I am using Ubuntu 14.04 and 12.04 with the latest updates behind a proxy server at my school. I had no problem a few months ago. However, over the past two months when I try to add a repository with add-apt-repository there is no key retrieved. I can then use sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys KEY with success, but this is annoying. I have created scripts that add PPAs, install software, and more that are now failing because of this issue.   Should I be filing a bug report? If so, could someone please direct me to where to file.   Here is what my terminal output looks like when trying to add the PPA for my-weather-indicator:   $ sudo add-apt-repository ppa:atareao/atareao  Applications from atareao  More info: https://launchpad.net/~atareao/+archive/ubuntu/atareao Press [ENTER] to continue or ctrl-c to cancel adding it  gpg: keyring `/tmp/tmp16ytp9px/secring.gpg' created gpg: keyring `/tmp/tmp16ytp9px/pubring.gpg' created gpg: requesting key 36FD5529 from hkp server keyserver.ubuntu.com gpgkeys: key A3D8A366869FE2DC5FFD79C36A9653F936FD5529 can't be retrieved gpg: no valid OpenPGP data found. gpg: Total number processed: 0  $ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 36FD5529 Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --homedir /tmp/tmp.fla11h2USs --no-auto-check-trustdb --trust-model always --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyring /etc/apt/trusted.gpg.d/steam.gpg --keyserver keyserver.ubuntu.com --recv-keys 36FD5529 gpg: requesting key 36FD5529 from hkp server keyserver.ubuntu.com gpg: key 36FD5529: public key "Launchpad PPA for atareao" imported gpg: Total number processed: 1 gpg:               imported: 1  (RSA: 1)   Update: I was able to get it working with the -E parameter for sudo, so the command that works is sudo -E add-apt-repository ppa:atareao/atareao. However, I don't understand why things worked without that before and now it does not. Also, this does not seem to explain why other commands with sudo work without the -E parameter. This solution comes from Ubuntu 10.10.
I'm trying to follow the  (on my Ubuntu 10.04 VM).  The first step is:  sudo add-apt-repository ppa:linaro-maintainers/toolchain   But when I run that I get:  Error reading https://launchpad.net/api/1.0/~linaro-maintainers/+archive/toolchain: &lt;urlopen error [Errno 110] Connection timed out&gt;   I'm guessing the problem is with my configuration for my employer's proxy server, particularly for HTTPS.  When I opened  in Firefox, I got "The connection has timed out".  I then went into Firefox Preferences -> Advanced -> Network -> Settings... and set HTTP Proxy to "gateway" and Port to 8080, and checked "Use this proxy server for all protocols".  Then the page loaded.  This supports my theory.  I've tried setting the http_proxy and https_proxy environment variables (both lower and upper case):  $ set | grep -i proxy HTTPS_PROXY=https://gateway:8080 HTTP_PROXY=http://gateway:8080 http_proxy=http://gateway:8080 https_proxy=https://gateway:8080   I also tried changing them to:  $ set | grep -i proxy HTTPS_PROXY=gateway:8080 HTTP_PROXY=gateway:8080 http_proxy=gateway:8080 https_proxy=gateway:8080   And I tried adding this second line to /etc/apt/apt.conf:  Acquire::http::proxy "http://gateway:8080/"; Acquire::https::proxy "https://gateway:8080/";   But I continue to get the same error.  How do I troubleshoot this?  Update: I followed the instructions in the  to  and got further:  $ sudo add-apt-repository ppa:linaro-maintainers/toolchain Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /etc/apt/secring.gpg --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv 1DD749B890A6F66D050D985CF1FCBACA7BE1F97B gpg: requesting key 7BE1F97B from hkp server keyserver.ubuntu.com gpgkeys: HTTP fetch error 7: couldn't connect to host gpg: no valid OpenPGP data found. gpg: Total number processed: 0   I wonder if the "HTTP fetch error" means I also need to add "Defaults env_keep = http_proxy" to /etc/sudoers...  Update #2: I added:  Defaults env_keep="http_proxy" Defaults env_keep="https_proxy"   ...as in , but I still get the same "gpgkeys: HTTP fetch error 7: couldn't connect to host" error.  And this is curious:  $ sudo env | grep proxy https_proxy=https://gateway:8080   ...because http_proxy isn't there.  Any advice is appreciated.  Update #3: Since the host of my VM is a laptop, I took it home and tried there (with no proxies):  $ sudo add-apt-repository ppa:linaro-maintainers/toolchain Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /etc/apt/secring.gpg --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv 1DD749B890A6F66D050D985CF1FCBACA7BE1F97B gpg: requesting key 7BE1F97B from hkp server keyserver.ubuntu.com gpg: key 7BE1F97B: public key "Launchpad Linaro Overlay PPA" imported gpg: Total number processed: 1 gpg:               imported: 1  (RSA: 1)   It worked.  So problem is related to proxy configuration.  But I suppose I have a workaround.
My MATLAB launcher doesn't work I've installed MATLAB R2011a on Ubuntu 11.10 today following . I've also followed the steps to create the launcher. It appeared, but when I click on it nothing happens. Does anyone knows what can I do to fix it? Additional info I can run it perfectly through terminal. My only problem is getting the launcher to work. To create the launcher I used :   Get an icon:  sudo wget http://upload.wikimedia.org/wikipedia/commons/2/21/Matlab_Logo.png -O /usr/share/icons/matlab.png   Get the launcher file:  sudo wget 'https://help.ubuntu.com/community/MATLAB?action=AttachFile&amp;do=get&amp;target=matlab-r2011a.desktop' -O /usr/share/applications/matlab.desktop Create a table with LaTeX I'm shooting with a Nikon 810, and my night shots often have a strong moire when I export them from Lightroom at 640x640 (optimized for Instagram).   This photo was shot at f2.8, ISO 4000, 15 seconds with a Nikkor 17-35mm. Does anyone know why this is happening?? Notify close voters when a closed question gets edited As mentioned in , a question closed because it was not well-phrased is currently very unlikely to be reopened after an edit clarifying the issues. Those who voted to close should at least be asked to reconsider and reopen the question after such an edit. Difference between Unity and GNOME I often come across the terms Unity and GNOME while reading about Ubuntu. I understand that Unity is the default desktop environment for Ubuntu. What is GNOME and how is it related to/different from Unity? First axiom of sheaves: in noetherian topological spaces the direct limit presheaf is a sheaf. Let $G$ be a finite group. For each positive integer $m$, if $x^{m}=e$ has at most $m$ solutions in $G$, $G$ is cyclic.   What I have thought is that $n=\sum_{d\mid n}\phi(d)$ can be used to solve this and showing that $|G|$ order element in $G$ exists is enough. Could a ship warp into Borg cube and destroy it? During the Wolf-359 incident, 39 starships were destroyed, and 11,000 people were killed or assimilated.  Why didn’t one of the smaller ships warp into that one Borg cube? Doesn’t warping into it destroy anything?  Even if it just warps through without touching, one could program the navicom to self destruct while the ship is in the middle of Borg cube. $\DeclareMathOperator{\tr}{tr}$Let's consider a $n \times n$ matrix and the sequence of traces $\tr(A)=\tr(A^{2})= \ldots = \tr(A^{n})=0$. How to prove that $A$ is a nilpotent matrix (a matrix so that $A^{k} \times u = 0$ for all $u \in V$ and for some $k$)?  Maybe it would be reasonable to consider $A$'s Jordan form (we assume that the action occurs over an algebraically closed field, such as $\mathbb{C}$). For example, suppose that we have found it and $A'$ consists of $m$ blocks of sizes $r_{1}, \ldots r_{m}$ ($r_{1}+r_{2}+\ldots+r_{m}=m, r_{i} \in \mathbb{Z}_{+}$) with $\alpha_{1}, \ldots \alpha_{m}$ as corresponding eigenvalues to each of the blocks. Then, according to the problem will get the system  $$\begin{align} r_{1}\alpha_{1}+&amp;\ldots+r_{m}\alpha_{m}=0 \\ r_{1}{\alpha_{1}}^{2}+&amp;\ldots+r_{m} {\alpha_{m}} ^{2}=0\\ &amp;\ ~\,\vdots \\ r_{1}{\alpha_{1}}^{n}+&amp;\ldots +r_{m}{\alpha_{m}}^{n}=0  \end{align}$$  But the system's analysis over $\mathbb{C}$ seems to be too much complicated.  Actually, the problem must have more or less simple solution.  Any piece of advice would be much appreciated. $X$,$Y$,$Z$ mutually independent implies $X+Y$ independent of $Z$ Supposing $X$, $Y$ and $Z$ and mutually independent real random variables, how can we prove that $X+Y$ and $Z$ are independent from the definition? If not from the definition, using $\sigma$-algebras?  I know that if $X$ and $Y$ are not independent this doesn't work so I know I have to make use of their independence in my proof but I can't figure out how. And it means that if I write the following, I'm making a mistake, and I can't find it:  $$\mathbb{P}(X+Y \leq k,Z \leq l)=\int_{\mathbb{R}} \mathbb{P}(X=x,Y \leq k-x, Z \leq l) dx=\int_{\mathbb{R}} \mathbb{P}(X=x,Y \leq k-x) \mathbb{P}(Z \leq l) dx = \mathbb{P}(Z \leq l)\int_{\mathbb{R}} \mathbb{P}(X=x,Y \leq k-x)dx= \mathbb{P}(Z \leq l) \mathbb{P}(X+Y \leq k) $$  PS: I have seen the proof here but it much more advanced stuff, kind of a sledgehammer... I have been trying for a long time to change Blender's icon, but no matter what I do, I am not allowed to edit anything in /snap/blender-tpaw/3/.  Here's what I tried:   Editing the files from nautilus without sudo. Editing the files from nautilus with sudo (sudo nautilus in terminal ). Using terminal commands such as cp or rm without sudo. Using terminal commands with sudo (such as sudo cp &lt;source&gt; /snap/blender-tpaw/3/ or sudo rm /snap/blender-tpaw/3/&lt;filename.ext&gt;) Doing everything above in a root terminal (using sudo -i)   In every case I get the following error:  cannot remove/copy '/snap/blender-tpaw/3/filename.ext': Read-only file system   where filename is the file and .ext is its extension.  This also applies to other snaps' files, not only Blender.  Am I doing something wrong here? Or is it just impossible to change those files? Although I don't think it is impossible because everything here from Ubuntu to Blender is open-source, so they have no reason to block us from modifying those files.  EDIT:  I used Main Menu (alacarte) to change the icon, but I still want to know why I cannot modify any snap file. Proof that a sum of Bernoulli rvs has Binomial distribution How do I list all of the files in a commit? I am looking for a simple Git command that provides a nicely formatted list of all files that were part of the commit given by a hash (SHA-1), with no extraneous information. I have tried: git show a303aa90779efdd2f6b9d90693e2cbbbe4613c1d  Although it lists the files, it also includes unwanted diff information for each. Is there another git command that will provide just the list I want, so that I can avoid parsing it from the git show output? How do you photograph rain? What are recommended settings for my Nikon Coolpix P1 to best portray rain?  Here's what I got. No retouching was applied.   The picture I took when the rain was heavy with the automatic settings:  The picture I took with the "Sports" program; by then, however, the rain was not as hard. Ugh, ugly gray strip at the bottom, that was the flat surface I put my camera on to get a stable picture.   My main problem is that the actual rain and hailstorm is very hard to see in the picture. The overall effect is, instead, of fog.    Follow-up from the thread, courtesy of more rain, now with less hailstorm and more thunder.  The feedback amounted to flash and faster shutter. I took a few photos and I'm having some trouble to reconstruct what I did to get each result. Two representative results:   Fast shutter, with some guest starring:I'm talking about that horrible building obviously. Faster shutter and flash:Kinda difficult to say those pictures were taken sixty seconds of each other. :)   I'm not sure, however, that either of this is really an improvement of the original results. How to stop "Monkey Test" and "Time Service" apps When I long-press the "home" button to close all apps, there is an app named "time service" with android symbol and another named "monkey test" that are always open.   How to stop this? Change all file type associations from one program to another Looking for Anime with a prince faking being mentally handicapped hiding a giant mech suit wreaking havoc This is all I can remember.  There are four worlds whose people and technology were all swapped so humans ended up with high tech mech suits that they used to kill each other. There was a supposedly handicapped prince who faked being mentally handicapped and had a giant mech suit hidden underground that he eventually used to wreak havoc on earth.  The protagonist also had a suit and he saved the day. He was in love with a girl who was from another world and when he saved the day, all the people and technology from the different worlds were sent back to their original one causing the girl to leave him. She had colored hair and the final scene was her waking up somewhere with some children commenting on her hair.  There may or may not have been a reference to the protagonists scars in the shape of the constellation of orion on his body.  Any ideas? I've searched the internet for two years trying to find it. I would like to know what would be the best way to do unit testing of a servlet.   Testing internal methods is not a problem as long as they don't refer to the servlet context, but what about testing the doGet/doPost methods as well as the internal method that refer to the context or make use of session parameters?  Is there a way to do this simply using classical tools such as JUnit, or preferrably TestNG? Did I need to embed a tomcat server or something like that? How to have a figure with caption in multicol environment? I am having the following problem with adding a figure inside the multicol environment:  \documentclass[10pt, twoside]{book} \usepackage{graphicx} \usepackage{subfig}  \begin{document}   \begin{multicols}{2}  a test file for picture inclusion along with the captions and labeling \begin{figure}  \centering  \includegraphics[width=5cma]{Cauchy_sequence_illustration-png}\\  \caption{Lets see}\label{pinki} \end{figure} \end{multicols}  \begin{figure}  \centering   \includegraphics[width=5cm]{Cauchy_sequence_illustration-png}\\  \caption{Lets see}\label{pinki} \end{figure}    \end{document}    After this while I am pressing Ctrl + Shift + X (usually I compile like this in DVI format and then clicking "dvi--->pdf" I convert it into PDF document.) the picture in multicol environment is not shown in YAP Viewer but the second one (which is outside of multicol environment) is shown along with the caption.  Kindly help me how to handle this problem. Please note that I am using the figure in .ps format. And I am not allowed to use any other format according to the instruction. Proving a simple graph is a connected graph Does any proof exist that a simple graph with $n$ vertices such that the least vertex degree is $\geq \frac{n-1}{2}$ is a connected graph? (i.e. does such a proof have a name?)