There are legitimate scenarios where an administrator needs to interact with the RDS CAL registry key. The most common is changing the licensing mode after initial deployment. For example, if a company switches from thin clients (Per Device) to roaming employees (Per User), an administrator can change the LicenseMode value from 2 (Per Device) to 4 (Per User). Another scenario is disaster recovery: after restoring a license server from backup, registry corruption may require manual cleanup of orphaned license entries. Third-party tools or scripts sometimes rely on reading these registry keys for inventory and monitoring.
However, the single most frequent – and dangerous – reason administrators touch this key is to circumvent licensing errors during the 120-day grace period. When an RDS server cannot reach a license server, it eventually stops accepting new connections. Unscrupulous or desperate guides online may suggest deleting or modifying registry keys to reset the grace period. This is a risky and often temporary hack.
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. rds cal license registry key
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.
Managing RDS Client Access Licenses (CALs) via the registry is often necessary when Group Policy or the Server Manager GUI fails to apply settings correctly. You can configure the licensing mode and the license server address directly through the Registry Editor. 1. Configure the RDS Licensing Mode
This registry key tells the RD Session Host whether to look for Per User or Per Device CALs.
Registry Path: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\Licensing Core
Action: Locate or create a DWORD (32-bit) value named LicensingMode. Values: 2 — Per Device mode. 4 — Per User mode. 2. Specify the RD License Server
If your Session Host cannot find the license server, you can manually point to it using the registry.
Registry Path: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TermService\Parameters\LicenseServers There are legitimate scenarios where an administrator needs
Action: Create a new Key (folder) under LicenseServers named with the FQDN or IP Address of your license server.
Note: You can also use the Microsoft Learn guide to verify if the server is properly configured via PowerShell as an alternative to registry edits. 3. Clear Cached Grace Period (Troubleshooting)
If you are seeing "The Remote Desktop trial period has expired" even after installing licenses, you may need to delete the cached grace period key to force a refresh.
Registry Path: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\GracePeriod
Action: You must first take ownership and grant yourself "Full Control" permissions for this key. Once done, delete the L$RTMTIMEB... binary value inside.
Reboot: A restart is required for this change to take effect and for the server to reach out to the specified license server. 4. Verify Activation
After making registry changes, use the RD Licensing Manager tool to confirm the server status.
Open Server Manager > Tools > Remote Desktop Services > Remote Desktop Licensing Manager. Let’s break down the most critical values inside
The server should show a green checkmark if it is activated and communicating correctly. License Remote Desktop session hosts | Microsoft Learn
Remote Desktop Services (RDS) Client Access License (CAL) system does not use a single "registry key" as a serial number. Instead, the registry is primarily used to manage the licensing mode , identify license servers , or reset the grace period 1. The "Grace Period" Registry Key
The most commonly referenced registry key regarding RDS licensing is the one that tracks the 120-day grace period. Once this period ends, users can no longer connect without a valid CAL.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\GracePeriod The "Timebomb"
: Inside this key, there is typically a binary entry starting with L$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
Let’s break down the most critical values inside the RCM key.