A common administrative task involving the registry is resetting the RDS Grace Period. When a Remote Desktop Session Host is activated, it enters a grace period (usually 120 days) before it requires CALs. If this period expires and you are troubleshooting license installation, you may need to reset this timer.
Registry Key Location:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\GracePeriod
Procedure:
To reset this, an administrator must delete the GracePeriod key. However, Windows protects this key with specific permissions.
When you decommission an old license server, your RDS host may still attempt to contact it. Removing the server’s entry from SpecifiedLicenseServers forces the host to fail over to another server.
| Component | Registry Path |
|-----------|----------------|
| RDS Licensing Server (Per User CAL issuance tracking) | HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TermServLicensing\Parameters\IssuedLicenses |
| RDS Session Host (License mode & server assignment) | HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\Licensing Core |
| License server discovery | HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\LicenseServers |
Key values in Licensing Core:
LicenseServers (MULTI_SZ): List of license servers used by the session host.This report details the technical location, structure, and function of the Windows Registry keys used to store Remote Desktop Services (RDS) Per-Device Client Access Licenses (CALs). It is intended for system administrators and IT auditors responsible for license compliance, migration, and troubleshooting.
The report clarifies the distinction between the License Server Registry (where issued licenses are stored) and the Client Device Registry (where received tokens are cached).
The RDS CAL registry key is not a direct license file but rather a storage location for licensing-related configuration and, in certain legacy or specific scenarios, license token information. Its primary role is to inform the RDS server about the licensing mode (Per User or Per Device) and, on a license server, to track issued CALs. The most critical keys reside in the Windows Registry under:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TermService\Parameters\License
Additionally, on a dedicated RDS License Server, license entries can be found in: rds cal license registry key
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TermServLicensing\Parameters
Within these paths, values such as LicenseMode (DWORD) determine whether the server enforces Per Device or Per User licensing. Other subkeys store unique license IDs, version information, and – historically – even temporary license certificates. When an RDS client connects, the server checks these registry values to verify that a valid CAL is available.
Get-WmiObject -Class Win32_TerminalServiceSetting -Namespace root\cimv2\terminalservices
Or the RD Licensing Manager GUI (licmgr.exe).
Configuring Remote Desktop Services (RDS) through the Windows Registry is a common task for system administrators troubleshooting licensing issues or setting up session hosts without using Group Policy Objects (GPO). Primary Registry Key Locations
There are several critical registry keys used to manage RDS Client Access Licenses (CALs), depending on whether you are defining the licensing mode, specifying a license server, or managing the grace period. Registry Path Value Name Licensing Mode
HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\Licensing Core LicensingMode Specified Server
HKLM\SYSTEM\CurrentControlSet\Services\TermService\Parameters\LicenseServers SpecifiedLicenseServers Policy-based
HKLM\SOFTWARE\Policies\Microsoft\Windows NT\Terminal Services LicensingMode & LicenseServers Grace Period
HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\GracePeriod A common administrative task involving the registry is
REPORT: RDS CAL License Registry Key Analysis
Date: October 26, 2023 Subject: Analysis of Remote Desktop Services (RDS) Client Access License (CAL) Registry Keys
If you want, I can produce:
In the fluorescent-lit hum of the Server Room, a junior admin named Leo stared at a flickering monitor. It was 4:45 PM on a Friday. He was trying to get a new Remote Desktop Session (RDS) host online, but every user who tried to log in was met with a cold, digital wall: “The remote session was disconnected because there are no Remote Desktop License Servers available.”
Leo had installed the licenses. He had activated the server. Yet, the server was acting like it had amnesia.
"It’s the registry," whispered Sarah, the senior lead, appearing like a ghost behind him. "The server is looking for a map it can't find."
She leaned over and opened regedit. They dove into the belly of the machine, navigating the hive:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\Licensing Core
"Look here," she pointed to the LicensingMode key. "It’s set to 5. That’s the ghost code. It doesn't know if it wants Per User or Per Device."
With a few keystrokes, they flipped the value to 4 (Per User). But the beast still wouldn't budge. Sarah knew they had to clear the "Grace Period" debris—the digital cobwebs left behind from when the server was free and young.
They navigated to:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\GracePeriod "The gatekeeper key," Leo muttered. LicenseServers (MULTI_SZ): List of license servers used by
Windows didn't want them there. It protected that key with ironclad permissions. Sarah right-clicked, seized Ownership from the SYSTEM, and granted herself full control. With a final, decisive click, she deleted the binary blob sitting inside. "Now," Sarah said, "give it a heartbeat."
Leo restarted the services. The progress bar crawled. He held his breath and tried a test login. Instead of an error, the desktop bloomed into view—icons, taskbars, and all. The registry key had been turned, the lock had clicked, and the users were finally home.
Remote Desktop Services (RDS) Client Access License (CAL) system does not use a single "registry key" as a serial number. Instead, the registry is primarily used to manage the licensing mode , identify license servers , or reset the grace period 1. The "Grace Period" Registry Key
The most commonly referenced registry key regarding RDS licensing is the one that tracks the 120-day grace period. Once this period ends, users can no longer connect without a valid CAL.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\GracePeriod The "Timebomb"
: Inside this key, there is typically a binary entry starting with L$RTMTIMEBOMB
. Deleting this entry resets the 120-day timer, though this requires taking ownership of the registry folder first.
: This is usually a temporary fix for administrators to restore connectivity while they troubleshoot or wait for license procurement. 2. Configuring the Licensing Mode
If your server is failing to recognize installed licenses, it may be because the Licensing Mode
(Per User vs. Per Device) is not correctly set in the registry. Microsoft Learn