CentOS4.6自带APACHE不能更改默认根目录，虚拟主机指向其他目录不认。是SELinux激活的原因，关闭他：
# vi /etc/selinux/config
# 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 - SELinux is fully disabled.
SELINUX=disabled
# SELINUXTYPE= type of policy in use. Possible values are:
# targeted - Only targeted network daemons are protected.
# strict - Full SELinux protection.
SELINUXTYPE=targeted
将SELINUX=disabled
重起机器，发现SSH链接不上了。以为修改错了，造成系统起不来了。而且控制终端也没用信号。网络断了。即使系统无法起来，终端也应该有信号。登录后，网络配置也丢失了。重新配置网络地址后，还是无法链接。到最后，换了一个网卡接口。可以了，接口坏了。