/etc/ssh/ssh_host_dsa_key

另外一个重新生成SSH主机密钥的方式是，使用ssh-keygen命令来手动生成。

1. $ sudo ssh-keygen -t rsa -f /etc/ssh/ssh_host_rsa_key
2. $ sudo ssh-keygen -t dsa -f /etc/ssh/ssh_host_dsa_key
3. $ sudo ssh-keygen -t ecdsa -f /etc/ssh/ssh_host_ecdsa_key

failed to start openssh server daemon code=exited status=255

打开配置文件 /etc/ssh/sshd_config 把默认的22端口改成高位端口后，用 systemctl restart sshd.service 重启sshd服务失败。
报错如下：

Job for sshd.service failed because the control process exited with error code. See “systemctl status sshd.service” and “journalctl -xe” for details.

systemctl status sshd.service 的输出如下：

● sshd.service – OpenSSH server daemon
Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled)
Active: activating (auto-restart) (Result: exit-code) since 四 2018-09-27 10:10:42 CST; 38s ago
Docs: man:sshd(8)
man:sshd_config(5)
Process: 47324 ExecStart=/usr/sbin/sshd -D $OPTIONS (code=exited, status=255)
Main PID: 47324 (code=exited, status=255)

9月 27 10:10:42 english systemd[1]: sshd.service: main process exited, code=exited, status=255/n/a
9月 27 10:10:42 english systemd[1]: Failed to start OpenSSH server daemon.
9月 27 10:10:42 english systemd[1]: Unit sshd.service entered failed state.
9月 27 10:10:42 english systemd[1]: sshd.service failed.

查看selinux是否关闭，执行getenforce

返回的是 Enforcing 。说明没有关闭
执行 setenforce 0 关闭selinux后，一切正常。