在FreeBSD中启动mysql时报错，ERROR! The server quit without updating PID file，通常这是可以查看目录下的.err日志，里面会记录一些具体的错误信息，对排错相当有用，内容如下：
110805 17:30:19 d_safe Starting mysqld daemon with databases from /usr/local/mysql5.5/data
110805 17:30:19 InnoDB: The InnoDB memory heap is disabled
110805 17:30:19 InnoDB: Mutexes and rw_locks use GCC atomic builtins
110805 17:30:19 InnoDB: Compressed tables use zlib 1.2.3
110805 17:30:19 InnoDB: Initializing buffer pool, size = 256.0M
110805 17:30:19 InnoDB: Completed initialization of buffer pool
InnoDB: Error: log file /usr/local/mysql5.5/data/ib_logfile0 is of different size 0 5242880 bytes
InnoDB: than specified in the .cnf file 0 67108864 bytes!
110805 17:30:19 [ERROR] Plugin 'InnoDB' init function returned error.
110805 17:30:19 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
110805 17:30:19 [ERROR] Unknown/unsupported storage engine: InnoDB
110805 17:30:19 [ERROR] Aborting
110805 17:30:19 [Note] /usr/local/mysql5.5/bin/mysqld: Shutdown complete
看到上面红色字体，显示错误是出在日志文件大小上，于是查看mysql的配置文件/etc/my.cnf
# Uncomment the following if you are using InnoDB tables
innodb_data_home_dir = /usr/local/mysql5.5/data
innodb_data_file_path = ibdata1:10M:autoextend
innodb_log_group_home_dir = /usr/local/mysql5.5/data
# You can set .._buffer_pool_size up to 50 - 80 %
# of RAM but beware of setting memory usage too high
innodb_buffer_pool_size = 256M
innodb_additional_mem_pool_size = 20M
# Set .._log_file_size to 25 % of buffer pool size
innodb_log_file_size = 64M
innodb_log_buffer_size = 8M
innodb_flush_log_at_trx_commit = 1
innodb_lock_wait_timeout = 50
配置文件中指定了innodb_log_file_size=64M，在看看我的数据库目录下，日志文件大小是不是64M，如下图，发现问题了，日志文件是5242880是5M
找到问题了，解决办法可以更改配置文件，也可以删除现在这个日志，再启动mysql这样它会重新生成这两个日志文件。
怎么会出现这个问题呢？
一般来说，是由于，在my.cnf中关于INNODB的一些配置是被注释的，在没有更改的情况下，系统就使用了默认值，这样，当你把关于innodb的配置选项注释去掉的时候，就会出现这个报错！