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ssh

1. Basic Usage

ssh {username}@{server}

2. Expose a service through the firewall

ssh -N -L {local port}:{target address}:{target port} {username}@{server}

-N: Do not execute a remote command. This is useful for just forwarding ports.

-L：Local, Indicates local port forwarding. All requests sent from this machine to the ‘{local port}’ are forwarded to the ‘{server}’, and then forwarded by the server to the ‘{destination port}’ of the ‘{destination address}’

Example

Suppose there is a web service on port 8080 on the server, but the server has a firewall that prevents external access to port 8080, but allows access to (ssh) port 22,

ssh -N -L {8080}:{127.0.0.1}:{8080} {username}@{server}

Now you can access the 8080 port of the server by accessing the 8080 port of your local machine.

3. Expose a service in the local network to the public

ssh -N -R {remote port}:{target address}:{target port} {username}@{server}

-R: Remote, Indicates remote port forwarding. All requests sent from the ‘{server}’ to the ‘{remote port}’ are forwarded to this machine, and then forwarded by this machine to the ‘{destination port}’ of the ‘{destination address}’

Example

Suppose there is a computer in a local network, and there is a web service running on port 8080 on this computer. And there is a server with a public IP address.

Goal: Expose the web service on the local network computer to the public

Execute the following command on the local network computer

ssh -R 8080:127.0.0.1:8080 {username}@{server}

Then modify /etc/ssh/sshd_config

GatewayPorts yes

4. Proxy Forwarding

Purpose: Use your local ssh key on the server, for example, clone your private repository on the server

  1. Input the following command in the command line to add your private key to the ssh-agent management

    eval "$(ssh-agent -s)" >/dev/null
ssh-add -q ~/.ssh/{private key}

  2. Enable the proxy forwarding feature of ssh

    ssh -A {username}@{server}

    Or add the following information to ~/.ssh/config

    Host server_ip
	Port 22
	User {username}
	IdentityFile ~/.ssh/{private key}
	ForwardAgent yes

5. ssh via proxy

Example

Host server_ip
   User {username}
   IdentityFile ~/.ssh/{private key}
   ProxyCommand nc -X 5 -x 127.0.0.1:7890 %h %p

6. proxy using ssh

ssh -D {local port} {username}@{server}

7. 特殊环境下ssh无法访问github问题

一些公司、学校实验室的防火墙，或者某些运营商，为了安全起见，会封锁 22 端口

使用ssh git clone会出现以下错误

zengls188@dell-Precision-7960-Tower ~/proj> git clone git@github.com:xxx/yyy.git
Cloning into 'yyy'...
ssh: Could not resolve hostname github.com: Temporary failure in name resolution
fatal: Could not read from remote repository.
 
Please make sure you have the correct access rights
and the repository exists.

解决办法：

在~/.ssh/config中添加如下配置

Host github.com
	Hostname ssh.github.com
	Port 443
	User git

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