Last modified: Mon Dec 28 01:06:43 GMT 1998

Introduction

Location

The files will automatically be re-read whenever you change them.

The Crontab File

Each line of a crontab file contains six fields each separated with white space. The first five fields are times when the command is to be executed and the last field is the command itself. The time fields consist of:-

field	Allowed Values
minute	0 - 59
hour	0 - 23
day of month	1 - 31
month	1 - 12
day of week	0 - 6 (0 is Sunday)

A field may be '*', which means 'any when' for that field.

Ranges of numbers are allowed. Ranges are two numbers separated with a hyphen. The specified range is inclusive. For example, 8-11 for an hours entry specifies execution at hours 8, 9, 10 and 11.

Lists are allowed. A list is a set of numbers (or ranges) separated by commas. Examples: 1,2,5,9 or 0-3,5,8-12.

Commands are actually small snippets of perl. They can be anything legal within perl and the context of the DXSpider cluster.pl daemon. The normal use will be connecting to another cluster and a set of routines are specially provided in the context of the DXCron package to make this easy. For example

  start_connect('gb7tlh') if !connected('gb7tlh')
    

There is absolutely no reason why you could not do something more complicated using information contained inside the DXSpider daemon, but this will obviously require a more complex line of code. You can also write your own functions, include them within the DXSpider system and call them from the crontab

A full crontab file could like like:-

  #
  # This is a sample crontab file 
  #
  #
  # check every 10 minutes to see if gb7tlh is connected and if not
  # start a connect job going

  0,10,20,30,40,50 * * * * start_connect('gb7tlh') if !connected('gb7tlh')

  # at 03:15 on Sundays start a job called 'analyse.pl' which does something
  # or other. This starts a new process and runs to completion, be careful
  # what you do with stdin and stdout as they are the same as those of
  # cluster.pl 

  15 3 * * 0 spawn('/spider/local/analyse.pl')

  # this is a pointless command which will echo the string shown
  # on the same terminal as the cluster.pl program after substituting
  # the values for mycall and version
 
  15,30 * * * spawn("echo $main::mycall is a DXSpider Version $main::version DX Cluster system")
	

Standard Routines

• connected(<callsign>) - returns true if the <callsign> is directly connected to this cluster node.

• start_connect(<script-name>) - starts a connection script just as if you had typed in connect script-name on the sysop console client.

• spawn(<command>) - start a <command> as a new process. This is used to do various batch jobs that you may wish to happen at certain times of the day or week that operate on your machine but don't require access to the real-time internals of the cluster daemon. You can execute just about any command you like, but be warned stdin and stdout are still connected to the same terminal (if any) as the cluster daemon. Any unix command and arguments can used, see exec in the perl documentation.

Caveats