to supplement https://github.com/PagerDuty/pagerduty-nagios-pl
pagerduty_nagios.pl does a good job of getting nagios events into pagerduty... this script provides the reverse, for a more round-trip-synced experience
more specifically, it polls pagerduty for new events since the last poll, checks whether they are acks or resolves, and if so applies those to their corresponding nagios alerts. i.e., if you ack in pagerduty, via sms or web ui or phone app, that ack will find it's way back to your nagios instance.
set up a cron like so:
* * * * * nagios /usr/local/bin/pd_ack_to_nagios_ack_poller.pl -p [my_pagerduty_token] -u [my_pagerduty_domain]
note this will generally need to be run as the nagios user so that it has write access to the nagios command pipe.