Linux telnet 安装及介绍 1、软件安装及配置1.1 安装telnet-server 、telnet 和 xinetd1.2 配置文件修改（CentOS 7 以上可跳过）1.3 启动服务并设置开机启动1.4 查看端口号是否监听正常 2、软件测试2.1 telnet 自测失败2.2 telnet 自测失败解决办法2.3 telnet 自测成功 3、telnet 端口号修改3.1 修改 telnet.socket 文件3.2 修改 /etc/services 中的默认端口3.3 修改 /etc/xinetd.conf 文件
1、软件安装及配置 1.1 安装telnet-server 、telnet 和 xinetd
telnet 的自启动依赖于 xinetd ，需要同时进行安装。
[root@Tang ~]# yum install xinetd telnet-server telnet -y 1.2 配置文件修改（CentOS 7 以上可跳过）现在很多 CentOS 7 版本安装 telnet-server 以及 xinetd 没有 telnet 的配置文件。
如果 telnet 文件不存在的话，可以跳过这部分的更改。
[root@Tang ~]# ll /etc/xinetd.d/telnetls: cannot access /etc/xinetd.d/telnet: No such file or directory如果下面文件存在，请更改配置 telnet 可以 root 登录，把 disable = no 改成disable = yes 。
[root@Tang yum.repos.d]# cat /etc/xinetd.d/telnet# 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} [root@Tang yum.repos.d]# vim /etc/xinetd.d/telnet[root@Tang yum.repos.d]# cat /etc/xinetd.d/telnet# default: on# description: The telnet server serves telnet sessions; it uses # unencrypted username/password pairs for authentication.service telnet{ disable = yes flags = REUSE socket_type = stream wait = no user = root server = /usr/sbin/in.telnetd log_on_failure += USERID}配置telnet登录的终端类型，在/etc/securetty文件末尾增加一些pts终端，如下
pts/0pts/1pts/2pts/3配置之后的显示
[root@Tang ~]# vim /etc/securetty[root@Tang ~]# tail -5 /etc/securettyxvc0pts/0pts/1pts/2pts/3 1.3 启动服务并设置开机启动 [root@Tang ~]# systemctl enable xinetd[root@Tang ~]# systemctl enable telnet.socketCreated symlink from /etc/systemd/system/sockets.target.wants/telnet.socket to /usr/lib/systemd/system/telnet.socket.[root@Tang ~]# systemctl start xinetd[root@Tang ~]# systemctl start telnet.socket 1.4 查看端口号是否监听正常 [root@Tang ~]# ss -tnl | grep 23LISTEN 0 128 :::23 :::* 2、软件测试 2.1 telnet 自测失败因为安装了 telnet 客户端，所以可以进行自测。
发现自测失败。
[root@Tang ~]# telnet localhostTrying ::1...Connected to localhost.Escape character is '^]'.Kernel 3.10.0-957.el7.x86_64 on an x86_64Tang login: rootPassword: Login incorrectTang login: Connection closed by foreign host. 2.2 telnet 自测失败解决办法修改 /etc/pam.d/remote 文件，对 第二行进行 注释。
# 查看文件[root@Tang ~]# cat /etc/pam.d/remote#%PAM-1.0auth required pam_securetty.soauth substack password-authauth include postloginaccount required pam_nologin.soaccount include password-authpassword include password-auth# pam_selinux.so close should be the first session rulesession required pam_selinux.so closesession required pam_loginuid.so# pam_selinux.so open should only be followed by sessions to be executed in the user contextsession required pam_selinux.so opensession required pam_namespace.sosession optional pam_keyinit.so force revokesession include password-authsession include postlogin# 修改文件[root@Tang ~]# vim /etc/pam.d/remote # 查看修改过后的文件[root@Tang ~]# cat /etc/pam.d/remote#%PAM-1.0#auth required pam_securetty.soauth substack password-authauth include postloginaccount required pam_nologin.soaccount include password-authpassword include password-auth# pam_selinux.so close should be the first session rulesession required pam_selinux.so closesession required pam_loginuid.so# pam_selinux.so open should only be followed by sessions to be executed in the user contextsession required pam_selinux.so opensession required pam_namespace.sosession optional pam_keyinit.so force revokesession include password-authsession include postlogin 2.3 telnet 自测成功 [root@Tang ~]# telnet localhostTrying ::1...Connected to localhost.Escape character is '^]'.Kernel 3.10.0-957.el7.x86_64 on an x86_64Tang login: rootPassword: Last failed login: Sun May 17 22:11:20 CST 2020 from localhost on pts/2There was 1 failed login attempt since the last successful login.Last login: Sun May 17 21:48:39 from bogon[root@Tang ~]# w 22:16:24 up 31 min, 4 users, load average: 0.00, 0.01, 0.04USER TTY FROM LOGIN@ IDLE JCPU PCPU WHATroot tty1 21:45 27:36 0.10s 0.10s -bashroot pts/0 bogon 21:47 27:52 0.00s 0.00s -bashroot pts/1 bogon 21:48 0.00s 0.03s 0.00s telnet localhostroot pts/2 localhost 22:16 0.00s 0.00s 0.00s w[root@Tang ~]# whoroot tty1 2020-05-17 21:45root pts/0 2020-05-17 21:47 (bogon)root pts/1 2020-05-17 21:48 (bogon)root pts/2 2020-05-17 22:16 (localhost) 3、telnet 端口号修改 3.1 修改 telnet.socket 文件 root@Tang ~]# cat /usr/lib/systemd/system/telnet.socket[Unit]Description=Telnet Server Activation SocketDocumentation=man:telnetd(8)[Socket]ListenStream=23Accept=true[Install]WantedBy=sockets.target[root@Tang ~]# vim /usr/lib/systemd/system/telnet.socket[root@Tang ~]# cat /usr/lib/systemd/system/telnet.socket[Unit]Description=Telnet Server Activation SocketDocumentation=man:telnetd(8)[Socket]ListenStream=9999Accept=true[Install]WantedBy=sockets.target[root@Tang ~]# systemctl restart telnet.socketWarning: telnet.socket changed on disk. Run 'systemctl daemon-reload' to reload units.[root@Tang ~]# systemctl daemon-reload[root@Tang ~]# ss -tnlState Recv-Q Send-Q Local Address:Port Peer Address:Port LISTEN 0 128 *:22 *:* LISTEN 0 100 127.0.0.1:25 *:* LISTEN 0 128 :::9999 :::* LISTEN 0 128 :::22 :::* LISTEN 0 100 ::1:25 :::* 3.2 修改 /etc/services 中的默认端口 [root@Tang ~]# cat /etc/services | grep ^telnettelnet 23/tcptelnet 23/udptelnets 992/tcptelnets 992/udptelnetcpcd 3696/tcp # Telnet Com Port Controltelnetcpcd 3696/udp # Telnet Com Port Control 3.3 修改 /etc/xinetd.conf 文件 # 增加如下内容# Defining Telnet service telnet { port 9090 #9090：请用自己的端口号代替 }