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使用 ssh 远程登录 Linux 时，使用公钥认证的方式比采用密码的方式更安全、更方便。本文简单的介绍如何在 Ubuntu 18.04 Server 中设置如何公钥认证方式登录。

本文假设的环境, 服务器OS: Ubuntu 18.04 Server, 其IP地址为: 192.168.31.60, 服务器已经配置了一个名为 stu 的用户，并通过一台安装 Ubuntu 18.04 的客户机来准备环境

在客户机上生成密钥对

在客户机上打开一个终端窗口，进入当前用户的用户目录。首先准备一个 .ssh 目录用来存放后面要生成的 key 的信息。顺序执行以下命令:

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mkdir -p $HOME/.ssh
chmod 0700 $HOME/.ssh

准备好目录以后，执行以下命令生成 key:

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ssh-keygen -t rsa -b 4096 -C "master-srv-01"

程序会提示一些问题，全面选择默认设置（回车即可）。 完成以后，系统显示:

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Your identification has been saved in /home/stu/.ssh/id_rsa.
Your public key has been saved in /home/stu/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:ppKqA/AMnFd1V1+9Y6qPIQz7EHAjr2XgB+O+T//4z30 master-srv-01
The key's randomart image is:
+---[RSA 4096]----+
|      .. . ...  o|
|     .  . .   . o|
|. . .* o       ..|
|oo .o O .      + |
|.+.  o BS     o .|
|. o ..=o=    .   |
|.   oo.+ o ..    |
|.  . .o + o.+ . E|
|.o.  ... +o+o+ ..|
+----[SHA256]-----+

生成以后，可以查看 .ssh 目录，可以看到生成了相关的文件，执行:

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ls -la .ssh

系统显示：

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-rw------- 1 stu stu 3243 Feb 13 00:36 id_rsa
-rw-r--r-- 1 stu stu  739 Feb 13 00:36 id_rsa.pub

把public key 安装到服务器上

这里，我们是使用 ssh-copy-id 命令来完成把 public key 安装道服务器上。执行

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ssh-copy-id -i $HOME/.ssh/id_rsa.pub stu@192.168.31.60

系统显示:

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/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/stu/.ssh/id_rsa.pub"
The authenticity of host '192.168.31.60 (192.168.31.60)' can't be established.
ECDSA key fingerprint is SHA256:jCPY99rJzLBUlUpBetgSr0RWbwRs/EGPhgcdJ0DS7bo.
Are you sure you want to continue connecting (yes/no)? yes
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
stu@192.168.31.60's password: 

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'stu@192.168.31.60'"
and check to make sure that only the key(s) you wanted were added.

说明安装成功。

测试登录

在客户机上执行：

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sh stu@192.168.31.60

如果前面的步骤都正常，应该可以登录到服务器上了，系统显示类似以下的信息:

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Welcome to Ubuntu 18.04.3 LTS (GNU/Linux 4.15.0-76-generic x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

  System information as of Thu Feb 13 00:57:38 UTC 2020

  System load:  0.0               Processes:             96
  Usage of /:   49.5% of 5.84GB   Users logged in:       0
  Memory usage: 7%                IP address for enp0s3: 192.168.31.60
  Swap usage:   0%

 * Multipass 1.0 is out! Get Ubuntu VMs on demand on your Linux, Windows or
   Mac. Supports cloud-init for fast, local, cloud devops simulation.

     https://multipass.run/

54 packages can be updated.
0 updates are security updates.


Last login: Thu Feb 13 00:50:39 2020 from 192.168.31.10