手把手教你解决MySQL服务启动失败排查并修复恢复启动问题

手把手教你解决MySQL服务启动失败排查并修复恢复启动问题

上次帮一个网友远程解决了一个问题，直接打赏了我，今天又一个网友打赏了我。

事件起因是这样的，网友在执行一条 SQL 时，提示错误。网友搜索得出答案，需要设置 sql_mode，她百度一番，然后进行了修改。

重启服务后，发现 MySQL 服务无法启动。

我问网友遇到了什么错误，对方给我发来了一个截图。

由于截图太小，看不全内容，因此进行了远程手把手教程。

我首先执行 mysql 的启动命令：

service mysql start

然后获得了启动报错信息。

Starting mysqld (via systemctl):  Job for mysqld.service failed because the control process exited with error code. See "systemctl status mysqld.service" and "journalctl -xe" for details. [FAILED]

这段内容翻译过来，就是提示我：“分别使用systemctl status mysqld.service和journalctl -xe查看服务启动失败的原因”。

于是，我先执行了 systemctl status mysqld.service 命令。

systemctl status mysqld.service

出现了下面的日志内容：

?.mysqld.service - SYSV: MySQL database server.
   Loaded: loaded (/etc/rc.d/init.d/mysqld)
   Active: failed (Result: exit-code) since Wed 2016-01-20 18:26:57 CST; 40s ago
     Docs: man:systemd-sysv-generator(8)
  Process: 2979 ExecStart=/etc/rc.d/init.d/mysqld start (code=exited, status=1/FAILURE)

 systemd[1]: Starting SYSV: MySQL database server....
 xttblog mysqld[2979]: MySQL Daemon failed to start.
 xttblog mysqld[2979]: Starting mysqld:  [FAILED]
 xttblog systemd[1]: mysqld.service: control process exited, code=exited status=1
 xttblog systemd[1]: Failed to start SYSV: MySQL database server..
 xttblog systemd[1]: Unit mysqld.service entered failed state.
 xttblog systemd[1]: mysqld.service failed.

上面这段错误日志，我没看出具体的错误原因。于是，就又执行了 journalctl -xe 命令。

-- Unit session-2.scope has begun starting up.
xttblog sshd[2916]: pam_unix(sshd:session): session opened for user spark by (uid=0)
xttblog su[2944]: (to root) spark on pts/1
xttblog su[2944]: pam_unix(su-l:session): session opened for user root by spark(uid=1000)
xttblog polkitd[909]: Registered Authentication Agent for unix-process:2974:117137 (system bus name :1.25
xttblog systemd[1]: Starting SYSV: MySQL database server....
-- Subject: Unit mysqld.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit mysqld.service has begun starting up.
xttblog mysqld[2979]: MySQL Daemon failed to start.
xttblog mysqld[2979]: Starting mysqld:  [FAILED]
xttblog systemd[1]: mysqld.service: control process exited, code=exited status=1
xttblog systemd[1]: Failed to start SYSV: MySQL database server..
[ERROR] Could not open file '/var/log/mysql/error.log' for error logging: No such file or directory
-- Subject: Unit mysqld.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit mysqld.service has failed.
-- 
-- The result is failed.
xttblog systemd[1]: Unit mysqld.service entered failed state.
xttblog systemd[1]: mysqld.service failed.
xttblog polkitd[909]: Unregistered Authentication Agent for unix-process:2974:117137 (system bus name :1.

上面的日志中，有一段很明显的内容。

“[ERROR] Could not open file '/var/log/mysql/error.log' for error logging: No such file or directory”

抓住重点信息，我在 /var/log/mysql/error.log 目录下，新建了 error.log 文件，并给上 755 权限。

然后，我再次启动 mysql 服务，service mysql start 成功启动！

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