# cron

cron is a 'daemon' (or 'service') that automatically runs jobs at a
given time. It is controlled by a 'cron table' or 'crontab'.

Cron jobs are listed in the crontab, one per line. Time to run a job is
specified by a six-part expression of the form:

    m h d M D cmd

where m is the minute, h the hour, d the day of the month, M the month,
and D the day of the week to run the command (here 'cmd').

Any of the first five parts can be '*', which means 'all'.

The first five parts can be replaced by one of these expressions:

    @yearly
    @monthly
    @weekly
    @daily
    @hourly
    @reboot

If a job run by cron produces output, the output is emailed to root.
You can send it elsewhere by setting MAILTO at the top of the crontab:

    MAILTO=email@foo.net

## examples

### crontab

List cron jobs for current user:

    crontab -l

List cron jobs for user 'jeff':

    crontab -u jeff

Edit cron jobs for current user:

    crontab -e

Change editor:

    EDITOR=emacs crontab -e

### cron jobs

Daily at 12:30 AM:

    30 0 * * * cmd

Every 5 minutes:

    */5 * * * * cmd

Every Sunday at 1:30 PM:

    30 13 * * 0 cmd

### etc

Don't send email:

    @daily cmd >/dev/null 2>&1

## friends

cronic: http://habilis.net/cronic/
shush: http://web.taranis.org/shush/
cronwrap (Python): https://pypi.python.org/pypi/cronwrap
cronwrap (C): http://www.uow.edu.au/~sah/cronwrap.html