move dir fundamentals to basics

basics/at.md

@@ -0,0 +1,34 @@
+`at` must be installed with:
+
+> sudo apt-get install at
+
+Then jobs can be specified with absolute time, such as:
+
+> at 16:20
+
+> at noon
+
+> at midnight
+
+> at teatime
+
+The jobs can also be specified relative to the current time:
+
+> at now +15 minutes
+
+Finally, accept the jobs with ^D.
+
+# Managing `at` Jobs
+
+Display a list of commands to run with:
+
+> atq
+
+`2	Sat Oct 20 16:00:00 2018 a roach-1`
+
+This will print all pending IDs.  Remove a job by the ID with:
+
+> atrm 2
+
+Check /var/spool/cron/
+