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SSH Secure Console Serial Switch, SSH Serial Port Switch

RS232 Remote Presence Management with Secure Shell

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How to Setup SERIMUX-S-x for Secure SSH Console Serial Switch for
Secure Password-less Authentication

Product Application Notes

Typographic Conventions:
  • Bold text: Text to be typed in on the computer.
  • Italic text: File name/location on the computer.
  • <enter>: Press the Enter/Return key.


SSH is often used to login from one system to another without requiring passwords. This is done by creating a private/public key pair at the client and then copying the public key to the SSH server. The following is the procedure to setup password-less authentication for the SERIMUX-S-x using an openSSH client on a Linux operating system. Other clients may provide different commands for generating the key pairs.

Generating Your Keys on a Linux machine:

When generating the keys from a Linux computer, login as the user that you will want to connect to the SERIMUX-S-x as.
  1. Connect to your Computer (from where you will be making the SSH connection to the SERIMUX-S-x unit).
  2. From the command prompt, generate your keys on the local computer by using the ssh-keygen program.

    Example: To generate RSA keys, issue the command:
    ssh-keygen -t rsa

    The SERIMUX-S-x supports RSA or DSA keys.

  3. When prompted to "Enter file in which to save the key", enter the path where you want the file to be stored, or press <enter> to accept the default location (~/.ssh/).
  4. When prompted to "Enter passphrase", press <enter> twice for no passphrase.
Two new files will be created in your home directory under .ssh. These two files will be your private key (id_rsa) and public key (

Setup SERIMUX-S-x for Secure Password-less Authentication:
  1. After you have created the public/private key pairs, you need to copy/add the newly created public key to the server (your SERIMUX-S-x unit).
  2. Copy your SSH public keys to the file authorized_keys in the directory /usr1/ on the SERIMUX-S-x unit.

    The keys can be copied through a USB flash drive, or by editing the file using the vi editor on SERIMUX-S-x unit and pasting the key.

    This can also be done using following command from your Linux machine:
    ssh root@remotehost "cat >> /usr1/authorized_keys" < ~/.ssh/

  3. 4. For units with firmware version 1.3 or less, or a unit upgraded from 1.3 or less, the following additional steps need to be done:
    1. Login to your SERIMUX-S-x unit using the root account in order to make changes to the configuration.
    2. Edit sshd config file on the SERIMUX-S-x unit using vi editor. The file is located at /etc/ssh/sshd_config on the unit.
    3. Change the default value of #AuthorizedKeysFile to AuthorizedKeysFile /usr1/authorized_keys".
    4. Issue command "serconfsave flash" on the SERIMUX-S-x command line to save the changed config back to flash.
    5. When finished, reboot the unit.

      This will save the config file. The above steps only need to be done once.
Using SSH key based authentication:

After completing the configurations, login to your client machine with the username that you have used to create the identity keys. If you have used the root user before while creating the public/private keys, then use the root user. You will not be prompted for password.