CentOS7.0下mysql服务启动失败的快速解决办法

启动mysql服务

[root@localhost~]#/etc/init.d/mysqld start

之后出现报错：

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]

根据提示分别使用systemctl status mysqld.service和journalctl -xe 来查看报错日志：

[root@localhost ~]#systemctl status mysqld.service
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=1
Jan 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.

[root@localhost~]journalctl -xe
-- 
-- 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/1
Jan 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 :1.25
Jan 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=1
Jan 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:

通过检查发现，这些错误并不能够有效解决mysql服务启动失败的问题。查看mysql服务的启动日志：

[root@localhost~]cat /var/log/mysqlg.log
2016-01-20T10:00:19.935771Z 0 [ERROR] /usr/sbin/mysqld: Cant create/write to file /var/run/mysqld/mysqld.pid (Errcode: 2 - No such file or directory)
2016-01-20T10:00:19.935795Z 0 [ERROR] Cant start server: cant create PID file: No such file or directory
160120 18:00:20 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended

查看日志发现mysql服务启动的时候不能创建PID文件。
在终端查看发现果然没有/var/run/mysqld这个文件，然后创建：

[root@localhost~]# mkdir -p /var/run/mysqld

然后重启mysql的服务，但是还是失败

[root@localhost~]# /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]

原来，/var/run/mysqld/的属主和属组还是root，mysql并不能在其中创建文件，后修改该目录的属主和属组，启动OK 。

[root@localhost~]# ls -ld /var/run/mysqld/
drwxr-xr-x 2 root root 40 Jan 20 18:28 /var/run/mysqld/
[root@localhost~]# chown mysql.mysql /var/run/mysqld/
[root@localhost~]# /etc/init.d/mysqld start
Starting mysqld (via systemctl):              [ OK ]