今天，啟動MySQL服務器失敗，如下所示：
<code>[root@spark01 ~]# /etc/init.d/mysqld start
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]
/<code>根據提示，分別使用systemctl status mysqld.service和journalctl -xe查看服務啟動失敗的原因
[root@spark01 ~]# systemctl status mysqld.service
<code>?.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)Jan 20 18:26:56 spark01 systemd[1]: Starting SYSV: MySQL database server....Jan 20 18:26:57 spark01 mysqld[2979]: MySQL Daemon failed to start.Jan 20 18:26:57 spark01 mysqld[2979]: Starting mysqld: [FAILED]Jan 20 18:26:57 spark01 systemd[1]: mysqld.service: control process exited, code=exited status=1Jan 20 18:26:57 spark01 systemd[1]: Failed to start SYSV: MySQL database server..Jan 20 18:26:57 spark01 systemd[1]: Unit mysqld.service entered failed state.Jan 20 18:26:57 spark01 systemd[1]: mysqld.service failed./<code>
[root@spark01 ~]# journalctl -xe
<code>-- -- Unit session-2.scope has begun starting up.Jan 20 18:26:48 spark01 sshd[2916]: pam_unix(sshd:session): session opened for user spark by (uid=0)Jan 20 18:26:52 spark01 su[2944]: (to root) spark on pts/1Jan 20 18:26:52 spark01 su[2944]: pam_unix(su-l:session): session opened for user root by spark(uid=1000)Jan 20 18:26:56 spark01 polkitd[909]: Registered Authentication Agent for unix-process:2974:117137 (system bus name :1.25Jan 20 18:26:56 spark01 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.Jan 20 18:26:57 spark01 mysqld[2979]: MySQL Daemon failed to start.Jan 20 18:26:57 spark01 mysqld[2979]: Starting mysqld: [FAILED]Jan 20 18:26:57 spark01 systemd[1]: mysqld.service: control process exited, code=exited status=1Jan 20 18:26:57 spark01 systemd[1]: Failed to start SYSV: MySQL database server..-- 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.Jan 20 18:26:57 spark01 systemd[1]: Unit mysqld.service entered failed state.Jan 20 18:26:57 spark01 systemd[1]: mysqld.service failed.Jan 20 18:26:57 spark01 polkitd[909]: Unregistered Authentication Agent for unix-process:2974:117137 (system bus name :1./<code>
但，可惜的時，這些信息並不能提供服務啟動失敗的真正原因。
這時候，不妨打開MySQL的告警日誌(linux一般在/var/log/mysqld.log)，畢竟，只要MySQL服務啟動，告警日誌都會有輸出信息的，果然
<code>2016-01-20T10:00:19.935771Z 0 [ERROR] /usr/sbin/mysqld: Can't create/write to file '/var/run/mysqld/mysqld.pid' (Errcode: 2 - No such file or directory)2016-01-20T10:00:19.935795Z 0 [ERROR] Can't start server: can't create PID file: No such file or directory160120 18:00:20 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended/<code>
MySQL服務在啟動的時候，不能創建pid文件。
在終端看一下該目錄是否存在，果然，不存在。
於是，創建了/var/run/mysqld/目錄，重啟MySQL服務
[root@spark01 ~]# mkdir -p /var/run/mysqld/
[root@spark01 ~]# /etc/init.d/mysqld start
<code>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]/<code>
依舊報錯，重新查看告警日誌，有以下輸出
<code>2016-01-20T10:28:37.183387Z 0 [ERROR] /usr/sbin/mysqld: Can't create/write to file '/var/run/mysqld/mysqld.pid' (Errcode: 13 - Permission denied)2016-01-20T10:28:37.183431Z 0 [ERROR] Can't start server: can't create PID file: Permission denied160120 18:28:37 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended160120 18:32:06 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql/<code>
原來，/var/run/mysqld/的屬主和屬組還是root，mysql並不能在其中創建文件，後修改該目錄的屬主和屬組，啟動OK。
<code>[root@spark01 ~]# ls -ld /var/run/mysqld/drwxr-xr-x 2 root root 40 Jan 20 18:28 /var/run/mysqld/[root@spark01 ~]# chown mysql.mysql /var/run/mysqld/[root@spark01 ~]# /etc/init.d/mysqld startStarting mysqld (via systemctl): [ OK ]/<code>
另一種錯誤
還有常見的另一種錯誤是
<code>May 29 19:04:53 localhost mysqld: 2018-05-29T11:04:53.723812Z 0 [ERROR] InnoDB: The innodb_system data file 'ibdata1' must be writableMay 29 19:04:53 localhost mysqld: 2018-05-29T11:04:53.723862Z 0 [ERROR] InnoDB: The innodb_system data file 'ibdata1' must be writableMay 29 19:04:53 localhost mysqld: 2018-05-29T11:04:53.723871Z 0 [ERROR] InnoDB: Plugin initialization aborted with error Generic errorMay 29 19:04:54 localhost mysqld: 2018-05-29T11:04:54.325440Z 0 [ERROR] Plugin 'InnoDB' init function returned error.May 29 19:04:54 localhost mysqld: 2018-05-29T11:04:54.325475Z 0 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.May 29 19:04:54 localhost mysqld: 2018-05-29T11:04:54.325483Z 0 [ERROR] Failed to initialize builtin plugins.May 29 19:04:54 localhost mysqld: 2018-05-29T11:04:54.325485Z 0 [ERROR] Aborting/<code>
The innodb_system data file 'ibdata1' must be writable
報錯原因大致為：你的數據文件不可寫
導致原因：yum安裝的mysql的擁有者是root，而mysql要求執行身份為mysql，權限問題導致數據文件不可寫
解決方法如下：
<code>[root@localhost ~]# chown -R mysql /var/lib/mysql[root@localhost ~]# systemctl start mysqld[root@localhost ~]# tailf /var/log/messages & 日誌打印：May 29 19:09:15 localhost mysqld: Version: '5.7.22' socket: '/var/lib/mysql/mysql.sock' port: 3306 MySQL Community Server (GPL)啟動成功/<code>
另外，這裡推薦我寫的文章雲服務器上安裝mysql的文章，嚴格按步驟 應該是不會出現以上錯誤的雲服務器Mysql安裝配置
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