有的时候别人可能登录不上你的电脑或者无法登录到服务器，最可能出现的问题就是ssh出现了问题。
[root@zong_pc zong]# /etc/init.d/sshd status //在linux下查看ssh的状态
openssh-daemon (pid 2309) 正在运行...
[root@zong_pc zong]#
[root@zong_pc zong]# /etc/init.d/sshd start //若是ssh处于关闭状态，则可以手动开启服务
[root@zong_pc /]# /etc/init.d/sshd close
用法： /etc/init.d/sshd {start|stop|restart|reload|force-reload|condrestart|try-restart|status}
[root@zong_pc /]# /etc/init.d/sshd stop
停止 sshd： [确定]
[root@zong_pc /]# /etc/init.d/sshd status
openssh-daemon 已停
[root@zong_pc /]# /etc/init.d/sshd start
正在启动 sshd： [确定]
[root@zong_pc /]# /etc/init.d/sshd stop
停止 sshd： [确定]
[root@zong_pc /]#
可以直接按以下方法操作：
vim /etc/ssh/sshd_config
截的部分代码：
39 # Authentication:
40
41 #LoginGraceTime 2m
42 PermitRootLogin no
43 #StrictModes yes
44 #MaxAuthTries 6
45 #MaxSessions 10
46
若PermitRootLogin后的参数为no，则会出现这样的提示：
[root@zong_pc ssh]# ssh 192.168.40.223
ssh: connect to host 192.168.40.223 port 22: No route to host
具体步骤总结：：
因此，只需将其后的参数改为yes就可以了。PermitRootLogin yes
修改完成后，
先打开ssh：/etc/init.d/sshd start
然后ssh需要重新启动 /etc/init.d/sshd restart
当然，也可能出现下面这种情况：
[root@localhost zhangna]# ssh 192.168.40.22
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
8b:d9:17:7d:97:d5:19:02:a1:27:9f:cc:b8:31:20:34.
Please contact your system administrator.
Add correct host key in /root/.ssh/known_hosts to get rid of this message.
Offending key in /root/.ssh/known_hosts:1
RSA host key for 192.168.40.22 has changed and you have requested strict checking.
Host key verification failed.
[root@localhost zhangna]# rm -rf /root/.ssh/known_hosts
[root@localhost zhangna]# ssh 192.168.40.22
The authenticity of host '192.168.40.22 (192.168.40.22)' can't be established.
RSA key fingerprint is 8b:d9:17:7d:97:d5:19:02:a1:27:9f:cc:b8:31:20:34.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.40.22' (RSA) to the list of known hosts.
Address 192.168.40.22 maps to localhost, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
root@192.168.40.22's password:
Last login: Wed Jan 13 10:46:24 2016 from 192.168.40.222
[root@localhost ~]#