$sduo apt-get install openssh-server Reading package lists… Done Building dependency tree Reading state information… Done Package openssh-server 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 openssh-server has no installation candidate
执行:sudo apt-get update 也提示更新失败，或者无内容可更新。
解决方案：sudo vim /etc/network/interfaces修改ip，重启。
执行：sudo apt-get update
问题解决：
http://blog.sina.com.cn/s/blog_3e28c8a50101cax0.html