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Maintaining Linux Systems

In this lab, we are going to practice scheduling updates, modifying NTP settings, and changing what kernel the server will reboot into. Understanding how to do these tasks will prepare you for various administrative duties in the future. *This course is not approved or sponsored by Red Hat.*

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Path Info

Clock icon Intermediate
Clock icon 30m
Clock icon Apr 05, 2019

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Table of Contents

  1. Challenge

    Schedule a Job Using the `at` Utility

    To schedule commands using the at command, you can run

    at 12:00am

    at> yum update -y

    Pressing Ctrl+D will show a message, then send you back to the shell.

    at> <EOT>

    You can run atq to verify that the command is scheduled.

    If you get an error similar to: Can't open /var/run/ to signal atd. No atd running?

    That means that the atd service isn't running. You can resolve that by running

    systemctl start atd

  2. Challenge

    Modify the NTP Pools to Keep Clocks Synchronized

    NTP configuration is set in /etc/chrony.conf.

    The lines that need to be modified are at the top of the file. Edit them to look like:

    server iburst




  3. Challenge

    Modify GRUB to Boot a Different Kernel

    List the currently installed kernels with grubby --info=ALL

    Find the line that looks like


    You'll see information about that kernel following the index.

    Run grubby --set-default-index=<index number>

    Run grubby --default-index to verify it worked.

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