解决Ubuntu20.04启动MySQL报错（Job for mysql.service failed because the control process exited with error）

运行环境：ubuntu20.04，mysql 8.0

mysql Ver 8.0.29-0ubuntu0.20.04.3 for Linux on x86_64 ((Ubuntu))

授人以鱼不如授人以渔：具体错误原因请到日志文件/var/log/mysql/error.log中排查（注意要放开日志文件的写入权限）

mysql启动时报错情况

sudo service mysql start # 启动
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Job for mysql.service failed because the control process exited with error code.
See “systemctl status mysql.service” and “journalctl -xe” for details.

sudo service mysql status # 查看状态；建议加上sudo，会有更详细的信息
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● mysql.service - MySQL Community Server
Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Wed 2024-02-28 10:10:31 CST; 10min ago
Process: 546126 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=1/FAILURE)

0.Ubuntu下的mysql相关文件介绍

（注意Centos等其他linux系统下的mysql相关文件路径与Ubuntu不一样）

配置文件：

/etc/mysql/mysql.conf.d/mysqld.cnf # 其中log_error对应的路径是ubuntu中mysql的日志存放位置（log_error = /var/log/mysql/error.log）
/etc/mysql/my.cnf # 启动配置
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日志文件：

/var/log/mysql/error.log # 由/etc/mysql/mysql.conf.d/mysqld.cnf中的log_error设置
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数据文件：

/var/lib/mysql # 注意：/var/lib/mysql千万不要删！这是存放mysql数据文件的目录
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运行时文件：

/var/run/mysqld
/tmp/data
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1.修改文件权限

# 可能需要创建/tmp/data、/var/run/mysqld【ubuntu18升级到20，需要增加/var/run/mysqld，并且需要sudo dpkg --configure -a】
sudo mkdir -p /var/run/mysqld /tmp/data
sudo chown -R mysql:mysql /var/lib/mysql /var/log/mysql /var/run/mysqld /tmp/data
sudo chmod -R 777 /var/lib/mysql /var/log/mysql /var/run/mysqld /tmp/data
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2.测试（可选）

mysqld_safe测试启动服务端（无需用户名和密码）

# 启动；并写入日志（可查看日志报错信息）
mysqld_safe --defaults-file=/etc/mysql/my.cnf
# /etc/mysql/my.cnf是ubuntu下的mysql启动参数配置文件
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注意，测试通过后，要关闭测试进程，否则报错。

客户端连接mysql服务端，mysql -u root -p

可能出现客户端报错：

ERROR 2002 (HY000): Can’t connect to local MySQL server through socket ‘/var/run/mysqld/mysqld.sock’ (2)

tail -n50 /var/log/mysql/error.log找到日志报错：

[ERROR] InnoDB: Unable to lock ./ibdata1, error: 11， Could not open or create the system tablespace.

原因：之前启动的mysqld_safe进程占用

解决：找到其他占用端口的进程，kill

ps -ef | grep mysql
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user0 618596 617876 0 13:17 pts/22 00:00:00 /bin/sh /usr/bin/mysqld_safe --defaults-file=/etc/mysql/my.cnf
user0 618942 618596 0 13:17 pts/22 00:00:05 /usr/sbin/mysqld --defaults-file=/etc/mysql/my.cnf --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib/mysql/plugin --log-error=/var/log/mysql/error.log --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/run/mysqld/mysqld.sock --port=3306

kill -9 618596 618942
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3.重启mysql

重启mysql服务端：

sudo service mysql restart
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sudo service mysql status查看正确的启动状态，示例如下：

● mysql.service - MySQL Community Server
Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
Active: active (running) since Wed 2024-02-28 13:57:17 CST; 16min ago
Process: 623015 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
Main PID: 623049 (mysqld)
Status: “Server is operational”
Tasks: 38 (limit: 347383)
Memory: 369.1M
CGroup: /system.slice/mysql.service
└─623049 /usr/sbin/mysqld