Generate ssh keys user for authentication, password-less logins, and other things.

# To generate a key interactively:
ssh-keygen

# To specify file in which to save the key:
ssh-keygen -f ~/.ssh/filename

# To generate a DSA 2048 bit (default) key:
ssh-keygen -t dsa

# To generate an RSA 4096 bit key with your email as a comment:
ssh-keygen -t rsa -b 4096 -C "email"

# To retrieve the key fingerprint from a host (useful for confirming the authenticity of the host when first connecting to it via SSH):
ssh-keygen -l -F remote_host

# To retrieve the fingerprint of a key in MD5 Hex:
ssh-keygen -l -E md5 -f ~/.ssh/filename

# To change the password of a key:
ssh-keygen -p -f ~/.ssh/filename