Problem with inactive agent in OSSEC Web Interface

I was just debugging OSSEC Web interface. Namely, it incorrectly showed that one host was not responding event though there were log entries that showed otherwise. The problem was that this particular host was transferred to another network, and thus, its address was changed.

I figured out that the list of available agents within Web interface is generated from a files found in /var/ossec/queue/agent-info directory. There, you'll find one file per agent. The file name itself consists of agent name and IP address separated by a single dash. In order to display if an agent is connected or not the PHP code from Web interface (which itself is placed in /usr/share/ossec-wui directory) obtains time stamp of a file belonging to a particular client and if this time stamp is younger that 20 minutes, it proclaims agent OK, otherwise, it shows it as inaccessible.

In this case it turned out that the old agent wasn't removed using manage_client tool (selecting option R, for remove). So, the old information remained, which wasn't updated and thus the Web interface reported inactive agent.