ssh-add

Add the default SSH keys to the agent

$ ssh-add

$ ssh-add [~/.ssh/id_ed25519]

$ ssh-add -l

$ ssh-add -L

$ ssh-add -d [~/.ssh/id_rsa]

$ ssh-add -D

$ ssh-add -t [3600] [~/.ssh/id_rsa]

ssh-add [-cDdKkLlqvXx] [-E fingerprinthash] [-S provider] [-t life] [file ..._]

ssh-add adds private key identities to the ssh-agent authentication agent. Without arguments, it attempts to add ~/.ssh/idrsa, ~/.ssh/idecdsa, ~/.ssh/id_ed25519, and corresponding FIDO keys.
Once keys are added to the agent, SSH can authenticate without requiring the passphrase for each connection. The agent must be running and the SSHAUTHSOCK environment variable must be set.
If a key requires a passphrase, ssh-add prompts from the terminal. The SSH_ASKPASS environment variable can specify a graphical password prompt program.

-l

List fingerprints of all identities in the agent

List public key parameters of all identities

Remove specified identity from the agent

Remove all identities from the agent

Set maximum lifetime for added keys (in seconds or sshd_config time format)

Lock the agent with a password

Unlock the agent

Load resident keys from a FIDO authenticator

Require confirmation before using the key

Verbose mode for debugging

Keys remain in memory while the agent runs; lock with -x on shared systems. The agent socket (SSHAUTHSOCK) must be protected from other users. Use -t to auto-expire keys for enhanced security.

ssh-add is part of OpenSSH, developed by the OpenBSD project. The SSH agent concept allows secure key management without repeatedly entering passphrases, originating from the SSH1 implementation in the 1990s.

ssh-agent(1), ssh(1), ssh-keygen(1), ssh-copy-id(1)