Nagios Hosts Down but services up

Something must be misconfigured somewhere, or the host is coming up quicker than the service checks failing. Even in the URL that Khaled posted it says host checks are done on-demand when a service changes state:

Hosts are checked by the Nagios daemon:

• At regular intervals, as defined by the check_interval and retry_interval options in your host definitions.
• On-demand when a service associated with the host changes state.
• On-demand as needed as part of the host reachability logic.
• On-demand as needed for predictive host dependency checks.

This basically says that Nagios will check on set intervals, and when a service changes state. When a service breaks (goes into a WARNING/CRITICAL state), a host check is executed, and if the host is seen as down, it should suppress the service notifications, assuming you have it configured that way. Can you show us your service and host definitions, masking any hostname/addresses to protect the innocent if you want.

As a side note, I've been using Nagios for years, and never had a service alert when a host is in a down state, unless I specifically configured it to do so.

You can do it by using CHANGE_NORMAL_SVC_CHECK_INTERVAL and CHANGE_NORMAL_HOST_CHECK_INTERVAL.

Add an event handler for your service:

define service {
    host_name              ...
    service_description    ...
    check_command          ...
    contact_groups         ...
    event_handler          change_check_interval
}

The change_check_interval was defined in commands.cfg:

define command {
    command_name    change_check_interval
    command_line    $USER1$/eventhandlers/change_check_interval.sh $SERVICESTATE$ $SERVICESTATETYPE$ $SERVICEATTEMPT$ $HOSTADDRESS$
}

The content of change_check_interval.sh:

#!/bin/bash

now=`date +%s`
commandfile='/usr/local/nagios/var/rw/nagios.cmd'

case "$1" in
    OK)
        ;;
    WARNING)
        ;;
    UNKNOWN)
        ;;
    CRITICAL)
        /bin/printf "[%lu] CHANGE_NORMAL_SVC_CHECK_INTERVAL;host1;service1;2\n" $now > $commandfile
        ;;
esac

exit 0

Make sure that external commands is enabled in nagios.cfg:

check_external_commands=1