skyPipes Manual Index
	cogNiTioN's Intro to Cron, "an introduction to cron, it covers the basics of what cron does, and how to use it".
	Aaron Brazell's Introducing Cron, how to use cron in conjunction with PHP.

  skyPulse is a crontab-scheduled php script that calls the page pulse.html in the application directory once each minute.

  During installation, a crontab was applied that enabled skyPulse. A crontab is, according to the crontab(1) man page, a table "used to drive the cron(8) daemon in Vixie Cron". Vixie Cron is, according to the cron(8) man page, a "daemon to execute scheduled commands", which looks at the crontab tables once a minute to run any currently scheduled commands. A crontab consists of a command to be executed and a schedule of when to execute it. In the case of skyPulse, the instruction looks like:
  * * * * * /usr/bin/php -q /root/skybuilders/skyPulse
  The stars stand for minute, hour, day of month, month, day of week. Since they are stars, the schedule means every minute, every hour, etc. The rest of the line in this case is the command to be run. /usr/bin/php is the php engine. -q is an option that tells php to suppress http headers, since this is being run at the command line and not from an http request. /root/skybuilders/skyPulse is the php script being handed to the engine to be run. The function of this script is to call the page pulse.html in the application directory.

  pulse.html is a script which initiates two important functions in the Advanced Router:
  It calls arrcApply.html as the root user and writes the output to arrcApply.log. arrcApply.html is the file that checks whether a new version of arrc.sh, the Advanced Rules and Routes shell script, has been generated by the web application and runs it in order to apply the configuration, generating an output log in arrc.log.
  It also calls gatewaysWake.sh as the root user. gatewaysWake.sh is a shell script generated by the web application in line with the configuration that sends a single ping to each external gateway, in order to bring up the associated interface in case of outage. As a part of Dead Gateway Detection, if a gateway should become unreachable, the Advanced Router will disable all associated routes, directing traffic out the other operational gateways. Without these pings to detect the the dead gateway's return to operation, the routes would never be restored.