How to Install and Enable OpenSSH on Ubuntu 20.04

https://linuxhint.com/how-to-install-and-enable-openssh-on-ubuntu/

https://linuxconfig.org/ubuntu-20-04-ssh-server

https://ubuntu.com/server/docs/service-openssh

 

OpenSSH, abbreviated from OpenBSD Secure Shell, is a tool used to secure remote connectivity between the host and its client via SSH protocol. Since it uses the SSH protocol for network communication, it cares about connection hijacking and attacks, and it also encrypts the network traffic communication by using different authentication methods. This post will learn how to install the OpenSSH server on Ubuntu 20.04 and how to enable it for remote network communication.

Installation

By default, remote access is not allowed in Ubuntu 20.04 using the SSH, and we first have to enable the SSH. Just follow the step-by-step guide given below, and you will have the OpenSSH server installed and enabled on your ubuntu 20.04 LTS system for remote access.

Step 1: Open up your terminal and update the system’s APT cache repository

First of all, fire up the terminal in your ubuntu system by using the shortcut keys (CTRL+ALT+T) and type the command given below to update the system’s APT cache repository.

$ sudo apt update

The system’s APT cache repository is updated successfully.

Step 2: Install OpenSSH server

Right after updating your system’s APT package repository, install the OpenSSH server on your Ubuntu machine by typing the command provided below.

$ sudo apt install openssh-server openssh-client

Type “Y” and hit “Enter” to grant permission for taking additional disk space for the OpenSSH server’s installation.

After taking some time, the OpenSSH server’s installation process will be completed, and the SSH server will automatically start.

Step 3: Verify that the SSH service is running

To verify the status of the SSH server, type the command given below.

$ sudo systemctl status ssh

If you have got the output that SSH service status is active, you must be perfectly ready to move forward.

Type “q” to go back and configure the firewall.

Step 4: Configure the firewall

Now you need to configure the firewall of Ubuntu using the UFW tool provided by Ubuntu itself. To enable the firewall for any remote machine to access this Ubuntu machine, you need to open an SSH port. The command for configuring and allowing remote access is typed below.

$ sudo ufw allow ssh

After allowing SSH, it is time to enable the firewall as well. To check if it is enabled or not, the command for checking the status of UFW is given below

$ sudo ufw status

If it is inactive and the case is the same for you, then you need to enable it by typing the command

$ sudo ufw enable

After enabling the UFW, check the status again

$ sudo ufw status

You can see that SSH port 22 is opened. If you have the same output as shown in the picture, then the system is ready for remote connections via SSH.

Conclusion

This post has shown you the step-by-step guide on how to install and enable the OpenSSH server on Ubuntu 20.04 for remote connections. After this configuration, you can log in to this machine from any remote machine via SSH.

https://blog.csdn.net/zhou562334410/article/details/82999673

ssh服务的管理命令

1.什么是ssh？

SSH（全称 Secure Shell)是一种加密的网络协议。使用该协议的数据将被加密，如果在传输中间数据泄漏，也可以确保没有人能读取出有用信息。要使用 SSH，目标机器应该安装 SSH 服务端应用程序，因为 SSH 是基于客户-服务模式的。 当你想安全的远程连接到主机，可中间的网络（比如因特网）并不安全，通常这种情况下就会使用 SSH。

ssh的连接方式

通常使用 SSH 的方式就是不加任何选项参数,仅仅输入 "ssh"。下面是示例：

2. ssh的远程主机连接

ssh     username@ip            表示文本模式的连接

ssh  -X  username@ip          表示可以在连接成功后开机图形

注意：第一次链接陌生主机是要建立认证文件；所以会询问是否建立，需要输入yes； 在次链接此台主机时，因为已经生成~/.ssh/know_hosts文件所以不需要再次输入yes。

远程复制：

          scp file root@ip:dir         上传

           scp root@ip:file dir        下载

.sshd的key认证

                   1.ssh-keygen                生成密钥的命令

           2.加密服务：

ssh-copy-id -i /root/.ssh/id_rsa.pub root@ip1           加密sshd服务   （ip1  为服务机的ip）

          3.分发钥匙：

scp /root/.ssh/id_rsa    root@ip2:/root/.ssh/        将钥匙发送到客户机上（ip2  为客户机ip）

            4.测试：

 在客户机中，ssh   root@ip2     连接时发现直接登陆不需要root登陆系统的密码认证

systemctl	服务控制命令
sysremctl    status   sshd	查看服务状态，inactive（不可用），active    （可用）
systemctl    start    sshd	开启服务
systemctl    stop     sshd	关闭服务
systemctl    restart  sshd	重启服务
systemctl    reload   sshd	重新加载服务配置
systemctl    enable   sshd	设置服务开机启动
systemctl    disable  sshd	设置服务开机不启动
systemctl    list-units	列出已经开启服务当前状态
systemctl    list-unit-files	列出所有服务开机启动的状态disable,enable  ,static
systemctl    list-dependencies	列出服务的依赖关系
systemctl    set-default  multi-user.target	设定系统启动级别为多用户模式
systemctl    set-default  graphical.target	设定系统启动级别为图形模式

3.指定端口

SSH 默认使用的端口号是 22。大多现代的 Linux 系统 22 端口都是开放的。如果你运行 ssh 程序而没有指定端口号，它直接就是通过 22 端口发送请求的。

一些系统管理员会改变 SSH 的默认端口号。让我们试试，现在端口号是 1234.要连上那主机，就要使用 **-p* 选项，后面在加上 SSH 端口号。一些系统管理员会改变 SSH 的默认端口号。让我们试试，现在端口号是 1234.要连上那主机，就要使用 *-p* 选项，后面在加上 SSH 端口号。

ssh  [远程主机的ip]   -p 1234

要改变端口号，我们需要修改 /etc/ssh/ssh_config 文件，找到此行：

Port 22

把它换成其他的端口号，比如上面示例的 1234 端口，然后重启 SSH 服务。

3. 添加sshd登陆登陆信息

vim /etc/motd            文件内容就是登陆后显示的信息

4.用户的登陆审计

     w                 查看正在使用当前系统的用户
              -f         查看使用来源
              -i         显示IP
     last        ##查看使用过并退出的用户信息

     lastb        ##试图登陆但没成功的用户