Man page contains; Root's crontab(5) file /etc/crontab has to contain the line */5 * * * * root /usr/libexec/atrun Crontab will try to execute command "root" and fail.
The instructions aren't wrong, but perhaps it would be more precise to change the description from "Root's crontab(5)" to "The system crontab(5)".
A commit references this bug: Author: wblock Date: Mon Jun 22 20:25:00 UTC 2015 New revision: 284709 URL: https://svnweb.freebsd.org/changeset/base/284709 Log: Call /etc/crontab the "system crontab", not "root's crontab". While here, fix some other wording issues PR: 201048 Submitted by: teksimian@gmail.com MFC after: 1 week Changes: head/libexec/atrun/atrun.man
Hah, I actually changed it to that same wording before seeing the followup! Yes, /etc/crontab is really the system crontab, and has that additional "who" parameter. Thanks!