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Troubleshooting SELinux

Mandatory access control (MAC) is an essential element to modern system security. SELinux is a common implementation of MAC that must be well understood by engineers in order to incorporate the most ideal security practices into production systems. This exercise delves into a common occurrence relating to MAC; troubleshooting a system that is experiencing errors as a consequence of SELinux. *This course is not approved or sponsored by Red Hat.*

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Path Info

Level
Clock icon Advanced
Duration
Clock icon 30m
Published
Clock icon Nov 05, 2018

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Table of Contents

  1. Challenge

    Verify there is an error by trying to access `localhost:80/index.html` using curl on the `www` host and check the audit log using sealert. Direct the output from sealert to `/home/cloud_user/seinfo.txt`.

    • Run curl localhost:80/index.html to confirm the error.
    • Run sealert -a /var/log/audit/audit.log > /home/cloud_user/seinfo.txt.

  2. Challenge

    Examine `/home/cloud_user/seinfo.txt` to figure out what is wrong and fix the error regarding `/var/www/html/index.html`.

    • Reviewing the seinfo.txt file should indicate the context for /var/www/html/index.html is incorrect.
    • Run restorecon /var/www/html/index.html to fix the issue.

  3. Challenge

    Restart `httpd` to check for other possible issues and correct any issues you might find.

    • Run systemctl restart httpd (note: httpd should fail to restart).
    • Based on journalctl --xe or by re-examining the audit log with sealert, you will see the file context is incorrect on /etc/httpd/conf/httpd.conf.
    • Run restorecon /etc/httpd/conf/httpd.conf to fix the context on httpd.conf.
    • Run systemctl start httpd and service should be restored.

  4. Challenge

    Confirm `localhost:80/index.html` loads correctly with curl on the `www` host.

    Run curl localhost:80/index.html and verify that you get the message "The website is up".

A Cloud Guru - Labs - Troubleshooting SELinux
Author
A Cloud Guru

The Cloud Content team comprises subject matter experts hyper focused on services offered by the leading cloud vendors (AWS, GCP, and Azure), as well as cloud-related technologies such as Linux and DevOps. The team is thrilled to share their knowledge to help you build modern tech solutions from the ground up, secure and optimize your environments, and so much more!

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