MySQL5.7 数据库启动失败解决方案

重启服务器后，mysql5.7数据库依然无法自动启动服务

[root@dba mysql-5.7]# bin/mysql -uroot -p
Enter password: 
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)
[root@dba mysql-5.7]# 
[root@dba mysql-5.7]# systemctl status mysqld.service
● mysqld.service - MySQL Server
   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
   Active: failed (Result: start-limit) since Fri 2023-04-14 10:16:07 CST; 23h ago
  Process: 1555 ExecStart=/opt/mysql/mysql-5.7/bin/mysqld --defaults-file=/etc/my.cnf --basedir=/opt/mysql/mysql-5.7 --datadir=/opt/mysql/mysql-5.7/data --plugin-dir=/opt/mysql/mysql-5.7/lib/plugin --log-error=/var/log/mysql/error.log --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/lib/mysql/mysql.sock --port=3306 (code=exited, status=1/FAILURE)
 Main PID: 1555 (code=exited, status=1/FAILURE)

Apr 14 10:16:07 dba systemd[1]: mysqld.service: main process exited, code=exited, status=1/FAILURE
Apr 14 10:16:07 dba systemd[1]: Unit mysqld.service entered failed state.
Apr 14 10:16:07 dba systemd[1]: mysqld.service failed.
Apr 14 10:16:07 dba systemd[1]: mysqld.service holdoff time over, scheduling restart.
Apr 14 10:16:07 dba systemd[1]: Stopped MySQL Server.
Apr 14 10:16:07 dba systemd[1]: start request repeated too quickly for mysqld.service
Apr 14 10:16:07 dba systemd[1]: Failed to start MySQL Server.
Apr 14 10:16:07 dba systemd[1]: Unit mysqld.service entered failed state.
Apr 14 10:16:07 dba systemd[1]: mysqld.service failed.
[root@dba mysql-5.7]# 
[root@dba mysql-5.7]# 

查看错误日志

cat /var/log/mysql/erorr.log

错误原因

MySQL找不到PID文件导致无法启动，可能的原因是MySQL配置文件中指定了不存在的PID文件路径或者MySQL用户没有写入该路径的权限。
之前的操作是测试mysql开机是否能自启动，直接使用root用户执行reboot命令。所以应该是由于服务器强制关机导致pid文件丢失。

解决方案

1. 确认pid文件位置(安装时没有在my.cnf文件中指定pid-file)，通过系统命令查询
   

2. 创建对应的目录并修改属主和权限（最好给 777权限）

[root@dba mysql-5.7]# mkdir -pv /var/run/mysqld
mkdir: created directory ‘/var/run/mysqld’
[root@dba mysql-5.7]# 
[root@dba mysql-5.7]# chown -v mysql:dbgrp /var/run/mysqld
changed ownership of ‘/var/run/mysqld’ from root:root to mysql:dbgrp
[root@dba mysql-5.7]# 
[root@dba mysql-5.7]# chmod -Rv 777 /var/run/mysqld/
mode of ‘/var/run/mysqld/’ changed from 0755 (rwxr-xr-x) to 0777 (rwxrwxrwx)
[root@dba mysql-5.7]# 

3. 创建一个pid文件并修改属主

[root@dba mysql-5.7]# 
[root@dba mysql-5.7]# touch /var/run/mysqld/mysqld.pid
[root@dba mysql-5.7]# 
[root@dba mysql-5.7]# chown -v mysql:dbgrp /var/run/mysqld/mysqld.pid 
changed ownership of ‘/var/run/mysqld/mysqld.pid’ from root:root to mysql:dbgrp
[root@dba mysql-5.7]# 

4. 启动数据库,启动成功

[root@dba mysql-5.7]# systemctl start mysqld.service
[root@dba mysql-5.7]# 
[root@dba mysql-5.7]# 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 2023-04-15 11:02:18 CST; 5s ago
 Main PID: 5734 (mysqld)
    Tasks: 27
   Memory: 133.8M
   CGroup: /system.slice/mysqld.service
           └─5734 /opt/mysql/mysql-5.7/bin/mysqld --defaults-file=/etc/my.cnf --basedir=/opt/mysql/mysql-5.7 --datadir=/opt/mysql/mysql-5.7/data --plugin-dir=/opt/mysql/mysql-5.7/lib/plugin...
Apr 15 11:02:18 dba systemd[1]: Started MySQL Server.
[root@dba mysql-5.7]#