How to disable host checks of existing hosts in Nagios?

Question

I have two hosts for which the hosts checks are no longer working (because the pings are stopped by a firewall), causing Nagios to send notifications about them and list them as DOWN and coloured red. I want to temporarily disable the host checks for these hosts (but not remove them, or disable the checks of the services on them, since those work fine). What is the best way to do this?

I have tried changing their definitions to use generic-host instead of use linux-server. Those templates are defined as follows:

define host{
        name                            linux-server    ; The name of this host template
        use                             generic-host    ; This template inherits other values from the generic-host template
        check_period                    24x7            ; By default, Linux hosts are checked round the clock
        check_interval                  5               ; Actively check the host every 5 minutes
        retry_interval                  1               ; Schedule host check retries at 1 minute intervals
        max_check_attempts              10              ; Check each Linux host 10 times (max)
        check_command                   check-host-alive ; Default command to check Linux hosts
        notification_period             workhours       ; Linux admins hate to be woken up, so we only notify during the day
                                                        ; Note that the notification_period variable is being overridden from
                                                        ; the value that is inherited from the generic-host template!
        notification_interval           120             ; Resend notifications every 2 hours
        notification_options            d,u,r           ; Only send notifications for specific host states
        contact_groups                  admins          ; Notifications get sent to the admins by default
        register                        0               ; DONT REGISTER THIS DEFINITION - ITS NOT A REAL HOST, JUST A TEMPLATE!
        }

define host{
        name                            generic-host    ; The name of this host template
        notifications_enabled           1               ; Host notifications are enabled
        event_handler_enabled           1               ; Host event handler is enabled
        flap_detection_enabled          1               ; Flap detection is enabled
        process_perf_data               1               ; Process performance data
        retain_status_information       1               ; Retain status information across program restarts
        retain_nonstatus_information    1               ; Retain non-status information across program restarts
        notification_period             24x7            ; Send host notifications at any time
        register                        0               ; DONT REGISTER THIS DEFINITION - ITS NOT A REAL HOST, JUST A TEMPLATE!
        max_check_attempts              1
        }

I had expected the host checks to stop, since generic-host has no check_command configured, but instead they continue (no idea what command Nagios is actually running) and the hosts stay on status DOWN.

I have also tried to add an empty check_command line to the definitions of the hosts, to override the check_command parameter to be blank, which the Nagios docs say should disable host checks, but then Nagios does not accept the configuration, saying that there "is no command named ''".

What I want is for Nagios to stop doing host checks for these hosts, and for the status to go back to OK/UP. What is the proper way to achieve that?

Answer 1

Have you tried clearing retention.dat? This would wipe out all current host and service status, all comments, downtime, etc. Essentially start with a clean state.

> cd /usr/local/nagios/var
> (optional) cp retention.dat retention.dat.backup
> rm retention.dat
> service nagios restart

Edit: This should go in tandem with the other solutions here.. disable host checks first, THEN do a reset by clearing retention data. This may or may not get the host states where you want them, but they'll no longer be DOWN or throwing notifications

Answer 2

You can force a host check to always return OK by using the check_dummy check command.

Place the following command definition in, for example, your commands.cfg file:

# 'check_dummy' command definition
# NOTE: This command always returns an 'OK' result no matter what.
define command{
        command_name    check_dummy
        command_line    $USER1$/check_dummy 0
}

Then in your host definition add the following line:

check_command   check_dummy

Restart the nagios service and your non-pingable host will now always be 'UP'.

Answer 3

You have several options and You do not even need edit config files.

1. You can disable notifications from Nagios web UI. All what do you need is find that host and proceed with Disable notifications for this host. Nagios will still check this host but notifications are not generated anymore. Notifications must by manually enabled after you fix the firewall problem.
2. You can Acknowledge this host problem on same place as you would disable notifications (web UI). This allows you to disable notifications and also put some comment/note to this problem. Notifications are automatically enabled when host change his status to UP (green).
3. You can even disable host check from web UI. Use Disable active checks of this host option along with Disable notifications for this host. This disable notification and also Nagios stop with pinging remote host. But do not forget to enable these options after you fix your firewall issue/rules.