CentOS7下MySQL服务启动失败原因及解决方法

在重启阿里的centos7服务器后,重启mysql 出现错误

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]

按照提示查看错误信息

[root@djaljdw ~]# systemctl status mysqld.service

● mysqld.service - sysv: mysql database server.
   loaded: loaded (/etc/rc.d/init.d/mysqld; bad; vendor preset: disabled)
   active: failed (result: exit-code) since thu 2019-08-22 14:42:39 cst; 1min 25s ago
     docs: man:systemd-sysv-generator(8)
  process: 2427 execstart=/etc/rc.d/init.d/mysqld start (code=exited, status=1/failure)

aug 22 14:42:37 izw91diu854rguz systemd[1]: starting sysv: mysql database server....
aug 22 14:42:39 izw91diu854rguz mysqld[2427]: mysql daemon failed to start.
aug 22 14:42:39 izw91diu854rguz mysqld[2427]: starting mysqld:  [failed]
aug 22 14:42:39 izw91diu854rguz systemd[1]: mysqld.service: control process exited, code=exited status=1
aug 22 14:42:39 izw91diu854rguz systemd[1]: failed to start sysv: mysql database server..
aug 22 14:42:39 izw91diu854rguz systemd[1]: unit mysqld.service entered failed state.
aug 22 14:42:39 izw91diu854rguz systemd[1]: mysqld.service failed.
hint: some lines were ellipsized, use -l to show in full.

[root@djaljdw ~]#  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.

发现里面并没有提供有用的错误信息

所以去查看mysql日志信息(/var/log/mysqld.log)

190822 14:44:42 [note] plugin 'federated' is disabled.
190822 14:44:42 innodb: the innodb memory heap is disabled
190822 14:44:42 innodb: mutexes and rw_locks use gcc atomic builtins
190822 14:44:42 innodb: compressed tables use zlib 1.2.3
190822 14:44:42 innodb: using linux native aio
190822 14:44:42 innodb: initializing buffer pool, size = 128.0m
190822 14:44:42 innodb: completed initialization of buffer pool
190822 14:44:42 innodb: highest supported file format is barracuda.
innodb: the log sequence number in ibdata files does not match
innodb: the log sequence number in the ib_logfiles!
190822 14:44:42  innodb: database was not shut down normally!
innodb: starting crash recovery.
innodb: reading tablespace information from the .ibd files...
innodb: restoring possible half-written data pages from the doublewrite
innodb: buffer...
190822 14:44:42  innodb: waiting for the background threads to start
190822 14:44:43 innodb: 5.5.59 started; log sequence number 1940403
190822 14:44:43 [note] server hostname (bind-address): '0.0.0.0'; port: 3306
190822 14:44:43 [note]   - '0.0.0.0' resolves to '0.0.0.0';
190822 14:44:43 [note] server socket created on ip: '0.0.0.0'.
190822 14:44:43 [error] /usr/libexec/mysqld: can't create/write to file '/var/run/mysqld/mysqld.pid' (errcode: 2)
190822 14:44:43 [error] can't start server: can't create pid file: no such file or directory

问题找到了:不能创建pid文件:没有这样的文件或目录

于是去查看,果然没有文件夹

[root@djaljdw ~]#  cd /var/run

[root@djaljdw ~]#  mkdir mysqld

[root@djaljdw ~]#  cd mysqld

[root@djaljdw ~]#  touch mysqld.pid

重启服务还是报错

于是又查看日志

190822 14:56:51 [note] plugin 'federated' is disabled.
190822 14:56:51 innodb: the innodb memory heap is disabled
190822 14:56:51 innodb: mutexes and rw_locks use gcc atomic builtins
190822 14:56:51 innodb: compressed tables use zlib 1.2.3
190822 14:56:51 innodb: using linux native aio
190822 14:56:51 innodb: initializing buffer pool, size = 128.0m
190822 14:56:51 innodb: completed initialization of buffer pool
190822 14:56:51 innodb: highest supported file format is barracuda.
innodb: the log sequence number in ibdata files does not match
innodb: the log sequence number in the ib_logfiles!
190822 14:56:51  innodb: database was not shut down normally!
innodb: starting crash recovery.
innodb: reading tablespace information from the .ibd files...
innodb: restoring possible half-written data pages from the doublewrite
innodb: buffer...
190822 14:56:51  innodb: waiting for the background threads to start
190822 14:56:52 innodb: 5.5.59 started; log sequence number 1940403
190822 14:56:52 [note] server hostname (bind-address): '0.0.0.0'; port: 3306
190822 14:56:52 [note]   - '0.0.0.0' resolves to '0.0.0.0';
190822 14:56:52 [note] server socket created on ip: '0.0.0.0'.
190822 14:56:52 [error] /usr/libexec/mysqld: can't create/write to file '/var/run/mysqld/mysqld.pid' (errcode: 13)
190822 14:56:52 [error] can't start server: can't create pid file: permission denied

发现:无法创建pid文件:权限被拒绝

解决办法:

修改 /var/run/mysqld/权限为mysql 

[root@djaljdw ~]#  chown -r mysql /var/run/mysqld

[root@djaljdw ~]#  chgrp -r mysql /var/run/mysqld

[root@djaljdw ~]#  chmod 777 /var/run/mysqld

重启服务完美解决

tip:看日志是解决问题的一个很好的办法!