centos6.2，停止mysqld然后修改/etc/my.cnf datadir的位置，启动mysqld提示FAILED，查看日志
120609 11:31:31 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
120609 11:35:12 mysqld_safe Starting mysqld daemon with databases from /mnt/hgfs/mysql_data
120609 11:35:13 [Warning] Can't create test file /mnt/hgfs/mysql_data/data.lower-test
120609 11:35:13 [Warning] Can't create test file /mnt/hgfs/mysql_data/data.lower-test
/usr/libexec/mysqld: Can't change dir to '/mnt/hgfs/mysql_data/' (Errcode: 13)
120609 11:35:13 [ERROR] Aborting
120609 11:35:13 [Note] /usr/libexec/mysqld: Shutdown complete
120609 11:35:13 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
新的datadir路径确实没问题，而且目录和目录下所有文件都是777权限，上层目录也有rx权限，只不过datadir和下属文件owner都是root（因为我用虚拟机挂载的windows的文件系统）。后来想到应该是selinux搞的鬼，设置为permissive模式之后正常启动mysqld。
[root@data selinux]# getenforce
Enforcing
[root@data selinux]# setenforce 0
[root@data selinux]# getenforce
Permissive
setenforce 1 设置SELinux 成为enforcing模式
setenforce 0 设置SELinux 成为permissive模式
彻底关闭，vi /etc/selinux/config 修改 SELINUX=disabled
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
# enforcing - SELinux security policy is enforced.
# permissive - SELinux prints warnings instead of enforcing.
# disabled - No SELinux policy is loaded.
SELINUX=disabled
# SELINUXTYPE= can take one of these two values:
# targeted - Targeted processes are protected,
# mls - Multi Level Security protection.
SELINUXTYPE=targeted