We are going to download and build a FreeRTOS simulator in our build environment:

1. Switch to your Ubuntu Terminal and change the current directory to /mnt:

$ cd /mnt

2. Download the source code of the FreeRTOS simulator:

$ wget -O simulator.zip http://interactive.freertos.org/attachments/token/r6d5gt3998niuc4/?name=Posix_GCC_Simulator_6.0.4.zip

3. Extract the downloaded archive:

$ unzip simulator.zip

4. Change the current directory to Posix_GCC_Simulator/FreeRTOS_Posix/Debug:

$ cd Posix_GCC_Simulator/FreeRTOS_Posix/Debug

5. Fix the minor mistake in makefile by running the following command:

$ sed -i -e 's/(.*gcc.*)-lrt(.*)/12 -lrt/' makefile

6. Build the simulator from the source code:

$ make

7. Start it:

$ ./FreeRTOS_Posix

At this point, the simulator is running.