SSH

If you have write access to a .ssh directory ( /home/someuser/.ssh ) you can add your id_rsa key to it and SSH in as that user with no need for passwords.

In terminal run ssh-keygen -t rsa -f ./id_rsa to create an id_rsa file in current directory, you can use an empty passphrase when prompted. Then add the contents of id_rsa.pub to authorized_keys within the users /.ssh directory.

Do a chmod 600 id_rsa on your end and then run ssh -i id_rsa user_name@hostname_or_ip to login.