ssh

• logout: exit or Ctrl-D (in shell it means end of input)

• run remote command without going into the remote shell: ssh user@hostname "command"

• ssh keys are stored in ~/.ssh

config file: .ssh/config

With the following in the config file, ssh dev will connect to the server.

Host dev
    User scott
    HostName orion.dev
    IdentityFile ~/.ssh/id_rsa

General structure of the config file

Host hostname1
    SSH_OPTION value
    SSH_OPTION value

Host hostname2
    SSH_OPTION value

Host *
    SSH_OPTION value

A single ssh command can match multiple sections in the config file. If multiple sections set the same SSH_OPTION, the first one wins. Therefore the generic settings (matching *) comes last.

Common ssh options includes:

• Hostname

• User

• SendEnv

• ProxyJump

• IdentityFile

• ForwardAgent

• Port

• AddKeysToAgent

• UseKeychain

• ServerAliveInterval

Refs

• https://linuxize.com/post/using-the-ssh-config-file/
• https://www.digitalocean.com/community/tutorials/how-to-configure-custom-connection-options-for-your-ssh-client

SCP

# Send local file to user home folder in server. Note the colon at the end.
scp localfile.txt [e-mail]:
# Send local file to a specific path in server
scp localfile.txt [e-mail]:/var/tmp
# Get file from server to current local folder
scp [e-mail]:filename.txt .
# use -r for directory

SSH Tunnel

Example: a remote database server (orion.dev:3306) only allows local access. On local machine we have a GUI tool, which can't connect to the remote database directly.

Solution: On local machine, use the following line to connect local port 9000 with server's port 3306 (via localhost:22, the port SSH uses). Note that the localhost in the following line refers to the remote server.

ssh -L 9000:localhost:3306 [e-mail]

Then the GUI tool can connect to localhost:9000 to access the remote database.