The correct variable syntax to populate a custom column in a horizontal discovery pattern is  $cmdb_ci_linux_server.u_custom_column.INSERT . This syntax indicates that the value of the custom column will be inserted into the cmdb_ci_linux_server table for the current CI.  The other options are either invalid or incorrect syntaxes for this operation 1 2 .

The Application Pattern Type is a pattern that discovers applications and their dependencies by using probes and sensors 1 .  It has two main components: the Run Order and the Identification Section 2 .  The Run Order defines the sequence of probes and sensors that Discovery uses to find and classify CIs 2 .  The Identification Section specifies the criteria that Discovery uses to identify CIs and their relationships 2 . The other options, CI Type and Operating System, are not specific to the Application Pattern Type.  They are used for other pattern types, such as the Horizontal Pattern Type and the Service Mapping Pattern Type 3  .

 Reconciliation rules are used to determine which data sources can update CI attributes in ServiceNow. Reconciliation rules can be static or dynamic, and they can be applied to specific CI classes, attributes, or discovery sources.  Reconciliation rules can also specify the actions to take when there are unmatched values, such as removing, ignoring, or updating them 1 .

In ServiceNow Discovery, when encountering the error 'Active, couldn't classify' during the discovery of a new SNMP network device, it typically indicates an issue with the classification process. Classification is a crucial initial step in the Discovery process, where the system determines the type of device it is interacting with. If an SNMP Classification rule for the new device type does not exist or needs updating, Discovery will be unable to classify and thus properly discover the device. Incorrect SNMP credentials or firewall issues usually result in different types of errors, such as authentication failures or no response from the device.

SNMP credentials are used by Discovery to communicate with devices that support the Simple Network Management Protocol (SNMP). SNMP credentials do not include a user name, just a password, called the community string. The default read-only community string for many SNMP devices is public, and Discovery will try that automatically.  Enter the appropriate SNMP credentials if they differ from the public community string 1 .

A /24 subnet IP Range means that there are 256 possible IP addresses in the range, from 0 to 255. A Shazzam batch size of 5000 means that Discovery will send 5000 ICMP packets at a time to scan the IP addresses. Therefore, Discovery will launch the Shazzam probe once for every 5000 IP addresses in the range, or 256 / 5000 = 0.0512 times. Since the number of times must be an integer, Discovery will round up to 1 and launch the Shazzam probe once. However, since the Shazzam probe is launched for each MID Server that is assigned to the Discovery Schedule, the actual number of times will depend on how many MID Servers are available. If there are N MID Servers, then the Shazzam probe will be launched N times, each sending 5000 ICMP packets to the same IP range. Therefore, the total number of times that the Shazzam probe will be launched during discovery is N * 1 = N.

The deletion strategy ‘Mark as absent’ means that when a related CI that was previously discovered by a pattern is no longer found, the install_status attribute of that CI is set to Absent. This indicates that the CI is missing or removed from the network.  The main CI (in this case, the Linux Server CI) is not affected by the deletion strategy of the related CI (in this case, the Disk CI) 1 2 .

References

1 : Set a deletion strategy - Product Documentation: San Diego - ServiceNow

2 : Network adapter status setting to “Absent” in EMC … - ServiceNow …

Tracked configuration files are files that contain settings and parameters of certain applications or devices that Discovery can find and add to the CMDB. Some of the benefits of tracked configuration files are:

Content version comparison: You can compare the content of different versions of the same configuration file and see the changes that occurred over time. This can help you troubleshoot issues, audit changes, and restore previous configurations if needed.

Files tracked as CIs: You can view the configuration files as configuration items (CIs) in the CMDB and see their relationships with other CIs, such as the applications or devices they belong to. This can help you understand the dependencies and impact of the configuration files on your IT environment.

The default thread count for a MID Server is 25. This means that the MID Server can run up to 25 worker threads simultaneously to execute the jobs assigned to it by the ServiceNow instance. The worker threads are divided into different thread pools based on the priority of the jobs. The MID Server can also adjust the thread count dynamically based on the system resources and the workload.  The thread count can be configured by changing the MID Server parameters in the ServiceNow instance 1 2 .  References  =  1 : MID Server Max Threads - Worker Groups - Priority and Queues - ServiceNow  2 : Product Documentation | ServiceNow

One method for deleting specific CIs not discovered in 30 days is to use a scheduled job that runs a script to query the CMDB for CIs that have not been updated by Discovery for a certain period of time, and then delete them or mark them as retired. This method can help you keep your CMDB clean and accurate, and avoid having stale or obsolete CIs. You can configure the scheduled job to run at a specific frequency and time, and specify the criteria for selecting the CIs to delete.