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。
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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.dsudo wget http://www.hop5.in/yum/el6/hop5.repo
4、安装docker-io
[root@localhost ~]# yum install docker-ioLoaded plugins: fastestmirror, securityLoading mirror speeds from cached hostfile * base: centos.excellmedia.net * epel: kartolo.sby.datautama.net.id * extras: centos.excellmedia.net * updates: centos.excellmedia.netSetting up Install ProcessResolving 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 ResolutionDependencies Resolved============================================================================================ Package Arch Version Repository Size============================================================================================Installing: docker-io x86_64 0.5.3-4.el6 hop5 1.2 MInstalling 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 kTransaction Summary============================================================================================Install 4 Package(s)Total download size: 34 MInstalled size: 159 MIs this ok [y/N]: yDownloading 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_debugRunning Transaction TestTransaction Test SucceededRunning 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 -hUsage 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 -r3.10.5-3.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/create2013/08/21 07:48:41 POST /v1.4/containers/c6bc9e80097e/start2013/08/21 07:48:41 POST /v1.4/containers/c6bc9e80097e/attach?logs=1&stderr=1&stdout=1&stream=1hello 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.com2013/08/21 08:02:15 POST /v1.4/containers/create2013/08/21 08:02:15 POST /v1.4/containers/c40a1244f9bc/start2013/08/21 08:02:15 POST /v1.4/containers/c40a1244f9bc/attach?logs=1&stderr=1&stdout=1&stream=1PING 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 ms64 bytes from ir1.fp.vip.ne1.yahoo.com (98.138.253.109): icmp_seq=2 ttl=48 time=329 ms64 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 2304msrtt 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-php2013/08/21 07:53:05 POST /v1.4/containers/create2013/08/21 07:53:05 POST /v1.4/containers/6d9fef14bd1a/start2013/08/21 07:53:05 POST /v1.4/containers/6d9fef14bd1a/attach?logs=1&stderr=1&stdout=1&stream=1Loaded plugins: fastestmirrorError: Cannot retrieve repository metadata (repomd.xml) for repository: base. Please verify its path and try againCould not retrieve mirrorlist http://mirrorlist.centos.org/?release=6&arch=x86_64&repo=os error was14: 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 dockeriptables -t nat -Fifconfig docker0 downbrctl delbr docker0docker -d
感谢sciurus在创建kernel-ml-aufs的相关文件时付出的辛勤工作。
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