added SELinux example to unix time step

unixisms/step5.md

@@ -4,10 +4,9 @@ Time is a fundamental part of productivity, but frameworks must be established
 to ensure that humans and computers can be on the same page about time.
 On Linux, one of these frameworks is the __unix epoch__. This is a standardized
 date and time that is defined as the beginning of time for unix systems.
-From this, an _epoch time_ (or _unix time_) is defined as the number of seconds
-that have elapsed since the __unix epoch__.
-
-The __unix epoch__ is defined as
+From this, an _epoch time_ (or _unix time_) is the number of seconds
+that have elapsed since the __unix epoch__. The __unix epoch__ is defined as
+Midnight UTC on January 1, 1970.
 
 Unix time is exceptionally well-documented online, and if you wish to learn more
 the [Wikipedia page](https://en.wikipedia.org/wiki/Unix_time) on the subject is a great place to start.
@@ -58,3 +57,25 @@ Notice that this specifies the date in the timezone for this lab system,
 Eastern Time.
 
 For more information on using `date`, check out the [date man page](https://man7.org/linux/man-pages/man1/date.1.html).
+
+An example of how you might run into unix time is available in this [SELinux troubleshooting article](https://www.redhat.com/sysadmin/selinux-denial2).
+The following example error is given:
+
+<pre class=file>
+type=AVC msg=audit(1600796109.687:168): avc:  denied  { read } for  pid=3912 comm="rhsmcertd-worker" name="virt.module" dev="dm-0" ino=50331783 scontext=system_u:system_r:rhsmcertd_t:s0 tcontext=system_u:object_r:root_t:s0 tclass=file permissive=0
+</pre>
+
+For this lab, we care about the second field in this error. You may recognize
+that ten digit number as a unix timestamp. To confirm, convert it to a standard
+date:
+
+`date --date @1600796109`{{execute T1}}
+
+<pre class=file>
+Tue Sep 22 13:35:09 EDT 2020
+</pre>
+
+The article that this error was taken from was published on November 16, 2020,
+which supports the fact that this was a unix timestamp generated during the
+process of writing the article. However, someone who is not familiar with the
+unix time format may never consider that this number relates to time at all.