Connecting Rational license server results in FLEXlm Error -15 Cannot connect to license server

Technote (troubleshooting)


Attempts to connect to an IBM Rational License server, which is up and running with valid license files installed results in the error "FLEXlm error -15 cannot connect to license server".


After a Rational product is installed, attempting to connect to license server using the License Key Administrator results in the FLEXlm -15 error.

Note: The client machine is not behind a firewall.


Not specifying the default lmgrd port number of 27000 may result in the failure of the client to connect to license server, even if the client machine is not behind a firewall.

Resolving the problem

Specify the default lmgrd port number of 27000 as follows:

  1. Open the License Key Administrator

  2. Click Settings > Server Ports...

  3. Type 27000 in the Port for "lmgrd" field

  4. Click OK

Related information

How to serve a license key to client machines through a
A Japanese translation is available
A simplified Chinese translation is available
A Korean translation is available

Document information

More support for:

Rational License Key Server
General Information

Software version:

Version Independent

Operating system(s):


Reference #:


Modified date:


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