CentOS 7下MySQL服务启动失败的快速解决方法

今天，启动mysql服务器失败，如下所示：

[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]

根据提示，分别使用systemctl status mysqld.service和journalctl -xe查看服务启动失败的原因

[root@spark01 ~]# 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@spark01 ~]# 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:2974:117137 (system bus name :1.

但，可惜的时，这些信息并不能提供服务启动失败的真正原因。

这时候，不妨打开mysql的告警日志，毕竟，只要mysql服务启动，告警日志都会有输出信息的，果然

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 directory
160120 18:00:20 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended

mysql服务在启动的时候，不能创建pid文件。

在终端看一下该目录是否存在，果然，不存在。

于是，创建了/var/run/mysqld/目录，重启mysql服务

[root@spark01 ~]# mkdir -p /var/run/mysqld/

[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]

依旧报错，重新查看告警日志，有以下输出

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 denied
160120 18:28:37 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
160120 18:32:06 mysqld_safe starting mysqld daemon with databases from /var/lib/mysql

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@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 start
starting mysqld (via systemctl):              [ ok ]

总结：

以前在玩kubernetes的时候，常遇到启动失败的情况，根据systemctl的提示，通过systemctl status mysqld.service和journalctl -xe命令查看服务启动失败的原因往往并不如人意，反而给了一种错误的暗示，以为这个跟系统有关。其实，通过查看服务的日志，往往更能清晰的知道服务启动失败的原因。

以上这篇centos 7下mysql服务启动失败的快速解决方法就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持。