If you can’t access the UNIX/Linux computers view in the Administration pane in Microsoft System Center 2012 R2 Operations Manager, then you probably receive the following error message:
[box] Date: 12/30/2017 7:48:49 PM Application: Operations Manager Application Version: 7.1.10226.1360 Severity: Error Message: System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.SystemCenter.CrossPlatform.UI.OM.Integration.UnixComputerOperatingSystemHelper.JoinCollections(IEnumerable`1 managementServers, IEnumerable`1 resourcePools, IEnumerable`1 unixcomputers, IEnumerable`1 operatingSystems) at Microsoft.SystemCenter.CrossPlatform.UI.OM.Integration.UnixComputerOperatingSystemHelper.GetUnixComputerOperatingSystemInstances(String criteria) at Microsoft.SystemCenter.CrossPlatform.UI.OM.Integration.Administration.UnixAgentQuery.DoQuery(String criteria) at Microsoft.EnterpriseManagement.Mom.Internal.UI.Cache.Query`1.DoQuery(String criteria, Nullable`1 lastModified) at Microsoft.EnterpriseManagement.Mom.Internal.UI.Cache.Query`1.FullUpdateQuery(CacheSession session, IndexTable& indexTable, Boolean forceUpdate, DateTime queryTime) at Microsoft.EnterpriseManagement.Mom.Internal.UI.Cache.Query`1.InternalSyncQuery(CacheSession session, IndexTable indexTable, UpdateReason reason, UpdateType updateType) at Microsoft.EnterpriseManagement.Mom.Internal.UI.Cache.Query`1.InternalQuery(CacheSession session, UpdateReason reason) at Microsoft.EnterpriseManagement.Mom.Internal.UI.Cache.Query`1.TryDoQuery(UpdateReason reason, CacheSession session) at Microsoft.EnterpriseManagement.Mom.Internal.UI.Console.ConsoleJobExceptionHandler.ExecuteJob(IComponent component, EventHandler`1 job, Object sender, ConsoleJobEventArgs args)[/box]
The issue occurs if the UNIX/Linux monitoring resource pool is deleted
To resolve the issue, follow these steps:
Get-SCXAgent
$SCXPool = Get-SCOMResourcePool -DisplayName "<New Resource Pool Name>"
Get-SCXAgent | Set-SCXResourcePool -ResourcePool $SCXPool