I had a working EC2 ubuntu instance (t1.micro) connected through an elastic IP, using an Amazon key pair for a passwordless ssh connection. After running fsck like the terminal suggested (wrong move, I know now), the system rebooted and I keep getting "Network Error: Connection Refused" when trying to connect via ssh. I managed to attach the instance's volume to an alternative instance, but I could not see what was wrong. I also tried "ssh -vvv" from an Ubuntu laptop, but got no useful output. Is there a log I can look at to see why ssh is refusing my connection?  Is there an alternative way I could debug this?
This is a  about Connection Refused    We see a lot of questions to the effect      When I try to connect to a system I get a message      Connection refused      Why is this ?
Does Stack Exchange use caching and if so, how? Recently, I read this  about how they have some of their infrastructure laid out. I was curious to know, does Stack Exchange use caching (both at the application layer and/or database layer) and if so, how? What is the cause of gravitional force of attraction? Ok,this is a silly question. But for quite long I have been thinking about this. What is gravitation all about?? My book directly writes since force of gravitation is directly proportional to the masses and inversly proportional to the square of the distance ie. $$F = G\frac{M_1 . M_2}{r^2}$$ . So is this gravitation all about? What is the cause of it? The book then says     We are not in the scope in classical approach so as to discuss the cause of this. However,as a matter of fact that if there are more than one mass,then there is gravitation as it is their fundamental property.( Cause of gravitation can be attributed to exchange of non-classical particles between the masses) .    Then it ended the talkings. What are those non-classical particles? Why and how are they exchanged? So far I have studied physics , I never found such weird phenomenon like this. I want to know what is the cause of gravitation and what is the cause of exchange of those so-called non-classical particles? And how do they do it? Would it help if you jump inside a free falling elevator? Imagine you're trapped inside a free falling elevator. Would you decrease your impact impulse by jumping during the fall? When? C++ iostream Corruption using stringstream Format string dynamically 14 months ago, an  supplement was published that discussed how the ranger described in the Player's Handbook was under powered. These rules reimagined the ranger's abilities, and suggested that an official version would be released later.     Finally, we come to implementation. If this iteration of the ranger, or a future revision of it, grades high enough, our plan is to present it as a revised ranger in a future D&amp;D sourcebook.   Does that Sourcebook exist yet? If not, have the devs given an update or told us their intentions? I'm just trying out Arduino Uno for the first time with 2 blinking LEDs on a breadboard. All the tutorials on the Internet seem to use a resistor. I do know the function of resistors, but does it really matter here? These LEDs are working just fine without a resistor. When to use a hyphen to coin a new word and when to omit a hyphen? Someone has asked for answer to these topics. However, I still want someone to provide me with simple and universal answers. I recently read a sentence from the English-speaking person. It is in an article. It is, ' The available options for mitigating pad cratering are not universally effective (see link below), but they may be helpful on a case by case basis until more crack resistant laminates are developed and become available.  '  If I am to write this, I will use 'a case-by-case basis until more crack-resistant laminates'   Can anyone tell me when to use a hyphen to coin a new word? Why is the t-test designed for small samples? I'm trying to write a small script to change the current directory to my project directory:  #!/bin/bash cd /home/tree/projects/java   I saved this file as proj, added execute permission with chmod, and copied it to /usr/bin. When I call it by: proj, it does nothing. What am I doing wrong? I have a sequence $T_1,T_2,\ldots$ of independent exponential random variables with paramter $\lambda$. I take the sum $S=\sum_{i=1}^n T_i$ and now I would like to calculate the probability density function.  Well, I know that $P(T_i&gt;t)=e^{-\lambda t}$ and therefore $f_{T_i}(t)=\lambda e^{-\lambda t}$ so I need to find $P(T_1+\cdots+T_n&gt;t)$ and take the derivative. But I cannot expand the probability term, you have any ideas? Redefining "cited on" string (and others) in biblatex Here $p$ and $q$ are co-prime integers. Is it necessarily an algebraic number? I want to prove that $xe^{-x}$ is bounded by some constant for all the $x \in [0, \infty)$. So I take derivative of this guy, and found that on $x \in [0, \infty)$, its derivative is positive from $[0, 1)$, $0$ at $x=1$, and negative from (1, in infinity). So  $xe^{-x}$ achieves its maximum in $[0, \infty)$ at $x=1$, which is $1/e$. However, to prove that it's bounded by $1/e$, I need to prove that as $x$ goes to infinity, $xe^{-x}$ converges to $0$. Because otherwise, if it went to some value below $(-1/e)$, $xe^{-x}$ would not be bounded by $1/e$. How can I prove that $xe^{-x}$ converges to $0$? I mean, as $x$ goes to infinity, $e^{-x}$ converges to zero, but at the same time, x diverges to infinity. How can I formally prove that the product term converges to $0$? Do I need to use the epsilon definition of convergence to prove it?  Could you just show me the formal proof of $xe^{-x}$ converges to $0$? Or is there's any other way to approach this question? My professor suggested that I should use the power series for $e^{-x}$...?   Your help is greatly appreciated! Thank you so much!  I hope you enjoy your Saturday! I am working on Ubuntu 12.04 64bit.  I want to add "Open terminal here" to Nautilus context or right-click menu but it tries to download 32bit version from Internet. What's the difference between convolution and crosscorrelation? What's the difference between convolution and crosscorrelation? So why do you use '-' for convolution and '+' for crosscorrelation? Why do we need the "time reversal on one of the inputs" when doing convolution? Why must a computer have a BIOS? The  software is built into the PC, and is the first code run by a   PC when powered on ('boot firmware'). When the PC starts up, the first   job for the BIOS is the power-on self-test, which initializes and   identifies system devices such as the CPU, RAM, video display card,   keyboard and mouse, hard disk drive, optical disc drive and other   hardware. The BIOS then locates boot loader software held on a   peripheral device (designated as a 'boot device'), such as a hard disk   or a CD/DVD, and loads and executes that software, giving it control   of the PC.[2] This process is known as booting, or booting up, which   is short for bootstrapping.   Which requisites determine that a computer system must have a BIOS installed on it?  Why can't the Operational System actually do all of the BIOS work? How do Muggle Wars affect the magical world? This came up to me while I was reading the question about Magical being using firearms in battle to raise their power (which I think I have a good answer for, but it's too long to fit in this question... and it would also be inappropriate).  Anyways, I was reading it and then the following thought came into my mind: If wizards decided to use guns on their battles (the ones agains Voldemort for instance), that would create that opening for much bigger battles than we see in the books (after all even a muggle can fire a gun, so lots of guns + the Imperio curse, and presto manifesto (is that racist? talking about wizards and all) you have yourself an army). Those kinds of battles, however, would most definitely not go unnoticed by the muggles - even though they wouldn't be able to link it to magic.  Well, that thought brought up my one and final question, which I bring forth to you guys. Is there any mention on how the Wizards and Witches viewed the two world wars (which had taken part by the time Harry got to Hogwarts, and which he had probably heard about in muggle school), and what was the Wizards' part in it? What about the cold war? Did the magical world even recognise the existence of weapons such as nukes, which could render all life on earth extinct?  EDIT  DVK has brought up an  regarding the connections between the Second World War and the wizarding world (more specifically, the wizard Grindelwald). Although it doesn't fully answer my question, it does help by showing that there was indeed some form of connection between the two world at the time. What's the best way to check if a String represents an integer in Java? I normally use the following idiom to check if a String can be converted to an integer.  public boolean isInteger( String input ) {     try {         Integer.parseInt( input );         return true;     }     catch( Exception e ) {         return false;     } }   Is it just me, or does this seem a bit hackish?  What's a better way?    See my answer (with benchmarks, based on the  by ) to see why I've reversed my position and accepted  to this problem.  I think this original code will be used by most people because it's quicker to implement, and more maintainable, but it's orders of magnitude slower when non-integer data is provided. All of my Firefox add-ons have been disabled suddenly, how can I re-enable them? All of my Firefox extensions were spontaneously and simultaneously disabled (converted to Legacy status) a few moments ago.  How can I re-enable them? Firefox 66.0.3 (64-bit)