無法啟動 sshd 服務：無法啟動 openssh.service：未找到單元

在虛擬 rhel 7.4 上，我在嘗試啟動 sshd 服務時遇到了一個奇怪的錯誤。

無法啟動 openssh.service：未找到單元

事實上，在 sshd 上嘗試任何操作時，我都會遇到同樣的錯誤 - 啟用、狀態或停止

我確實嘗試重新啟動實例，但似乎沒有任何效果。

在您可以執行 OpenSSH 伺服器之前，您必須安裝它，但實際上您並沒有安裝它。要解決此問題，請安裝 OpenSSH 伺服器。

[root@localhost ~]# yum install openssh-server
Loaded plugins: product-id, search-disabled-repos, subscription-manager
Resolving Dependencies
--> Running transaction check
---> Package openssh-server.x86_64 0:7.4p1-16.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
Package           Arch      Version           Repository                  Size
================================================================================
Installing:
openssh-server    x86_64    7.4p1-16.el7      rhel-7-server-beta-rpms    458 k

Transaction Summary
================================================================================
Install  1 Package

Total download size: 458 k
Installed size: 971 k
Is this ok [y/d/N]: y
Downloading packages:
openssh-server-7.4p1-16.el7.x86_64.rpm                     | 458 kB   00:00     
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
 Installing : openssh-server-7.4p1-16.el7.x86_64                           1/1 
 Verifying  : openssh-server-7.4p1-16.el7.x86_64                           1/1 

Installed:
 openssh-server.x86_64 0:7.4p1-16.el7                                          

Complete!

該服務預設啟用，但如果您確實需要管理它，systemd 單元名稱為sshd.

[root@localhost ~]# systemctl start sshd
[root@localhost ~]# systemctl status sshd
● sshd.service - OpenSSH server daemon
  Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled)
  Active: active (running) since Sat 2018-03-24 17:37:23 EDT; 41s ago
    Docs: man:sshd(8)
          man:sshd_config(5)
Main PID: 1373 (sshd)
  CGroup: /system.slice/sshd.service
          └─1373 /usr/sbin/sshd -D

Mar 24 17:37:23 localhost.localdomain systemd[1]: Starting OpenSSH server dae...
Mar 24 17:37:23 localhost.localdomain sshd[1373]: Server listening on 0.0.0.0...
Mar 24 17:37:23 localhost.localdomain sshd[1373]: Server listening on :: port...
Mar 24 17:37:23 localhost.localdomain systemd[1]: Started OpenSSH server daemon.
Hint: Some lines were ellipsized, use -l to show in full.

引用自：https://serverfault.com/questions/904430