December 29, 2007 CRON 8

### NAME

cron - daemon to execute scheduled commands (Vixie Cron)

### SYNOPSIS

cron [-x debugflags]

### DESCRIPTION

cron is normally started during system boot by rc.d(8) framework, if cron is switched on in rc.conf(5).

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)). 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`) 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 -x flag turns on some debugging flags. debugflags is comma-separated list of debugging flags to turn on. If a flag is turned on, cron writes some additional debugging information to system log during its work. Available debugging flags are:

sch
  scheduling
proc
  process control
pars
  parsing
load
  database loading
misc
  miscellaneous
test
  test mode - do not actually execute any commands
bit
  show how various bits are set (long)
ext
  print extended debugging information

### FILES

```/var/cron/tabs`
  cron spool directory
```/etc/crontab`
  system crontab
```/var/log/cron`
  log file for cron events

### SEE ALSO

crontab(1), crontab(5)

### AUTHORS

Paul Vixie
<paul@vix.com>