I can not install nor upgrade anything  'can not get lock var/lib/dpkg/lock-frontend. it is held by the process 2469 ...'  could you suggest what to do to ?
I'm trying to run this command in the terminal:  sudo apt install software-properties-common   This is the error message I get:  E: Could not get lock /var/lib/dpkg/lock-frontend - open (11: Resource temporarily unavailable)   E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend),     is another process using it?
How to find out if an item is present in a std::vector? In C++, what is a virtual base class? I want to know what a "virtual base class" is and what it means.  Let me show an example:  class Foo { public:     void DoSomething() { /* ... */ } };  class Bar : public virtual Foo { public:     void DoSpecific() { /* ... */ } }; I compile most of my documents via Makefiles which take care of the bibliography, indexes, etc. Often I'd like to compile different versions from the same TeX file changing only small things (e.g. a beamer presentation plus a version with the handout option).  Is there any standard mechanism for passing parameters to the TeX file so that I can just type make handout to get the handout version in the above example? Proving $ \binom n 0 ^2 + \binom n 1 ^2 + \dots + \binom n n ^2 = \binom { 2n} n $ without induction I have to prove that: $$ \binom n 0 ^2  + \binom n 1 ^2  + \dots + \binom n n ^2 = \binom { 2n} n $$  I don't want a complete solution, but only a hint. I am trying to write a bash script for testing that takes a parameter and sends it through curl to web site.  I need to url encode the value to make sure that special characters are processed properly.  What is the best way to do this?    Here is my basic script so far:  #!/bin/bash host=${1:?'bad host'} value=$2 shift shift curl -v -d "param=${value}" http://${host}/somepath $@ How do I debug permissions? How can I prove these are the adjoint operators? How and when is old-releases.ubuntu.com updated? The old-releases.ubuntu.com mirror hosts the repositories for EOL Ubuntu releases. The  currently lists up to 11.10 (or 12.04.3 if you count point upgrades), but the  lists up to 13.04. Why the discrepancy? When will the main page be updated? When will the newest EOL release (13.10) be shifted here? Possible Duplicate:          How do you convert a C++ string to an int?  Assume you are expecting the string to have actual numbers in it ("1", "345", "38944", for example).  Also, let's assume you don't have boost, and you really want to do it the C++ way, not the crufty old C way. Print file content without the first and last lines Permission for snap applications I have some trouble with the Ubuntu notepadqq package. After opening a file from my apache webroot I cannot see any content. Saving the file is also not possible. I thougt this would be a classic permission issue. Therefore, I changed the group of the webroot from root to www-data and added my user to this group. Permissions are 775, so in theory it should now be possible for me to edit files in my webroot. But nevertheless, when I open a file of this directory with notepadqq, it still only shows an empty file.  When using gksudo notepadqq I get the following error message:  No protocol specified QXcbConnection: Could not connect to display :0   I figured out that notepadqq is a so called snap application and I wonder if this is the reason for my problems.  Can someone give me a hint how I could fix this issue (without using 777 permissions)? Are beamer, hhline, and [table]{xcolor} incompatible? The following example works as expected:  \documentclass{article} \usepackage[table]{xcolor} \usepackage{makecell, multirow}     \renewcommand\theadfont{\normalsize\bfseries\color{white}}     \renewcommand{\theadgape}{} \usepackage{hhline}  \begin{document} \centering     \setlength\arrayrulewidth{2pt}     \arrayrulecolor{yellow}     \def\clinecolor{\hhline{&gt;{\arrayrulecolor{yellow}}--%                             &gt;{\arrayrulecolor{gray}}-}}     \setlength\extrarowheight{2pt} \begin{tabular}{ c | c | c }%     \rowcolor{gray} \multicolumn{2}{c|}{\thead{AAA -- BBBB}}    &amp;                                   \\     \clinecolor     \rowcolor{gray} \color{white} AAA   &amp;   \color{white} BBB   &amp;   \multirow{-2}{*}{\thead{CCC}}   \\     \hhline{&gt;{\arrayrulecolor{yellow}}-|-|-}     \rowcolor{gray!25} aaa                 &amp;   bbb                 &amp;   ccc                             \\     \hline     \rowcolor{gray!25} ddd             &amp;   eee                 &amp;   fff     \end{tabular} \end{document}     But the following not:  \documentclass[xcolor=table]{beamer} \usepackage{makecell, multirow}     \renewcommand\theadfont{\normalsize\bfseries\color{white}}     \renewcommand{\theadgape}{} \usepackage{hhline}  \begin{document} \begin{frame} \frametitle{test} \centering     \setlength\arrayrulewidth{2pt}     \arrayrulecolor{yellow}     \def\clinecolor{\hhline{&gt;{\arrayrulecolor{yellow}}--%                             &gt;{\arrayrulecolor{gray}}-}}     \setlength\extrarowheight{2pt} \begin{tabular}{ c | c | c }%     \rowcolor{gray} \multicolumn{2}{c|}{\thead{AAA -- BBBB}}    &amp;                                   \\     \clinecolor     \rowcolor{gray} \color{white} AAA   &amp;   \color{white} BBB   &amp;   \multirow{-2}{*}{\thead{CCC}}   \\     \hhline{&gt;{\arrayrulecolor{yellow}}-|-|-}     \rowcolor{gray!25} aaa                 &amp;   bbb                 &amp;   ccc                             \\     \hline     \rowcolor{gray!25} ddd             &amp;   eee                 &amp;   fff                             \\     \hhline{|-|-|-|}     \end{tabular} \end{frame} \end{document}     Why are the in beamer rules so strangely misplaced? Is there some workaround? JavaScript open in a new window, not tab I have a select box that calls window.open(url) when an item is selected.  Firefox will open the page in a new tab by default.  However, I would like the page to open in a new window, not a new tab.    How can I accomplish this? How many irreducible monic quadratic polynomials are there in $\mathbb{F}_p[X]$? Can some of you help me with my homework?     I had to count the irreducible, quadratic, monic polynomials in $\mathbb{F}_p[X]$ for arbitrary $p$.    I will show you what I tried myself.  Research effort  First of all the set $\{X^ 2 + bX +c : b, c \in \mathbb{F}_p \}$ contains $p^2$ elemenst. We need to substract the amount of elements that is reducible. These elements are exactly the set $A = \{(X+c)(X+d) : c, d \in \mathbb{F}_p \}$. There are $p(p-1)$ pairs of $(a,b) \in \mathbb{F}_p \times \mathbb{F}_p$ such that $a \neq b$, and there are $p$ pairs such that $a=b$.     When $a$ and $b$ are unequal, whe know that $a$ and $b$ can be swapped without changing anything to the polynomial $(X+a)(X+b)$, so I obtained that $|A| \leq p +(p-1)- \frac{1}{2}(p-1)=p-\frac{1}{2}(p-1)$.  In other to find out these are the elements, or that there are still less, I thought I had to assume that $(X+c)(X+d) = (X+\gamma)(X+\delta)$, to deduce some information about the realation between $(c,d)$ and $(\gamma, \delta)$, but this led to taking square roots in $\mathbb{F}_p$, and I am not familiar with that.  Could you please provide me some more information? Is there a name for an element $z$ such that $\,zx = z = xz\,$ for all $x$? Is there a general name for the following properties, (similar to the properties of existence of an additive identity, existence of multiplicative identity etc):   For any given set, the intersection with the empty set results in the empty set. For any real number, multiplication with zero results in zero. I'm trying to use the ant migration tool to retrieve all the Custom Metadata records for a single Custom Metadata Type.  However, I can't figure out the syntax.  I would think that something like this would work:    &lt;Package xmlns="http://soap.sforce.com/2006/04/metadata"&gt;     &lt;types&gt;         &lt;members&gt;State_Sales_Tax.*&lt;/members&gt;         &lt;name&gt;CustomMetadata&lt;/name&gt;     &lt;/types&gt;     &lt;types&gt;         &lt;members&gt;State_Sales_Tax__mdt&lt;/members&gt;         &lt;name&gt;CustomObject&lt;/name&gt;     &lt;/types&gt;     &lt;version&gt;36.0&lt;/version&gt; &lt;/Package&gt;   but no dice. Firmware vs. Software How do I change my default browser? Is there an option to change my default browser for all my applications? Disable commandButton after first click to prevent double submission I have an apex:commandButton on a visualforce page that invokes a method on the controller. There is currently no rerender value set for the button. Instead the controller method returns a PageReference to redirect the user as required.  E.g.  Visualforce:  &lt;apex:commandButton value="Save" action="{!save}"/&gt;   Controller:  public PageReference save() {     // save body ...      // return the user the a parent opportunity     return new PageReference('/' + opp.Id); }   Users are currently able to click on the resulting save button multiple times before the controller completes and returns the PageReference to redirect the browser to an opportunity.  How can I disable the commandButton after the first click?    I tried wrapping the commandButton in an actionStatus and facet, but the need to define the rerender property prevented the resulting PageReference redirect.  E.g.  This will render nicely in the browser and prevent multiple clicks, but doesn't redirect to the Opportunity on completion.  &lt;apex:actionStatus id="saveStatus"&gt;     &lt;apex:facet name="stop"&gt;         &lt;apex:commandButton value="Save" action="{!save}" status="saveStatus" rerender="saveParentBlock" /&gt;     &lt;/apex:facet&gt;     &lt;apex:facet name="start"&gt;         &lt;apex:commandButton value="Saving..." disabled="true" status="saveStatus"/&gt;     &lt;/apex:facet&gt; &lt;/apex:actionStatus&gt;     There is a similar question . I need to support an existing PageReference redirect, which slightly alters the requirements.  Force.com Discussion Boards:   Ideas: Can someone explain the dollar sign in Javascript?