How to Start the Linux learning?

Dear all, I am an antenna and RF circuilt enginneer. For the common work, I find the Linux is also very important for me. I have some

basic knowledge of C language. Could anyone introduce me any web links or how to start the Linux learning?

In my work, I designed the antenna and wireless module for IOT(Internet of Things) application. To completely master the project, I also want to know how

to make the wireless module work correctly in the Linux environment, such as the device driver development.

Thank you very much in advance!

[

learning linux:
http://unix.t-a-y-l-o-r.com/


device drivers:
http://freesoftwaremagazine.com/articles/drivers_linux/

joshuacp said:

...I have some basic knowledge of C language. Could anyone introduce me any web links or how to start the Linux learning?

Click to expand...

If you want to write device drivers, you need to know about the intimate details of the hardware. It is more about the programming and less about linux. Yes, a good grasp of C (perhaps some C++) will help.

The device drivers are basically an interface between the hardware and software. The idea is to present a rather standard look and feel as far as the user space programs go.

Look up the source codes from lib/modules/... ... .../kernel/drivers/net... -select some related device and locate the module and then look up the source.

Boring but rewarding.

the device driver ultimately runs on the OS or as part of it and thus interracts with it, how does one not need intimate understanding of the Linux kernel for that purpose?

Most device drivers attach themselves to the kernel with hooks. Some basic device drivers are built-in the kernel. In unix (and in Linux as well) most of the device drivers appear as files (see /dev directory) and the most common calls are open, close, read and write. Yes, you will need some basic ideas about the kernel and the architecture but not all the intimate details. I have never written a device driver but I guess that it is not going to be a difficult task.

That is the basic reason I recommend to take a look at the source code of a device driver you are going to write (a similar one; there are hundreds of them)- then you will have some idea about the way to go. They are basically libraries but have an extension of .ko - if you are careful, the same (well, almost) source can be used for windows and linux (well, some basic modifications may be needed).

And the best part is that there are forums where you can get real expert help. Frankly, I myself do not understand the language the experts speak.

srizbf said:

[

learning linux:
http://unix.t-a-y-l-o-r.com/


device drivers:
http://freesoftwaremagazine.com/articles/drivers_linux/

Click to expand...

Hi, srizbf, thank you very much for your valuable web links.

- - - Updated - - -

Yes, your suggestion is very useful for my starting. For the starting point, I need not to get too much about Linux kernel. Just read the device driver example source code and get to how to code the first device driver for my project.

You need to figure out first whether it is going to be a block or a character device. A block device driver works on a buffer that can be transmitted to the device hardware in one go: hard disks are block devices. Character devices are simpler: they work on a character -by -character basis- only one byte is transmitted or received at one go- e.g., serial device drivers.

They are very similar to library subroutines. gcc has suitable options to compile these kernel modules. They are loaded by modprobe or insmod command.

Wifi drivers tend to be messy because they have a large number of parameters- these are configured by the iwconfig command. I recommend you first try without security features enabled- these additional features can be added later once you get the stuff up and running.

Wifi drivers work similar to the mobile cell- they have a build in concept of cells. If you can see the device in lspci or lsusb the basic structure is accessible to linux. If you do not see your device in the lspci or lsusb command, there will be additional work.

I started to learn Linux due to the fact that it runs on a RaspBerry Pi board, that it is its os. It was relatively easy to learn it to the degree were I was able to do cross development, in my case using Python 3. So I had Windows 10 on my PC and Raspbial Jessie, the Linux distribution for the Raspi and using the PYCharm IDE from Jetbrains. So I got to the point where I could have the desktop of each of my 2 Raspi boards connecting them via WLAN and having entries for both on a free DNS provider. You can then work on your Raspis from your PC as if the screen and Keyboard/mouse were connected directly to the Raspis.

But then, even having my os up-to-date, having powerful protection software running on my PC it was attacked successfully via the raspi boards. I only could get over this by updating to Windows 10.

I am giving my own experience in learning Linux by running it on a Raspi. Security is key if you want to develop for something that will be connected to the Internet! So my focus moved from learning how to work with Linux to learn how to make it as secure as possible, or as it is named this days, less vulnerable. So I started this second step in learning Linux by focusing on learning how to setup Linux in such a way that the attack to my PC is less likely to succeed.

Virtualization is, to my personal opinion, one of the tracks to reduce the vulnerability, both of the target and the host environment, when developing. It starts with learning how to define your workflow. So I started by moving away from doing development work in the native environment of my host machine and working out of a virtual machine on my host. The second step is to have software that I run on my target "connected device", here a Raspi, within a virtual environment on Raspian. So when ever an attack to my setup is successful I revert to the previous status of my virtual machines.

As by law providers of "connected devices" can be suit if their devices are used in a DDoD , learning how to start a design by starting with the security concept of it frm the very beginning:



Actually this days i.e. ARM has announced in 4Q16 2 new ARM Cortex M devices, 23 and 33, being the first a ARM Cortex M0/0+ and the other an ARM Cortex M3/M4 kind of device. FreeScale i.e. has announced to have their implementation available for the general public in late 1Q17, the "i.MX8". These new devices in the case of ARM implement what is called the "TrustedZone". You can find valuable learning material on the website of ARM. In general this new TrustedZone functionality is part of the ARMv8 architecture. I see forward to what I do name "Raspberry Pi 4", which hopefully will have a SoC with cores that fully implement the TrustedZone concept and a version of Linux that uses this functionality.



This graphic shows how a TrustedZone is organized. What is really "new" is this kind of security features and the adaptation of a mature technology of virtualization into what is called "deeply embedded systems", the kind of boards with a micro controller that connect to the Internet as we often use in electronic systems.



A key concept and tool used to create virtual machines is the one of the "Hypervisors". It exists in 2 types as shown in the graphic above. A hypervisor type 2 is the kind of setup we can use on a host machine running Windows or Linux using i.e. "VirtualBox". On the physical hardware the os runs as we are used to and the virtual machine runs as an application. Hypervisor type 2 runs directly on the hardware, called "bare metall" and over it you have the virtual machines running.

The kind of virtualization shown with "Hypervisor Type 2" is better suited for deeply embedded systems and is more prone to make real time coding possible. So on a Raspi, on a board running Linux the easy way is to run hypervisor type 2 kind of tools for virtualization, as long as real time is not a demand. But is you run a connected device more like an Arduino kind, were resources are a scarce resource, the type1 approach running of a hardware that in the case of ARM implements its architecture ARMv8.



Another technique that is starting to play an important role is Containerization! The dominant marketshare tool here is "Docker"! The graph compares virtualization and Containerization. Again the role of Linux is key in my personal opinion!

In hypervisors type 1 you use the terms Domain0 and DomainU.

Domain0 is the priviledged os, Linux, running and its job is to manage the hypervisor type 1 and its so called "guest virtual machines" or DomainU which are created from there. Each guest os believes to be running alone of the hardware due to the fact that the hypervisor type 1 ensures all calls to the hardware are routed properly. Architectures like TrustedZone offer multiple sets os registers involved in executing calls by drivers of the guest os to the hardware. To achieve this You have an additional level of privilege that alone is entitled to use the "TrustedZone" hardware resources, while the privileged Linux drivers do operate at a priviledge level between the level 2 used for trustedZone and the none priviledged user applications.

Now Docker and the container functionality it offers uses a Linux Kernel, that is part of the Docker engine. Containers are a structure that contains all it needs to execute the application it contains, allowing to move the applications within its container to any environment that supports and executes Docker. Its isolation is more like the one we know exists for applications in an os like Windows or Linux.

Now it is interesting to tell you, that Docker exists native in Windows 10 Pro and Enterprise versions of Windows only. And I did find it also interesting that Docker for Windows includes a Linux Kernel! By the way, Intel also offers its virtualization support as it was the dominant CPU for Servers over decades and so their knowledge of virtualization is very mature as is this true for Microsoft.

Containers blends beautifully to the "Micro Systems" software concept, where containers are the receptacle for a micro service. For us more interested in the electronics and so into deeply embedded systems the fact that containers demand far less system resources than it is the case of virtualization, as I described above! Also real time behavior benefits from it. It just takes a couple of minutes after installing Docker environment on your host machine with Windows and create a container and have it implement a "Hello World" application. This makes it worth to look into it!

So my personal goal to achieve the smallest possible vulnerability in my experiments goes a "hybrid" approach, by the way that is what is currently pursued to combine the benefits of virtualization and containerization! Learning about containers and about Linux and virtualization it becomes evident that by setting up the parameters of the containers and virtualization not to have the default values allows to achieve the best value possible for the vulnerability of the setup for my experiments:



I do work on my host machine running Windows 10 Pro using a virtual machine in which I do execute Docker that has a Linux Kernel. This host machine communicates with my experiment setups via WLAN to Raspis with a IP address stores on a DNS Server. As you can get Raspis for a 2 digit cost they do not increase my costs for experiments in a critical way, but allow me to benefit from the vulnerability limiting effect from working in a Linux environment and the tools presented here. From each of the Raspis I do access vial GPIO communication with ARDUINO or similar controllers like those from NXP of those integrated into the Trinamic IDE for stepper motors.

I hope I have been able to present and share with you the fact that learning Linux is not difficult, but to use hardware with Linux connected to the Internet demands, in my personal opinion having suffered serious consequences, to learn how to setup Linux and use it in a as safe as possible way. I hope I have been able to present the 2 concepts which in my opinion combined make it as expensive as it can be to potential attackers. Not really having anything economically valuable available, the effort to attack me successful would be hard to justify! I do plan to use the topics addressed in my experiments in a model sail boat I am working on. So the connectivity available today and the revolutionary evolution that the technologies related have due to IoT, IIoT, autonomous cars and many more areas have convinced me to invest in learning how to work with as little as possible vulnerability.

Nice description (although I did not follow many things but that does not matter anyway) but only a few comments.

Security can be interpreted in several ways;

1. Vulnerability; you have left a door open by mistake; this is easy to repair.

2. The DDoS attack (you wrote DDoD but I think you meant DDoS) is a brute force attack; you can counterbalance it but cannot be stopped completely.

3. Good data and bad data shares the same path; such attacks cannot be prevented.

4. If you go to a fake site and put your bank login details, no degree of security can stop such attacks.

@c_mitra: It is more then understandable that if a reader is not familiar with the topics I do prsent, it is hard to follow and digest everything. I am dealing with those topics slow, due to health problems, but since more then one year. I still have the goal to be ready to restart my experiments sometime late in 2017.

As to your response to the term"security" and/or "vulnerability" you are totally right. As you correctly stated in your response, the scope of the topics presented already is very wide and hard to digest. If I would have expanded my contribution to try to present as complete as possible the topics I would have made a contribution hard to justify to be adequate for this thread. I just tried, referring to my personal experiences, to present what to my believe is an important message for beginners into the topic of Linux and deeply embedded systems. Take a good look into the security/vulnerability issues. A big challenge I was and am confronted with as a beginner in Linux for the type of usage I do plan is to balance between learning about topics, getting the big picture of the topics and try to translate this into a definition of a workflow.

A very good source for learning are for me on one side the eBooks available from Packt publisher and their newsletters offering special deals for some of their products. It was the most importance tool for me to get to know about the existence of such topics related to my studies.

The second very valuable source are the MOOC courses offered from a number of sites. MOOC are university courses from a wide range of universities worldwide which are fully Internet based and consist of lecture videos, reading materials, study groups totally for free as long as you do not want to have them certified to you. Then they charge a small amount. "edx.com", "coursera.com", "MIT opencourseware" and many more. As i am a native spanish and german language speaker I do also use to investigate courses offered from universities in countries with those languages additionally to english!

So when trying to learn about security and/or vulnerability a source to get an understanding about the environment in which those objectives are being pursued, cryptology courses are a very good source to start. Here the link of an MOOC course delivered by the Stanford University via "Coursera". You learn that one of the first steps is to get aware of the fields in which a system might be exposed, the kind of "vulnerability areas" starting by getting to know "Alice and Bob". The course is a good source already in its first lectures to learn about the view of experts on the topic of vulnerability and the goals a protection scheme tries to achieve.

So I hope I have respectfully answered to your valuable response and explained why I did stay probably prohibitively superficial when addressing that important topics.