SSH (Secure Shell) is a cryptographic network protocol that provides an encrypted channel for remote command-line login, command execution and file transfer, by default on TCP port 22.
Why it matters
SSH is the standard way to administer Linux servers. It replaced unencrypted tools like Telnet. Authentication can use passwords or, more safely, public-private key pairs.
Because port 22 is constantly scanned by bots, hardening matters: use keys, disable password login, and limit who can connect.
Example
ssh-keygen -t ed25519
ssh-copy-id deploy@203.0.113.10
ssh deploy@203.0.113.10The first command creates a key pair, the second installs the public key on the server, and the third logs in without a password.
Common mistakes
- Allowing password login and direct root login on a public server.
- Ignoring host key warnings, which may indicate a man-in-the-middle attack.
- Sharing one private key among several people instead of one per person.
Related
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This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.