#  Licensing


## Who needs a license for kdb+?

Everyone. All use of kdb+ is governed by a license. Without one, kdb+ signals an error [`'k4.lic`](../basics/errors.md#k4.lic) and aborts.

64-bit installations require a **license key file**: `k4.lic`, or `kc.lic` for kdb+ On Demand.

If both are found, the `kc.lic` file is used.


## Obtain a license key file

You can get a commercial license for kdb+ or you can use KDB-X Community Edition, which is free for personal and commercial use, subject to [usage restrictions](https://code.kx.com/licensing/usage-restrictions.html#kdb-x-community-edition-download).

> **Tip — Get KDB-X Community Edition**
>
>
> You can get a free, non time-limited license for the next evolution of kdb+ with KDB-X Community Edition. For more information and to get started right away, see [Get KDB-X Community Edition](https://developer.kx.com/products/kdb-x/install).
>
### Commercial License

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 sales@kx.com.

## 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](install.md#step-3-install-the-license-file) for your operating system.) 
Restart your kdb+ session and note the change in the banner. 
```txt
tom@mb13:~/q$ q
KDB+ 3.6 2018.07.30 Copyright (C) 1993-2018 Kx Systems
m64/ 2()core 8192MB tom mb13.local 192.168.1.44 EXPIRE 2019.05.15 tom@kx.com #400
q)til 6
0 1 2 3 4 5
q)
```

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.

### License errors

A list of possible errors can be found [here](../basics/errors.md#license-errors).


### 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.

> **Tip — Folder not file**
>
>
> Like `QHOME`, `QLIC` points to a folder, not a file. For example,
>
> ```bash
> QLIC='/Users/simon/q'
> ```
>
Note: If a license file is found in the current working directory it will be used preferentially over any found in `QLIC` and `QHOME`.

## 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](../kb/cpu-affinity.md), or kdb+ will signal `'cores` and abort.
```txt
KDB+ 3.6 2018.07.30 Copyright (C) 1993-2018 Kx Systems
m64/ 4(3)core 16384MB simon simon-macos.local 127.0.0.1   simon@kx.com #40000

'cores
```

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`](../ref/dotz.md#zc-cores) – not the physical cores of the system, but rather the number the process is allowed to use
-   the first element of [`.z.l`](../ref/dotz.md#zl-license) 

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


> **Tip — 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 `mymbp.fritz.box`. kdb+ then signals a host error on launch. 
>
> Linux and macOS users can restore their hostnames from the command shell, e.g. 
>
> ```bash
> scutil --set HostName "mymbp.local"
> ```
>
## License questions

Designated Contacts should send license questions to licadmin@kx.com. 

## 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 failover@kx.com to request a temporary failover license to allow use of a different machine or IP address.