What's the meaning of -i in ssh?

What does the -i tag add to a command such as:

ssh -i path-to-pem-file ubuntu@ip-address

2 Answers

From the manpage:

-i identity_file Selects a file from which the identity (private key) for public key authentication is read. The default is ~/.ssh/identity for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2. Identity files may also be specified on a per-host basis in the configuration file. It is possible to have multiple -i options (and multiple identities specified in configuration files). If no certificates have been explicitly specified by the CertificateFile directive, ssh will also try to load certificate information from the filename obtained by appending -cert.pub to identity filenames.

Basically, it's telling the SSH command to look at the key file you need for authentication on the destination server. If you use key authentication and were provided a certificate, this is where you want to specify it. If you use normal password auth, ignore that option.

Also, for the future, it's easier to Google things like this. You'll spend less effort, and you'll get an answer faster.

From the man page

-i identity_file

 Selects a file from which the identity (private key) for public key authentication is read. The default is ~/.ssh/identity for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2. Identity files may also be specified on a per-host basis in the configuration file. It is possible to have multiple -i options (and multiple identities specified in configuration files). If no certificates have been explicitly specified by the CertificateFile directive, ssh will also try to load certificate information from the filename obtained by appending -cert.pub to identity filenames.