gentoo-overlay/sys-process/fcron/files/crontab.2

# /etc/crontab:
# This is fcron's special systab and *not* root's crontab!

# Global variables
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/

# "run-crons" from sys-process/cronbase package doesn't allow selective
# runs like "run-parts" from sys-apps/debianutils. So every time
# "run-crons" gets executed it loops through
# /etc/cron.{hourly,daily,weekly,monthly} and executes one after another if
# lastrun lock file isn't in place.
# Without fcron's "serial(true)" option it would be possible that a lastrun
# lock file which should have been removed still exists when "run-crons"
# starts so that a promptly execution of all cronjobs isn't always
# guaranteed.

!serial(true)
00   *    *    *    *     /bin/rm -f /var/spool/cron/lastrun/cron.hourly
00   00   *    *    *     /bin/rm -f /var/spool/cron/lastrun/cron.daily
00   00   *    *    6     /bin/rm -f /var/spool/cron/lastrun/cron.weekly
00   00   1    *    *     /bin/rm -f /var/spool/cron/lastrun/cron.monthly
*/10 *    *    *    *     /usr/bin/test -x /usr/sbin/run-crons && /usr/sbin/run-crons
!serial(false)