Node js : How to access local variable between the methods
What is the scope of variables in JavaScript?
Restricting SSH sessions for accounts on ubuntu server May someone please show me how I would restrict accounts/people logging into an ubuntu 10.04 server by SSH to a single active session at a time for each account that logs into the server.  Regards I have to move a MongoDB Collection (Size: 1TB+) from Sharded MongoDB Cluster to another[5 shards on both clusters]. During this operation, it is assumed that the accompanying program will be offline, so no need to worry about inconsistent data, but I need to minimize the downtime.  I've tried testing it with mongodump and mongorestore, but looks like that is taking ages to finish.  Please share your experiences for such kind of scenarios.  Note: Cluster has only one collection, so I am open at cluster level sync as well. I am having a serious trouble finding an agreement between the two facts in Special Relativity:  (1) given two events $A$ and $B$ in spacetime separeted by a spacelike interval $s$, the distance in space between the two events will be the shortest in the reference frame which the two events occur simultaneously:   The invariance of the interval says $s^2=(\Delta x)^2-(c\Delta t)^2$ and $\Delta x$ is minimum when $\Delta t=0$  (2) the length contraction says $L=\dfrac{L_0}{\gamma}$ where $\gamma=(1-(v/c)^2)^{-1/2}$ , $L_0$ is the proper length of an object in a reference frame which the object is at rest and $L$ is the length of the object in a reference frame which the object moves with speed $v$ in the $x$ direction.  This says that the lenght of the object in the $x$ direction is the largest in the comoving reference frame of this object.  The question is: According to (1), the reference frame in which two events $A$ and $B$ occur simultaneously is the reference frame that gives the shortest distance in space between the two events. Let $A$ and $B$ be the two end points of a meter stick in a reference frame in which the stick is at rest and at time $t=0$. This two events occur simultaneously, so the distance in space between the two is the shortest acording to (1). But according to (2) shouldn't this distance be the largest?  What is wrong? Expansion of $(1+px+qx^2)^8\equiv 1+8x+52x^2+kx^3$... $(1+px+qx^2)^8 \equiv  1+8x+52x^2+kx^3...$  Given that expression, calculate the values of p, q, and k.  I'm guessing this is a trinomial that needs to be turned into a binomial, but how would you do it? I have no idea. Why is WebDriver instance declared static in Page Object model structure in Selenium? I am a complete newbie in Selenium and java in general. I am trying to use the Page object model with Page factory to create Page object class for the Login page of an application. I am reading lot of sample code on the web tutorials and there the "Webdriver"  reference is delared as "static". Is it that other classes can use the Base class driver instance?  package com.test.login;  import org.openqa.selenium.WebDriver; import org.openqa.selenium.WebElement; import org.openqa.selenium.support.FindBy;  public class LoginPage {      **public static WebDriver driver = null;**      public LoginPage(WebDriver driver) {         this.driver = driver;            PageFactory.initelements(driver, this);     }      @FindBy(xpath = "//input[contains(@id,'username')]")     public WebElement User_ID      @FindBy(xpath = "//input[contains(@id,'password')]")     public WebElement Password;      @FindBy(xpath = "//input[contains(@id,'login')]")     public WebElement Login_Button;   LoginTestClass.java  public class LoginPageTest{     WebDriver driver;     LoginPage loginpage = PageFactory.initElements(Login.class); I want that my monitor turns off when I am inactive for a while, but I do not want that I am prompted for a password when I revoke my pc. In Ubuntu 16.04 it was possible to disable the lock but still enable the screensaver as explained .  In Ubuntu 18.04 I entered the following in terminal:  dconf-editor   and disabled ubuntu-lock-on-suspend:    However, since I made this change, my monitor never suspends anymore. I tried restart but it didn't help.  Any ideas how I can disable lock but still enable suspend mode? If you have a statically allocated array, the Visual Studio debugger can easily display all of the array elements.  However, if you have an array allocated dynamically and pointed to by a pointer, it will only display the first element of the array when you click the + to expand it.  Is there an easy way to tell the debugger, show me this data as an array of type Foo and size X? We write all postive whole integers after the comma, how do we prove that this is an irrational number? ($0.1234567891011121314...$) Dictionary application needs to download dictionary "Apple Dictionary" before use I'm repeatedly being asked to download the "Apple Dictionary" when I open the dictionary application.     Dictionary application needs to download dictionary "Apple Dictionary" before use.   This doesn't happen every time I open it. I haven't pinned down specific usage cases where this message appears, but I think it may be every time after I reboot my computer.  Is there anyway for the Dictionary application to remember that I have "Apple Dictionary" permanently? This has only started happening after I upgraded from OS X Mountain Lion to macOS Sierra. What does "T" mean in C#? I have a VB background and I'm converting to C# for my new job.  I'm also trying to get better at .NET in general.  I've seen the keyword "T" used a lot in samples people post.  What does the "T" mean in C#?  For example:  public class SomeBase&lt;T&gt; where T : SomeBase&lt;T&gt;, new()   What does T do? Why would I want to use it? I'm trying to show that  $$\delta\big(f(x)\big) = \sum_{i}\frac{\delta(x-a_{i})}{\left|{\frac{df}{dx}(a_{i})}\right|}$$  Where $a_{i}$ are the roots of the function $f(x)$. I've tried to proceed by using a dummy function $g(x)$ and carrying out:  $$\int_{-\infty}^{\infty}dx\,\delta\big(f(x)\big)g(x)$$  Then making the coordinate substitution $u$ = $f(x)$ and integrating over $u$. This seems to be on the right track, but I'm unsure where the absolute value comes in in the denominator, and also why it becomes a sum.  $$\int_{-\infty}^{\infty}\frac{du}{\frac{df}{dx}}\delta(u)g\big(f^{-1}(u)\big) = \frac{g\big(f^{-1}(0)\big)}{\frac{df}{dx}\big(f^{-1}(0)\big)}$$  Can any one shed some light? Wikipedia just states the formula and doesn't actually show where it comes from. How can I add metadata to NTFS files/folders? I want to tag different file types (i.e. .pdf, .epub, .iso, .bin, folders,..) using the same descriptive fields. For example i would like a metadata field "type" which would be "eBook" on pdf- and epub-files, "CD-Image" on iso- and bin-files.  I read about Alternate Data Streams (ADS) to make this possible. Does anyone know a good program for Windows 7 to tag different files and search for them? It is important for me, that the metadata is NOT stored in a separate database. I move the files a lot and need to stay flexible (ADSs 'stick' to the files).  Any ideas? How to prevent my screens from turning off, when the screen is locked? I would like to have my screen fully powered at all times, but it goes to standby once I lock my PC. Vi on Linux: show ^M line endings for DOS-format files On Solaris, if you open a file in vi that has Windows line endings, this shows up as ^M at the end of every line.  On Linux, vi is cleverer and understands the Windows file format, and does not display ^M.  Is there a setting to make Linux vi behave the same as Solaris in this respect?  A common problem for us is copying a shell script off a (Windows) dev box and forgetting to dos2unix it, and then being confused when it doesn't work properly. On Solaris the problem is obvious as soon as you vi the file, but not on Linux.  Thanks. How to check if a macro value is empty or will not create text with plain TeX conditionals? I have a macro which holds some text value, e.g. \macro{some text}. If it is empty, I would like for nothing to appear in the document, but it has some content of any kind which would produce text displayed in the document, I would like a message to appear, "Text: some text".   \macro{} would be considered empty. \def\somedata{}, \macro{\somedata} would be considered empty. \macro{0} would be considered not empty.   I have tried making a TeX conditional which can check if the value is not empty, but nothing I tried works, e.g.:  \ifx #1 {} \else     Text: #1 \fi  \ifx#1{} \else     Text: #1 \fi  \ifx #1 \nil \else     Text: #1 \fi  \ifx#1!="" \else     Text: #1 \fi   What is the correct syntax for creating a conditional in plain TeX with checks if a value is not empty? Summary table with a field that shows components of each summarized record I have a table with 2 fields the first is for community and the second for the main community that it belongs to, as in the image  I want to summarize the second field (Belongs_to) but with an extra field (multiple value field) that shows components of each main community, as in the image  Could anyone help me please? Typesetting of negative versus minus? I've occasionally seen a negative (when a number is simply negative, not a subtraction), typeset as negative sign that's slightly skinnier and above the centre line of text. Is this proper notation for mathematics and how would one go about typesetting this in LaTeX?   Edit  I believe that calculators were what happened to give me this idea, couldn't find it in any of my math books. Thank you all for the help, it's much appreciated.     Thank you 'Antal S-Z' for the photo link.  However, the question remains, how exactly would I typeset this? Why is it “a defeated Napoleon, not “the defeated Napoleon” who rode off the battlefield and into exile? I noticed an infinite article; ‘a’ was used before ‘defeated Napoleon’ in the following sentence of Jeffery Archer’s novel, "Fales Impression" :  “General Sir Harry Wentworth sat at the right hand of the Iron Duke that night, and was commanding his left flank when a defeated Napoleon rode off the battlefield and into exile."  I’m curious to know why it should be “a defeated Napoleon,” not “the defeated Napoleon” or simply “defeated Napoleon.” Isn’t it only one Napoleon who was defeated the battle and exiled (to St. Helena). It looks like as though there were many (defeated) Napoleons who were exiled.  It’s always headache for me to handle articles as we Japanese (I think Chinese too) don’t have article as the basic part of speeches in our language system. I’ve studied it on English grammar text books at school, but have never reached full understanding of the usage of articles, because we don’t have that practice. Is there any special knack to master how to use articles? Let $n&gt;0$ and assume that $\chi^{(n)} \in \mathrm{Irr}(G)$ for every $\chi \in \mathrm{Irr}(G)$. Show that $G = H \times A$, where $A$ is abelian and $(|H|, n) = 1$.  $\chi^{(n)}$ is defined by $\chi^{(n)}(g) = \chi(g^n)$. $\mathrm{Irr}(G)$ is the set of all irreducible characters of $G$.  Here are the hints in the book:   Let $d = (|G|,n)$. Show that it is no loss to assume that $(|G|/d,n) = 1$. Let $A = \bigcap_{\chi \in \mathrm{Irr}(G)} \mathrm{ker} \chi^{(n)}$. Show that $A = \{g \in G | g^n=1\}$ and $|A| = d$. Let $H = \bigcap \{\mathrm{ker} \chi | \chi \in \mathrm{Irr}(G), \chi^{(n)} = 1_G\}$. Show $|G : H| = d$.   Hint 1 and 2 are easy, and it is easy to deduce the result from the hints. As for hint 3, I have proven that $\{ g \in G | (o(g), n) = 1 \} \subseteq H$, and that $|G : H| \mid d$. And I am stuck here.  Can anyone help me? How to define binary operation on arbitrary set in order to create a group structure.