275 lines
7.8 KiB
Markdown
275 lines
7.8 KiB
Markdown
---
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layout: post
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title: "Linux SSH 服务的安装和使用"
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subtitle: ""
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description: "本文简要的对 Linux 下 SSH 服务的安装、配置和使用进行说明。"
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excerpt: "用于指导 Linux 下 SSH 服务的配置。"
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date: 2022-10-10 16:48:00
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author: "Rick Chan"
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tags: ["Applications", "SSH"]
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categories: ["Software"]
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published: true
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math: false
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---
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- [1. 安装 SSH Server](#1-安装-ssh-server)
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- [2. 开启 SSH 服务](#2-开启-ssh-服务)
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- [3. SSH 登陆](#3-ssh-登陆)
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- [4. SCP 上传和下载](#4-scp-上传和下载)
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- [5. 免密访问](#5-免密访问)
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- [6. Client SSH Config 文件](#6-client-ssh-config-文件)
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- [6.1. 增加 ssh-rsa 授权方式](#61-增加-ssh-rsa-授权方式)
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- [6.2. 设置 Host 用户名和端口](#62-设置-host-用户名和端口)
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- [6.3. 关闭授权验证](#63-关闭授权验证)
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- [7. SSH 隧道](#7-ssh-隧道)
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- [8. 常见问题汇总](#8-常见问题汇总)
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- [8.1. timeout in locking authority file /home/\<user\>/.Xauthority](#81-timeout-in-locking-authority-file-homeuserxauthority)
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## 1. 安装 SSH Server
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```bash
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# Ubuntu
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sudo apt install openssh-server
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# Manjaro
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sudo pacman -S openssh
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# 生成 Host Key
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sudo ssh-keygen -A
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```
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## 2. 开启 SSH 服务
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当目标机上有 SSHD 的情况下，可以开启 SSHD 服务。编写 sshd_config 文件，放置到 /etc/ssh 下，内容如下：
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```ini
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# Package generated configuration file
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# See the sshd_config(5) manpage for details
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# What ports, IPs and protocols we listen for
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Port 22
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# Use these options to restrict which interfaces/protocols sshd will bind to
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#ListenAddress ::
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#ListenAddress 0.0.0.0
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Protocol 2
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# HostKeys for protocol version 2
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HostKey /etc/ssh/ssh_host_rsa_key
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HostKey /etc/ssh/ssh_host_dsa_key
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HostKey /etc/ssh/ssh_host_ecdsa_key
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HostKey /etc/ssh/ssh_host_ed25519_key
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#Privilege Separation is turned on for security
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UsePrivilegeSeparation yes
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# Lifetime and size of ephemeral version 1 server key
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KeyRegenerationInterval 3600
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ServerKeyBits 1024
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# Logging
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SyslogFacility AUTH
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LogLevel INFO
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# Authentication:
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LoginGraceTime 120
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#PermitRootLogin prohibit-password
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PermitRootLogin yes
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StrictModes yes
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RSAAuthentication yes
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PubkeyAuthentication yes
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#AuthorizedKeysFile %h/.ssh/authorized_keys
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# Don't read the user's ~/.rhosts and ~/.shosts files
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IgnoreRhosts yes
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# For this to work you will also need host keys in /etc/ssh_known_hosts
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RhostsRSAAuthentication no
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# similar for protocol version 2
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HostbasedAuthentication no
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# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
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#IgnoreUserKnownHosts yes
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# To enable empty passwords, change to yes (NOT RECOMMENDED)
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PermitEmptyPasswords no
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# Change to yes to enable challenge-response passwords (beware issues with
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# some PAM modules and threads)
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ChallengeResponseAuthentication no
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# Change to no to disable tunnelled clear text passwords
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#PasswordAuthentication yes
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# Kerberos options
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#KerberosAuthentication no
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#KerberosGetAFSToken no
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#KerberosOrLocalPasswd yes
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#KerberosTicketCleanup yes
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# GSSAPI options
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#GSSAPIAuthentication no
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#GSSAPICleanupCredentials yes
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X11Forwarding yes
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X11DisplayOffset 10
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PrintMotd no
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TCPKeepAlive yes
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#UseLogin no
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#MaxStartups 10:30:60
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#Banner /etc/issue.net
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# Allow client to pass locale environment variables
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AcceptEnv LANG LC_*
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#Subsystem sftp /usr/lib/openssh/sftp-server
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Subsystem sftp internal-sftp
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# Set this to 'yes' to enable PAM authentication, account processing,
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# and session processing. If this is enabled, PAM authentication will
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# be allowed through the ChallengeResponseAuthentication and
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# PasswordAuthentication. Depending on your PAM configuration,
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# PAM authentication via ChallengeResponseAuthentication may bypass
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# the setting of "PermitRootLogin without-password".
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# If you just want the PAM account and session checks to run without
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# PAM authentication, then enable this but set PasswordAuthentication
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# and ChallengeResponseAuthentication to 'no'.
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UsePAM yes
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```
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注意以上配置使用了内置 SFTP 服务（“Subsystem sftp internal-sftp”）。之后既可以使用 SCP 上传和下载文件，也可以使用 SFTP 上传下载文件。
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之后在目标机上
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```bash
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# 开机自运行
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sudo systemctl enable sshd.service
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# 启动 sshd 服务
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sudo systemctl start sshd.service
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# 查看 sshd 服务状态
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sudo systemctl status sshd.service
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# 或（ubuntu12）
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sudo /etc/init.d/ssh restart
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```
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如果没有 systemd，可以使用如下命令：
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```bash
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sudo service ssh start
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```
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## 3. SSH 登陆
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在开发机上
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```bash
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ssh <User Name>@<IP> -p <port>
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```
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不加 -p 参数，则默认使用 22 端口。
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## 4. SCP 上传和下载
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SCP 上传
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```bash
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scp <Local Path or File> <User Name>@<IP>:<Path or File>
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```
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SCP 下载
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```bash
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scp <User Name>@<IP>:<Path or File> <Local Path or File>
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```
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SCP 一次传输多个文件
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```bash
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scp <User Name>@<IP>:<Path>/\{file1,file2\} .
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# 还可以使用正则表达式，如：
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scp <User Name>@<IP>:<Path>/* .
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scp <User Name>@<IP>:<Path>/*.txt .
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```
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## 5. 免密访问
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ssh 登陆或 scp 的时候每次都输入密码很麻烦，如果用于访问 SSH 服务器的客户端值得信任的话可以授权该主机用户免密登陆。做法是先在客户端生成密钥对，如果已有密钥对可跳过本步骤：
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```bash
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ssh-keygen [-t rsa|ecdsa]
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```
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之后在客户端使用：
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```bash
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ssh-copy-id -p <port> <User Name>@<IP>
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# 后续按照提示进行操作即可
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```
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命令将客户端的 ssh public key 提供给服务器（或者将公钥文件内容添加到 /home/\<user>/.ssh/authorized_keys 文件中.），之后该客户端的授权账号（拥有该密钥对的账号）就可以免密访问服务器了。
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在服务器的 \<User Home\>/.ssh/authorized_keys 文件中可以看到已授权客户端公钥，删除公钥可取消对应客户端账户的免密访问权限。
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## 6. Client SSH Config 文件
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Client SSH Config 一般为 ~/.ssh/config，可用于 Host 配置，包括设置授权方式，设置 Host 用户名和端口等。
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### 6.1. 增加 ssh-rsa 授权方式
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当出现以下问题：
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```bash
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no matching host key type found. Their offer: ssh-rsa
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```
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可通过修改 ~/.ssh/config 来解决：
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```bash
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Host *
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HostkeyAlgorithms +ssh-rsa
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PubkeyAcceptedKeyTypes +ssh-rsa
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```
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### 6.2. 设置 Host 用户名和端口
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```bash
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Host <addr>
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HostName <name>
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User <usr>
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Port <port>
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```
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### 6.3. 关闭授权验证
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SSH 客户端每连接一台新主机都要进行授权验证，并询问用户是否同一，并将主机信息记录到 known_hsots 文件里。有些时候需要使用自动化流程，此时无法处理授权验证过程，此时可修改 ~/.ssh/config 文件（不存在则手动创建），增加如下两行：
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```bash
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StrictHostKeyChecking no
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UserKnownHostsFile /dev/null
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```
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*关闭授权验证将增加 SSH 的安全隐患。*
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## 7. SSH 隧道
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可以通过 SSH 隧道创建基于 SSH 加密传输的其他服务。比如通过 SSH 隧道创建远程桌面 VNC，示例如下：
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```bash
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# Server 端开启 SSH 服务后再开启 VNC 服务，默认使用 5901 端口
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vncserver :1
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# Client 端通过 SSH 隧道将 Server 的 5901 端口映射到本地的 5901 端口
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ssh -g -L 5901:localhost:5901 [-p <server ssh port>] <user>@<remote addr>
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# 输入密码后登录服务器
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# Client 通过 VNC 客户端连接 localhost:5901 即可访问 Server 的 VNC 服务
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# 使用完毕后退出登录即可关闭 SSH 隧道
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```
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## 8. 常见问题汇总
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### 8.1. timeout in locking authority file /home/\<user\>/.Xauthority
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SSH 客户端连接到服务器时卡顿并出现“/usr/bin/xauth: timeout in locking authority file /home/\<user>/.Xauthority”错误。
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通过 strace 可以发现，xauth 会不断去访问 .Xauthority-* 文件，这些是用于 xauth 的 lock 文件，可能是某些访问异常中断导致这些文件残留，此时直接删除掉对应的文件即可。
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```bash
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rm -rf ~/.Xauthority-*
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```
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