安装telnet服务

#环境

os: OpenSUSE Tumbleweed
pc: Thinkpad T460s

#描述

远程登陆方式主要有三种：

1 明文文本模式:telnet,rsh等，不安全，现在很少使用，但在一些特殊场所还会有所使用。
2 加密文本模式:ssh
3 图形模式：xdmcp,vnc,rdp等

1.查询系统中是否已经安装了telnet服务

1	[root@ovirt ~]# rpm -qa \|grep telnet

2.安装telnet-server服务端及telnet客户端包

1	[root@ovirt ~]# yum install telnet-server talnet

3.telnet服务是由xinetd守护进程维护的，需要启动xinetd服务

1	[root@ovirt ~]# yum install xinetd

4.rhel7版本使用systemd代替init.d维护启动进程，7版本以下使用init.d管理

1	[root@ovirt ~]# systemctl start xinetd

7版本以下修改/etc/xinetd.d/telnet

[root@hostovirt ~]# vi /etc/xinetd.d/telnet 
# default: on
# description: The telnet server serves telnet sessions; it uses \
#       unencrypted username/password pairs for authentication.
service telnet
{
        flags           = REUSE
        socket_type     = stream        
        wait            = no
        user            = root
        server          = /usr/sbin/in.telnetd
        log_on_failure  += USERID
        disable         = no    # 这个配置项由yes修改为no
[root@ovirt ~]# service xinetd start

5.启动telnet-server,7版本使用systemd,7版本以下使用init.d启动xinetd后会自动启动telnet

1	[root@ovirt etc]# systemctl start telnet.socket

6.防火墙开放端口

1 2	[root@ovirt etc]# firewall-cmd --zone=public --add-port=23/tcp success

iptables操作方法：

1
2
3

[root@hostovirt ~]# iptables -I INPUT -p tcp --dport 23 -j ACCEPT
[root@ovirt etc]# firewall-cmd --zone=public --list-ports
23/tcp

7.使用nmap查看端口状态,STATE为open状态

haotianfei@tianfei-opensuse:~> nmap 192.168.56.101 -p 23
Starting Nmap 7.70 ( https://nmap.org ) at 2018-10-11 14:41 CST
Nmap scan report for ovirt.wasu (192.168.56.101)
Host is up (0.00037s latency).

PORT   STATE    SERVICE
23/tcp filtered telnet

Nmap done: 1 IP address (1 host up) scanned in 0.05 seconds

haotianfei@tianfei-opensuse:~> nmap 192.168.56.101 -p 23
Starting Nmap 7.70 ( https://nmap.org ) at 2018-10-11 14:43 CST
Nmap scan report for ovirt.wasu (192.168.56.101)
Host is up (0.00032s latency).

PORT   STATE SERVICE
23/tcp open  telnet

Nmap done: 1 IP address (1 host up) scanned in 0.05 seconds

8.出于安全原因，默认telnet终端是不能登陆的，暂时移除/etc/securetty

haotianfei@tianfei-opensuse:~> telnet -l root 192.168.56.101
Trying 192.168.56.101...
Connected to 192.168.56.101.
Escape character is '^]'.
Password: 
Login incorrect

ovirt login: 
[root@ovirt etc]# mv /etc/securetty{,.bak}
haotianfei@tianfei-opensuse:~> telnet -l root 192.168.56.101 23
Trying 192.168.56.101...
Connected to 192.168.56.101.
Escape character is '^]'.
Password: 
Last failed login: Thu Oct 11 02:44:46 EDT 2018 from ::ffff:192.168.56.1 on pts/1
There were 3 failed login attempts since the last successful login.
Last login: Thu Oct 11 02:35:13 from ::ffff:192.168.56.1
[root@ovirt ~]#