# Some useful ssh config option Link: [https://taozhi.medium.com/some-useful-ssh-config-option-7858a58c5e7b](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`.
![](https://miro.medium.com/v2/resize:fit:945/1*EFp-htHJ0ldUFPSLuPU1YA.png)
# 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](https://linux.die.net/man/5/ssh_config). If you have any useful ssh config you are using, please comment it, let using it together.