ssh-add

ssh-add adds private key identities to the OpenSSH authentication agent (ssh-agent)

• https://man.openbsd.org/ssh-add
• https://linux.die.net/man/1/ssh-add

ssh-add
(no output)

ssh-add id_ed25519_your_key
Enter passphrase for id_ed25519_your_key:
Identity added: id_ed25519_your_key (USERNAME@HOSTNAME)

ssh-add
Could not open a connection to your authentication agent.

Solution:
Execute ssh-agent

ssh-add -l
256 SHA256:CjrlsnBNyafdafasfasdfasdfasfasdf Name@machine (ED25519)

ssh-add -l 
The agent has no identities.

ssh-add -L

ssh-add -K

ssh-add -A, deprecated in fauvour --apple-use-keychain and --apple-load-keychain.
No identity found in the keychain.

• Ubuntu: ssh-add --help
• ssh-add --help (MacOS)

Related terms

• ssh-agent
• ssh-copy-id

See also

• ssh-add [ -K | -l | --help ], ssh-agent
• OpenSSH (changelog): /etc/ssh/sshd_config | /etc/ssh/ssh_config | ~/.ssh/ | openSSL | sshd logs | sftp | scp | authorized_keys | ssh-keygen | ssh-keyscan | ssh-add | ssh-agent | ssh | Ssh -O stop | ssh-copy-id | CheckHostIP | UseKeychain, OpenSSF, ~/.ssh/authorized_keys