UBUNTU开启TELNET服务

1. sudo apt-get install xinetd telnetd
2. 安装成功后，系统也会有相应提示，

sudo vi /etc/inetd.conf并加入以下一行
telnet stream tcp nowait telnetd /usr/sbin/tcpd /usr/sbin/in.telnetd
3. sudo vi /etc/xinetd.conf并加入以下内容：
# Simple configuration file for xinetd
#
# Some defaults, and include /etc/xinetd.d/


defaults
{


# Please note that you need a log_type line to be able to use log_on_success
# and log_on_failure. The default is the following :
# log_type = SYSLOG daemon info


instances = 60
log_type = SYSLOG authpriv
log_on_success = HOST PID
log_on_failure = HOST
cps = 25 30
}


includedir /etc/xinetd.d
4. sudo vi /etc/xinetd.d/telnet并加入以下内容：
# default: on
# description: The telnet server serves telnet sessions; it uses \
# unencrypted username/password pairs for authentication.
service telnet
{
disable = no
flags = REUSE
socket_type = stream
wait = no
user = root
server = /usr/sbin/in.telnetd
log_on_failure += USERID
}
5. 重启机器或重启网络服务sudo /etc/init.d/xinetd restart
6. 使用TELNET客户端远程登录即可进行非root用户访问。
7.使用root登录： mv /etc/securetty /etc/securetty.bak 这样root可以登录了。也可这样:
修改/etc/pam.d/login这个文件。只需将下面一行注释掉即可。
#auth required lib/security/pam_securetty.so


8. 详细配制/etc/xinetd.d/telnet
service telnet
{
disable =no
bind =192.168.1.2
only_from=192.168.1.0/24
#上面这两行说明仅提供内部网段！
Instance =UNLIMITED
Nice =0
Flags =REUSE
socket_type=stream
wait =no
user =root
#server =/usr/sbin/telnetd
server =/usr/sbin/in.telnetd
server_args =-a none
log_on_failure +=USERID
}

service telnet
{
disable =no
bind =140.116.142.196
only_from=140.116.0.0/16
no_access=140.116.32.{10,26}
#上面三行设置外部较为严格的限制
instance =10
umask =022
nice =10
flags =REUSE
socket_type=stream
wait =no
user =root
#server =/usr/sbin/telnetd
server =/usr/sbin/in.telnetd
log_on_failure +=USERID
}
9.加设防火墙iptables：
如果想要针对192.168.0.0/24这个网段及61.xxx.xxx.xxx这个IP进行telnet开放，可以增加下面几行规则：
/sbin/iptables -A INPUT -p tcp -i eth0 -s 192.168.0.0/24 --dport 23 -j ACCEPT
/sbin/iptables -A INPUT -p tcp -i eth0 -s 61.xxx.xxx.xxx --dport 23 -j ACCEPT
/sbin/iptables -A INPUT -p tcp -i eth0 --dport 23 -j DROP


10.加设防火墙/etc/hosts.allow(deny)机制：
上面开放了192.168.0.0/24这个网段，但是如果您只想让其中的192.168.0.1~192.168.0.5进入，可以设置如下 ：

vi /etc/hosts.allow
in.telnetd:192.168.0.1,192.168.0.2,192.168.0.3,192.168.0.4,192.168.0.5:allow


centos :telnet
http://tiger506.blog.51cto.com/318536/385344
如果telnet localhost出现：
-bash: telnet: command not found
的错误，安装telnet客户端
sudo yum install telnet