一、概述

搭建mysql数据库并做安全加固
ln -s /dev/null /home/mysql/.mysql_history
vi /home/mysql/.profile
export MYSQL_HISTFILE=/dev/null

第二次登陆到root，切换mysql用户，直接报错
-bash: /dev/null: Permission denied
-bash: /dev/null: Permission denied
-bash: /dev/null: Permission denied
-bash: /dev/null: Permission denied
-bash: /dev/null: Permission denied
-bash: /dev/null: Permission denied

查看/dev/null权限
ll /dev/null
-rwxr-x---  1 root root           9 Jul 25 17:07 null

而其他正常的权限如下
crw-rw-rw-   1 root   wheel         3,   2 Jul 25 14:08 null

解决步骤如下：
rm -f /dev/null; mknod -m 666 /dev/null c 1 3