Floating license manager guide


This page explains how to run the floating license manager ampl_lic and related programs, to start serving floating licenses and to manage their use.

Need help with a floating license that has already been installed?
To install a floating license for the first time, see our Installation Guide.
To set options of the floating license manager, consult our Configuration Guide.
To interpret and fix error conditions, consult our Troubleshooting Guide.


AMPL’s floating license mechanism is implemented by ampl_lic, a program that functions as a license manager for both servers and clients. This page is guide to using the ampl_lic command to start and stop the license manager and to monitor the status of floating licenses. The general form of the command is

ampl_lic keyword [arguments]

The presentation on this page is organized according to the possible values of keyword, as follows:

  • start: start the license manager process and keep it running

  • stop: stop the license manager process

  • restart: stop and then start the license manager process

  • checkout (and return): manually check out and return licenses for offline use

  • status (and netstatus): query the state of the license manager and the licenses in use

  • licshow (and ipranges): view the license file in use, and its IP address restrictions

These keywords can be used with ampl_lic either on the computer designated as the license server, or on a client computer, except for a few cases indicated in our descriptions.


To make floating licenses available, the AMPL floating license manager, ampl_lic, needs to be started on the computer that acts as a license server. The same ampl_lic program must also be started on each client computer where a floating license will be used. Once started on any particular computer, ampl_lic will continue to run until it is terminated, usually by a logout or shutdown. Thus it normally only needs to be started when the computer is restarted or a new user logs in.

This section gives instructions for starting the floating license manager by explicitly invoking the ampl_lic program. Notes on starting the license manager automatically on startup or login are also provided, with instructions for getting more information. Separate instructions are provided for Windows, Linux, and macOS.

Starting AMPL or a licensed solver should also cause the license manager to be started if it is not already running. In that case an explicit invocation of ampl_lic is not needed.

Windows. For security reasons, the floating license manager must be invoked with a full pathname:

full-pathname\ampl_lic [start]

For example in a Windows command-prompt window you might type C:\Users\Smith\Desktop\AMPL\ampl_lic. (The start keyword is optional.)

The command window in which ampl_lic is started must remain open to keep ampl_lic running. As an alternative, to avoid keeping a command window active, you can invoke the auxiliary program alic_run by typing it in a command window (and then closing the window) or double-clicking the alic_run.exe icon. An icon labeled alic_run: running ampl_lic will then appear in the taskbar at the bottom of the Windows screen; you can click on it to bring up a message window that may contain some diagnostic information.

We also offer an ampl_lic_service that invokes ampl_lic.exe when Windows is started up, so that the ampl_lic program will be run by the LocalService account rather than by any logged-in user. This can be desirable when the machine hosting the AMPL floating license server is centrally managed. Contact licensing@ampl.com for installation details.

Linux. For security reasons, the floating license manager must be invoked with a full pathname:

full-pathname/ampl_lic [start]

For example in a Linux command window you might type /home/Smith/AMPL/ampl_lic. (The start argument is optional.) If the ampl_lic program is in the current directory, then you can use the shorter form


(An equivalent form `pwd`/ampl_lic is required by some Linux shells.) After the startup is completed, control returns to the command window and ampl_lic continues running in the background.

To automate the process of starting the license manager, ampl_lic can be started by a simple shell script in one of the directories of scripts that get run when the system boots. Details depend on specifics of the Linux installation; contact licensing@ampl.com for assistance.

macOS. For security reasons, the floating license manager must be invoked with a full pathname:

full-pathname/ampl_lic [start]

For example in a macOS Terminal window you might type /Users/smith/Desktop/AMPL/ampl_lic. (The start argument is optional.) If the current directory contains the ampl_lic program, then you can use the shorter form


After the startup is completed, control returns to the command window and ampl_lic continues running in the background.

The process of starting the license manager can be automated by placing an appropriate startup file in the folder /Library/LaunchDaemons. Contact licensing@ampl.com to request detailed instructions for this option.


When a floating license server or client is logged out or shut down, the ampl_lic process normally catches an appropriate shutdown signal and udpates current license information to a state file before terminating. The process can also be stopped manually with the command

ampl_lic stop

If ampl_lic is manually stopped on a client computer, licensed programs continue to run. When ampl_lic is subsequently restarted, it reads its saved state file, checks for licensed processes that are still running, and updates its state accordingly. It then checks in with the license manager on the server, which returns (among other things) a checksum of what it thinks is the local manager’s state. The client license manager then corrects the server’s view if necessary.


After any change to an AMPL floating license file (ampl.netlic or ampl.lic), the license manager must be restarted on the computer where the change has been made. This can be conveniently done by issuing the command

ampl_lic restart

which has an effect similar to stopping and then starting ampl_lic, except that the port does not have to be rebound (which can take several minutes on some systems).

checkout, return

Normally floating licenses are automatically checked out when a licensed programs starts, and are automatically returned after termination of a licensed program. There is an option to check out a license manually, however, in which case it remains on the client computer until it is manually returned. This can be useful when the client computer will be temporarily moved to a location where it does not have access to the license server, such as for a demo at a customer site.

Floating licenses are manually checked out by a command of the form

ampl_lic checkout program [count] [program [count]] ...

where program is the name of a licensed program and optionally count is the number of floating licenses to be checked out. In the most common situation, only one license of AMPL and of some solvers needs to be checked out, and count can be omitted. For example, you might specify ampl_lic checkout ampl minos knitro to check out one license each for AMPL and the MINOS and Knitro solvers.

A similar command requests that checked-out licenses be returned:

ampl_lic return program [count] [program [count]] ...

Licenses are not actually returned until all processes using them have ended. An ampl_lic return statement may specify only some of the licenses that have been manually checked out, in which case the remaining licenses remain with the client until returned by a subsequent ampl_lic return statement.

status, netstatus

A summary of all floating licenses in use can be requested with the command

ampl_lic netstatus

issued on the server or on any client. This command communicates directly with the server, and hence can be used on a client even where the ampl_lic program is not currently running.

Any computer can request a summary of its local floating license activity with the command

ampl_lic status

If an ampl_lic process is running, this command first tries to return any licenses held as specified by the current LIC_HOLD setting. It then displays a report of the licensed processes currently running on the computer and of licenses that the computer is holding for other reasons, such as previous use of ampl_lic checkout or failure to communicate with the server to return licenses.

If there is no ampl_lic process running, ampl_lic status displays an error message. Thus, invoking ampl_lic status is a way to check whether the local license manager is running.

The local (client) license manager may hold licenses because it cannot communicate with the network (server) license manager to return them, perhaps because the network license manager has been stopped or because the network has gone down. In this case, the local manager tries periodically to reestablish contact with the network license manager. The period between tries starts at 15 seconds and increases by 15 second increments up to 15 minutes. If you know that the network manager has just become available again, invoking ampl_lic status will cause the local manager to return licenses immediately.

If you kill a licensed process or the process faults, the network license manager may still think the process is running. Invoking ampl_lic statuswill cause the manager to check which processes are still running and to return any licenses that are no longer in use.

licshow, ipranges

If ampl_lic is running locally, the output from

ampl_lic licshow

reports the full pathname by which ampl_lic was invoked and the full pathname and contents of the ampl.netlic or ampl.lic file that it read.

The ampl.netlic file on the server may be configured to accept checkout requests only from certain IP addresses. A list of allowable IP addresses and/or address ranges can be included in the license file when it is generated, and may also be modified by the user through IPRANGE and ADDRANGE settings. The current list of valid IP addresses can be seen by invoking

ampl_lic ipranges

on the server or any client.