ILMT is the IBM License Metric Tool, and for anyone running IBM software on virtualized infrastructure it is the single most important piece of software you may not be watching. It is free. IBM gives it to you. And it is the only thing standing between the IBM bill you expect and one several times larger, because ILMT is what qualifies you to pay for the capacity your software actually uses instead of every core in the hardware it could theoretically touch. The audit claims that hurt most are rarely about software companies used too much. They are about this tool, quietly misconfigured, for months nobody noticed.
What does ILMT actually do?
It counts cores, and it counts the right ones.
IBM prices a large part of its software portfolio in PVUs, Processor Value Units, a figure derived from the processor cores available to the software. On a physical server with no virtualization, that count is simple. On a virtual estate, where one IBM product might run in a virtual machine using four cores on a host that has sixty-four, the count is the whole question. ILMT is the tool IBM sanctions to measure the four rather than the sixty-four. It discovers where PVU products run, measures the virtual cores available to them, and produces the reports that prove the number.
Without that proof, IBM does not assume the four. It assumes the sixty-four.
Why does ILMT decide your bill?
Because IBM has two prices for the same software, and ILMT is the switch between them.
Sub-capacity licensing charges you for the virtual cores your software can actually use. It is the reason virtualization saves money on IBM licensing at all.
Full-capacity licensing charges you for every physical core in the server the software could run on, used or not.
On a consolidated virtual estate, the gap between those two numbers is not a rounding error. Compliance analyses of real environments put it in the range of several times the sub-capacity figure, because modern hosts pack far more cores than any single workload uses. Sub-capacity is not a discount you ask for. It is a position you qualify for, and ILMT is the qualification.
What are the rules that keep sub-capacity alive?
Three conditions, and industry compliance reviews describe all three as routinely broken.
Deploy within 90 days. ILMT must be installed within 90 days of your first sub-capacity eligible deployment. Install it late and, per compliance analysis of IBM’s terms, the sub-capacity benefit runs from the installation date forward, not backward to cover the gap.
Scan every eligible host. The tool has to cover every host running PVU products, on its regular scan cycle. A host that runs the software but sits outside ILMT’s coverage is a host IBM can price at full capacity. Reviews of real estates repeatedly find ILMT running, but not running everywhere.
Generate and retain reports for two years. The quarterly reports must not only be generated, they must still exist when an audit arrives. This is the quiet one. Compliance reviewers find estates that produced the reports and never kept them, which breaks the two-year audit trail and forfeits sub-capacity for the gap, even though the tool was technically running the whole time.
Break any one of these, and the affected software can drop to full capacity for the entire period the condition was broken. Not a warning. A repriced bill.
Why is a monitoring tool the biggest risk in an IBM audit?
Because it converts an administrative lapse into a capacity claim, and the two look nothing alike until the letter arrives.
Nobody sets out to run ILMT badly. It happens the way entropy always happens in enterprise IT. A new virtualization host gets added and never joined to ILMT’s coverage. An upgrade quietly stops the reports generating. A server team reorganizes and the two-year retention job falls off someone’s list. Each is small. Each is invisible in day-to-day operations. And each one, at audit time, becomes IBM’s argument to price a virtual workload against a physical server.
This is why the first 48 hours after an IBM audit letter turn on one question before any other: what does our ILMT position actually look like, right now, across every host? If the answer takes more than a day to produce, that is the answer.
How do you get your ILMT position right?
Before an audit, not during one.
Confirm coverage. Every host running a PVU product, joined to ILMT, scanning on cycle. The gap you are looking for is the host that runs the software but nobody added to the tool.
Confirm retention. Reports generated quarterly and kept for two years, provably. Generation without retention earns nothing.
Confirm scope. Which of your IBM products are actually PVU sub-capacity eligible, because those are the ones ILMT protects, and the rest are measured on their own metrics.
Then reconcile the number. What ILMT reports against what you are licensed for. This is where IBM cost optimization work usually finds that the real position is more defensible than an audit assumes, in both directions.
Where UMS fits
We spent years running audits for the software publishers, and we know exactly how a full-capacity claim gets built, because we used to build them. On IBM specifically, UMS IBM audit defense starts with the ILMT position, the coverage, the retention, the scope, and rebuilds your real sub-capacity number before IBM’s full-capacity assumption gets to stand.
We are paid only from the savings we find. No savings, no fee. If IBM software runs anywhere in your virtual estate, give us 30 minutes before your next true-up or audit response.
Frequently asked questions
What is ILMT? ILMT is the IBM License Metric Tool, free software from IBM that discovers where IBM PVU-based products run and measures the virtual processor cores available to them. It is the tool that lets you pay for the capacity your IBM software actually uses on virtualized infrastructure, rather than every core in the physical hardware. Without it, IBM’s default position is full-capacity licensing.
Why does ILMT matter for IBM licensing costs? Because IBM offers two prices for the same software. Sub-capacity licensing charges you for the virtual cores your software can use. Full-capacity charges you for every physical core in the server it could theoretically run on. On a consolidated virtual estate that difference can be several times the bill, and correctly deployed ILMT is what qualifies you for the lower one.
What are the ILMT sub-capacity requirements? Three conditions keep sub-capacity alive: deploy ILMT within 90 days of your first sub-capacity eligible installation, keep it scanning every host that runs PVU products on its regular cycle, and generate and retain the quarterly reports for two years. Industry compliance analyses describe all three as commonly broken, and any one of them failing can drop the affected software to full-capacity pricing.
What happens if ILMT is not installed or not compliant? IBM’s position defaults to full-capacity licensing for the period the condition was broken. If ILMT was never deployed, deployed late, not scanning every eligible host, or the reports were not retained, IBM can price the affected software against all physical cores rather than the virtual cores it used, which is how a monitoring gap becomes a seven-figure audit claim.
How long do we have to keep ILMT reports? Two years. The reports must exist when an audit arrives, not just have been generated at the time. Compliance reviews repeatedly find estates that ran the reports but never retained them, which breaks the two-year audit trail and forfeits sub-capacity for the gap even though the tool was technically running.
Does ILMT cover every IBM product? No. ILMT is specifically the mechanism for PVU-based sub-capacity licensing. Other IBM metrics, such as per-user or resource-value-unit models, are measured differently, and some products have their own tooling. The first step in any IBM position is knowing which of your products are PVU sub-capacity eligible, because those are the ones ILMT protects.
Source notes
- Sub-capacity licensing FAQs, Compliance (IBM Passport Advantage): IBM’s own statement that approved tooling, including ILMT, is required for sub-capacity licensing, and that the customer carries the compliance responsibility.
- IBM Sub-Capacity Licensing and ILMT Compliance (Redress Compliance): the specific 90-day deployment window, the scan-coverage requirement, the two-year retention rule, the full-capacity consequence, and the several-times cost multiplier, all attributed to their analysis of real estates.
- UMS IBM audit defense: the UMS service page for IBM licensing, sub-capacity, and audit response.