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Working with Essential Red Hat Linux System Administration Tools

In this lab we are going to make sure we have the minimum knowledge required to successfully pass the RHCE on RHEL8. We're going to present a scenario that will test an exam candidate's knowledge of how to use `grep` and configure `ssh` to help students succeed at this exam. *This course is not approved or sponsored by Red Hat.*

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Path Info

Clock icon Beginner
Clock icon 15m
Clock icon Oct 18, 2019

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Table of Contents

  1. Challenge

    Find the Username That the Other Admin Created

    There are over 25,000 lines in /tmp/logfile so we don't want to do it by hand. While we don't know the exact format we're searching for, we're fairly confident that it's some form of the word "username".

    grep -e 'user.*name' -i /tmp/logfile

    That will match any iteration of 'user', followed by any character (or no character), followed by 'name'.

  2. Challenge

    Create an SSH Key

    Use the command ssh-keygen to generate a key that we can use to copy to the other server to allow passwordless connections.

  3. Challenge

    Copy the SSH Key to Both cloud_user and the User Whose Name You Discovered in the First Task

    Use the ssh-copy-id command to copy the SSH key to both the cloud_user and the new user name:

    [cloud_user@Server1 ]# ssh-copy-id cloud_user@&ltServer2_INTERNAL_IP_ADDRESS>
    [cloud_user@Server1 ]# ssh-copy-id &ltUSERNAME>@&ltServer2_INTERNAL_IP_ADDRESS>

    Now we can test with two ssh commands:

    ssh cloud_user@&ltServer2_INTERNAL_IP_ADDRESS&gt

    Back out of that login, and try it for the other user:

    ssh &ltUSERNAME&gt@&ltServer2_INTERNAL_IP_ADDRESS&gt

    Just be sure you've substituted the correct Server2_INTERNAL_IP_ADDRESS and USERNAME in the commands. We should now be able to perform passwordless ssh logins.

  4. Challenge

    Ensure That No One Can Use a Password to Log into Server2

    Now get out of that shell and come back in as cloud_user. Once we've logged in, we need to edit /etc/ssh/sshd_config and, with whichever text editor we like best, change the PasswordAuthentication variable to no. We're using vi as an example here:

    [cloud_user@Server2 ]# sudo vi /etc/ssh/sshd_config

    Once we've done that, restart the SSH daemon using sudo systemctl restart sshd.

    To test, try to log in with a password:

    [cloud_user@Server2 ]# ssh -o PreferredAuthentications=password cloud_user@localhost

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