There is growing use of Internet-of-Things (IoT) and Cyber-Physical Systems (CPS) in industry, homes, cars, and other environments, and several operating systems have been proposed to manage these environments. The growing use of long-lived IoT and CPS has made them susceptible to obsolescence and change, just like "normal" software, demanding systematic support for periodic updates of their embedded software. However, there is little empirical data about the structure, architecture, specifications, and dependencies of these subsystems. This article presents an analysis of over-the-air (OTA) update support in 26 existing open-source IoT/CPS operating systems and embedded software projects, performed primarily by examining their documentation and supplementing with occasional source code examination. We found that seven projects give details of an OTA update mechanism; four projects do not report details of OTA update mechanisms, but third-party developers implemented specific solutions to support OTA updates using these projects; and the remaining 15 projects do not report a particular update capability at all in their documentation. This study will allow extending, organize, and compare OTA update capabilities of future IoT/CPS operating systems.