启动mysql时报错Failed to start mysqld.service: Unit not found-CFANZ编程社区

问题描述：启动mysql时报错Failed to start mysqld.service: Unit not found，如下所示：
数据库：mysql 5.7.42
系统：rhel 7.3
1、问题重现
--mysql安装过程
[root@leo-mysql-master ~]# yum localinstall https://dev.mysql.com/get/mysql57-community-release-el7-8.noarch.rpm
[root@leo-mysql-master ~]# yum install -y mysql-community-server
Transaction Summary
==============================================================================================================================================
Install  3 Packages (+2 Dependent packages)

Total download size: 211 M
Downloading packages:
warning: /var/cache/yum/x86_64/7Server/mysql57-community/packages/mysql-community-common-5.7.42-1.el7.x86_64.rpm: Header V4 RSA/SHA256 Signature, key ID 3a79bd29: NOKEY
Public key for mysql-community-common-5.7.42-1.el7.x86_64.rpm is not installed
(1/5): mysql-community-common-5.7.42-1.el7.x86_64.rpm                                                                  | 311 kB  00:00:00     
(2/5): mysql-community-libs-5.7.42-1.el7.x86_64.rpm                                                                    | 2.6 MB  00:00:01     
(3/5): mysql-community-libs-compat-5.7.42-1.el7.x86_64.rpm                                                             | 1.2 MB  00:00:00     
(4/5): mysql-community-client-5.7.42-1.el7.x86_64.rpm                                                                  |  28 MB  00:00:05     
(5/5): mysql-community-server-5.7.42-1.el7.x86_64.rpm                                                                                                                                                             | 179 MB  00:00:25     
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total                                                                                                                                                                                                    7.6 MB/s | 211 MB  00:00:27     
Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql
Importing GPG key 0x5072E1F5:
 Userid     : "MySQL Release Engineering <mysql-build@oss.oracle.com>"
 Fingerprint: a4a9 4068 76fc bd3c 4567 70c8 8c71 8d3b 5072 e1f5
 Package    : mysql57-community-release-el7-8.noarch (installed)
 From       : /etc/pki/rpm-gpg/RPM-GPG-KEY-mysql


Public key for mysql-community-common-5.7.42-1.el7.x86_64.rpm is not installed


 Failing package is: mysql-community-common-5.7.42-1.el7.x86_64
 GPG Keys are configured as: file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql

--此后启动报错如下
[root@leo-mysql-master ~]# systemctl start mysqld.service
Failed to start mysqld.service: Unit not found.

2、异常原因
在使用yum -y install mysql-community-server命令安装mysql时并未安装成功(原因：密钥已安装但不适用此软件包),
安装时报错"Public key for mysql-community-common-5.7.42-1.el7.x86_64.rpm is not installed",
此后使用"systemctl start mysqld.service"命令启动MySQL报"Failed to start mysqld.service: Unit not found."错误

3、解决方案
--在安装mysql之前导入2022年密匙.
[root@leo-mysql-master ~]# rpm --import https://repo.mysql.com/RPM-GPG-KEY-mysql-2022
--重新安装mysql
[root@leo-mysql-master ~]# yum install -y mysql-community-server     
--启动mysql进程
[root@leo-mysql-master ~]# systemctl start mysqld.service
[root@leo-mysql-master ~]# systemctl status mysqld.service
● mysqld.service - MySQL Server
   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
   Active: active (running) since Sat 2023-07-01 11:02:18 CST; 10s ago
     Docs: man:mysqld(8)
           http://dev.mysql.com/doc/refman/en/using-systemd.html
  Process: 10944 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS)
  Process: 10881 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
 Main PID: 10947 (mysqld)
   CGroup: /system.slice/mysqld.service
           └─10947 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid

Jul 01 11:02:06 leo-mysql-master systemd[1]: Starting MySQL Server...
Jul 01 11:02:18 leo-mysql-master systemd[1]: Started MySQL Server.

说明：如上所示，成功启动mysql进程.

参考文档：https://blog.csdn.net/qq_43788878/article/details/128233209