graphdriver] using prior storage driver \"devicemapper\""
Nov 28 00:23:16 localhost.localdomain docker[13326]: time="2015-11-28T00:23:16.120977430-08:00" level=info msg="Option DefaultDriver: bridge"
Nov 28 00:23:16 localhost.localdomain docker[13326]: time="2015-11-28T00:23:16.121023378-08:00" level=info msg="Option DefaultNetwork: bridge"
Nov 28 00:23:16 localhost.localdomain docker[13326]: time="2015-11-28T00:23:16.134260533-08:00" level=warning msg="Running modprobe bridge nf_nat br_netfilter failed with message: modprobe: WARNING: Module br_netfilter not found.\n, error: exit status 1"
Nov 28 00:24:15 localhost.localdomain systemd[1]: docker.service operation timed out. Terminating.
Nov 28 00:24:15 localhost.localdomain systemd[1]: Failed to start Docker Application Container Engine.
Nov 28 00:24:15 localhost.localdomain systemd[1]: Unit docker.service entered failed state.

用docker -d命令的输出内容是：

[root@localhost /]# docker -d
Warning: '-d' is deprecated, it will be removed soon. See usage.
WARN[0000] please use 'docker daemon' instead.          
ERRO[0000] WARNING: No --storage-opt dm.thinpooldev specified, using loopback; this configuration is strongly discouraged for production use 
INFO[0000] Listening for HTTP on unix (/var/run/docker.sock) 
INFO[0000] [graphdriver] using prior storage driver "devicemapper" 
INFO[0000] Option DefaultDriver: bridge                 
INFO[0000] Option DefaultNetwork: bridge                
WARN[0000] Running modprobe bridge nf_nat br_netfilter failed with message: modprobe: WARNING: Module br_netfilter not found.
, error: exit status 1 
INFO[0000] Firewalld running: true                      
INFO[0000] Loading containers: start.                   
..
INFO[0000] Loading containers: done.                    
INFO[0000] Daemon has completed initialization          
INFO[0000] Docker daemon                                 commit=bb472f0/1.8.2 execdriver=native-0.2 graphdriver=devicemapper version=1.8.2