Docker.io 是轻量级的“容器引擎+映像仓库”，在LXC（linux轻量级容器）的基础上构建，可以运行任何应用程序。

docker.io的核心层由以下几个部分组成:

1、可执行程序，“/usr/bin/docker”

2、docker.io网站上有一系列创建好的操作系统和应用程序映像

3、AUFS（另一个统一文件系统）来实现文件系统的快照，文件变化，控制只读或读写的需求。

4、LXC（Linux轻量级容器）

5、Cgroups（各种资源和命名空间的管理）

在本文写作的时候，最新版本是0.5.3，但目前开发很活跃，一些功能和特性可能在新版本中会发生变化。

按下面的步骤安装docker.io：

0、安装centos6.x

1、因为selinux和LXC有冲突，所以需要禁用

[root@localhost ~]# cat /etc/selinux/config 
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#       enforcing - SELinux security policy is enforced.
#       permissive - SELinux prints warnings instead of enforcing.
#       disabled - SELinux is fully disabled.
SELINUX=disabled
# SELINUXTYPE= type of policy in use. Possible values are:
#       targeted - Only targeted network daemons are protected.
#       strict - Full SELinux protection.
SELINUXTYPE=targeted

2、配置Fedora EPEL 源

sudo yum install http://ftp.riken.jp/Linux/fedora/epel/6/i386/epel-release-6-8.noarch.rpm

3、配置hop5.in源

cd /etc/yum.repos.d
sudo wget http://www.hop5.in/yum/el6/hop5.repo

4、安装docker-io

[root@localhost ~]# yum install docker-io
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
 * base: centos.excellmedia.net
 * epel: kartolo.sby.datautama.net.id
 * extras: centos.excellmedia.net
 * updates: centos.excellmedia.net
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package docker-io.x86_64 0:0.5.3-4.el6 will be installed
--> Processing Dependency: lxc >= 0.8.0 for package: docker-io-0.5.3-4.el6.x86_64
--> Processing Dependency: kernel-ml-aufs >= 3.10.5 for package: docker-io-0.5.3-4.el6.x86_64
--> Running transaction check
---> Package kernel-ml-aufs.x86_64 0:3.10.5-3.el6 will be installed
---> Package lxc.x86_64 0:0.8.0-3.el6 will be installed
--> Processing Dependency: liblxc.so.0()(64bit) for package: lxc-0.8.0-3.el6.x86_64
--> Running transaction check
---> Package lxc-libs.x86_64 0:0.8.0-3.el6 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

============================================================================================
 Package                   Arch              Version                  Repository       Size
============================================================================================
Installing:
 docker-io                 x86_64            0.5.3-4.el6              hop5            1.2 M
Installing for dependencies:
 kernel-ml-aufs            x86_64            3.10.5-3.el6             hop5             33 M
 lxc                       x86_64            0.8.0-3.el6              hop5             81 k
 lxc-libs                  x86_64            0.8.0-3.el6              hop5             75 k

Transaction Summary
============================================================================================
Install       4 Package(s)

Total download size: 34 M
Installed size: 159 M
Is this ok [y/N]: y
Downloading Packages:
(1/4): docker-io-0.5.3-4.el6.x86_64.rpm                              | 1.2 MB     00:03     
(2/4): kernel-ml-aufs-3.10.5-3.el6.x86_64.rpm                        |  33 MB     00:33     
(3/4): lxc-0.8.0-3.el6.x86_64.rpm                                    |  81 kB     00:00     
(4/4): lxc-libs-0.8.0-3.el6.x86_64.rpm                               |  75 kB     00:00     
--------------------------------------------------------------------------------------------
Total                                                       896 kB/s |  34 MB     00:39     
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing : lxc-libs-0.8.0-3.el6.x86_64                                              1/4 
  Installing : lxc-0.8.0-3.el6.x86_64                                                   2/4 
  Installing : kernel-ml-aufs-3.10.5-3.el6.x86_64                                       3/4 
  Installing : docker-io-0.5.3-4.el6.x86_64                                             4/4 
  Verifying  : kernel-ml-aufs-3.10.5-3.el6.x86_64                                       1/4 
  Verifying  : lxc-0.8.0-3.el6.x86_64                                                   2/4 
  Verifying  : lxc-libs-0.8.0-3.el6.x86_64                                              3/4 
  Verifying  : docker-io-0.5.3-4.el6.x86_64                                             4/4 

Installed:
  docker-io.x86_64 0:0.5.3-4.el6                                                            

Dependency Installed:
  kernel-ml-aufs.x86_64 0:3.10.5-3.el6               lxc.x86_64 0:0.8.0-3.el6              
  lxc-libs.x86_64 0:0.8.0-3.el6                     

Complete!
[root@localhost ~]#

5、检查安装情况

[root@localhost ~]# docker -h
Usage of docker:
  -D=false: Debug mode
  -H=[unix:///var/run/docker.sock]: tcp://host:port to bind/connect to or unix://path/to/socket to use
  -api-enable-cors=false: Enable CORS requests in the remote api.
  -b="": Attach containers to a pre-existing network bridge. Use 'none' to disable container networking
  -d=false: Daemon mode
  -dns="": Set custom dns servers
  -g="/var/lib/docker": Path to graph storage base dir.
  -p="/var/run/docker.pid": File containing process PID
  -r=false: Restart previously running containers

6、要想docker正常运行还需要在/etc/fstab里增加cgroup文件系统

[root@localhost ~]# echo "none                    /sys/fs/cgroup          cgroup  defaults        0 0" >> /etc/fstab

[root@localhost ~]# mount /sys/fs/cgroup

只有重新启动才能挂载/sys/fs/cgroup（因为当前运行的内核不支持cgroup），所以上面挂载的命令也可以不执行，但系统需要重新启动。

7、重启系统，选择“3.10.5-3.el6.x86_64”内核

8、系统启动后，确认当前运行的内核

[root@localhost ~]# uname -r
3.10.5-3.el6.x86_64

[root@localhost ~]# grep aufs /proc/filesystems 
nodev   aufs

9、以守护模式运行docker.io（在一个新的终端里）

[root@localhost ~]# docker -d 
2013/08/21 07:47:07 WARNING: Your kernel does not support cgroup swap limit.
2013/08/21 07:47:07 Listening for HTTP on /var/run/docker.sock (unix)

10、在centos6.4容器里输出hello world

[root@localhost ~]# docker run centos:6.4 echo "hello world"
2013/08/21 07:48:41 POST /v1.4/containers/create
2013/08/21 07:48:41 POST /v1.4/containers/c6bc9e80097e/start
2013/08/21 07:48:41 POST /v1.4/containers/c6bc9e80097e/attach?logs=1&stderr=1&stdout=1&stream=1
hello world

11、从容器里测试ping

[root@localhost ~]# docker -dns '8.8.8.8' run centos:6.4 ping -c 3 yahoo.com
2013/08/21 08:02:15 POST /v1.4/containers/create
2013/08/21 08:02:15 POST /v1.4/containers/c40a1244f9bc/start
2013/08/21 08:02:15 POST /v1.4/containers/c40a1244f9bc/attach?logs=1&stderr=1&stdout=1&stream=1
PING yahoo.com (98.138.253.109) 56(84) bytes of data.
64 bytes from ir1.fp.vip.ne1.yahoo.com (98.138.253.109): icmp_seq=1 ttl=48 time=323 ms
64 bytes from ir1.fp.vip.ne1.yahoo.com (98.138.253.109): icmp_seq=2 ttl=48 time=329 ms
64 bytes from ir1.fp.vip.ne1.yahoo.com (98.138.253.109): icmp_seq=3 ttl=49 time=302 ms

--- yahoo.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2304ms
rtt min/avg/max/mdev = 302.032/318.318/329.656/11.807 ms

常见错误：

"DNS/Networking Errors inside the docker"

[root@localhost ~]# docker -dns="8.8.8.8" run centos:6.4 yum install hiphop-php
2013/08/21 07:53:05 POST /v1.4/containers/create
2013/08/21 07:53:05 POST /v1.4/containers/6d9fef14bd1a/start
2013/08/21 07:53:05 POST /v1.4/containers/6d9fef14bd1a/attach?logs=1&stderr=1&stdout=1&stream=1
Loaded plugins: fastestmirror
Error: Cannot retrieve repository metadata (repomd.xml) for repository: base. Please verify its path and try again
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=6&arch=x86_64&repo=os error was
14: PYCURL ERROR 6 - "Couldn't resolve host 'mirrorlist.centos.org'"

可以执行下面的命令来重置docker的运行环境，从而解决上述问题。

pkill docker
iptables -t nat -F
ifconfig docker0 down
brctl delbr docker0
docker -d

感谢sciurus在创建kernel-ml-aufs的相关文件时付出的辛勤工作。

http://www.oschina.net/translate/nstalling-dockerio-on-centos-64-64-bit?cmp