ubuntu 14.04 安装 docker 的命令为 apt-get install docker.io
注意：要启动docker需要输入：docker.io，不太简洁，为此建议设置一个链接：
sudo ln -s /usr/bin/docker.io /usr/bin/docker， 这样就可以直接输入docker来运行命令了。
消息来自于：http://weibo.com/genedna
ubuntu 14.04 安装 docker 的命令为 apt-get install docker.io
注意：要启动docker需要输入：docker.io，不太简洁，为此建议设置一个链接：
sudo ln -s /usr/bin/docker.io /usr/bin/docker， 这样就可以直接输入docker来运行命令了。
消息来自于：http://weibo.com/genedna
[sudo] password for appadmin:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package docker.io is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'docker.io' has no installation candidate
为什么安装手册上 ubuntu 14.04给个命令是 curl -sSL https://get.docker.com/ | sh？ 结果 安装失败了！
The following packages have unmet dependencies:
docker-engine : Depends: libsystemd-journal0 (>= 201) but it is not installable
Recommends: aufs-tools but it is not installable
Recommends: cgroupfs-mount but it is not installable or
cgroup-lite but it is not going to be installed
Recommends: git but it is not installable
Recommends: yubico-piv-tool (>= 1.1.0~) but it is not installable
E: Unable to correct problems, you have held broken packages.