SSH Connection refused after running pkill
What causes the 'Connection Refused' message?
Computing $\lim_{(x,y)\to (0,0)}\frac{x+y}{\sqrt{x^2+y^2}}$ What is the result of  $\lim_{(x,y)\to (0,0)}\frac{x+y}{\sqrt{x^2+y^2}}$ . I tried to do couple of algebraic manipulations, but I didn't reach to any conclusion.  Thanks a lot. Superscript in CSS only? How can I get superscript done, only in CSS?  I have a stylesheet where I mark the external links with a superscript character, but I'm having a hard time getting the character aligned correctly.  What I have currently, looks like this:  a.external:after {   font-size: 50%;   vertical-align: top;   content: "+"; }   but it doesn't work.  Naturally, I'd use the &lt;sup&gt;-tag, only if content would allow for HTML... How do you open a command line? How do you access the command line or run option to put the commands into the system? What are 'user' and 'system' times measuring in R system.time(exp) output? What free Remote Desktop (server) solutions are there? I know Ubuntu comes with a "Remote Desktop" option that appears to be a straightforward VNC server, and I'm trying to understand the alternatives. Here are the possibilities I've heard about so far:   VNC  VNC + SSH Tunnelling NX Server, free edition FreeNX NeatX X2Go X11 Forwarding over SSH xrdp    I'm coming at this from a Windows user's perspective: To the best of my experience, RDP (aka Terminal Services) is a reasonably secure (barring mitm/server spoofing), efficient desktop sharing protocol with well-supported clients, that can be exposed to the internet when necessary without major fears of intrusion. To the best of my knowledge straight VNC is none of those things, which is where I get confused - why wouldn't a better desktop sharing technology be developed or used in the open-source world? I know VNC can be wrapped with SSH, but that seems beyond the reach of a casual user. X11 forwarding over SSH may be more or less efficient, I have no idea, but is definitely even more complicated, and doesn't (as far as I know) give you access to already-running stuff (no desktop sharing as such, just remote application running).  So, I'd like any feedback/preferences amongst these or any other "Free" desktop sharing options, using these criteria and/or any others:   Security (esp. for access across internet) Efficiency (bandwidth usage, responsiveness, etc) Free-ness, as in Speech (not sure where RDP or FreeNX lie for this) Free-ness, as in Beer (are there any commercial solutions with usable dependable free offerings?) Ease of use (server and client side) Cross-OS Client availability Cross-OS Server availability Support for independent sessions and shared (and/or "Console") sessions Ongoing support/maintenance/development   Thanks! Possible Duplicate:          I'm working on a website that displays distance to various locations to the nearest 1/10 mile. One of the developers (a non-native speaker) asked me an interesting question: If the distance is 1.0 mile(s), is that singular or plural? Clearly, anything other that 1.0 is plural, but is it:     1.0 miles away   or     1.0 mile away   The first option sounds more correct to my ear, but the voice of my elementary school language arts tells me that the latter option is correct.  Edit: Added the word 'away' to the example. It doesn't change the question, but might provide clarity for the answer. Also, regarding numbers between 0 and 1, after more thought, I'm not sure that the answer is as clear as I originally thought. See . Are fractions with prime numerator and denominator dense? Previously I thought this is a universal theorem, for one can prove it in the one dimensional case using variational principal.   However, today I'm doing a homework considering a potential like this:$$V(r)=-V_0\quad(r&lt;a)$$$$ V(r)=0\quad(r&gt;a)$$ and found that there is no bound state when $V_0a^2&lt;\pi^2\hbar^2/8m$.  So what's the condition that we have at least one bound state for 3D and 2D? Query to compare the structure of two tables in MySQL To automate the backup process of one of my MySQL databases, I would like to compare the structure of two tables (current version vs old version).  Can you think of a query that can compare two tables?  Here are some example tables that you can compare.   CREATE TABLE product_today (   pname VARCHAR(150),   price int,   PRIMARY KEY (pname) );  CREATE TABLE product_yesterday (   pname VARCHAR(150),   price int,   PRIMARY KEY (pname) );  CREATE TABLE product_2days_back (   pname VARCHAR(15),   price int,   PRIMARY KEY (pname) );   The first two tables have identical structures. The last one is different. I just need to know whether two tables have different structures or not. I'm not interested in the how they differ. A lady and a monster A famous problem:  A lady is in the center of the circular lake and a monster is on the boundary of the lake. The speed of the monster is $v_m$, and the speed of the swimming lady is $v_l$. The goal of the lady is to come to the ground without meeting the monster, and the goal of the monster is to meet the lady.  Under some conditions on $v_m,v_l$ the lady can always win. What if these conditions are not satisfied?  Edited: the monster cannot swim. If the conditions are not satisfied, then monster can always perform a strategy such that the lady will not escape the lake. On the other hand this strategy is not desirable for both of them because they do not reach their goals. As there was mentioned, this deals with undecidability of the problem. On the other hand, if you imagine yourself to be this lady/monster, you can be interested in the strategy which is not optimal. What is it? If there are such strategies in the game theory?  Edited2: My question is more general in fact. If we have a game with one parameter $v$ when two players $P_1, P_2$ are enemies and if $v&gt;0$ then for any strategy of $P_2$ the player $P_1$ wins. If $v\leq 0$ then for any strategy of $P_2$ there is a strategy of $P_1$ such that $P_2$ does not win and vice versa. I am interested in this case. From the mathematical point of view as I have understood the problem is undecidable since there is no an ultimate strategy neither for $P_1$ nor for $P_2$. But we are solving somehow these problem IRL. Imagine that you are a lady in this game - then you would like to win anyway even while knowing that your strategy can be covered by the strategy of the monster. On the other hand, the monster knows that if he will cover all strategies of the lady she will never reach the shore and he will never catch her. I mean they have to develop some non-optimal strategies. I hope now it's more clear. I never dealt with Android devices before so I'm completely newbie at it, please comment if something is too simple.  Say I purchase , that has got Android Froyo 2.2 installed in it.  If there is a new version of Android released tomorrow or next month, will I be able to update it (like I will be able to update my iPod Touch 4 to iOS 5)? Is past simple ever justified with 'by'? Can anyone shed some light on the following aspect?  By 5 PM I gave him the book.  By 5 PM I had given him the book.  In both the sentences the book was given before 5 PM and no later than 5 PM. But I can't understand then what the difference between them is. a Also is it right to use simple past with 'by' at all? If yes, then why and if not, then why is it incorrect to use simple past with 'by'? Akhil showed that the  is the same as the continuum, using as a step the observation that continuous functions that agree at rational points must agree everywhere, since the rationals are dense in the reals.  This isn't an obvious step, so why is it true? In my opinion the accepted answer should permanently stick as only the original question submitter has the ability to accept. I try to understand why for a connected Lie group $G$ the first fundamental group $\pi_1(G)$ is abelian, and mainly why the second fundamental group is trivial $\pi_2(G)=0$?  Thanks for anyone who give me references for a 'simple proof' of these results How to have a one-to-many relationship with a privileged child? Spotlight overrides first character What's wrong: I hit CMD+SPACE to open up spotlight, typically type in the name of the application I want to start, hit enter and either the wrong app or no app at all will start, because the app name is missing the first character. "Learn to type" I hear you say but wait: as I enter the first character in the search bar, the cursor jumps to the beginning of the line and my second character input overrides the first one. So entering for example "ever", in order to start Evernote, will result in "ver". "php" to start PHPStorm will result in "hp" and start my damn HP printer app and so on.   This cursor jump to the beginning of the line will not happen in any other application and even if I accept the fact that my cursor jumps from time to time, I don't get why the second character overrides the first one. I'm not even sure if you can configure your Mac to always override the character at current position, but I surely haven't.  So this keeps on happening quite regularly and I cannot reproduce it. It just happens and when I try it again (close Spotlight, CMD+SHIFT again), it won't happen again, even if I give it like 5 tries or so.  It won't kill me but I am a software developer myself and this kind of bugs just leave me frustrated plus I can not imagine that this is the desired behavior. I have seen some talk about this issue on the internet but I did not come across a solution..  I have 3 MacBooks, different ages, all with German keyboard layouts and German set as system language and they all do this. Just mentioning this, because after that fact, I can barely imagine this isn't affecting at least a lot, if not all, MacBook (Pro?) users.   13" Pro 2010 or so 15" Pro Retina 2013 13" Pro Retina 2015   They all run El Capitan but I already encountered this before. I don't know the OS X version I had installed when I first stumbled across it. D'Alemberts Principle to solve a Classical Mechanics problem I found this question on this very site and was curious on how to solve it using D'Alembert's Principle  .I already know how to do it by balancing the torque about toppling point so please don't post the latter as an answer . My attempt was to displace the upper sphere by $d\theta$ which gives its virtual displacement as  $rd{\theta}cos(\theta)$j(notice we are only interested in the y component becuz the only component of the applied force which is gravity in this case is the y component in the dot product the other components vanish) similarly the cylinder is also displaced $r'd{\phi}cos(\phi)$ where r' is the distance from the point of toppling of the center of mass. $r'cos(\phi)=H/2=r(1+sin(\theta))$ ,$r'sin(\phi)=R=r(1+cos(\theta))$ and $tan(\phi)=H/2R$ the equation coming from D'Alemberts principle is $mgrcos(\theta)d\theta=Mgr'cos(\phi)\phi$ I tried solving this but couldn't arrive at the right answer. Any help would be appreciated! Which function ($f$) is continuous nowhere but $|f(x)|$ is continuous everywhere?   I found this question , the question seems much interesting but for obvious reason it is closed there, I was wondering how to derive such a function? What are the pros and cons of engineered hardwood? Are there any downsides to engineered hardwood? I'm looking to install hardwood in dining room and kitchen areas.