SecureCRT远程连接The remote system refused the connection问题

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今天用SecureCRT远程连接Linux（Centos 7）时，连不上，报错The remote system refused the connection.
于是就百度，首先查看sshd服务有没有启动

只有ssh-agent，于是去启动sshd
执行如下命令
cd /etc/init.d
systemctl restart sshd.service
没有成功，报错Job for sshd.service failed because the control process exited with error code. See "systemctl status sshd.service" and "journalctl -xe" for details.。

再使用这个命令journalctl -xe看错误信息，具体报错信息如下。

[root@localhost ssh]# systemctl restart sshd.service Job for sshd.service failed because the control process exited with error code. See "systemctl status sshd.service" and "journalctl -xe" for details. [root@localhost ssh]# journalctl -xe 12月 05 10:45:01 localhost.localdomain sshd[11508]: Permissions 0715 for '/etc/ssh/ssh_host_rsa_key' are too open. 12月 05 10:45:01 localhost.localdomain sshd[11508]: It is required that your private key files are NOT accessible by others. 12月 05 10:45:01 localhost.localdomain sshd[11508]: This private key will be ignored. 12月 05 10:45:01 localhost.localdomain sshd[11508]: key_load_private: bad permissions 12月 05 10:45:01 localhost.localdomain sshd[11508]: Could not load host key: /etc/ssh/ssh_host_rsa_key 12月 05 10:45:01 localhost.localdomain sshd[11508]: @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 12月 05 10:45:01 localhost.localdomain sshd[11508]: @ WARNING: UNPROTECTED PRIVATE KEY FILE! @ 12月 05 10:45:01 localhost.localdomain sshd[11508]: @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 12月 05 10:45:01 localhost.localdomain sshd[11508]: Permissions 0715 for '/etc/ssh/ssh_host_ecdsa_key' are too open. 12月 05 10:45:01 localhost.localdomain sshd[11508]: It is required that your private key files are NOT accessible by others. 12月 05 10:45:01 localhost.localdomain sshd[11508]: This private key will be ignored. 12月 05 10:45:01 localhost.localdomain sshd[11508]: key_load_private: bad permissions 12月 05 10:45:01 localhost.localdomain sshd[11508]: Could not load host key: /etc/ssh/ssh_host_ecdsa_key 12月 05 10:45:01 localhost.localdomain systemd[1]: sshd.service: main process exited, code=exited, status=1/FAILURE 12月 05 10:45:01 localhost.localdomain sshd[11508]: @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 12月 05 10:45:01 localhost.localdomain sshd[11508]: @ WARNING: UNPROTECTED PRIVATE KEY FILE! @ 12月 05 10:45:01 localhost.localdomain sshd[11508]: @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 12月 05 10:45:01 localhost.localdomain sshd[11508]: Permissions 0715 for '/etc/ssh/ssh_host_ed25519_key' are too open. 12月 05 10:45:01 localhost.localdomain sshd[11508]: It is required that your private key files are NOT accessible by others. 12月 05 10:45:01 localhost.localdomain sshd[11508]: This private key will be ignored. 12月 05 10:45:01 localhost.localdomain sshd[11508]: key_load_private: bad permissions 12月 05 10:45:01 localhost.localdomain sshd[11508]: Could not load host key: /etc/ssh/ssh_host_ed25519_key 12月 05 10:45:01 localhost.localdomain sshd[11508]: sshd: no hostkeys available -- exiting. 12月 05 10:45:01 localhost.localdomain systemd[1]: Failed to start OpenSSH server daemon. -- Subject: Unit sshd.service has failed -- Defined-By: systemd -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel -- -- Unit sshd.service has failed. -- -- The result is failed. 12月 05 10:45:01 localhost.localdomain systemd[1]: Unit sshd.service entered failed state. 12月 05 10:45:01 localhost.localdomain systemd[1]: sshd.service failed. 12月 05 10:45:01 localhost.localdomain polkitd[7760]: Unregistered Authentication Agent for unix-process:11502:197209 (system bus name :1.14 lines 1492-1525/1525 (END)

看到很多Permissions这个词，权限。
诸如；
Permissions 0715 for '/etc/ssh/ssh_host_rsa_key' are too open.
key_load_private: bad permissions
的错，这是一些密钥文件，也就是说没有权限访问这几个文件，可我用的root啊也没权限，奇怪了。

那么我们看看这三个文件现在的权限是什么。切到/etc/ssh下ll查看，这三个文件的权限是755，感觉没啥问题啊。继续百度吧。

搜了好久，有篇博文说执行这个命令
chmod 600 /etc/ssh/ssh_host_rsa_key /etc/ssh/ssh_host_ecdsa_key /etc/ssh/ssh_host_ed25519_key
也就是修改这个三个文件的权限为600