Some useful ssh config option

Link: https://taozhi.medium.com/some-useful-ssh-config-option-7858a58c5e7b 

 When managing multiple Linux servers, we use SSH for logging in and performing tasks. Understanding how to configure SSH properly is essential for efficient server management. 

 Basic Config 

 Host my_jump identityfile "~/.ssh/my_jump" hostname 47.254.197.212 hostkeyalias my_jump user root port 22 

 In the above config, “my_jump” is the hostname supporting wildcards to match multiple servers simultaneously. 

 The identityfile specifies the authorized private keys, hostname is the server’s IP address, and hostkeyalias is useful for connecting to the server when its IP address changes without needing to update known_hosts. The user and port specify the SSH login credentials. 

 Reuse the sock 

 Upon relogging into the server, how can we bypass entering the password and reuse the previous session to quickly reconnect? We should the control setting in ssh config. 

 Host * serveraliveinterval 60 keepalive yes controlmaster auto controlpath ~/.ssh/socks/%h-%k-%p-%r controlpersist yes 

 By using the above configuration, we set the controlpath for all servers using the ‘*’ symbol in the Host field. The controlpath specifies the socket path. 

 %h represents the host IP. 

 %k represents the hostname. 

 %p represents the port. 

 %r represents the username. 

 When you connect to a server using ssh, you should see a socket file present.  ~/.ssh/socks . 

 

 

 

 

 

 

 

 

 

 

 

 Set Jump Server 

 To secure production servers inaccessible for direct login, we can first connect to a jump server, then use SSH through the jump server to access the production server. Automating this process is possible by configuring ProxyCommand or ProxyJump in the SSH settings. 

 Config the jump server a and b first. 

 Host jump-server-a HostKeyAlias jump-server-a Hostname 100.97.200.66 Host jump-server-b HostKeyAlias jump-server-b Hostname 100.97.200.67 Host jump-server-* HashKnownHosts no ServerAliveInterval 60 Port 22 User root PreferredAuthentications publickey IdentityFile ~/.ssh/id_taozhi Controlpath ~/.ssh/socks/%h-%k-%p-%r ControlMaster auto ControlPersist 5m setenv LC_ALL=C.UTF-8 

 Config the production servers 

 Host production-server-a ProxyJump jump-server-a Host production-server-b ProxyJump jump-server-b Host production-server-c ProxyCommand ssh -W %h:%p jump-server-b Host production-server-* LogLevel ERROR UserKnownHostsFile /dev/null StrictHostKeyChecking no Port 22 User root IdentityFile ~/.ssh/id_taozhi controlmaster no setenv LC_ALL=C.UTF-8 

 Following configuration, we can login to the production server locally. 

 ssh -o Hostname=172.16.28.19 production-server-a 

 You can log in to the production server with one command now. 

 

 Conclusions 

 SSH is a versatile command with numerous configuration options. More options can be found for reading  here . If you have any useful ssh config you are using, please comment it, let using it together.