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Who needs a license for kdb+?

Everyone. All use of kdb+ is governed by a license.

64-bit installations require a license key file: k4.lic or kc.lic.

Free 64-bit kdb+ On-Demand Personal Edition is for personal, non-commercial use. Currently, it may be used on up to 2 computers, and up to a maximum of 16 cores per computer, but is not licensed for use on any cloud – only on personal computers. It may not be used for any commercial purposes. See the full terms and conditions.

It requires a kc.lic license key file and an always-on internet connection to operate.

Use of commercial kdb+ is covered by your license agreement with KX.

Your copy of kdb+ will need access to a valid license key file.

If you wish to begin using kdb+ commercially, please contact

License key files

All 64-bit versions of kdb+ need a valid license key file to run. Without one, kdb+ signals an error 'k4.lic and aborts.

tom@mb13:~/q$ q
KDB+ 3.6 2018.07.30 Copyright (C) 1993-2018 Kx Systems
m64/ 2()core 8192MB tom mb13.local

The license key file is k4.lic, or kc.lic for kdb+ On Demand. If both are found, the kc.lic file is used.

Obtain a license key file


Follow the download instructions to get your kc.lic.


To begin using kdb+ commercially, contact

Install the license key file

Save a copy of the license key file (k4.lic or kc.lic) in the QHOME folder. (See installation instructions for your operating system.) Restart your kdb+ session and note the change in the banner.

tom@mb13:~/q$ q
KDB+ 3.6 2018.07.30 Copyright (C) 1993-2018 Kx Systems
m64/ 2()core 8192MB tom mb13.local EXPIRE 2019.05.15 #400
q)til 6
0 1 2 3 4 5

Note the license number (#400 in the example) and quote it in any correspondence about the license.

If you are sharing use of a commercial license, you will probably want to set the environment variable QLIC to the path of the license key file, as below.

Keeping the license key file elsewhere

The default location for the license key file is the QHOME folder. You do not have to keep the license key file there. You can use the environment variable QLIC to specify a different filepath.

Folder not file

Like QHOME, QLIC points to a folder, not a file. For example,


Licensing server for kdb+ On Demand

As well as a license key file, kdb+ On Demand also requires frequent contact with the KX licensing server. For this you need an always-on Net connection.

If kdb+ cannot contact the KX server it will abort with a timestamped message.

'2018.03.28T11:20:03.831 couldn't connect to license daemon -- exiting

If an HTTP proxy is required, the environment variables http_proxy or HTTP_PROXY define the URL of the HTTP proxy to use. Since 4.1t 2022.11.01,4.0 2022.10.26,4.0ce 2022.09.16 the on-demand system honours the NO_PROXY/no_proxy environment variables, with the lowercase version taking precedence.

Core restrictions

If the license is for fewer cores than the total number on the machine, the number of cores available to kdb+ must be restricted with OS programs, or kdb+ will signal 'cores and abort.

KDB+ 3.6 2018.07.30 Copyright (C) 1993-2018 Kx Systems
m64/ 4(3)core 16384MB simon simon-macos.local #40000


As long as you use taskset or numa correctly, the binary will not abort itself.

You can see the number of cores entitled to a q process:

  • by looking at the banner, e.g. …m64/ 4(3)core… – the 4 here is the number of cores reported by the OS, and the 3 is the number of cores licensed
  • with .z.c – not the physical cores of the system, but rather the number the process is allowed to use
  • the first element of .z.l

The number of licensed cores is always 16 for the on-demand license.

License errors

On the road

The license key file binds the interpreter to your computer’s hostname. For example, for a Mac named mymbp the hostname might be mymbp.local. When traveling you may find a network has changed the hostname, for example to mymbp.lan or kdb+ then signals a host error on launch.

Linux and macOS users can restore their hostnames from the command shell, e.g.

scutil --set HostName "mymbp.local"

License questions

Designated Contacts should send license questions to

Emergency failover licenses

In case of an emergency, such as a hardware or infrastructure failure that renders your license key file unusable, the Designated Contact can email to request a temporary failover license to allow use of a different machine or IP address.