Hi, I am running Nagios on CentOS release 5.5 (Final). Any clue about the below warning? Please let me know if any one needs any additional information. /usr/sbin/nagios -v /etc/nagios/nagios.cfg Nagios 2.12 Copyright (c) 1999-2007 Ethan Galstad (http://www.nagios.org) Last Modified: 05-19-2008 License: GPL Reading configuration data... Running pre-flight check on configuration data... *Warning: Size of service_message struct (8376 bytes) is > POSIX-guaranteed atomic write size (512 bytes). Service checks results may get lost or mangled!* Checking services... Checked 341 services. Checking hosts... Checked 27 hosts. Checking host groups... Checked 13 host groups. Checking service groups... Checked 3 service groups. Checking contacts... Checked 27 contacts. Checking contact groups... Checked 10 contact groups. Checking service escalations... Checked 0 service escalations. Checking service dependencies... Checked 0 service dependencies. Checking host escalations... Checked 0 host escalations. Checking host dependencies... Checked 0 host dependencies. Checking commands... Checked 77 commands. Checking time periods... Checked 4 time periods. Checking extended host info definitions... Checked 0 extended host info definitions. Checking extended service info definitions... Checked 0 extended service info definitions. Checking for circular paths between hosts... Checking for circular host and service dependencies... Checking global event handlers... Checking obsessive compulsive processor commands... Checking misc settings... Total Warnings: 1 Total Errors: 0 Things look okay - No serious problems were detected during the pre-flight check Regards Kaushal