su切换的原因

hosthouse

我由root转换到普通用户ipnetv4下出现这样的问题
su: warning: cannot change directory to /home/ipnetv4/: Permission denied
su: /bin/bash: Permission denied

我chmod 755 home解决了su: warning: cannot change directory to /home/ipnetv4/: Permission denied

不过su: /bin/bash: Permission denied 这个是什么原因呢？
请教一下各位
-rwxr-xr-x  1 root root 616312 2004-12-07  /bin/bash