| CRON(8) | System Manager's Manual | CRON(8) | 
cron —
| cron | [ -n] [-xdebugflags] | 
cron is normally started during system boot by
  rc.d(8) framework, if cron is
  switched on in rc.conf(5).
It will return immediately so you don't have to start it with ‘&’.
cron searches
    /var/cron/tabs for crontab files which are named
    after accounts in /etc/passwd. Crontabs found are
    loaded into memory. cron also searches for
    /etc/crontab which is in a different format (see
    crontab(5)). Finally
    cron looks for crontabs in
    /etc/cron.d if it exists, and executes each file as
    a crontab.
When cron looks in a directory for
    crontabs (either in /var/cron/tabs or
    /etc/cron.d) it will not process files that:
MAXNAMLEN.cron then wakes up every minute, examining
    all stored crontabs, checking each command to see if it should be run in the
    current minute. When executing commands, any output is mailed to the owner
    of the crontab (or to the user named in the MAILTO
    environment variable in the crontab, if such exists).
Events such as START and
    FINISH are recorded in the
    /var/log/cron log file with date and time details.
    This information is useful for a number of reasons, such as determining the
    amount of time required to run a particular job. By default, root has an
    hourly job that rotates these log files with compression to preserve disk
    space.
Additionally, cron checks each minute to
    see if its spool directory's modtime (or the modtime on
    /etc/crontab or /etc/cron.d)
    has changed, and if it has, cron will then examine
    the modtime on all crontabs and reload those which have changed. Thus
    cron need not be restarted whenever a crontab file
    is modified. Note that the
    crontab(1) command updates
    the modtime of the spool directory whenever it changes a crontab.
The following options are available:
-xcron writes some additional debugging
      information to system log during its work. Available debugging flags are:
    -ncron.If time has moved forward, those jobs that would have run in the interval that has been skipped will be run immediately. Conversely, if time has moved backward, care is taken to avoid running jobs twice.
Time changes of more than 3 hours are considered to be corrections to the clock or timezone, and the new time is used immediately.
SIGHUP, the cron daemon will close and
  reopen its log file. This is useful in scripts which rotate and age log files.
  Naturally this is not relevant if cron was built to use
  syslog(3).
cron spool directory| October 12, 2011 | NetBSD 9.4 |