the host may be down,or there may be a problem with the network connection. Sometimes such problems can also be caused by a misconfigured firewall.

遇到这样的问题可能有这几个情况:
1、在安装centos的时候没安装ssh
2、sshd_config与ssh_config配置问题
3、IP问题
4、防火墙问题

一、安装CentOS SSH
yum install ssh
二、启动SSH
service sshd start

三、进入系统文件etc/ssh/sshd_config文件配置

1.vi /etc/ssh/sshd_config 将PermitRootLogin的注释取消，或者将no改为yes。
2.service sshd restart
3.setup命令进入将防火墙关闭。

四、进入系统文件 /etc/ssh/ssh_config文件配置

在终端下面输入：vi /etc/ssh/ssh_config

去掉Port 22前面的#号

Port 22

五、配置IP

ifconfig eth0 192.168.121.11

This error indicates that SSH Secure Shell for Workstations cannot establish a connection to the remote host computer. There are several reasons that might cause this situation.

It may be that you have simply made a typing mistake, and there is an error in the name of the remote host computer. In this case you should also receive an error stating that the host is unknown.

Check that you have defined the correct port number for the connection. The port can be changed on the Connection page of the Settings dialog.

There may be problems with the configuration or physical setup of the network connection. Verify that other network connections are functioning.

This problem may also arise if your local system is protected by a firewall and the firewall has not been properly configured. If you suspect that this is the case, ask your local system administrator to reconfigure the firewall.

There may also be a temporary problem with the remote host computer. If this is the case, you should wait for a while and try to connect again later. Contact the administrator of the remote host computer for additional information.

这个错误表示工作站的SSH安全Shell不能建立到远程主机电脑的连接。有几个原因可能导致这种情况。

这可能是因为你只是做了一个打字错误，有一个错误在远程主机的计算机名称。在这种情况下，你也应该会收到一个错误，说明该主机是未知。

检查是否已定义为连接正确的端口号。可以改变端口上的连接“页面设置”对话框。

有可能是与网络连接的配置或物理安装的问题。确认网络连接是否正常。

如果您的本地系统防火墙和防火墙没有正确配置的保护，这个问题也可能出现。如果怀疑是这种情况，请问您的本地系统管理员重新配置防火墙。

也有可能是一个与远程主机上的临时问题。如果是这样的话，你应该等待一段时间，并尝试再次连接后。更多信息，远程主机的计算机管理员联系。

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