The blue mini-USB console cable that is included with the IR829 (and other 800 series devices) connects the mini-USB console port, under the screwed down plate, to a USB port on your Linux machine. The trick is identifying the specific device to use for the COM port. These Cisco Console instructions are very good. They will work for you with /dev/ttyUSB1. Though the instructions are from the Ubuntu site, they should work just the same with pretty much any version of Linux. Have tested them with the Ubuntu Desktop 14.04 LTS version of Linux.
Also see How to use the IR829 Mini-USB Console Cable with OSX El Capitan 10.11, The specified item was not found. and .