Build error on using mkfifo

Hi,
I tried to use mkfifo in my Px4 module, but when i build it, i get: undefined reference to 'mkfifo' from the linker.
Isn’t it a default part of libc library ?
Should i add something to my CMakeLists.txt ?

You need to check if it is enabled for your board.

Check the docs: http://nuttx.org/Documentation/NuttxUserGuide.html#mkfifo
And the defconfig, e.g. for fmu-v3: https://github.com/PX4/Firmware/blob/cd9b3d6b2741bf696a97a7ac6f01d8dddec36e05/boards/px4/fmu-v3/nuttx-config/nsh/defconfig#L46
According to http://nuttx.org/doku.php?id=documentation:nuttshell you need:

 CONFIG_PIPES && CONFIG_DEV_FIFO_SIZE > 0