记录Docker in Docker 安装（CentOS7）

主机系统： CoreOS

iZwz9id7ajv83ikpa2hhn2Z ~ # cat /etc/os-release
NAME="Container Linux by CoreOS"
ID=coreos
VERSION=1590.0.0
VERSION_ID=1590.0.0
BUILD_ID=2017-11-08-0831
PRETTY_NAME="Container Linux by CoreOS 1590.0.0 (Ladybug)"
ANSI_COLOR="38;5;75"
HOME_URL="https://coreos.com/"
BUG_REPORT_URL="https://issues.coreos.com"
COREOS_BOARD="amd64-usr"复制代码

因为CoreOS没有包管理工具且是只读文件系统，不能方便的安装流行的Linux世界的软件，因此打算在CoreOS上在运行个CentOS7，而后在容器内部再部署一套Docker，一下是遇到的额问题的解决。

首先启动CentOS容器：
docker run -d --name=ctj --restart=always -e "container=docker" --privileged=true -p 2222:22 -p 2121:21 -v /sys/fs/cgroup:/sys/fs/cgroup -v /var/run/docker.sock:/var/run/docker.sock -v /root:/root -v /home:/home centos /usr/sbin/init

特别解释：

在CentOS7下若是默认不加init启动命令的话不会启动systemd进程的，报错docker Failed to get D-Bus connection ,参考资料： yhz61010.iteye.com/blog/235259…

进入容器后，执行下面命令：

yum makecache 
yum install -y epel-release

sed -e 's!^mirrorlist=!#mirrorlist=!g' -e 's!^#baseurl=!baseurl=!g'   -e 's!//download\.fedoraproject\.org/pub!//mirrors.ustc.edu.cn!g'  -e 's!http://mirrors\.ustc!https://mirrors.ustc!g'  -i /etc/yum.repos.d/epel.repo /etc/yum.repos.d/epel-testing.repo 

yum makecache
 yum install htop

yum install kubernetes.x86_64 -y复制代码

经过安装kubernetes工具包会自动安装Docker，

执行： docker version:
发现 daemon进程没启动：

/❯❯❯ docker version
Client:
 Version:         1.12.6
 API version:     1.24
 Package version: docker-1.12.6-61.git85d7426.el7.centos.x86_64
 Go version:      go1.8.3
 Git commit:      85d7426/1.12.6
 Built:           Tue Oct 24 15:40:21 2017
 OS/Arch:         linux/amd64
Cannot connect to the Docker daemon. Is the docker daemon running on this host?复制代码

而后执行： dockerd 又报如下错

INFO[0000] libcontainerd: new containerd process, pid: 624
WARN[0001] devmapper: Usage of loopback devices is strongly discouraged for production use. Please use `--storage-opt                    dm.thinpooldev` or use `man docker` to refer to dm.thinpooldev section.
WARN[0001] devmapper: XFS is not supported in your system. Either the kernel doesn't support it or mkfs.xfs is not in your PATH. Defaulting to ext4 filesystem INFO[0001] devmapper: Creating filesystem ext4 on device docker-0:46-2619452-base INFO[0001] devmapper: Error while creating filesystem ext4 on device docker-0:46-2619452-base: exec: "mkfs.ext4": exe cutable file not found in $PATH WARN[0001] devmapper: Failed to deactivatePool: Device is Busy FATA[0001] Error starting daemon: error initializing graphdriver: exec: "mkfs.ext4": executable file not found in $PA TH复制代码

这里有两个问题，一个是 没有安装 iptables，另外一个问题是 没有 mkfs.ext4 命令，
执行 yum install -y e4fsprogs iptables.x86_64
而后加载ext4模块， modprobe ext4 再执行 dockerd 发现能启动了

虽然有error但不影响使用，而后Ctrl^c 退出，使用 systemctl enable docker 容许自启动，systemctl start docker 启动Docker，

来个命令测试下：

如今 Docker内再启动Docker完成，开始发挥你的想象力吧!