Article ID: 10013, created on Mar 3, 2011, last review on Sep 9, 2016

  • Applies to:
  • Operations Automation


A VPS-related task fails in Parallels Operations Automation (POA) with the following error message:

Connection to VZAgent was closed: poll_write efds

The same issue may cause inability to login to VZPP with the following error in CP:

There is no host with ID=xxx.


This is a general error message that indicates a problem with the connection from POA to the Virtuozzo Agent (VZAgent, PVA Agent) on the Parallels Virtuozzo Containers (PVC) server where the container is running.

There are several possible causes:

  • The PVC server is not available. For example, it has been turned off or some critical error occurred on a server, causing it to hang

  • The VZAgent service is not running on the PVC server

  • TCP ports 4433/4434 are closed in the firewall on the PVC server (or on intermediate routers in the datacenter), so POA cannot establish a connection to VZAgent

  • An unsupported PVC version has been installed

  • The root credentials for the PVC server do not correspond with the credentials in the POA database


  1. Check the POA VPS Hosting Deployment Guide to ensure a supported PVC version is installed on the PVC server.

  2. Perform these basic operations to find out whether the PVC server is available from POA:

    • Ping the PVC server from the POA Management Node

    • Check you can log into the PVC server by SSH/RDP

    • Use the telnet utility on the POA Management Node to check connectivity to ports 22 (SSH) or 3389 (RDP)

    • Use traceroute to check the routing path from POA to the PVC server

    • Use KVM/local console to check the server status if possible
  3. Check if ports 4433/4434 are being listened to locally on the PVC server:

    • Windows:

      > netstat -ano | findstr ":443[34]"
    • Linux:

      # netstat -antp | grep ":443[34]"

    Check the status of the VZAgent service on the PVC server and start it if it is not running:

    • Windows:

      > net start | findstr "Agent"
    • Linux:

      # vzagent_ctl status
      # pvaagent status
  4. Use the basic network utilities on the POA Management Node to check if POA can connect to ports 4433/4434 on the PVC server:

    # nmap -P0 <PVC_SERVER> -p 4433,4434
    # telnet <PVC_SERVER> 4433
    # netcat <PVC_SERVER>:4433
    # openssl s_client -connect <PVC_SERVER>:4434 -cipher ADH-AES256-SHA

    Replace <PVC_SERVER> in the commands above with the IP address or hostname of the PVC server in question.

    Check/configure firewall rules on the PVC server in accordance with the Parallels Knowledgebase articles:

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VPS task fails

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The host is presently unavailable. Please try again later

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