环境：mysql主从，一台主机，一台备机。都是虚拟机。备机仅仅用来备份，不用于业务。关闭主机mysql服务，关闭主机系统，加内存。、备机不变。

开启主机。内存加好。EIPDB1:~ # free -mtotal used free shared buffers cachedMem: 48274 2509 45764 0 19 378-/+ buffers/cache: 2111 46162Swap: 10236 0 10236开启mysql服务报错。EIPDB1:~ # mysqld service status171016 23:57:43 [ERROR] Fatal error: Please read "Security" section of the manual to find out how to run mysqld as root!
171016 23:57:43 [ERROR] Aborting
171016 23:57:43 [Note] mysqld: Shutdown complete
EIPDB1:~ # service mysqld statusMySQL is running but PID file could not be found failedEIPDB1:~ # service mysqld startStarting MySQL.....................................................................................................The server quit without updating PID file (/eipdb1/mysql/data/EIPDB1.pid).
解决：先查看了下，空间充足，没问题。EIPDB1:/usr/local # df -hFilesystem Size Used Avail Use% Mounted on/dev/sda3 40G 9.1G 29G 25% /devtmpfs 24G 356K 24G 1% /devtmpfs 24G 100K 24G 1% /dev/shm/dev/sda1 98M 75M 19M 80% /boot/dev/sdb1 490G 26G 465G 6% /eipdb1
可能是mysqld进程卡死，杀掉进程。EIPDB1:~ # ps aux | grep mysqlroot 3442 0.0 0.0 11292 1576 ? S Oct16 0:00 /bin/sh /eipdb1/mysql/bin/mysqld_safe --datadir=/eipdb1/mysql/data --pid-file=/eipdb1/mysql/data/EIPDB1.pidmysql 4034 4.2 3.1 5907700 1538808 ? Sl Oct16 1:12 /eipdb1/mysql/bin/mysqld --basedir=/eipdb1/mysql --datadir=/eipdb1/mysql/data --plugin-dir=/eipdb1/mysql/lib/plugin --user=mysql --log-error=/eipdb1/mysql/data/EIPDB1.err --pid-file=/eipdb1/mysql/data/EIPDB1.pid --socket=/tmp/mysql.sock --port=3306root 5588 0.0 0.0 5704 800 pts/0 S+ 00:22 0:00 grep mysql
EIPDB1:~ # kill -9 3442EIPDB1:/usr/local # kill -9 4034
重新启动mysql服务：EIPDB1:/usr/local # service mysqld startStarting MySQL... doneEIPDB1:/usr/local # service mysqld statusMySQL running (6322) doneEIPDB1:/usr/local # ps aux | grep mysqlroot 5733 0.0 0.0 11504 1596 pts/0 S 00:30 0:00 /bin/sh /eipdb1/mysql/bin/mysqld_safe --datadir=/eipdb1/mysql/data --pid-file=/eipdb1/mysql/data/EIPDB1.pidmysql 6322 1.0 2.1 5839204 1065996 pts/0 Sl 00:30 0:01 /eipdb1/mysql/bin/mysqld --basedir=/eipdb1/mysql --datadir=/eipdb1/mysql/data --plugin-dir=/eipdb1/mysql/lib/plugin --user=mysql --log-error=/eipdb1/mysql/data/EIPDB1.err --pid-file=/eipdb1/mysql/data/EIPDB1.pid --socket=/tmp/mysql.sock --port=3306root 6398 0.0 0.0 5700 800 pts/0 S+ 00:32 0:00 grep mysql
备库同步正常：mysql> show slave status \G;*************************** 1. row ***************************Slave_IO_State: Waiting for master to send eventMaster_Host: 10.0.2.206Master_User: slave_userMaster_Port: 3306Connect_Retry: 60Master_Log_File: master-binlog.000062Read_Master_Log_Pos: 44601Relay_Log_File: eipdb2-relay-bin.000166Relay_Log_Pos: 44751Relay_Master_Log_File: master-binlog.000062Slave_IO_Running: YesSlave_SQL_Running: Yes
完成。