E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied) E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), are you root?   I've done everything i could and i still get this can anyone help?
I have just booted my clean Ubuntu 18.04 LTS VM and tried to install some application with sudo apt install.  But got error message:     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?   What process created the /var/lib/dpkg/lock-frontend file in Ubuntu? How to gently stop it and take manual control on APT?
The new top bar is out on meta. Consider it a beta EDIT Dec 4 -  We're doing it live! Please post bugs or concerns as questions tagged [top-bar]  We have rolled out our 95% completed top bar for feedback.  Note:   We are still adding a few final features, so if you have a request for a feature that is not there you might hold off on that for a day or two Yes, the bar is black1. Also give that a day or two to sink in.   I also want to specifically address the meta/main/chat links.  I'm very aware that many of you like having the links at the top of the page and that this new version is different.  The thought process behind moving these links is that the "site switcher" should be an automatic place to go when you are on a site and want to go to another one. If you haven't already developed the muscle memory for these links, getting between them required a bit of a cognitive load: You must first decide that you want to switch sites and then you have to decide which area to go to to switch.  Also, we find that less familiar users aren't entirely clear what a standalone link that says "main" or "meta" actually does... Not to mention that it hurts my UX sensibilities that we are dynamically changing links in an element that should be fixed.  It is true that we have added a click in the process, but we have also removed a lot of clicks for other common actions that are much more frequent than switching between main and meta.  All I ask is that you give it a few days and see if the new "switch sites at the top left" paradigm grows on you.  What do you think?  1.  points out that technically it's not quite black. So I have been tasked to make an array without duplicated values from another existing array. So I did it, but I want to know is there some other better way to do that. Example input/output: Input: 10, 15, 10, 5, 1, 3 Output: 10, 15, 5, 1, 3 So here is my code. #include &lt;stdio.h&gt;  int main(void) {   const int MAX_ARRAY_SIZE = 5;    int m[MAX_ARRAY_SIZE], p[MAX_ARRAY_SIZE];     for(int i = 0; i &lt; MAX_ARRAY_SIZE; i++) {     printf(&quot;Enter number: &quot;);     scanf(&quot;%d&quot;,&amp;m[i]);   }   int k = 0;   int dup = 0;   for(int i =0; i &lt; MAX_ARRAY_SIZE; i++) {     for(int j = i +1; j &lt;MAX_ARRAY_SIZE; j++) {         if(m[i] == m[j]) {             dup = 1;         }     }     if(dup != 1) {       p[k++] = m[i];     }     dup = 0;   }    printf(&quot;The new array without repeated values\n&quot;);   for(int i = 0; i &lt; k; i++) {     printf(&quot;%d\n&quot;,p[i]);   }    return 0; }  I'm not sure if this is the right and simple way I do that. I want some suggestions. Thanks in advance. :) Find the inverse of a Trig Matrix I don't have a clue of what's going on. We haven't learn this in class so I need all the help possible. The more detailed of an explanation, the better. Thanks in advance. The only info I have is that this matrix is Orthogonal. Which means I know the answer, just don't know how to get it.  \begin{bmatrix}        \cos\theta &amp; -\sin\theta \\        \sin\theta &amp; \cos\theta       \end{bmatrix} How to change file extension at runtime in Java I was looking at  on why  and emission lines don't cancel out:      An experiment shining light on the material and looking at the   reflected spectrum will see absorption lines at those frequencies,   because the relaxation of the excited electrons will emit back   radiation all around randomly, whereas the reflected spectrum is at a   specific angle.   However it is not totally convincing to me. The photons that get emitted towards the center of the Sun (by the electrons in higher energy states that absorbed a photon earlier) would get absorbed again when they hit a different electron (and then re-emitted) and would eventually make it out. So why don't absorption and emission lines cancel out in our Sun? Several companies are commercializing tests for telomere length such as this one . I understand the basic mechanism for why telomeres shorten during DNA replication, but how good is the evidence that telomere length is a reliable indicator of healthspan/lifespan? using apt-cache search I am learning how to use apt. When I do an apt-cache search git to see all packages matching git, I see a bunch of packages whose descriptions have nothing to do with git. Why is this so and how can I fix it? (Ubuntu 12.04.2 LTS).  Also, why is the search functionality found in a command that has "cache" in its name? What does search functionality have to do with caches?  Thanks. Should questions having lots of downvotes be downvoted further? Is down-voting an already heavily down-voted/closed question kind of like kicking a dead horse? Is this bad practice? How can I access a JavaScript object which has spaces in the object's key? Assurance that ST_Envelope works with geography as expected Using PostGIS, I have a table of data with geographic points defined as last_known_coordinates GEOGRAPHY(POINT,4326). I want to find all of these within a geographic bounding box with given top left and bottom right geographic coordinates, and be sure that the calculations are geographic, not geometric, e.g. that the results account for the curvature of the earth. The query I'm using contains the fragment: last_known_coordinates &amp;&amp; ST_MakeEnvelope(?, ?, ?, ?, 4326)::geography As you can tell I'm a bit new to this, and I know what I want, but not necessarily how to do it correctly. Other answers hint that this is correct, but I'd like to know for sure: Will this point data and SQL fragment take into account the curvature of the Earth in the bounding box? Command to perform a recursive chmod to make all .sh files within a directory executable? Integral Inequality $|f''(x)/f(x)|$ Let $f$ be a $C^2$ function in $[0,1]$ such that $f(0)=f(1)=0$ and $f(x)\neq 0\,\forall x\in(0,1).$ Prove that  $$\int_0^1 \left|\frac{f{''}(x)}{f(x)}\right|dx\ge4$$ I know that taking the derivative of position with respect to time defines what we call velocity, but I've never heard of physicist going in the opposite direction with position. Is there any application for the integral of position with respect to time?  Maybe with respect to something else? For $p,q$ prime and $p \neq q$ show that $C_p \times C_q \cong C_{pq}$ Here are my thoughts so far:    $C_p = \langle x \mid x^p =e\rangle$ $C_q = \langle y \mid y^q =e\rangle$ $C_p \times C_q$ has elements of the form $(x^a,y^b)$ There are $p$ possible values for $x^a$ and $q$ possible values for $y^b$. So there are $pq$ possible elements in $C_p \times C_q$. $C_{pq} = \langle z\mid z^{pq} = e\rangle$ and there are $pq$ elements in this group. For an isomorphism from $C_p \times C_q$ to $C_{pq}$ we send $(e,e)$ to $e$ to ensure that the identities are mapped to each other. However, I'm not sure how to define an isomorphism for the other elements. Introduction to proofs with a fair amount of hand-holding? Euclid Lemma proof reasoning This question is more concerned with understanding the reasoning behind mathematical proving rather than explaining this specific proof. I understand why this proof works.   This is the proof of Euclid Lemma from Wikipedia:      This   states that if $x$ and $y$ are relatively prime integers (i.e. they   share no common divisors other than 1) there exist integers $r$ and   $s$ such that      $rx+sy=1$. Let $a$ and $n$ be relatively prime, and assume that   $n|ab$. By Bézout's identity, there are $r$ and $s$ making      $rn+sa=1$. Multiply both sides by $b$:      $rnb+sab=b$. The first term on the left is divisible by $n$, and the   second term is divisible by $ab$, which by hypothesis is divisible by   $n$. Therefore their sum, $b$, is also divisible by $n$.   I am mostly concerned with this statement:      Multiply both sides by $b$:   My question is why this multiplication by $b$ happens. Is it because the person proving this observed that multiplying the equation by $b$ he would get a sum of two multiples of $n$? Or is there a mathematical rule by which we know that the next step is multiplying by $b$?  I am aware that this question might seem trivial to people here, but I just want to make sure. Force figure placement in text For a prime $p \equiv 1$ or $3$ (mod $8$), show that the equation $x^{2} + 2y^{2} = p$ has a solution. For a prime $p \equiv 1$ or $3$  (mod $8$), show that the equation $x^{2} + 2y^{2} = p$ has a solution.   I'd like to see an elementary proof. Can we re-request features that were declined a sufficient while ago? Is it possible to import comments into a chat room without the link appearing? Question: For an answer on a stack exchange site with say 8 comments, how can I / is it possible to import the comments into a chat room? Background: I was helping with a  and made several comments before I saw the link to auto-import comments into a chat room.  This was awesome by the way!! Note that the person who asked the question left a link to the chat room in a comment. I wanted to make a similar chat room  because I edited an answer which wasn't mine and added a paragraph.  I wanted to chat with the answer's author @JonHopkins to say, 'hey feel free to remove my edit -- just wanted to add my $0.02' -- especially as the stack exchange engines said not to add an additional answer.  HOWEVER, there was no link to auto-import the comments -- probably because I hadn't previously left one, but I'm not sure. So I ask here, Stack Exchange Gurus, could a static link be added to auto-import a series of comments into a chat session?