刚安装的Mysql数据库，root用户systemctl status mysqld.service启动mysql时，一直报权限不足，排查了各种文件，放开了权限，还是一直报“Failed to get properties: Access denied”。

确定所有跟mysql相关的文件都属于mysql用户组，权限也放开的情况下启动时，仍报权限不足，如图：

[root@localhost data]# /bin/systemctl status mysqld.service
Failed to get properties: Access denied

最后发现是防火墙没关，关闭防火墙。

[root@localhost data]# setenforce 0

[root@localhost data]# /bin/systemctl status mysqld.service
● mysqld.service - LSB: start and stop MySQL
   Loaded: loaded (/etc/rc.d/init.d/mysqld; disabled; vendor preset: disabled)
   Active: failed (Result: start-limit) since 四 2020-07-02 15:03:57 CST; 1h 21min ago
     Docs: man:systemd-sysv-generator(8)
 Main PID: 115373 (code=exited, status=0/SUCCESS)

7月 02 15:03:57 localhost.localdomain systemd[1]: Failed to start MySQL Server.
7月 02 15:03:57 localhost.localdomain systemd[1]: Unit mysqld.service entered failed state.
7月 02 15:03:57 localhost.localdomain systemd[1]: mysqld.service failed.
7月 02 15:03:57 localhost.localdomain systemd[1]: mysqld.service holdoff time over, scheduling restart.
7月 02 15:03:57 localhost.localdomain systemd[1]: Stopped MySQL Server.
7月 02 15:03:57 localhost.localdomain systemd[1]: start request repeated too quickly for mysqld.service
7月 02 15:03:57 localhost.localdomain systemd[1]: Failed to start MySQL Server.
7月 02 15:03:57 localhost.localdomain systemd[1]: Unit mysqld.service entered failed state.
7月 02 15:03:57 localhost.localdomain systemd[1]: mysqld.service failed.
Warning: mysqld.service changed on disk. Run 'systemctl daemon-reload' to reload units.
[root@localhost data]# /bin/systemctl start mysqld.service
Warning: mysqld.service changed on disk. Run 'systemctl daemon-reload' to reload units.
Job for mysqld.service failed because the control process exited with error code. See "systemctl status mysqld.service" and "journalctl -xe" for details.

查看mysql状态，Mysql状态已经修改，需要重新加载配置选项，reload下。然后再次启动，并查看mysql状态。

[root@localhost data]# systemctl daemon-reload
[root@localhost data]# /bin/systemctl start mysqld.service
[root@localhost data]# /bin/systemctl status mysqld.service
● mysqld.service - MySQL Server
   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; disabled; vendor preset: disabled)
   Active: active (running) since 四 2020-07-02 16:26:36 CST; 5s ago
     Docs: man:mysqld(8)
           http://dev.mysql.com/doc/refman/en/using-systemd.html
  Process: 121919 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS)
  Process: 121863 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
 Main PID: 121921 (mysqld)
   CGroup: /system.slice/mysqld.service
           └─121921 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid --skip-grant-tables

7月 02 16:26:32 localhost.localdomain systemd[1]: Starting MySQL Server...
7月 02 16:26:36 localhost.localdomain systemd[1]: Started MySQL Server.

启动正常。

注：个人遇到的问题，并一定是所以这种情况都这样处理，更多这种问题还是权限不足造成，mysql启动项权限没有放开，无法启动。