不小心将服务器OS给重启了，再启动数据库的时候，出现了很奇怪的问题
[root@dev run]# service mysql restart
ERROR! MySQL server PID file could not be found!
Starting MySQL.. ERROR! The server quit without updating PID file (/var/lib/mysql/run/mysql.pid).
无法启动mysql，后来上网找了一下解决方法，无非就是以下几种
1. 注释/etc/my.cnf里的skip-federated注释掉即#skip-federated；
2. my.cnf文件配置过高，重新定义其中的参数（根据服务器情况定义）；
3. 杀掉mysql_safe和mysqld进程，然后再重启；
4. 当前日志文件过大，超出了my.cnf中定义的大小（默认为64M），删除日志文件再重启；
但是在主机中：
1． 注释中无skip-federated这个选项
2． My.cnf是自己优化过的，断电之前正常使用，不是这个的问题
3． Ps –ef | grep mysql 根本就没有mysql的僵尸进程
4． 没有这个问题
基本上网上的所有方式都试过了，都无法解决问题，然后在数据库的data目录(mysql/data)查看错误日志,我的服务器是localhost.localdomain.err文件,也可能是
(/var/lib/mysql/log/error.log)
2014-06-10 11:52:46 15921 [Note] InnoDB: Database was not shutdown normally!
2014-06-10 11:52:46 15921 [Note] InnoDB: Starting crash recovery.
2014-06-10 11:52:46 15921 [Note] InnoDB: Reading tablespace information from the .ibd files...
2014-06-10 11:52:46 15921 [ERROR] InnoDB: Attempted to
open a previously opened tablespace. Previous tablespace
raildb/base_company_fullname uses space ID: 4 at filepath:
./raildb/base_company_fullname.ibd. Cannot open tablespace
mysql/slave_master_info which uses space ID: 4 at filepath:
./mysql/slave_master_info.ibd
2014-06-10 11:52:46 7ff29246d720 InnoDB: Operating system error number 2 in a file operation.
InnoDB: The error means the system cannot find the path specified.
InnoDB: If you are installing InnoDB, remember that you must create
InnoDB: directories yourself, InnoDB does not create them.
InnoDB: Error: could not open single-table tablespace file ./mysql/slave_master_info.ibd
InnoDB: We do not continue the crash recovery, because the table may become
InnoDB: corrupt if we cannot apply the log records in the InnoDB log to it.
InnoDB: To fix the problem and start mysqld:
InnoDB: 1) If there is a permission problem in the file and mysqld cannot
InnoDB: open the file, you should modify the permissions.
InnoDB: 2) If the table is not needed, or you can restore it from a backup,
InnoDB: then you can remove the .ibd file, and InnoDB will do a normal
InnoDB: crash recovery and ignore that table.
InnoDB: 3) If the file system or the disk is broken, and you cannot remove
InnoDB: the .ibd file, you can set innodb_force_recovery > 0 in my.cnf
InnoDB: and force InnoDB to continue crash recovery here.
140610 11:52:46 mysqld_safe mysqld from pid file /var/lib/mysql/run/mysql.pid ended
第一处标黄，提示是数据库没有正常关闭
第二处标蓝，提示正在从.ibd files读取tablespace information
第三处标红，就是开始error的地方，大概意思就是读取不到raildb这个库的tablespace
下边说的就是一些处理这个问题的方法，就不一一翻译了
最后我感觉是因为断电之前，mysql没有正常关闭，造成了raildb这个库的一些异常，我采用的解决方法是在innoDB，强制覆盖
Vi /etc/my.cof 增加一行 innodb_force_recovery= 1
然后重启,接着报错:
mysqld: File './mysql-bin.index' not found (Errcode: 13)
查看data目录下mysql-bin.index是存在的,怀疑是权限问题,对整个mysql目录重新赋权:
chown -R mysql:mysql mysql
再次重启,问题解决...