You might have SSHed into servers hundreds of times.

You might have used ssh-add to load keys into your agent.

You might have used scp to copy files back and forth between your machine and server.

But have you ever paused and looked at the bigger picture?

All these commands come from one place — the OpenSSH suite. It’s much more than just ssh and scp.

OpenSSH components

OpenSSH has 11 major components.

SSH Server Component

1) sshd

The SSH daemon that listens for incoming connections. It does the following.

• Runs on servers
• Handles authentication
• Spawns user sessions
• Applies security policies

2) sftp-server

Subsystem used by sshd to serve SFTP requests.

SSH Client Components

3) ssh

The main SSH client. It handles the following.

• Login to servers
• Run commands
• Port forwarding
• Agent forwarding
• Multiplexing

4) scp

Secure copy (file transfer using SSH).

5) sftp

SFTP interactive client (FTP-like interface over SSH).

Key Management + Agent

6) ssh-keygen

Generates, inspects, converts, and manages SSH keys.

7) ssh-agent

This is a background process that holds private keys securely.

8) ssh-add

This is used to add keys to the agent.

SSH Utilities

9) ssh-keyscan

Fetches public keys from remote servers for host verification.

10) ssh-keysign

Helper for host-based authentication.

Multiplexing / Public Key Infrastructure

11) moduli + supporting libraries

Used for Diffie-Hellman key exchange groups.

(Not an executable, but a core part of OpenSSH.)

Other components

These are still part of OpenSSH:

• ssh-copy-id (scripts for copying keys — shipped in portable versions)
• scp progress meter
• ssh-pkcs11-helper (for hardware tokens)
• ssh-sk-helper (for FIDO/U2F keys)

Final Summary — OpenSSH Components