ssh连接ubantu系统
描述：新安装的ubantu系统，ssh连接发现22端口拒绝，登陆服务器发现没有ssh
1.安装ssh服务
1 apt-get install openssh-server
报错：
1 # apt-get install opens-server 2 Reading package lists... Done 3 Building dependency tree... Done 4 Package aptitude is not available, but is referred to by another package. 5 This may mean that the package is missing, has been obsoleted, or 6 is only available from another source 7 E: Package has no installation candidate
2.解决
2.1 update && upgrade
1 apt-get update #如果提示失败，执行下一条命令 2 apt-get upgrade
update和upgrade区别：
- update的作用是从/etc/apt/source.list文件中定义的源中去同步包的索引文件，即运行这个命令其实并没有更新软件，而是相当于windows下面的检查更新，获取的是软件的状态。
- 而upgrade则是更据update命令同步好了的包的索引文件，去真正地更新软件。
此时重新安装安装，成功
1 apt-get install openssh-server
2.2 更换源
如果还是失败，可以尝试更换源：
1 vim /etc/apt/sources.list
参考：