1.Ubuntu安装telnet
安装openbsd-inetd sudo apt-get install openbsd-inetd 安装telnetd sudo apt-get install telnetd 重启openbsd-inetd sudo /etc/init.d/openbsd-inetd restart 查看telnet运行状态 sudo netstat -a | grep telnet 登录 telnet IP address
访问：
hongdada@ubuntu:~$ telnet 192.168.1.203 22 Trying 192.168.1.203... telnet: Unable to connect to remote host: Connection refused
使用 netstat -napt查看端口是否被监听
hongdada@ubuntu:~$ netstat -napt （并非所有进程都能被检测到，所有非本用户的进程信息将不会显示，如果想看到所有信息，则必须切换到 root 用户） 激活Internet连接 (服务器和已建立连接的) Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 0.0.0.0:6379 0.0.0.0:* LISTEN - tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN - tcp 0 0 0.0.0.0:23 0.0.0.0:* LISTEN - tcp 0 0 192.168.1.203:44850 124.192.164.34:80 ESTABLISHED 5200/chrome tcp 0 0 192.168.1.203:39874 119.75.213.61:443 ESTABLISHED
发现22并没有被监听
安装OpenSSH
hongdada@ubuntu:~$ sudo apt-get install openssh-server [sudo] hongdada 的密码： 正在读取软件包列表... 完成 正在分析软件包的依赖关系树 正在读取状态信息... 完成 下列软件包是自动安装的并且现在不需要了： linux-headers-4.4.0-21 linux-headers-4.4.0-21-generic linux-headers-4.4.0-62 linux-headers-4.4.0-62-generic linux-headers-4.4.0-63 linux-headers-4.4.0-63-generic linux-headers-4.4.0-64 linux-headers-4.4.0-64-generic linux-headers-4.4.0-66 linux-headers-4.4.0-66-generic linux-image-4.4.0-21-generic linux-image-4.4.0-62-generic linux-image-4.4.0-63-generic linux-image-4.4.0-64-generic linux-image-4.4.0-66-generic linux-image-extra-4.4.0-21-generic linux-image-extra-4.4.0-62-generic linux-image-extra-4.4.0-63-generic linux-image-extra-4.4.0-64-generic linux-image-extra-4.4.0-66-generic 使用'sudo apt autoremove'来卸载它(它们)。 将会同时安装下列软件： ncurses-term openssh-client openssh-sftp-server ssh-import-id 建议安装： ssh-askpass libpam-ssh keychain monkeysphere rssh molly-guard 下列【新】软件包将被安装： ncurses-term openssh-server openssh-sftp-server ssh-import-id 下列软件包将被升级： openssh-client 升级了 1 个软件包，新安装了 4 个软件包，要卸载 0 个软件包，有 136 个软件包未被升级。 需要下载 1,222 kB 的归档。 解压缩后会消耗 5,145 kB 的额外空间。 您希望继续执行吗？ [Y/n] Y 获取:1 http://mirrors.aliyun.com/ubuntu xenial-updates/main amd64 openssh-client amd64 1:7.2p2-4ubuntu2.2 [587 kB] 获取:2 http://mirrors.aliyun.com/ubuntu xenial/main amd64 ncurses-term all 6.0+20160213-1ubuntu1 [249 kB] 获取:3 http://mirrors.aliyun.com/ubuntu xenial-updates/main amd64 openssh-sftp-server amd64 1:7.2p2-4ubuntu2.2 [38.7 kB] 获取:4 http://mirrors.aliyun.com/ubuntu xenial-updates/main amd64 openssh-server amd64 1:7.2p2-4ubuntu2.2 [338 kB] 获取:5 http://mirrors.aliyun.com/ubuntu xenial/main amd64 ssh-import-id all 5.5-0ubuntu1 [10.2 kB] 已下载 1,222 kB，耗时 1秒 (1,221 kB/s) 正在预设定软件包 ... (正在读取数据库 ... 系统当前共安装有 383933 个文件和目录。) 正准备解包 .../openssh-client_1%3a7.2p2-4ubuntu2.2_amd64.deb ... 正在将 openssh-client (1:7.2p2-4ubuntu2.2) 解包到 (1:7.2p2-4ubuntu2.1) 上 ... 正在选中未选择的软件包 ncurses-term。 正准备解包 .../ncurses-term_6.0+20160213-1ubuntu1_all.deb ... 正在解包 ncurses-term (6.0+20160213-1ubuntu1) ... 正在选中未选择的软件包 openssh-sftp-server。 正准备解包 .../openssh-sftp-server_1%3a7.2p2-4ubuntu2.2_amd64.deb ... 正在解包 openssh-sftp-server (1:7.2p2-4ubuntu2.2) ... 正在选中未选择的软件包 openssh-server。 正准备解包 .../openssh-server_1%3a7.2p2-4ubuntu2.2_amd64.deb ... 正在解包 openssh-server (1:7.2p2-4ubuntu2.2) ... 正在选中未选择的软件包 ssh-import-id。 正准备解包 .../ssh-import-id_5.5-0ubuntu1_all.deb ... 正在解包 ssh-import-id (5.5-0ubuntu1) ... 正在处理用于 man-db (2.7.5-1) 的触发器 ... 正在处理用于 ufw (0.35-0ubuntu2) 的触发器 ... 正在处理用于 systemd (229-4ubuntu16) 的触发器 ... 正在处理用于 ureadahead (0.100.0-19) 的触发器 ... 正在设置 openssh-client (1:7.2p2-4ubuntu2.2) ... 正在设置 ncurses-term (6.0+20160213-1ubuntu1) ... 正在设置 openssh-sftp-server (1:7.2p2-4ubuntu2.2) ... 正在设置 openssh-server (1:7.2p2-4ubuntu2.2) ... Creating SSH2 RSA key; this may take some time ... 2048 SHA256:Fggzi+si7eAimez/6obJ9ykFiTnBvfOkQk1D3G198KI root@ubuntu (RSA) Creating SSH2 DSA key; this may take some time ... 1024 SHA256:l1qkn+YwdNyBnNVurPG2Qg22CrVL/41VAyqqZr6I1Lc root@ubuntu (DSA) Creating SSH2 ECDSA key; this may take some time ... 256 SHA256:QCmE/BZXVtoThmb0gmxbRD7+vzTX+cbVud6e9EXW2cE root@ubuntu (ECDSA) Creating SSH2 ED25519 key; this may take some time ... 256 SHA256:1D0iLpOURGJF4sMTzCoittU3V27FyXO72hr/HFJtO2U root@ubuntu (ED25519) 正在设置 ssh-import-id (5.5-0ubuntu1) ... 正在处理用于 systemd (229-4ubuntu16) 的触发器 ... 正在处理用于 ureadahead (0.100.0-19) 的触发器 ... 正在处理用于 ufw (0.35-0ubuntu2) 的触发器 ... hongdada@ubuntu:~$ ps -e|grep ssh 6549 ? 00:00:00 sshd hongdada@ubuntu:~$ netstat -antp|grep 22 （并非所有进程都能被检测到，所有非本用户的进程信息将不会显示，如果想看到所有信息，则必须切换到 root 用户） tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN - tcp 1 0 192.168.1.203:41412 23.219.133.226:443 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:42228 117.122.217.6:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:42222 117.122.217.6:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:43846 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:51622 124.192.164.48:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:43850 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 0 0 192.168.1.203:40188 115.28.122.210:80 TIME_WAIT - tcp 0 0 192.168.1.203:43802 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 32 0 192.168.1.203:41390 23.219.133.226:443 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:42224 117.122.217.6:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:42226 117.122.217.6:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:43824 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:34240 13.124.96.226:80 CLOSE_WAIT 5200/chrome tcp 32 0 192.168.1.203:41394 23.219.133.226:443 CLOSE_WAIT 5200/chrome tcp 0 0 192.168.1.203:43854 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:43804 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:51004 119.75.222.191:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:45140 52.221.26.127:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:52822 59.110.88.38:80 CLOSE_WAIT 5200/chrome tcp 0 1 192.168.1.203:43178 119.75.222.22:80 FIN_WAIT1 - tcp 1 0 192.168.1.203:42206 117.122.217.6:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:34306 13.124.96.226:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:43164 119.75.222.22:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:42218 117.122.217.6:80 CLOSE_WAIT 5200/chrome tcp 0 0 192.168.1.203:43848 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:43176 119.75.222.22:80 CLOSE_WAIT 5200/chrome tcp 0 0 192.168.1.203:43840 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:34238 13.124.96.226:80 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:43412 124.14.17.221:80 CLOSE_WAIT 5200/chrome tcp 0 0 192.168.1.203:41392 23.219.133.226:443 ESTABLISHED 5200/chrome tcp 0 1 192.168.1.203:51006 119.75.222.191:80 FIN_WAIT1 - tcp 0 0 192.168.1.203:43826 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:43844 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 32 0 192.168.1.203:41396 23.219.133.226:443 CLOSE_WAIT 5200/chrome tcp 0 0 192.168.1.203:43800 180.76.22.33:443 CLOSE_WAIT 5200/chrome tcp 1 0 192.168.1.203:34236 13.124.96.226:80 CLOSE_WAIT 5200/chrome tcp 0 0 192.168.1.203:58226 203.208.43.90:80 ESTABLISHED 5200/chrome tcp 0 0 192.168.1.203:58224 203.208.43.90:80 ESTABLISHED 5200/chrome tcp 1 0 192.168.1.203:45142 52.221.26.127:80 CLOSE_WAIT 5200/chrome tcp6 0 0 :::22 :::* LISTEN - hongdada@ubuntu:~$ telnet 127.0.0.1 22 Trying 127.0.0.1... Connected to 127.0.0.1. Escape character is '^]'. SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu2.2 Protocol mismatch. Connection closed by foreign host. hongdada@ubuntu:~$
Ubuntu 默认安装了client端，但是没有安装Server端，所以现在要安装openssh-server
sudo apt-get install openssh-server
安装以后查看22端口是否被监听
netstat -antp|grep 22
如果只有ssh-agent那ssh-server还没有启动，需要/etc/init.d/ssh start或者service ssh start，如果看到sshd那说明ssh-server已经启动了。
ssh-server配置文件位于/ etc/ssh/sshd_config，在这里可以定义SSH的服务端口，默认端口是22，你可以自己定义成其他端口号，如222。然后重启SSH服务：
sudo /etc/init.d/ssh restart
现在使用xshell访问Ubuntu
连接：
Xshell 5 (Build 1124) Copyright (c) 2002-2017 NetSarang Computer, Inc. All rights reserved. Type `help' to learn how to use Xshell prompt. [c:~]$ Connecting to 192.168.1.203:22... Connection established. To escape to local shell, press 'Ctrl+Alt+]'. Welcome to Ubuntu 16.04.2 LTS (GNU/Linux 4.4.0-83-generic x86_64) * Documentation: https://help.ubuntu.com * Management: https://landscape.canonical.com * Support: https://ubuntu.com/advantage 140 个可升级软件包。 0 个安全更新。 Last login: Tue Jul 18 23:51:42 2017 from 192.168.1.222 hongdada@ubuntu:~$