TopolearnReaching servers, cloud VMs and containers' hosts over SSH is a basic skill for any developer or operator.
SSH is a protocol for secure remote access. A client (ssh) connects to a server (sshd), normally on TCP port 22. Everything is encrypted, and both sides authenticate: the server proves its identity with a host key, and you prove yours with a password or, better, a key pair.
The basic command:
ssh alice@server.example.comlogs in asalice. Withoutuser@, your local username is used.-p 2222connects to a non-standard port.-i ~/.ssh/work_keypicks a specific private key.-v(up to-vvv) prints debugging output when a connection fails.
Once connected you get a normal shell on the remote machine. exit or Ctrl-d closes it. If the connection hangs (say, after a network change), the escape sequence Enter ~ . (Enter, then tilde, then dot) kills the session from the client side; ~? lists other escapes.
On the very first connection to a host, ssh shows the server's key fingerprint and asks whether to trust it. That question matters; the next lesson explains why.
OpenSSH ships with Linux, macOS and Windows 10/11, so ssh is usually already there. To accept connections, a machine needs the server package (openssh-server on Debian/Ubuntu) running.
Example
ssh alice@203.0.113.10 # log in as alice
ssh -p 2222 deploy@build.example.com
ssh -i ~/.ssh/work_ed25519 alice@server
ssh -v alice@server # debug a failing connection
# inside the session
whoami && hostname # alice / server
exit # or Ctrl-d
# frozen session? press: Enter ~ .Remember
- ssh user@host, -p for port, -i for a key, -v to debug
- exit or Ctrl-d closes; Enter ~ . kills a frozen session
- Both server (host key) and user are authenticated
Watch out for
- Pressing Ctrl-C on a frozen session; it is sent to the remote side, use Enter ~ . instead.