screen的使用
screen是一个用于管理远程会话的程序，在很多时候会遇到这种情况，我们通过ssh登陆到某台服务器并同时启用多个需要占用当前终端的会话，这时候就要开多个ssh连接，多个窗口切来切去很是不便。然而我们使用screen的话就不必这个麻烦了，我们只要通过命令crtl+a c就可以开一个新的终端，crtl+a a切到最近使用的终端，ctrl+a [0-9]切到对应的终端上去。
screen还有一个很酷的功能就是在你离开的时候仍可保留会话的状况，当你重新登陆时恢复原会话。
启用screen
[sunchao@mail2 ~]$ screen
恢复会话
screen -R
列出可用的会话
[sunchao@mail2 ~]$ screen -ls
There is a screen on:
763.pts-31.mail2 (Attached)
1 Socket in /tmp/uscreens/S-sunchao.
可以使用-r恢复指定会话，发现有两个会话死掉了：
[sunchao@mail2 status]$ screen -r
There are screens on:
19875.pts-7.mail2 (Dead ???)
3964.pts-15.mail2 (Dead ???)
Remove dead screens with 'screen -wipe'.
There is no screen to be resumed.
删除死掉的会话：
[sunchao@mail2 status]$ screen -wipe 3964.pts-15.mail2
There is a screen on:
3964.pts-15.mail2 (Removed)
1 socket wiped out.
No Sockets found in /tmp/uscreens/S-sunchao.
[sunchao@mail2 status]$ screen -r
There is no screen to be resumed.
一个screen会话
[sunchao@mail2 ~]$ screen -r
There is a screen on:
12381.pts-6.mail2 (Attached)
There is no screen to be resumed.
[sunchao@mail2 ~]$ ps aux |grep screen
sunchao 6416 0.0 0.0 2708 848 pts/2 S+ 21:11 0:00 screen -r
sunchao 10426 0.0 0.0 2060 516 pts/5 S+ 21:15 0:00 grep screen
[sunchao@mail2 ~]$ kill -9 6416
[sunchao@mail2 ~]$ screen -r