Comment 2 for bug 1405265

The agent works in the next way - it finds the server which it needs to connect to, then sleeps for a random period of time, then executes ohai, then parses the data from its output, sends the info to the server and exits. In my case the agent hangs on the ohai step. Ohai in its turn opens all the plugins it has, one of them is "filesystem.rb", which executes a set of commands collecting the data about all filesystems at the moment. The process "blsid -s TYPE" hangs and the agent's process never finishes its job, so the node appears as "Offline" in the Fuel UI.
In order to resolve the current issue, I had to restart multipathd process so that it releases all non-existing devices, after that it becomes possible to kill those blkid processes as well.
Once I removed the plugin from ohai directory, the agent started to operate properly.