$ Linux Command

Network

ssh-keygen

Generate, inspect, and manage SSH keys.

sshkeysecurityauthentication

Additional Notes

ssh-keygen creates and manages SSH key pairs used for passwordless login, Git hosting, automation, deployment, and server administration. It can also show fingerprints, change passphrases, create known-host hashes, and generate key revocation data.

A key pair has a private key and a public key. Keep the private key secret. Copy the public key to servers or services that should trust it.

Syntax

ssh-keygen [options]
ssh-keygen -t type -f keyfile -C comment

Parameters

  • type: Key type such as ed25519 or rsa.
  • keyfile: Output private key path. The public key is usually written with .pub appended.
  • comment: Label stored in the public key, often an email or purpose.
  • options: Generation, inspection, conversion, and passphrase flags.

Common Options

  • -t TYPE: Choose key type. ed25519 is a common modern choice.
  • -f FILE: Choose key file path.
  • -C COMMENT: Add or replace a public-key comment.
  • -b BITS: Set key size for key types that use bit length, such as RSA.
  • -N PASSPHRASE: Set a new passphrase non-interactively.
  • -p -f FILE: Change a private key passphrase.
  • -l -f FILE: Show a key fingerprint.
  • -y -f FILE: Print the public key from a private key.

Examples

ssh-keygen -t ed25519 -C "me@example.com"

Create a modern SSH key with a useful comment.

ssh-keygen -t ed25519 -f ~/.ssh/deploy_key -C "deploy key"

Create a named key file for deployment.

ssh-keygen -l -f ~/.ssh/id_ed25519.pub

Show the fingerprint of a public key.

ssh-keygen -y -f ~/.ssh/id_ed25519 > ~/.ssh/id_ed25519.pub

Regenerate the public key from a private key.

ssh-keygen -p -f ~/.ssh/id_ed25519

Change a private key passphrase.

Practical Notes

  • Use a passphrase for keys that protect important systems.
  • Do not share private keys. Share only .pub files.
  • Keep permissions strict: chmod 700 ~/.ssh and chmod 600 ~/.ssh/id_* for private keys.
  • Use ssh-copy-id or manual authorized_keys edits to install public keys on servers.