FreeKB - SSH ssh-keygen command (create a public / private key pair)
SSH - ssh-keygen command (create a public / private key pair)

The ssh-keygen command is used to create a public certificate and private key pair. The key pair is intended to be used for making a connection to an SSH server. By default, an RSA keypair will be created.

. . .
Generating public/private rsa key pair.


Or, the following command line options can be used so that you are not prompted for input.

  • -t (type) such as rsa or dsa
  • -N (passphrase)
  • -f (key file) such as /home/john.doe/.ssh/id_rsa
  • <<< n is used to not overwrite id_rsa and if they already exist
  • 2>&1 >/dev/null suppresses output
[root@server1 ~]# ssh-keygen -t rsa -N '' -f /home/john.doe/.ssh/id_rsa <<< n 2>&1 >/dev/null


If the private key already exists, such as id_rsa, you can create the public certificate using the private key, like this.

ssh-keygen -y -f /home/john.doe/.ssh/id_rsa > /home/john.doe/.ssh/


It is always recommended to secure the keypair with a strong, unique passphrase.

Created directory '/home/john.doe/.ssh'.
Enter passphrase (empty for no passphrase):


The public certificate and private key are created.

Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/
The key fingerprint is:
a6:4e:fd:17:67:69:19:b5:22:0a:16:53:cf:47:b3:b3 root@server1
The key's randomart image is:
+--[ RSA 2048]----+
|        ..   o   |
|       o  o . o .|
|        o  o + ..|
|       o   ...+. |
|      . S . .E.+ |
|       + .  . *  |
|      o .    =   |
|     o   .  .    |
|      .   ..     |


Configure the .ssh directory to only the directory owner (john.doe in this example) has read/write/execute permission, and configure the public/private key pair so that only the onwer has read/write permission.

chmod 700 /home/john.doe/.ssh
chmod 600 /home/john.doe/.ssh/id_rsa
chmod 600 /home/john.doe/.ssh/


Optionally, use the ssh-add command to store your identity in the keychain.

eval `ssh-agent -s`
ssh-add /home/john.doe/.ssh/id_rsa


The content of will be something like this (without the line breaks).

ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAqphOmkv0RPMn48EwCRED/eSSYsbyrRlxymWdEA/
K6w== john.doe@client


If your SSH server is OpenSSH, you can add the public certificate to the authorized_keys file on the OpenSSH server. If the OpenSSH server is configured to accept connection using a public / private key pair, you should be able to connect to the OpenSSH server with the public / private key pair you just created.


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