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启动mysqld服务失败，报错如下：

1. [root@LCM01GCM01 ~]# service mysqld start   
2. 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.
3.                                                            [FAILED]

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既然有了提示，先看下有什么帮助没有

1. [root@LCM01GCM01 ~]# systemctl status mysqld.service
2. Loaded: loaded (/etc/rc.d/init.d/mysqld)
3.    Active: failed (Result: exit-code) since Wed 2016-01-20 18:26:57 CST; 40s ago
4.      Docs: man:systemd-sysv-generator(8)
5.   Process: 2979 ExecStart=/etc/rc.d/init.d/mysqld start (code=exited, status=1/FAILURE)
7. Jan 20 18:26:56 spark01 systemd[1]: Starting SYSV: MySQL database server....
8. Jan 20 18:26:57 spark01 mysqld[2979]: MySQL Daemon failed to start.
9. Jan 20 18:26:57 spark01 mysqld[2979]: Starting mysqld:  [FAILED]
10. Jan 20 18:26:57 spark01 systemd[1]: mysqld.service: control process exited, code=exited status=1
11. Jan 20 18:26:57 spark01 systemd[1]: Failed to start SYSV: MySQL database server..
12. Jan 20 18:26:57 spark01 systemd[1]: Unit mysqld.service entered failed state.
13. Jan 20 18:26:57 spark01 systemd[1]: mysqld.service failed.

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1. [root@LCM01GCM01 ~]# journalctl -xe
2. --
3. -- Unit session-2.scope has begun starting up.
4. Jan 20 18:26:48 spark01 sshd[2916]: pam_unix(sshd:session): session opened for user spark by (uid=0)
5. Jan 20 18:26:52 spark01 su[2944]: (to root) spark on pts/1
6. Jan 20 18:26:52 spark01 su[2944]: pam_unix(su-l:session): session opened for user root by spark(uid=1000)
7. Jan 20 18:26:56 spark01 polkitd[909]: Registered Authentication Agent for unix-process:2974:117137 (system bus name :1.25
8. Jan 20 18:26:56 spark01 systemd[1]: Starting SYSV: MySQL database server....
9. -- Subject: Unit mysqld.service has begun start-up
10. -- Defined-By: systemd
11. -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
12. --
13. -- Unit mysqld.service has begun starting up.
14. Jan 20 18:26:57 spark01 mysqld[2979]: MySQL Daemon failed to start.
15. Jan 20 18:26:57 spark01 mysqld[2979]: Starting mysqld:  [FAILED]
16. Jan 20 18:26:57 spark01 systemd[1]: mysqld.service: control process exited, code=exited status=1
17. Jan 20 18:26:57 spark01 systemd[1]: Failed to start SYSV: MySQL database server..
18. -- Subject: Unit mysqld.service has failed
19. -- Defined-By: systemd
20. -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
21. --
22. -- Unit mysqld.service has failed.
23. --
24. -- The result is failed.
25. Jan 20 18:26:57 spark01 systemd[1]: Unit mysqld.service entered failed state.
26. Jan 20 18:26:57 spark01 systemd[1]: mysqld.service failed.
27. Jan 20 18:26:57 spark01 polkitd[909]: Unregistered Authentication Agent for unix-process:2974:117137 (system bus name :1.

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然而，好像这些信息对我们来说并没有什么用处，什么守护进程没启动，我们也不能知如何去启动这些，这个时候我们查看一下mysql自带的告警日志，路径一般在/var/log/mysqld.log下面

1. [root@LCM01GCM01 ~]# tail -200f  /var/log/mysqld.log
2. 2018-12-07 T10:00:19.935771Z 0 [ERROR] /usr/sbin/mysqld: Can"t create/write to file "/var/run/mysqld/mysqld.pid" (Errcode: 2 - No such file or directory)
3. 2018-12-07T10:00:19.935795Z 0 [ERROR] Can"t start server: can"t create PID file: No such file or directory
4. 181207 18:00:20 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended

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这个时候我们就明白了，/var/run/mysqld/这个目录不存在，wu，查找下确实没有这个文件。这里我们有两种解决方案
第一种自己创建 /var/run/mysqld/ 这个目录，重新启动mysqld服务

1. [root@LCM01GCM01 ~]# mkdir -p /var/run/mysqld/
2. [root@LCM01GCM01 ~]# service mysqld start   
3. 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.
4.                                                            [FAILED]

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依旧报错，重新查看告警日志，有以下输出

1. 2018-12-070T10:28:37.183387Z 0 [ERROR] /usr/sbin/mysqld: Can"t create/write to file "/var/run/mysqld/mysqld.pid" (Errcode: 13 - Permission denied)
2. 2018-12-070T10:28:37.183431Z 0 [ERROR] Can"t start server: can"t create PID file: Permission denied
3. 181207 18:28:37 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
4. 181207 18:32:06 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql

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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。

1. [root@LCM01GCM01 ~]# ls -ld /var/run/mysqld/
2. drwxr-xr-x 2 root root 40 Jan 20 18:28 /var/run/mysqld/
3. [root@LCM01GCM01 ~]# chown mysql.mysql /var/run/mysqld/
4. [root@LCM01GCM01~]# service mysqld start
5. Starting mysqld (via systemctl):                           [  OK  ]

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上面第一种解决方案为临时性的方案，你会发现当虚拟机reboot的话，又会启动不成功，那个目录又不删除了，因此我们修改一下存放mysqld.pid的目录，有两个配置文件

1. vi  /etc/my.cnf
3. socket=/var/lib/mysql/mysql.sock
5. # Disabling symbolic-links is recommended to prevent assorted security risks
6. symbolic-links=0
8. log-error=/var/log/mysqld.log
9. pid-file=/createByhujian/mysqld/mysqld.pid

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1. vi  /etc/init.d/mysqld
3. get_mysql_option mysqld datadir "/var/lib/mysql"
4. datadir="$result"
5. get_mysql_option mysqld socket "$datadir/mysql.sock"
6. socketfile="$result"
7. get_mysql_option mysqld_safe log-error "/var/log/mysqld.log"
8. errlogfile="$result"
9. get_mysql_option mysqld_safe pid-file "/createByhujian/mysqld/mysqld.pid"
10. mypidfile="$result"

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红色的部分是我自己在根目录下创建的目录 /createByhujian/mysqld

1. mkdir -p /createByhujian/mysqld
2. chown mysql.mysql /createByhujian/mysqld

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重启mysqld服务成功，一劳永逸
有什么问题可以下方留言讨论哦！
  
  

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