第一种方法：
屏蔽telnet功能。
telnet功能被屏蔽掉后，任何用户都无法登录，当然ROOT也无法登录。但这种方法太过极端。故不可取。
第二方法：
在/etc/default/login中增加一行命令
CONSOLE＝tty01
经过这样设置后，用户只能在第一个控制台上以ROOT登录。任何其他控制台和所有远程用户均无法登录。
第三种方法：
只允许指定的用户以ROOT用户远程登录
若服务器的地址为134.33.86.13;允许地址为134.33.86.17和134.33.86.18的机器以ROOT登录。
1. 首先编辑/etc/hosts文件，内容如下：
127.0.0.1 local
134.33.86.13 jnzy.jndx.com
134.33.86.17 root2
134.33.86.18 root3
2. 写一段程序放入文件/.profile中
# @(#) root.profile 68.1 98/01/20
#
# Copyright (C) 1989-1998 The Santa Cruz Operation, Inc.
# All Rights Reserved.
# The information in this file is provided for the exclusive use of
# the licensees of The Santa Cruz Operation, Inc. Such users have the
# right to use, modify, and incorporate this code into other products
# for purposes authorized by the license agreement provided they include
# this notice and the associated copyright notice with any such product.
# The information in this file is provided "AS IS" without warranty.
#
TY=`tty|cut -b 9-12`
WH=`finger|cut -b 32-79|grep "$TY"|cut -b 29-39`
KK=`tty|cut -b 6-9`
if [ "$KK" = "ttyp" ]
then
WH=$WH
else
WH="local"
fi
trap 1 2 3 9 15
if [ "$WH" = "local" -o "$WH" = "root2" ]
then
SHELL=/bin/sh
HOME=/
PATH=/bin:/etc:/usr/bin:/tcb/bin:/zy
# set terminal type
eval `tset -m scoansi:${TERM:-scoansi} -m :\?${TERM:-scoansi} -e -r -s -Q`
export TERM PATH SHELL HOME
[ -x /bin/mesg ] && mesg n # if mesg is installed...
date
else
echo "you can not telnet by root：\07\07" #拒绝登录并响铃告警
echo "press any key to exit"＃按任意键退出
read sad
exit
fi
这样只有在IP地址为134.33.8.17和134.33.86.18两台机器上能以ROOT用户登录，其他地址不可以用ROOT登录。
从而保证系统安全。