I am building a docker image based on Ubuntu 20.04 and one of the commands is: apt update &amp;&amp; apt install -y python3-arrow python3-pip python3-paho-mqtt  As the installation proceeds, I am at some point requested to interactively choose the place I an in, when installing tzdata (which breaks the docker build): (...) Setting up libfakeroot:amd64 (1.24-1) ... Setting up libsasl2-modules-db:amd64 (2.1.27+dfsg-2) ... Setting up tzdata (2020d-0ubuntu0.20.04) ... debconf: unable to initialize frontend: Dialog debconf: (TERM is not set, so the dialog frontend is not usable.) debconf: falling back to frontend: Readline Configuring tzdata ------------------  Please select the geographic area in which you live. Subsequent configuration questions will narrow this down by presenting a list of cities, representing the time zones in which they are located.    1. Africa      4. Australia  7. Atlantic  10. Pacific  13. Etc   2. America     5. Arctic     8. Europe    11. SystemV   3. Antarctica  6. Asia       9. Indian    12. US Geographic area:   Is it possible to force a non-interactive installation of this dependency of one of the installed packages?
If I run:  sudo apt-get --yes install postfix    or  sudo bash -c 'yes | apt-get --yes install postfix'   an interactive prompt appears to configure postfix. I need to automate the installation of postfix (I can modify the configuration files after the install).  Is there some magic that lets me install postfix (and other package) without human intervention?
Multiple submit buttons in an HTML form Let's say you create a wizard in an HTML form. One button goes back, and one goes forward. Since the back button appears first in the markup when you press Enter, it will use that button to submit the form.  Example:    &lt;form&gt;   &lt;!-- Put your cursor in this field and press Enter --&gt;   &lt;input type="text" name="field1" /&gt;    &lt;!-- This is the button that will submit --&gt;   &lt;input type="submit" name="prev" value="Previous Page" /&gt;    &lt;!-- But this is the button that I WANT to submit --&gt;   &lt;input type="submit" name="next" value="Next Page" /&gt; &lt;/form&gt;     I would like to get to decide which button is used to submit the form when a user presses Enter. That way, when you press Enter the wizard will move to the next page, not the previous. Do you have to use tabindex to do this? We learned in Thor: Ragnarok that Mjolnir is only a focus for Thor's power, not the source. If so, when a worthy​ being lifts Mjolnir and gains "the power of Thor", where are they getting the power from? Exercise from Atiyah-Macdonald, Chapter 1, 2.iv) Let $A$ be a ring and let $A[x]$ be the ring of polynomials in an indeterminate $x,$ with coefficients in $A.$ Let $f=a_0 + a_1x+\cdots+a_nx^n \in A[x].$ $f$ is said to be primitive if $(a_0,a_1,\ldots,a_n)=(1).$     Prove that if $f,g\in A[x],$ then $f$ and $g$ are primitive $\Rightarrow$ $fg$ is primitive.   I know Gauss lemma holds true for UFDs, but in this case it isn't required $A$ to be UFD: is it possible to drop the assumption, or is some hypothesis missing here? I forgot my password of a TrueCrypt file I used a few years ago.  How would I go about 'cracking' it? I'm not sure if there is a way to attack it or if it can only be done by brute-force. I used it on a Mac. I still have the Mac I used it on, but of course turned that off many times since I used it.   I have a passphrase that I thought would relate to this file. Maybe I used some variant of it. But might be something completely different. I have some other words that I might have used, but would need give it another thought how I could have used those.  Is there an automated way to test variations on what I think the passphrase was to regain access to the volume? Is there any other way I might regain access? Windows 7 unidentified network (or limited access) after hibernate My windows 7 network will show limited access or unidentified network after coming up from hibernation.  In the office I normally use LAN connection, I turn-off my wireless card (DELL Latitude has on/off switch for the wireless card). When I back at home I will turn on the wireless card, but it will take about 15 seconds to detect my home WIFI and then show limited access. I will have to restart the notebook and it will be able to connect to my WIFI and internet.  The problem will be solved if I restart the notebook, but that defeats the purpose of hibernation doesn't it?  I have tried uninstalling the wireless card driver but still does not solve it. I also tried updating my network card driver but windows says I am using the latest driver. On support.dell.com also showing I am using the latest driver. jQuery/JavaScript to replace broken images Let us denote by $\chi(G)$ the chromatic number, which is the smallest number of colours needed to colour the graph $G$ with $n$ vertices. Let $\bar{G}$ be the complement of $G$. Show that  (a) $\chi(G)+\chi(\bar{G}) \leq n+1$  (b) $\chi(G)\chi(\bar{G}) \geq n$  I was able to prove (a) using induction. Any hints on proving (b)? How do I design a 2A or more power supply for my consumer USB devices? I understand that many of my consumer devices charged by USB ports can charge at higher rates than 0.5A.  However, in testing, I've found they don't consume more than this. Test Setup  I have a power supply that outputs between 0 and 30 volts, and 0 to 20 amps. I set the voltage to 5 volts, then connected up a female USB to the wires correctly. When I plug in a Samsung Galaxy S4 Mini, it pulls around 0.44 amps. It is the same with a Samsung Galaxy Tab Pro. However, when I connect an iPad Air with an official lightning cable, it only pulls around 0.11 amps. Also, I tried connecting a ZGPAX S28 smartwatch and it was still about 0.44-0.45 amps.  The power supply is more than capable of outputting the maximum 2.1 amps, so why doesn't it to at least the tablets? What do I need to do in my test setup to convince the devices to consume their maximum charging current? Prove inequality $n<3^n$ using mathematical induction Prove that $n&lt;3^n$ where $n \in \mathbb N$,  when $ n=1 $, I have proved it's true. And assumed when $n = p$ , $p&lt;3^p$ is true. Can any body help me in showing that it is true for $n =p+1$ Matrix Group induction proof and order of elements question $H$ is the set of the matrices $A$ of the form $$A= \begin{pmatrix} \cos(\theta) &amp; \sin (\theta) \\ -\sin (\theta) &amp; \cos (\theta)\end{pmatrix}$$  where $0\leq \theta &lt; 2\pi$  is a group with respect to matrix multiplication.  Question part (1) Prove by induction that  for any $\theta$ and any positive integer $n$,  $$\begin{pmatrix} \cos(\theta) &amp; \sin (\theta) \\ -\sin (\theta) &amp; \cos (\theta)\end{pmatrix}^{n} = \begin{pmatrix} \cos(n\theta) &amp; \sin (n\theta) \\ -\sin (n\theta) &amp; \cos (n\theta)\end{pmatrix}$$   When $n =1$ we have $$\begin{pmatrix} \cos(\theta) &amp; \sin (\theta) \\ -\sin (\theta) &amp; \cos (\theta)\end{pmatrix}^{1} = \begin{pmatrix} \cos(\theta) &amp; \sin (\theta) \\ -\sin (\theta) &amp; \cos (\theta)\end{pmatrix}$$   and clearly this holds for the base case.   Now I'm going to assume true when $n=k$ and try and prove for $k+1$. So we have   $$\begin{pmatrix} \cos(\theta) &amp; \sin (\theta) \\ -\sin (\theta) &amp; \cos (\theta)\end{pmatrix}^{k}\begin{pmatrix} \cos(\theta) &amp; \sin (\theta) \\ -\sin (\theta) &amp; \cos (\theta)\end{pmatrix}^{1} = \begin{pmatrix} \cos(k\theta + \theta) &amp; \sin (k\theta + \theta) \\ -\sin (k\theta + \theta) &amp; \cos (k\theta + \theta)\end{pmatrix}$$   Now I'm sure I can cheese this, but is there some clever way to pull this apart? I want to just be able to say something like the determinant of the left side is $1^{k+1}$ and its the same on the right ...  Question part (2) Find an element of $H$ of order 5.  Here I'm totally lost, I seem to think that every element is of order 1 cause the determinant is 1.  Question part (3) Find an element of $H$ of infinite order.  Again I'm lost; I want to somehow make the determinant 0 for this but it can never be 0 for any $\theta$. I'm trying to load data from different tables using left outer joins into a QgsVectorLayer. The approach I'm following so far is the one from the developers cookbook . The underlying database is postgres. The query returns correct data, including a geometry column, however I can't figure out how to get the join inside the query to work with . As the table the data come from needs to be specified, is it even possible to do so?  Would approaching the problem using psycopg2 be more suited, and if so, is there a way to create a layer from the result set? The only way I can think of is creating an empty layer and adding each feature individually by looping over the result set. But possibly there is an easier way?  Sadly, using the builtin DB Manager is not an option. The layer has to be added programmatically. User and associated Post Generating DLL assembly dynamically at run time Currently I have some code that is being generated dynamically.  In other words, a C# .cs file is created dynamically by the program, and the intention is to include this C# file in another project.  The challenge is that I would like to generate a .DLL file instead of generating a C# .cs file so that it could be referenced by any kind of .NET application (not only C#) and therefore be more useful. This is a neat little problem that I was discussing today with my lab group out at lunch. Not particularly difficult but interesting implications nonetheless  Imagine there are a 100 people in line to board a plane that seats 100. The first person in line realizes he lost his boarding pass so when he boards he decides to take a random seat instead. Every person that boards the plane after him will either take their "proper" seat, or if that seat is taken, a random seat instead.  Question: What is the probability that the last person that boards will end up in his/her proper seat.  Moreover, and this is the part I'm still pondering about. Can you think of a physical system that would follow this combinatorial statistics? Maybe a spin wave function in a crystal etc... Would Gollum qualify, as a Ringbearer, to go to the Undying Lands? Traditionally  at the end of a filename after uploading it via the image uploader. That doesn't seem to work any more. I've tested it on Q&amp;A as well as chat.        (Yes, I know big M doesn't work)  Could we have this fixed please? How to install the most common plugins? How to read command line arguments of another process in C#? Creating if-else condition with ArcGIS API for JavaScript combo boxes? How did Harry, Ron and Hermione buy presents for each other? I have been re-reading the Harry Potter books again and I noticed that Harry, Ron and Hermione have been giving each other Christmas presents each year at Hogwarts. How have they been able to buy each other presents if they are not allowed to go out of Hogwarts?   From their third year on they could visit the village and buy presents there, but what about the first two years? Did they give their personal belongings? Or did they just happen to have boxes of chocolates or books to give each other?