SSH Configuration File

In the SSH configuration file, you can customize the connection settings for specific hosts, including identity authentication keys, connection options, and ports. The SSH configuration file is usually located in ~/.ssh/config, and if the file does not exist, you can create it manually. Here are some common configuration options and examples.

1. Edit or create the SSH configuration file

First, ensure you have a configuration file. If the file does not exist, you can create it using the following command:

touch ~/.ssh/config

Then, you can open it using a text editor, for example:

nano ~/.ssh/config

2. Common items in the configuration file

1) Set up SSH configuration for GitHub

If you have multiple GitHub accounts or need to customize the configuration, you can set up specific settings for github.com:

Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa
  IdentitiesOnly yes
  PreferredAuthentications publickey

• Host github.com：Configure github.com as the host (you can use any name, and reference it later).
• HostName github.com：The actual host address.
• User git：The user for GitHub login is git, not your GitHub username.
• IdentityFile ~/.ssh/id_rsa：Specify the path to the private key file used.
• IdentitiesOnly yes：Ensure the SSH client only uses the key specified in IdentityFile, not other keys.
• PreferredAuthentications publickey：Set the preferred authentication method to public key.

2) Customize the SSH connection port

If you need to connect to GitHub or other servers through a non-default port, you can specify the port, for example, using port 443 (the alternative port for GitHub):

Host github.com
  HostName github.com
  User git
  Port 443
  IdentityFile ~/.ssh/id_rsa

3) Multiple GitHub account configuration

If you have multiple GitHub accounts and want to use different SSH keys, you can configure different Host names for each account. For example:

# 账号 1
Host github-acc1
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa_acc1

# 账号 2
Host github-acc2
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa_acc2

Then, use the following commands to specify different GitHub accounts:

git clone git@github-acc1:username/repository.git
git clone git@github-acc2:username/repository.git

4) Specify connection timeout

If you want to set a connection timeout, you can use ConnectTimeout:

Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa
  ConnectTimeout 10

5) Use a proxy server

If you need to connect to SSH through a proxy server, you can set ProxyCommand:

Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa
  ProxyCommand nc -X 5 -x proxy.example.com:1080 %h %p

• -X 5：Specify the use of SOCKS5 proxy.
• -x proxy.example.com:1080：The address and port of the proxy server.

3. Configuration file format description

• Host：Specify the host alias for the configuration item, you can use different aliases as needed. For example, you can use github.com or github-acc1 instead of the specific host address.
• HostName：Specify the actual host address, for example, github.com.
• User：The username used during login (for GitHub, it is git).
• IdentityFile：Specify the path to the private key file.
• Port：Specify the SSH connection port.
• ConnectTimeout：Set the number of seconds for the connection timeout.
• ProxyCommand：Set up SSH connection through a proxy server.

4. Save and test the configuration

After completing the configuration, save the file and exit the editor (for example, press Ctrl+X in nano and then press Y to confirm the save).

Next, you can test if the configuration is effective:

ssh -T git@github.com

If the configuration is correct, SSH will use the options in the configuration file to connect, and should be able to successfully authenticate.

5. Summary

By modifying the ~/.ssh/config file, you can easily create different configuration items for multiple hosts, different keys, and connection settings, which can simplify commands and improve efficiency.