<h1 id="kernel">Kernel<a aria-hidden="true" class="anchor-heading icon-link" href="#kernel"></a></h1>
The kernel is the part of the OS that serves as the master control program of all processes thought of as back-end.
<ul>
<li>it is the lowest level of <a href="/notes/1j3g1u7kbq5zk7lj1dt1fzk">Abstraction</a> in the <a href="/notes/ZaTr28eWk1DrXOEsc1YVb">OS</a>.</li>
<li>It provides an interface to hardware devices, and manages system processes, memory and other resources</li>
</ul>
The OS runs the kernel as fully trusted software. Once root access (kernel space) is granted to the kernel, a user can command the OS to do anything.
<ul>
<li>therefore, the kernel is what must implement protection mechanisms that cannot be subverted by untrusted software executing in <a href="/notes/ZaTr28eWk1DrXOEsc1YVb#user-space-userland-and-kernel-space1">user space</a>.</li>
</ul>
The <a href="/notes/ZaTr28eWk1DrXOEsc1YVb">operating system</a> uses the kernel to perform grunt work involved in bridging the gap between the computer's hardware and its software.
<ul>
<li>the kernel talks to the hardware via drivers (which are loaded as kernel extensions) and/or firmware</li>
<li>ex. when an application wants to change the system volume, it submits a request to the kernel to perform the action. Because of the speaker drivers which it has access to via the kernel module (like a built-in extension; provides the same benefit), the kernel can control the volume</li>
</ul>
The kernel provides services that...
<ul>
<li>handle I/O</li>
<li>maniupulate the file system</li>
<li>start and stop programs</li>
<li>schedule access to avoid conflicts when programs try to access the same resource or device simultaneously. </li>
<li>handle other common "low-level" tasks that most programs share, </li>
</ul>
The kernel also plays a big part in resource management, managing resources like memory and CPU.
<ul>
<li>the kernel must manage how memory is used, which means it has to be fully aware of how it is being used. It has to know exactly where in memory any process's resources will reside.</li>
<li>naturally, the kernel tries to optimize the usage of the resources it manages. It is fine if memory usage is high, even for moderate usage. The kernel knows how to remove things from memory in order to make space for the higher priority data.</li>
</ul>
Failures can lead to deadlocks, resulting in the whole system halting because resources used by one application are needed by another.
Technically speaking, <a href="/notes/93de42ca-53ea-460a-baa7-b9ec5c47cb1e">Linux</a> is not an operating system; it refers to the kernel itself. This misunderstanding is somewhat justified, given how integral the kernel is to the <a href="/notes/ZaTr28eWk1DrXOEsc1YVb">OS</a>
<ul>
<li>examples of operating systems in Linux are Ubuntu, Mint, Debian etc.</li>
</ul>
Like any piece of software, the kernel is versioned. If we want to see our kernel and its version, issue:
<pre class="language-sh"><code class="language-sh">uname
uname -r
</code></pre>
<hr>
Children
<ol>
<li><a href="/notes/g7huvr8z8rbvdpqm24z3kag">Device Driver</a></li>
<li><a href="/notes/o3pgogrf5w0a9ex1s4bgx7x">Scheduler</a></li>
</ol>
<hr>
Backlinks
<ul>
<li><a href="/notes/ZaTr28eWk1DrXOEsc1YVb">OS</a></li>
<li><a href="/notes/pkzexc7idaumzqrad29kp3n">Virtual Memory</a></li>
<li><a href="/notes/1j3g1u7kbq5zk7lj1dt1fzk">Abstraction</a></li>
<li><a href="/notes/g7huvr8z8rbvdpqm24z3kag">Device Driver</a></li>
</ul>

Kernel

tech

This Dendron vault of tech knowledge is organized according to domains and their sub-domains, along with specific implementation of those domains.

For instance, Git itself is a domain. Sub-domains of Git would include topics like `commit`,
`tags`, `reflog` etc., while implementations of each of those could be `cli`, `strat`
(strategies), `inner` (inner workings), and so on.

The goal of the wiki is to present data in a manner that is from the perspective
of a querying user. Here, a user is a programmer wanting to get key information
from a specific domain. For instance, if a user wants to use postgres functions
and hasn't done them in a while, they should be able to query
`postgres.functions` to see basic implementations, as well as common patterns
that have been employed in the past.

This wiki has been written with myself in mind. While learning each of these
domains, I have been sensitive to the "aha" moments and have noted down my
insights as they arose. I have refrained from capturing information that I
considered obvious or otherwise non-beneficial to my own understanding.

As a result, I have allowed myself to use potentially arcane concepts to help
explain others. For example, in my note on [[unit testing|testing.method.unit]],
I have made reference to the [[microservices|general.arch.microservice]] note.
The ability to analogize between different concepts captured in different notes
allows an opportunity to build strong generalized understandings. Given that
you'd have to understand microservices to be able to draw that same parallel
that I've already drawn, these links won't work for everyone. Since these notes
are written for myself, I have been fine with taking these liberties and leaning
on them heavily.

What I hope to gain from this wiki is the ability to step away from any
given domain for a long period of time, and be able to be passably useful for
whatever my goals are within a short period of time. Of course this is all
vague sounding, and really depends on the domain along with the ends I am
trying to reach.

To achieve this, the system should be steadfast to:
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	- Some concepts might realistically belong to multiple domains. For instance, the concept of *access modifiers* can be found in both `C#` and `Typescript`. Therefore, this note should be abstracted to a common place, such as [[OOP|paradigm.oop]].

This Dendron notebook is the sister vault to the general [Second Brain](https://tech.kyletycholiz.com).

## Tags
Throughout the garden, I have made use of tags, which give semantic meaning to the pieces of information.

- `ex.` - Denotes an *example* of the preceding piece of information
- `spec:` - Specifies that the preceding information has some degree of *speculation* to it, and may not be 100% factual. Ideally this gets clarified over time as my understanding develops. I try to go back after I have better understood the topic and clear out the notes of `spec:` tags
- `anal:` - Denotes an *analogy* of the preceding information. When I can, I attempt to link concepts to others that I have previously learned.
- `mn:` - Denotes a *mnemonic*
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## Resources
### UE (Unexamined) Resources
Often, I come across sources of information that I believe to be high-quality. They may be recommendations or found in some other way. No matter their origin, I may be in a position where I don't have the time to fully examine them (and properly extract notes), or I may not require the information at that moment in time. In cases like these, I will add reference to a section of the note called **UE Resources**. The idea is that in the future when I am ready to examine them, I have a list of resources that I can start with. This is an alternative strategy to compiling browser bookmarks, which I've found can quickly become untenable.

### E (Examined) Resources
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### Resources
This heading is for inexhaustible resources. 
- A prime example would be a quality website that continually posts articles.  - Another example would be a tool, such as software that measures frequencies in a room to help acoustically treat it.
