After running apt update I noticed that update info is being downloaded using HTTP.    After running upgrade, I see that upgrades are being downloaded from HTTP too.     My understanding is that HTTP is essentially insecure, i. e. open to intercept and replacement of data. Are the upgrades thus unsafe? Or do I misunderstand something?
Are repository updates secure?  As a bear of little brain from the developer side, I cannot understand why the repository list is http://security.ubuntu.com and the other http(unsecured) sites listed in /etc/apt/sources.list.  Without a certificate chain match this appears as "ask any responder for a list of packages to update" instead of "ask the ubuntu.com site..."  Can any network choose to spoof the update sites, and is this a common practice to provide a locally cached and vetted copy?
AMD GPU Material in "material preview mode" and "rendered mode", is entirely gray as background. Only outline is displayed Bump right-aligned text to next line iff no room Does anyone know why typedefs of class names don't work like class names for the friend declaration?  class A { public: };  class B : public A { public:    typedef A SUPERCLASS; };  typedef A X;  class C { public:    friend class A;             // OK    friend class X;             // fails    friend class B::SUPERCLASS; // fails }; Here is my question:  Is a homeomorphism, that is, a continuos function whose inverse function is also continuous, always bijective? I am unable to find the link for downloading Ubuntu 16.04 onto my   desktop/laptop. I am able to see the link only for 18.04, but I need 16.04. When should I begin publishing? I looked up several tutorials on how to install and they dont work. I do everything correctly but then i get this:     The file   '/home/mike/Downloads/minecraft.jar'   is not marked as executable.  If this   was downloaded or copied from an   untrusted source, it may be dangerous   to run.  For more details, read about   the executable bit.   I run the minecraft.jar with the Sun java runtime 6 but it doesnt work:/. Any help would be greatly appreciated! Batch export Photoshop layers to individual PNG files I am a web dev and competent in Fireworks, but not so much in Photoshop.  I have just received a layered PSD file to turn into a web page.  Can anyone tell me the easiest way to export all layers to individual png files?  There are lots of layers and doing this manually seems wrong.  I have seen  but it does seem there should be native functionality for this in PS.  I have access to Photoshop CS4. Any pointers appreciated. JavaScript: client-side vs. server-side validation Which is better to do client side or server side validation?  In our situation we are using    jQuery and MVC.   JSON data to pass between our View and Controller.     A lot of the validation I do is validating data as users enter it. For example I use the the keypress event to prevent letters in a text box, set a max number of characters and that a number is with in a range.   I guess the better question would be, Are there any benefits to doing server side validation over client side?    Awesome answers everyone. The website that we have is password protected and for a small user base(&lt;50). If they are not running JavaScript we will send ninjas. But if we were designing a site for everyone one I'd agree to do validation on both sides. mongodb $exists always returning 0 Is the integral $\int_1^\infty\frac{x^{-a} - x^{-b}}{\log(x)}\,dx$ convergent? What is the distribution of the sum of non i.i.d. gaussian variates? If $X$ is distributed $N(\mu_X, \sigma^2_X)$, $Y$ is distributed $N(\mu_Y, \sigma^2_Y)$ and $Z = X + Y$, I know that $Z$ is distributed $N(\mu_X + \mu_Y, \sigma^2_X + \sigma^2_Y)$ if X and Y are independent.  But what would happen if X and Y were not independent, i.e. $(X, Y) \approx N\big( (\begin{smallmatrix} \mu_X\\\mu_Y \end{smallmatrix}) , (\begin{smallmatrix} \sigma^2_X &amp;&amp; \sigma_{X,Y}\\ \sigma_{X,Y} &amp;&amp; \sigma^2_Y \end{smallmatrix}) \big) $  Would this affect how the sum $Z$ is distributed? Let $A$ and $B$ be two real $n\times n$ matrices such that $AB-BA=A$ Prove that $A$ is not invertible and that $A$ is nilpotent.  My attempt is the following. It holds that $AB=(B+I)A$ If $A$ were invertible, $B=A^{-1}(B+I)A$. Taking trace on both sides yields $tr(B)=tr(B)+n$, hence $n=0$, which is a contradiction. I can't prove that $A$ is nilpotent though. Expectation of truncated normal As a new user, I find it impossible to contribute to the community or to even begin contributing. I know why the reputation system is in place and I respect it, but at the same time it is too hard on new users.  It started with me wanting to upvote a question...     "Vote Up requires 15 reputation"   Just to appreciate a good question that helped me I need 15 rep? OK..., so I find out how I can get reputation points. More or less, I need to ask a question for +5 and add an answer for +10. I don't have any questions at the moment and I don't want to spam a random question, but I did happen to have a slightly different answer to the earlier question that I wanted to upvote. So I try to answer...     This question is protected to prevent "thanks!", "me too!", or spam answers by new users. To answer it, you must have earned at least 10 reputation on this site.   Now... I know this doesn't apply to every question, but at the same time, this means I'm forced to answer yet another question, and I don't want to go around looking for random questions and spam irrelevant answers...  Now I'm stuck. So I try to talk to some other users in the chat rooms about how to go about getting reputation points and how they first started. I entered into a "casual chat room".     You must have 20 reputation on Meta Stack Overflow to talk here.   Yes... I can understand why this is enforced, because we don't want new users to spam chat rooms, but all I wanted to do was ask for help. So I can't even talk to anyone about my newbie problems. So okay, I'll just settle for upvoting comments in the question that helped me. I don't see an upvote hover-over button so I can't even do that.    So now I'm stuck at 1 reputation point, unable to cross that 15 rep barrier, and even after posting this question I'll only have 6 rep points and still unable to do anything, and I'll be forced to look for questions to answer. Yes, I should be contributing to the community, but I shouldn't need to begin answering or making questions to upvote questions and answers. This only spurs more spam/irrelevant answers if anything.   Very, very, very new-user unfriendly. Residue theorem with $\frac{1}{2\pi}\int_{0}^{2\pi}e^{\cos\theta}\cos(n\theta) d\theta$. The following integral should be doable using the residue theorum:     $$\frac1{2\pi}\int_{0}^{2\pi}e^{\cos\theta}\cos(n\theta) \,d\theta$$ Why couldn't Ellie's experience be corroborated by simply re-using the machine? How are answers with the same vote score sorted? When a new question is asked how are the answers sorted?  I just answered a question and there were two other answers.  All three answers have 0 votes and no edits.  Immediately after I answered my answer appeared first.  Now the order refreshed,  it appears they are sorted by reputation. If $\mid a_{jj}\mid \gt \sum_{i \neq j} \mid a_{ij} \mid$ then vectors $a_1,\dots ,a_n \in \mathbb{R}^n$ are linearly indendent. Let $a_1,\dots ,a_n \in \mathbb{R}^n$ with $a_i = (a_{i1}, \dots , a_{in})$.  Show that when $\mid a_{jj}\mid \gt \sum_{i \neq j} \mid a_{ij} \mid \; \forall \; j\in \{1,\dots ,n\}$, then $a_1,\dots ,a_n$ are linearly independent.  I want to show that the matrix \begin{matrix} a_{11} &amp; a_{21} &amp; \cdots &amp; a_{n1} \\ a_{12} &amp; a_{22} &amp; \cdots &amp; a_{n2} \\ \vdots &amp; &amp; \ddots &amp; \\ a_{1n} &amp; a_{2n} &amp; \cdots &amp; a_{nn} \end{matrix} can be transformed into an upper triangular matrix with all entries in the main diagonal $\neq 0$.  For the cases $n=1$ and $n=2$ this is easy. However, I fail to show this for the general case; the problem being that the tranformations mess up the coefficients such that I can't use the assumption on the $a_{jj}$'s anymore.  I'm pretty sure that this has already been solved somewhere on here, but I don't know how to search for it. Fantasy series with Celtic overtones, intermittent stone magic, and ongoing slow magic I checked this series out of the library during college, maybe 15 years ago now.    It was based around 'stone magic' – magical stones that granted their bearers enormous power.  Unfortunately, the power of these stones is intermittent, they'll fade out for a long time then fade back in.  The main characters dealt with a 'master' stone of some sort, the first to restore, last to die.  It's also the key to granting other people access to their own powers – I think seals had magic fish they swallowed, which keyed off the master stone, and in the last book I think the character created magic staves for another race. It also had 'slow magic' – longer to set up, less apparently potent than stone magic, but the slow magic, given time to work it, could still be powerful and dramatic.  It just took time and preparation instead of brute force. In one book, the main character faces off against the source (or something like that) of magic, and is about to win when it's discovered she's pregnant.  The source – a dragon? – isn't allowed to harm anyone who doesn't come to it freely, so the main character is forbidden to finish the trial.  In the sequel, her daughter repeats the trial, and becomes immensely powerful by winning, but there was a cost of some sort, something that transformed her A lot of the naming made me think it had a Celtic root.