MentOS (Mentoring Operating System) is an open source educational operating system. The goal of MentOS is to provide a project environment that is realistic enough to show how a real Operating System work, yet simple enough that students can understand and modify it in significant ways.

There are so many operating systems, why did we write MentOS? It is true, there are a lot of education operating system, BUT how many of them follow the guideline de fined by Linux?

MentOS aims to have the same Linux's data structures and algorithms. It has a well-documented source code, and you can compile it on your laptop in a few seconds!

If you are a beginner in Operating-System developing, perhaps MentOS is the right operating system to start with.

Parts of MentOS are inherited or inspired by a similar educational operating system called DreamOs written by Ivan Gualandri.

2. Prerequisites

MentOS is compatible with the main unix-based operating systems. It has been tested with Ubuntu, WSL1, WSL2, and MacOS.

2.1. Generic Prerequisites

3.1.1. Compile

For compiling the system:

nasm
gcc
make
cmake
git
ccmake (suggested)

Under MacOS, for compiling, you have additional dependencies:

i386-elf-binutils
i386-elf-gcc

3.1.2. Execute

To execute the operating system, you need to install:

qemu-system-i386 (or qemu-system-x86)

3.1.3. Debug

For debugging we suggest using:

cgdb
xterm

2.2. installation Prerequisites

Under Ubuntu, you can type the following commands:

sudo apt-get update && sudo apt-get upgrade -y
sudo apt-get install -y build-essential git cmake qemu-system-i386 
sudo apt-get install -y cgdb xterm

Under MacOS you also need to install the i386-elf cross-compiler. The simplest installation method is through Homebrew package manager. Install Homebrew if you don't already have it, and then type the following commands:

brew update && brew upgrade
brew install i386-elf-binutils i386-elf-gcc git cmake qemu nasm
brew install cgdb xterm #<- for debug only

3. Compiling MentOS

Compile and boot MentOS with qemu:

cd <clone_directory>
mkdir build
cd build
cmake ..
make
make qemu

To login, use one of the usernames listed in files/etc/passwd.

4. Change the scheduling algorithm

MentOS provides three different scheduling algorithms:

Round-Robin
Priority
Completely Fair Scheduling

If you want to change the scheduling algorithm:


cd build

# Round Robin scheduling algorithm
cmake -DSCHEDULER_TYPE=SCHEDULER_RR ..
# Priority scheduling algorithm
cmake -DSCHEDULER_TYPE=SCHEDULER_PRIORITY ..
# Completely Fair Scheduling algorithm
cmake -DSCHEDULER_TYPE=SCHEDULER_CFS ..

make
make qemu

Otherwise you can use ccmake:

cd build
cmake ..
ccmake ..

Now you should see something like this:

BUILD_DOCUMENTATION              ON
CMAKE_BUILD_TYPE
CMAKE_INSTALL_PREFIX             /usr/local
DEBUGGING_TYPE                   DEBUG_STDIO
ENABLE_BUDDY_SYSTEM              OFF
SCHEDULER_TYPE                   SCHEDULER_RR

Select SCHEDULER_TYPE, and type Enter to scroll the three available algorithms (SCHEDULER_RR, SCHEDULER_PRIORITY, SCHEDULER_CFS). Afterwards,

<press c>
<press g>
make
make qemu

5. Use Debugger

If you want to use GDB to debug MentOS:

cd build
cmake ..
make
make qemu-gdb

If you did everything correctly, you should have 3 windows with:

Kernel Booting on qemu
Shell with video printing of statistics previously discussed
Debugger cgdb with code screening

Developers

Main Developers:

Enrico Fraccaroli
- Mr. Wolf
Alessandro Danese, Luigi Capogrosso, Mirco De Marchi
- Protection ring
- libc
Andrea Cracco
- Buddy System, Heap, Paging, Slab, Caching, Zone
- Process Image, ELF
- VFS: procfs
- Bootloader
Linda Sacchetto, Marco Berti
- Real time scheduler
Daniele Nicoletti, Filippo Ziche
- Real time scheduler (Asynchronous EDF)
- Soft IRQs
- Timer
- Signals