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 -m
total used free shared buffers cached
Mem: 48274 2509 45764 0 19 378
-/+ buffers/cache: 2111 46162
Swap: 10236 0 10236
开启mysql服务报错。
EIPDB1:~ # mysqld service status
171016 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 status
MySQL is running but PID file could not be found failed
EIPDB1:~ # service mysqld start
Starting 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 -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 40G 9.1G 29G 25% /
devtmpfs 24G 356K 24G 1% /dev
tmpfs 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 mysql
root 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.pid
mysql 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=3306
root 5588 0.0 0.0 5704 800 pts/0 S+ 00:22 0:00 grep mysql
EIPDB1:~ # kill -9 3442
EIPDB1:/usr/local # kill -9 4034
重新启动mysql服务：
EIPDB1:/usr/local # service mysqld start
Starting MySQL… done
EIPDB1:/usr/local # service mysqld status
MySQL running (6322) done
EIPDB1:/usr/local # ps aux | grep mysql
root 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.pid
mysql 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=3306
root 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 event
Master_Host: 10.0.2.206
Master_User: slave_user
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: master-binlog.000062
Read_Master_Log_Pos: 44601
Relay_Log_File: eipdb2-relay-bin.000166
Relay_Log_Pos: 44751
Relay_Master_Log_File: master-binlog.000062
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
完成。
