E: The repository 'http://ppa.launchpad.net/webupd8team/atom/ubuntu focal Release' does not have a Release file
What can I do if a repository/PPA does not have a Release file?
How to detect using c# if a pendrive is plugged into a USB port? Is there a way to find out when in a LAN anyone plugs in a pendrive to the USB port?  Programatically (in C# preferably) or through some tool. Basically I'd imagine a client application sits on each terminal and monitors the USB ports and sends the information to the server.   a.) Can I get the details of the file(s) being copied? b.) Is there a way to do this without a client application?   EDIT  I dont want to disable the USB port entirely. its to be on a need to have basis. Basically just want the users on the LAN to share data responsibly and know that whatever data is tranfered is monitored and logged and can be questioned later. Is $\sqrt{x^2}=|x|$ or $=x$? Isn't $(x^2)^\frac12=x?$ $|x|=\sqrt{x^2}$ as  shows. But, as $(x^2)^\frac12=x$, I can't understand where am I wrong interpreting Square-root. I usually compress my tex PDFs with ghostscript:  pdflatex -shell-escape file.tex  gs -sDEVICE=pdfwrite        \    -dCompatibilityLevel=1.4   \    -dPDFSETTINGS=/prepress      \    -dNOPAUSE -dQUIET -dBATCH      \    -sOutputFile=file_compressed.pdf \     file.pdf   Normally that works well, but if I have relative links to local files, the links don't work afterwards.  Minimal example:  \documentclass{beamer} \usepackage{hyperref}  \begin{document}     \begin{frame}         \href{run:./audio.mp3}{test}     \end{frame} \end{document}   The link works in file.pdf but not in file_compressed.pdf. Is there any pdflatex or ghostscript setting that retains the link in the compressed version?  I use Acrobate Reader 10.1.14 for viewing, Ghostscript 9.10 and pdfTeX 3.14159265-2.6-1.40.15 (TeX Live 2014) on OS X 10.9.5.    Update: The breakage of hyperlinks had nothing to do with compressing the PDFs. The breakage happened for all re-processing of PDFs containing hyperlinks in its input PDF. How to pass multiple operator properties via UI layout? Order discrete x scale by frequency/value Expressing the area of the cross section of a cylinder I was able to solve similar questions where a triangle was involved, but this one has had me looping and pondering on it for the past week.  The Condition: Let $r$ be a positive constant. Consider the cylinder $x^2+y^2\leq r^2$ and let C be  part of the cylinder that satisfies $0\leq z\leq y$.  The questions:  (1) Consider the cross section of $C$ by the plane $x=t(-r\leq t\leq r)$ and express its area in terms of $r,t$  (2) Calculate the volume of $C$, and express it in terms of $r$.  (3) Let $a$ be the length of the arc along the base of the circle $C$ from the point $(r,0,0)$ to the point $(r cos\theta,r sin\theta,0)(0\leq\theta\leq\pi)$. Let $b$ be the length of the line segment from the point $(r cos\theta, r sin\theta, 0)$ to the point $(r cos\theta, r sin\theta, r sin\theta)$. Express $a$ and $b$ interms of $r,\theta$  (4)Calculate the are of the side of $C$ with $x^2+y^2=r^2$, and express it in terms of $r$.  Here are the expected answers(which I keep failing to get to):  (1) $\frac{1}{2}(r^2-t^2)$  (2) $\frac{2}{3}r^3$  (3) $r\theta$ and $r sin\theta$  (4) $2r^2$ How do I turn off the arrow for desktop icons? What kind of substitution should I use to obtain the following integrals? $$\begin{align} \int_0^1 \ln \ln \left(\frac{1}{x}\right)\,dx &amp;=\int_0^\infty e^{-x} \ln x\,dx\tag1\\ &amp;=\int_0^\infty \left(\frac{1}{xe^x} - \frac{1}{e^x-1} \right)\,dx\tag2\\ &amp;=-\int_0^1 \left(\frac{1}{1-x} + \frac{1}{\ln x} \right)\,dx\tag3\\ &amp;=\int_0^\infty \left( e^{-x} - \frac{1}{1+x^k} \right)\,\frac{dx}{x},\qquad k&gt;0\tag4\\ \end{align}$$  This is not homework problems and I know that the above integrals equal to negative of the Euler–Mascheroni constant. I got these integrals while reading this Wikipedia page: . According to Wikipedia, the Euler–Mascheroni constant is defined as the limiting difference between the harmonic series and the natural logarithm: $$\gamma=\lim_{N\to\infty} \left(\sum_{k=1}^N \frac{1}{k} - \ln N\right)$$ but I don't know why can this definition be associated to the above integrals?  I can obtain the equation $(1)$ using substitution $t=\ln \left(\frac{1}{x}\right)\rightarrow x=e^{-t} \rightarrow dx=-e^{-t}\,dt$ and I know that $$\int_0^\infty e^{-x} \ln x\,dx=\Gamma'(1)=\Gamma(1)\psi(1)=-\gamma$$ but I can't obtain the rest. Any idea? Any help would be appreciated. Thanks in advance. Waiting for a file to be created in C# How to disk copy with unreadable sectors? I want to clone a whole disk bytewise, something like  dd if=/dev/$SRC of=/dev/$DST bs=65536 count=$count   There are better tools for the job, which understand the file system (Windows) and work faster (I don't care), but they fail because of unreadable sectors on the old source disk.  There's actually a single invalid block I have to skip. So I thought about using dd multiple times like  dd if=/dev/$SRC of=/dev/$DST bs=65536 count=... dd if=/dev/zero of=/dev/$DST bs=65536 count=... skip=... seek=... dd if=/dev/$SRC of=/dev/$DST bs=65536 count=... skip=... seek=...   with replacing the broken sector data by zeros. Is this a valid approach? I found this  which confuses me. Cannot add a NOT NULL column with default value NULL in Sqlite3 Has it been practically proven that quantum superposition exists ? If yes, how does it even work? How can I find the unit vector of a three dimensional vector? For example, I have a problem that I am working on that tells me that I have a vector $\hat{r}$ that is a unit vector, and I am told to prove this fact:     $\hat{r} = \frac{2}{3}\hat{i} - \frac{1}{3}\hat{j} - \frac{2}{3}\hat{k}$   I know that with a two-dimension unit vector that you can split it up into components, treat it as a right-triangle, and find the hypotenuse. Following that idea, I tried something like this, where I found the magnitude of the vectors $\hat{i}$ and $\hat{j}$, then using that vector, found the magnitude between ${\hat{v}}_{ij}$ and $\hat{k}$:     $\left|\hat{r}\right| = \sqrt{\sqrt{{\left(\frac{2}{3}\right)}^{2} + {\left(\frac{-1}{3}\right)}^{2}} + {\left(\frac{-2}{3}\right)}^{2}}$   However, this does not prove that I was working with a unit vector, as the answer did not evaluate to one. How can I find the unit vector of a three-dimensional vector?  Thank you for your time. Computing: $\int_0^1 \sqrt[3]{x\log{\frac{1}x}} \, \mathrm dx$ the slash (/) after a directory name on shell commands I have a little question here.  If I have two files, say filea and fileb, mv filea fileb would   delete fileb rename filea to fileb   Then if I have two directories, say dira and dirb, mv dira dirb would   move dira into dirb (it will become dirb/dira)   Noting that in both cases there are no notice or message, then this is pretty inconsistent to me. I think mv dira dirb should just overwrite dirb with the contents of dira (or merge the two directories under a directory named dirb).  I remember reading somewhere that a directory name with a slash (like dira/) is treated like a directory, and name with no slash (like dira) is treated like a file (to certain extents, of course). Anyway now I want to make the shell (zsh and possibly bash) respect my notation of a directory by using a slash. Is there a terminal option which enable me to enforce that?  To clarify, here is my desired behaviour:   mv dira dirb results in dirb being overwritten with the contents of dira mv dira dirb/ results in dira being moved into dirb (in dirb/dira)   Has anyone thought the same way as me? Or am I just weird? Is it ever bad to use \left and \right? For mathematics, is it ever disadvantageous to use \left(  and \right)  in equations?  I can't see any way that doing this would hinder the typesetting, so why isn't () just converted into \left( \right) automatically? This would save a lot of typing.  Cheers! New Graphics Card Preventing Boot Up I have defined my own language whose syntax is very close to the one of Pascal. I would like to type the following program for instance. Many people use the packages algorithmicx or algorithm2e to print programs, but it seems that we have to use their specific keywords of its syntax like procedure, end while.  I just want to indent spaces when needed, and bold some words when I want (sorry that I could not bold letters in the following figure). Do I have to use  texttt for each line? Also, with verbatim, I could not bold words...  Also, as the program is not large, I would need to put it on the left side of the page, and leave space for some explanasion text on its right hand side. So I  guss I need to get them all together, and use multicols.  Could anyone help?  program test                                      some text here var   i : integer;                                    ...    b : boolean; begin    i := 1;                                        ...    b := true;    while i &lt; 15 do       i := i  + 1;       b := not b                                  some text here    od end   Edit1: Following @Werner's tabbing solution, I have made the code a minipage:  \begin{minipage}[t]{0.48\linewidth}% \begin{tabbing} Werner's solution \end{tabbing} \end{minipage}\hfill \begin{minipage}[t]{0.48\linewidth} a paragraph \end{minipage}   Actually as the code shows, I want the texts to be another separated minipage on the right hand side of the code. I have then 2 questions:   is it reasonable to make 0.48\linewidth instead of 0.5\linewidth? 0.48\linewidth is a conventional choice? is it possible to make a frame around the code, and use \caption and \label to make it a reference (I prefer figures)? Moderncv adding date of birth to personal information How does Ubuntu flavor iso differ from a desktop package? TL;DR: how does an Ubuntu flavor iso installation ( for example Lubuntu ) differ from installing a desktop package via apt-get ? (for instance sudo apt-get install lubuntu-desktop)  Context for the question:   Some time ago I answered a question on AskUbuntu , where I tested in virtual machine removing unity-desktop and installing ubuntu-gnome-desktop. That makes the boot logo ( plymouth ) change, desktop changes, different packages get installed (gnome-network-manager instead of network-manager , if I am not mistaken). It appeared that in effect I've switched to different Ubuntu flavor, even though I started out with the standard Ubuntu system. Hence the question: what differentiates the pre-made Ubuntu flavor iso from installing a package ? Is it all the same base underneath the hood or does installation from iso have specific configurations ? If it's possible to install a flavor via package manager, why then separate flavor iso's exist ? (obvious answer is user convenience, but I think there has to exist other reasons. Canonical is a business , and it makes not a lot of sense for a business to provide additional flavor iso , if a sysadmin or end-user can get the same thing via package manager by themselves).