215 Matching Annotations
  1. Dec 2021
    1. 12

      using the given R= values we must recognize that this is R=[x1,x2] x [y1,y2]. set up the double integral with these values with respect to x and y. Solving this integral will give you the volume of the area of the rectangle.

      I am unsure of how to do D

    2. 9

      Form this problem i recommend starting off drawing the rectangle, this is not necessary though.

      Find the x1 and x2 values for your integral with respect to x and do the same for y. use the given function f(x,y) and solve the integral. now since we are looking for the average value of the rectangle, we use the dimensions provided to get LxH. use the reciprocal of this to find the average value

  2. Nov 2021
    1. How to Create a Minimum Viable Product (MVP): Best Examples and Key BenefitsDmitryCEOMVPProduct GuideHomeBlogEntrepreneurshipHow to Create a Minimum Viable Product (MVP): Best Examples and Key BenefitsPublishedFeb 14, 2019UpdatedNov 26, 202139 min readAs an entrepreneur, you may eventually come to the point of planning a startup and launching your software product. Initially, you only have the idea of the project. What’s next? MVP development for startups is something that will help you at the beginning. You will learn what it is from this article. But first, some statistics. In 2020 the failure rate of startups exceeded 90%. And Euler Hermes’ latest research is even more disappointing. It shows that the number of global business bankruptcies will have increased by 15% by 2022. Can you guess what the reason is? It is a lack of demand among the users in the market. That’s why when you have a brilliant idea, do not rush building a fully-featured product and spending months on hard work. There’s a more efficient way to initially understand whether your idea will be required in the market. And this implies developing a minimum viable product (MVP). This popular approach in startup product development will help you test your business idea and save both time and resources. This way, you understand what users need and can create an offering that they are ready to pay for. Thanks to this article, you will know how to define a minimum viable product. You will also learn all about the MVP approach. We will start with the definition of this term and take a look at the best minimum viable products built by famous companies. Finally, we will provide you with a step-by-step guide on how to create a minimum viable product.

      Thanks to this article, you will know how to define a minimum viable product. You will also learn all about the MVP approach. We will start with the definition of this term and take a look at the best minimum viable products built by famous companies. Finally, we will provide you with a step-by-step guide on how to create a minimum viable product.

    1. Avoid These Costly Mistakes During Web Application DevelopmentDmitryCEOCustom SoftwareHomeBlogTechnologyAvoid These Costly Mistakes During Web Application DevelopmentPublishedJan 16, 2020UpdatedJan 16, 202015 min readAccording to the Startup Genome Report, over 90% of startups fail after launch. There can be different reasons like skipping the market research, hiring wrong specialists, too early scaling, and so on. However, one of the most important elements of startup success is the product you provide. Neglecting estimates, avoiding the MVP stage, designing unnecessary functionality, and saving time on testing may become fatal errors that can result in a complete failure. In this article, we will tell you about the most costly mistakes you should avoid during web app development to succeed after product launch.

      According to the Startup Genome Report, over 90% of startups fail after launch. There can be different reasons like skipping the market research, hiring wrong specialists, too early scaling, and so on.

      However, one of the most important elements of startup success is the product you provide. Neglecting estimates, avoiding the MVP stage, designing unnecessary functionality, and saving time on testing may become fatal errors that can result in a complete failure.

      In this article, we will tell you about the most costly mistakes you should avoid during web app development to succeed after product launch.

    1. Spree Commerce: How to Quickly Build an Ecommerce WebsiteAlinaE-Commerce & SaaS StrategistMarketplaceProduct GuideHomeBlogEntrepreneurshipSpree Commerce: How to Quickly Build an Ecommerce WebsitePublishedAug 31, 2020UpdatedAug 31, 202011 min readThe hype around Amazon and eBay has driven up the demand for marketplace development services. Business owners turn to software consultancies to launch a thriving e-commerce website. Here comes a question: what do they need to get the most successful online marketplace website? We believe that a profitable e-commerce project starts with the right tech stack. The main qualities that a modern marketplace should possess are scalability, easy customizations, and flexibility. Therefore, it’s important to choose the technologies that will help these qualities.

      The hype around Amazon and eBay has driven up the demand for marketplace development services. Business owners turn to software consultancies to launch a thriving e-commerce website. Here comes a question: what do they need to get the most successful online marketplace website?

      We believe that a profitable e-commerce project starts with the right tech stack. The main qualities that a modern marketplace should possess are scalability, easy customizations, and flexibility. Therefore, it’s important to choose the technologies that will help these qualities.

    1. "The Guide to Social Science Data Preparation and Archiving is aimed at those engaged in the cycle of research, from applying for a research grant, through the data collection phase, and ultimately to preparation of the data for deposit in a public archive: " from tweet

    1. Use Lagrange multipliers to find the maximum and minimum values of f(x,y)=3x−4y subject to the constraint ,x2+3y2=129, if such values exist. maximum = minimum =

      The partial derivative of f with respect to a variable = (lambda)(partial derivative of g with respect to a variable)

      you know what function is F because it is usually given to us as f(x,y,z).

      you know what function is G because it is usually set equal to a constant

      Find these values for X, Y, Z

      plug these X, Y, Z values into the original function G =constant and solve for lambda

      We take the value of Lambda that we have obtained and plug it into our original x=, y= and z= values.

      This will give us the values of X, Y, Z

      We take the X, Y, Z values an plug it into the function F

      this will give us A Max or a Min

      Usually if the value is a negative it is a minimum

      usually if the value is positive it is a maximum

  3. Oct 2021
    1. Let f(x,y)=1/x+2/y+3x+4y in the region R where .x,y>0. Explain why f must have a global minimum at some point in R (note that R is unbounded---how does this influence your explanation?). Then find the global minimum. minimum =

      For this qyuestion you first take the aprtia lderivative of x and y, set these =0 and solve for the x= and y= values. next we find the fxx and fyy and fxy/fyx second order partial derivatives. now we plug in our x= and y= values into all of the found partial derivatives and add them up.

    1. (a) In which direction should you move if you want the concentration to increase the fastest?

      What should be done for this is taking the partial derivative with respect to x,y,z. set that up in vector form as < fx(xyz), fy(xyz), fz(xyz)> then we plug in the point (-1,1,-1).

  4. Sep 2021
    1. 2.

      A) We know that acceleration is the derivative of the velocity, so to find the velocity while given acceleration we need to find the integral of each given element. then plug in 0 as it is given that the initial velocity is V(0).

      B) the position vector is the integral of the velocity vector . then you also plug in 0 for t as it is given r(0).

    1. Local governments can use participatory “co-design” principles and practices to help ensure that their programs and products that use open data are designed to meet the needs of current and potential users.
  5. Aug 2021
    1. How Much Does it Cost to Build a Website Like IndeedDmitry ChekalinChief Executive OfficerProduct GuideHomeBlogEntrepreneurshipHow Much Does it Cost to Build a Website Like IndeedJan 23, 202021 min readJob search websites have revolutionized the employer-employee relationships. No printed classifieds on the walls and no extra movements. Everything you need to do is to visit such a platform, enter the position details and choose the most relevant option to hire or apply for. Indeed is the most visited platform among other job-related online marketplaces. In this article, you will find out what makes Indeed so famous and special. Besides, we will discuss the challenges you may face before and during the development process, the things to consider before starting, and the functionality your platform should have. On the whole, you will know how to create a job search website like Indeed using 3 effective solutions.

      Job search websites have revolutionized the employer-employee relationships. No printed classifieds on the walls and no extra movements. Everything you need to do is to visit such a platform, enter the position details and choose the most relevant option to hire or apply for. Indeed is the most visited platform among other job-related online marketplaces.

      In this article, you will find out what makes Indeed so famous and special. Besides, we will discuss the challenges you may face before and during the development process, the things to consider before starting, and the functionality your platform should have. On the whole, you will know how to create a job search website like Indeed using 3 effective solutions.

    1. How to Build a Marketplace Website MVP and Not FailDmitry ChekalinChief Executive OfficerKate DavydovaMarketplace Growth StrategistMarketplaceMVPHomeBlogEntrepreneurshipHow to Build a Marketplace Website MVP and Not FailApr 9, 202013 min readDo you want to know how to build a marketplace website that will become popular and profitable? And you don’t want to risk money and waste a lot of time, right? A great plan is to start with a minimum viable product (MVP). This way you will not spend a lot of time and money, and you will get valuable feedback on the product and its primary features. Using this approach, you will definitely understand whether your idea is worth investing in or not. Today, we want to discuss how to build a marketplace MVP through several simple steps.

      Do you want to know how to build a marketplace website that will become popular and profitable? And you don’t want to risk money and waste a lot of time, right?

      A great plan is to start with a minimum viable product (MVP). This way you will not spend a lot of time and money, and you will get valuable feedback on the product and its primary features. Using this approach, you will definitely understand whether your idea is worth investing in or not.

      Today, we want to discuss how to build a marketplace MVP through several simple steps.

  6. Jul 2021
    1. It’s hard to imagine now that only some decades ago people had to purchase and download software for all possible needs on their PCs. No matter the task, every new tool took some space on the hard drive and every program update was a nightmare. Why? Because it needed extra space and pretty much of your time and effort if something went wrong. Those days are gone thanks to cloud computing and SaaS products.These software as a service tools have changed the way we work and use software for good. As per recent forecasts, this market is going to reach $623 billion by 2023. So let’s find out what are SaaS perspectives in the near future, why it’s better to start off with a SaaS minimum viable product, and how to create a SaaS MVP.

      Every new piece of software took the space on a hard drive. The update usually took us several hours. Gladly, these days are in the past. The forecasts predict that the SaaS market will reach $623 billion by 2023. We have dived deep into the SaaS domain and created a guide on how to start with a cloud website.

  7. Jun 2021
  8. May 2021
    1. Stephan Lewandowsky. (2021, May 16). An update to the ‘politics’ page of our COVID-19 vaccination communication handbook. Thanks to @kostas_exarhia for his diligent and constant work on this 1/n https://t.co/ezztaLMEBG [Tweet]. @STWorg. https://twitter.com/STWorg/status/1393996441966858242

    1. a cheat sheet is available showing how to convert example commands from the manual of filter-branch into filter-repo commands.
    1. The command nix-shell will build the dependencies of the specified derivation, but not the derivation itself. It will then start an interactive shell in which all environment variables defined by the derivation path have been set to their corresponding values, and the script $stdenv/setup has been sourced. This is useful for reproducing the environment of a derivation for development.

      QUESTION: What exactly does nix-shell execute from the Nix expression (i.e., shell.nix, default.nix, etc.)?

      ANSWER: Based on my current understanding, the answer is everything. It calls $stdenv/setup (see annotation below) to set up the most basic environment variables (TODO: expand on this), and "injects" the most common tools (e.g., gcc, sed) into it.

      It also defines the phases (TODO: verify this) and builder functions, such as genericBuilder. For example, the default builder is just two lines:

      source $stdenv/setup
      genericBuild
      

      TODO: pkgs/stdenv/generic/builder.sh is a mystery though.

      QUESTION: Once dropping into nix-shell, how do I know what phases to execute by looking at a default.nix? (E.g., [..]freeswitch/default.nix)

      ANSWER: As far as I can tell, one can override the phases in their Nix build expression (to build the derivation, see at the bottom), but they won't get executed as only the $stdenv/setup (see above) will get sourced, and no builders are called that, in return, invoke the phases (again, see above).

      So if one is using nix-shell

      • to create/hack on a package, the person has to manually invoke the builder or phases (TODO: still fuzzy on this subject)

      • to set up an environment, then one doesn't even have to worry about builders/phases because we just use nix-shell to clear the environment and to inject tools that we need for a given task

      QUESTION: When dropping into nix-shell, is this Nix expression (i.e., freeswitch/default.nix) executed? Or just parts of it?

      ANSWER: As stated above, all of the input Nix expression is evaluated, but no builders and build phases are called; although, nothing prevents one to override the phases, in case they are creating/hacking on a package.

      QUESTION:

      The command nix-shell will build the dependencies of the specified derivation, but not the derivation itself.

      What is the "derivation" here exactly? I know that it is a build expression, but does that mean the default.nix (or other Nix expression) nix-shell is invoked with?

      <sup>This statement also seems like a contradiction with how `nix-shell` works (i.e., if one issues `nix-shell -p curl`, then `curl` will be available in that sub-shell), but `-p` acts like a shortcut to as if `curl` had been listed in `buildInputs` so this is not the case.</sup>

      ANSWER: I have the feeling my confusion comes from the fact that the term "derivation" is used ambiguously in the manuals, sometimes to mean multiple things (see list below).

      TODO: Substantiate this claim, and make sure that it not coming from my misunderstanding certain topics.

      • Nix build expression (such as default.nix) whose output is going to become the store derivation itself (see last item at the bottom about the Nix manual's glossary definition)

      • store derivation.

      Had multiple cracks at unambiguously define what a derivation is, and here's a list of these:

      QUESTION: What is the difference between nix-shell -p and nix-shell invoked with a Nix expression of mkShell (or other that achieves the similar effect)?

      QUESTION: nix-shell does not create a sub-shell, so what does it do? (clarification: so nix-shell indeed does it; I confused it with nix shell)

  9. Apr 2021
    1. Definition of Done

      A great article on how the DOD applies now to the Scrum Guide and the Scrum Team. The emphasis that the entire Scrum Team creates the DOD prevents from misunderstandings in the future, as I’ve personally witnessed in the past.

      https://www.scrum.org/resources/blog/2020-scrum-guide-definition-done-created-scrum-team

    2. Introduction of Product Goal

      How do Product Goal and Release Goal relate? Is the Product Goal the product vision and Release Goal is helping us to define relevant Sprint Goals to achieve the Release Goal?

      Good reads about the Product Goal: https://www.scrum.org/resources/blog/scrum-guide-2020-update-introducing-product-goal

      https://www.scrum.org/resources/blog/product-goal

    3. 2020 Scrum Guides

      Several articles on Scrum.org describe and discuss the 2020 changes: https://www.scrum.org/scrum-guide-2020

    4. removing any remaining inference to IT work (e.g. testing, system, design, requirement

      Things that have been removed:

      • The prescriptive elements of the Sprint Review.
      • The detailed outcomes defined in the purpose of the Sprint Retrospective.
      • The improvements that will be implemented in the next Sprint from the Retrospective.
      • Refinement usually consumes no more than 10% of the capacity of the team.
      • How to monitor progress towards the goal in Product Backlog.
      • The use of an organization’s “Definition of Done”.
      • The three questions for the Daily Scrum.
      • Meeting after the Daily Scrum for detailed discussions, replanning, etc

      Source: https://www.scrum.org/resources/blog/scrum-guide-2020-update-what-has-been-removed

    1. “The entire Scrum Team is accountable for creating a valuable, useful Increment every Sprint.” While there are still explicit accountabilities for the Product Owner, Scrum Master, and Developers, all three roles must work together effectively in order to be successful with Scrum.

      While the SM worked closely with the Dev team to support them creating the DOD, with this new emphasis on entire Scrum Team the potentially odd moments of ownership and contribution from the SM/PO to the DOD are less likely to happen.

    2. everyone on the Scrum Team should care about and contribute to quality.

      This is where the new Scrum Guide 2020 generates some leverage for Coached and the Testing Engineers (as part of DEV). Testing/Quality is everyone’s job on the Scrum Team. Including all DEV, PO and SM.

    1. “Who cares? Let’s just go with the style-guide” — to which my response is that caring about the details is in the heart of much of our doings. Yes, this is not a major issue; def self.method is not even a code smell. Actually, that whole debate is on the verge of being incidental. Yet the learning process and the gained knowledge involved in understanding each choice is alone worth the discussion. Furthermore, I believe that the class << self notation echoes a better, more stable understanding of Ruby and Object Orientation in Ruby. Lastly, remember that style-guides may change or be altered (carefully, though!).
    2. Similarly to fashion, code style reflects our credo as developers, our values and philosophy.
    3. Yet, it certainly is important to make the proper choices when picking up style. Similarly to fashion, code style reflects our credo as developers, our values and philosophy. In order to make an informed decision, it’s mandatory to understand the issue at stake well. We all have defined class methods many times, but do we really know how do they work?
    1. Promouvoir l’activité physique des jeunes Élaborer et développer un projet de type Icaps

      les parents sont cités 119 fois dans ce document PDF

    1. Elaborer un contrat local de santé en 8 étapes Publié le 10/03/2021 • Par Auteur associé • dans : A la Une santé social, Actu expert santé social, Actu juridique, Fiches de droit pratique, France

      Ville-futur-sure-sante La Gazette Le contrat local de santé est conclu entre l'agence régionale de santé et une ou plusieurs collectivités ou intercos. Il peut associer des acteurs provenant de différents secteurs. S’il n’a pas vocation à se substituer aux dispositifs locaux existants, le contrat local de santé doit s'articuler avec eux afin de favoriser une approche globale de la santé. Retour sur une élaboration en 8 étapes.

    1. The best procedure is the one you don’t need. If the UI is crystal clear and leads the customer through a task, a procedure isn’t necessary. Start there.
    1. I actually think this is Not Constructive, since there's no absolute rule about which pairings can be joined into a single word or hyhenated, and it's pointless having "votes" here about each specific case. Follow a style guide if you have one, or search Google Books and copy whatever the majority do. Or just make your own decision.
  10. Mar 2021
    1. Qualinclus, Guide d'auto-évaluation pour une école inclusive permet de nourrir la réflexion et les échanges pour les équipes pédagogiques et éducatives qui mettent en place une démarche d'auto-évaluation et d'amélioration continue de la qualité. Il s'adresse aux chefs d'établissement et à l'ensemble de la communauté éducative.

    1. Les principaux biais à connaîtreen matière de recueil d’informationen matière de recueil d’information
  11. Feb 2021
    1. Samedi 30 janvier 2021, le, rapporteur général de l’Observatoire de la laïcité, et, un administrateur national de la Ligue de l’enseignement en charge de la laïcité, étaient les invités de la, coprésidente de la FCPE. Un webinaire destiné à échanger avec les présidents départementaux de la FCPE autour de la laïcité à l’école.

    1. A Nix expression describes everything that goes into a package build action (a “derivation”)

      Come up with an ultimate definition for what a "derivation" is.

      So round up all the places where it is mentioned across Nix* manuals, and check out these:


      From Nix Pills section 6.1. The derivation function (see annotation):

      A derivation from a Nix language view point is simply a set, with some attributes. Therefore you can pass the derivation around with variables like anything else.

      So there is clearly an ambiguity between what derivations are perceived to be and what is stated in the Eelco Dolstra's PhD thesis. Or maybe I'm having issues with reading comprehension again...

    2. For each output declared in outputs, the corresponding environment variable is set to point to the intended path in the Nix store for that output. Each output path is a concatenation of the cryptographic hash of all build inputs, the name attribute and the output name. (The output name is omitted if it’s out.)

      QUESTION: So when I see $out in a builder script, it refers to the default output path because the output attribute in the Nix expression has never been explicitly set, right?

    3. A derivation causes that derivation to be built prior to the present derivation; its default output path is put in the environment variable.

      That is, if an input attribute is a reference to a derivation in the Nix store, then

      1. that derivation is built first (after a binary substitute is not found, I presume), and
      2. the path to the built package (for a better word) is handed to the shell build script.
    4. derivationA description of a build action. The result of a derivation is a store object. Derivations are typically specified in Nix expressions using the derivation primitive. These are translated into low-level store derivations (implicitly by nix-env and nix-build, or explicitly by nix-instantiate).

      Organically related to the annotation regarding my nix-shell confusion.

      The dissection of this definition to show why I find it lacking:

      A description of a build action.

      The first (couple) time(s) I read the manuals, this description popped up in many places, and I identified it with Nix expression every time, thinking that a derivation is a synonym for Nix expression.

      Maybe it is, because it clearly tries to disambiguate between store derivations and derivation in the last sentence.

      The result of a derivation is a store object.

      Is this store object the same as a store derivation?

      Derivations are typically specified in Nix expressions using the `derivation primitive. These are translated into low-level store derivations (implicitly by nix-env and nix-build, or explicitly by nix-instantiate).

      QUESTION: So, the part of the Nix build expression (such as default.nix) where the derivation primitive is called (explicitly or implicitly, as in mkDerivation) is the derivation, that will be ultimately be translated into store derivations?

      ANSWER: Start at section 15.4 Derivation.


      QUESTION: Also, why is typically used here? Can one define derivations outside of Nix expressions?

      ANSWER(?): One could I guess, because store derivations are ATerms (see annotation at the top), and the Nix expression language is just a tool to translate parameterized build actions into concrete terms to build a software package. The store derivations could be achieved using different means; e.g., the way Guix uses Guile scheme to get the same result))


      I believe, that originally, derivation was simply a synonym to store derivation. Maybe it still is, and I'm just having difficulties with reading comprehension but I think the following would be less misleading (to me and apart from re-writing the very first sentence):

      Derivations are typically the result of Nix expressions calling the derivation primitive explicitly, or implicitly usingmkDerivation`. These are translated into low-level store derivations (implicitly by nix-env and nix-build, or explicitly by nix-instantiate).

    5. $stdenv/setup

      QUESTION: Does this refer to pkgs/stdenv/generic/setup.sh? According to 6.5 Phases in the Nixpkgs manual?

      ANSWER: I'm pretty sure it does. It sets up the environment (not sure how yet; I see the env vars, but not the basic commands - sed, awk, etc. - that are listed below) and defines a bunch of functions (such as genericBuilder) but it doesn't call these functions!

    6. The function mkDerivation in the Nixpkgs standard environment is a wrapper around derivation that adds a default value for system and always uses Bash as the builder, to which the supplied builder is passed as a command-line argument. See the Nixpkgs manual for details.

      "Documented" in the Nixpkgs manual under 6.1 Using stdenv.

      Used the double-quotes above because I don't consider it well documted. Will give it a try too; worst case scenario is that I'll fail as well.

    7. C.12. Release 1.6 (2013-09-10)In addition to the usual bug fixes, this release has several new features:The command nix-build --run-env has been renamed to nix-shell.
    8. See annotations with the build-phases tag.


      Why are the build phases not enumerated in the Nix manual? If the instructions on how to create a derivation (and thus, a package) then why not go all in instead of spreading out information in different manuals, making the subject harder to grasp?...

      (By the way, it is documented in the Nixpkgs manual under 6.5 Phases; not sure why it is not called build phases when every page refers to them like that.)

    9. Chapter 14. A Simple Nix Expression

      This such a stupid move to go through a derivation example before introducing the language.

    10. Add the package to the file pkgs/top-level/all-packages.nix. The Nix expression written in the first step is a function; it requires other packages in order to build it. In this step you put it all together, i.e., you call the function with the right arguments to build the actual package.

      In addition to this rant, step 3. should be more generic, instead of tying it to Nixpkgs; at least, either show how to build your own Nix expression repo, or don't add this step, but it is not at all necessary to write a derivation. There is a Nixpkgs manual for a reason.

    11. $ nix-env -i firefox --substituters ssh://alice@avalon This works similar to the binary cache substituter that Nix usually uses, only using SSH instead of HTTP

      So a substitute is a built binary for a given derivation, and a substituter is a server (or binary cache) that serves pre-built binaries, right?

      Update: in the next line it says that "it will fall back to using the binary cache substituter", so I guess that answers it.

    12. substitute

      this is another key topic. Also:

      • substitute vs. substituter => this (I think)

      See annotations with the substitute tag

    13. When you ask Nix to install a package, it will first try to get it in pre-compiled form from a binary cache. By default, Nix will use the binary cache https://cache.nixos.org; it contains binaries for most packages in Nixpkgs. Only if no binary is available in the binary cache, Nix will build the package from source. So if nix-env -i subversion results in Nix building stuff from source, then either the package is not built for your platform by the Nixpkgs build servers, or your version of Nixpkgs is too old or too new.

      binary caches tie in with substitutes somehow; get to the bottom of it. See annotations with the substitute tag.

      Maybe this?

    14. closure

      Another gem: who knows what a "closure" is.

      [This highlight] (a couple lines below) implicitly explains it though:

      The command nix-copy-closure copies a Nix store path along with all its dependencies to or from another machine via the SSH protocol. It doesn’t copy store paths that are already present on the target machine.

      or this, also just a couple lines below:

      the closure of a store path (that is, the path and all its dependencies)

    15. the closure of a store path (that is, the path and all its dependencies)
    16. The command nix-copy-closure copies a Nix store path along with all its dependencies to or from another machine via the SSH protocol. It doesn’t copy store paths that are already present on the target machine. For example, the following command copies Firefox with all its dependencies:
    17. subscribes you to a channel that always contains that latest version of the Nix Packages collection.

      That is a misleading statement. The latest version is where the master branch points, isn't it?

      So a channel points to a Nixpkgs commit (on a branch named after the channel) where all packages inside are deemed stable, and all packages are built to have available binary substitutes by a (hydra) build farm.

    18. A Nix channel is just a URL that points to a place that contains a set of Nix expressions and a manifest.
    19. garbage collector roots

      Definitely avoid this, when a term is used but only introduced formally way later. (There is also a reference to "garbage collector roots" almost at the beginning as well.)

    20. $ nix-env --switch-profile /nix/var/nix/profiles/my-profile $ nix-env --switch-profile /nix/var/nix/profiles/default These commands switch to the my-profile and default profile, respectively. If the profile doesn’t exist, it will be created automatically.

      learn more about profiles; creating new profiles was new info

    21. Chapter 10. ProfilesProfiles and user environments are Nix’s mechanism for implementing the ability to allow different users to have different configurations, and to do atomic upgrades and rollbacks.
    22. user environment
    23. In Nix, different users can have different “views” on the set of installed applications. That is, there might be lots of applications present on the system (possibly in many different versions), but users can have a specific selection of those active — where “active” just means that it appears in a directory in the user’s PATH. Such a view on the set of installed applications is called a user environment, which is just a directory tree consisting of symlinks to the files of the active applications.
    24. nix-env -qas

      ... and it takes AGES to complete

    25. 4.3.1. Change the Nix store path prefix

      There is a lot of place in this manual (and probably in the others as well) where the prefix is referred to (usually with italics, such as "prefix/store"), so in the book

      • this should be linked to this section (or the one in the book), and

      • establish a clear and well-communicated notation to convey this

    26. At the same time, it is not possible for one user to inject a Trojan horse into a package that might be used by another user.
    27. Chapter 6. SecurityNix has two basic security models. First, it can be used in “single-user mode”, which is similar to what most other package management tools do: there is a single user (typically root) who performs all package management operations. All other users can then use the installed packages, but they cannot perform package management operations themselves.Alternatively, you can configure Nix in “multi-user mode”. In this model, all users can perform package management operations — for instance, every user can install software without requiring root privileges. Nix ensures that this is secure. For instance, it’s not possible for one user to overwrite a package used by another user with a Trojan horse.

      Would have been nice to link these to the install chapter where single- and multi-user modes were mentioned.

      How would this look in a topic-based documentation? I would think that his chapter would be listed in the pre-requisites, and it could be used to buld different reading paths (or assemblies in DocBook, I believe) such as practical, depth-first (if there are people like me who want to understand everything first), etc.

    28. reentrancy
    29. You can uninstall Nix simply by running: $ rm -rf /nix
    30. $ mkdir /nix $ chown alice /nix

      Traditionally, when a command should be invoked with sudo, it is either included in the example, or the shell indicator is # instead of $.

    31. To explicitly select a single-user installation on your system:

      It should be noted in this section also that since nix 2.1.0, single user install is the default.

    32. nix-shell '<nixpkgs>' -A pan

      What is happening here exactly?

      nix-shell's syntax synopsis always bugged because it looks like this

      SYNOPSIS
      nix-shell [--arg name value] [--argstr name value] [{--attr | -A} attrPath] [--command cmd] [--run cmd] [--exclude regexp] [--pure] [--keep name] {{--packages | -p} packages...  | [path]}
      

      and the canonical example is nix-shell '<nixpkgs>' -A pan; what tripped me up is that path is usually the first in examples, and I thought that the position of arguments are strict. As it turns out, nix-shell -A pan '<nixpkgs> is just as valid.

      Side note<br> Apparently there is no standard for man pages. See 1, 2.

      '<nixpkgs>' path is the one specified in the NIX_PATH environment variable, and -A pan looks up the pan attribute in pkgs/top-level/all-packages.nix in the Nixpkgs repo.

    33. since packages aren’t overwritten, the old versions are still there after an upgrade. This means that you can roll back to the old version:

      Wouldn't hurt to tell folks that this is a convenience layer, and one could also just use the old package from the /nix/store, even though that path would be long and obscure; one could use symlinks of course.

      Or, onc could just use nix-shell -p that specifies a specific version (that's already in the store), but, of course, it's not that simple...

      https://github.com/NixOS/nixpkgs/issues/9682

  12. Jan 2021
  13. Dec 2020
    1. When the RFC 822 format ([28], [4]) is being used, the mail data include the header fields such as those named Date, Subject, To, Cc, and From.

      This just answered my question regarding the quote from "Postfix: The Definitive Guide":

      ENVELOPE ADDRESSES AND MESSAGE HEADERS A common source of confusion for email users is the fact that the To: address in email message headers has nothing to do with where a message is actually delivered. The envelope address controls message delivery. In practice, when you compose a message and provide your MUA with a To: address, your MUA uses that same address as the envelope destination address, but this is not required nor is it always the case. From the MTA’s point of view, message headers are part of the content of an email message. The delivery of a message is determined by the addresses specified during the SMTP conversation. These addresses are the envelope addresses , and they are the only thing that determine where messages go. See Section 2.2.8 later in the chapter for an explanation of the SMTP protocol.

      Mailing lists and spam are common examples of when the envelope destination address differs from the To: address of the message headers.

      Also an answer to this question.

    1. Include articles, such as the. Articles help readers and translation software identify the nouns and modifiers in a sentence. Examples Empty the container. The empty container
    1. Use display as a general term for any visual output device, including the built-in display on a computing device and an external monitor or projector.