I removed some required permissions on my C drive by mistake and now web browsers and Outlook are not working. How can I restore these permissions (I don't know how many and which one has been removed).
I have an external hard drive and I did something which I shouldn't have done, and I am annoyed that many files are prompting me about Administrator permissions to move a folder.  They are regular files.  How do I reset all the permission on the external hard drive?
Can't execute terminal commands: "the command 'sudo' is available in '/usr/bin/sudo'" I need a step-by-step, simple and easy way to configure swappiness. How do I give text or an image a transparent background using CSS? I need to find algorithm that can calculate centroid A (aka gravity center, geometric center, center of mass) from the figure where circles T1,T2,T3,T4,T5,..,Tn intersect AND length of line R from centroid to farthest corner of mentioned figure   Following information is given:   T1   Latitude    =   56.999883   Longitude   =   24.144473   Radius  =   943 T2   Latitude    =   57.005352   Longitude   =   24.151168   Radius  =   857 T3   Latitude    =   57.005352   Longitude   =   24.163356   Radius  =   714 T4   Latitude    =   56.999042   Longitude   =   24.168506   Radius  =   714 T5   Latitude    =   56.994226   Longitude   =   24.15709    Radius  =   771   Result should look like this:  A Latitude = XX.XXXXXXX    Longitude = XX.XXXXXXX  Radius = XX    As you probably already figured out, I am working on software that can find device location by closest Wifi Access Points or Mobile Base stations, as number of access points or base stations might change, I need an algorithm that can adapt to uncertain amount of points.  There are some similar questions  and , but none of them exactly answers to my question. What do I need to install LED strip lighting? I've been looking to install LED strips, either RGB or white for lighting and ambiance. It wouldn't be the main lighting of the room, so no necessity for high power LEDs.  The perimeter of the room is a little less than 25 meters. Looking around in online stores, I saw that the reels come in maximum lengths of 5 meters, so I would need five of those.  What I'm not sure is how to connect the strips together.  I was looking at , or  with .  If I choose the white LEDs, what power supply, controller, and connector would you recommend to be able to daisy chain the strips?  If I choose the RGB LEDs, what kind of data repeaters would work to be able to control all the strips at once? Just ran the latest batch of updates on 20.04 (Xubuntu), and now I'm getting a GRUB error: symbol 'grub_calloc' not found  I'm dropped into the 'grub rescue' shell, but have no idea what to do there that might be useful. To me, 'symbol not found' implies some sort of build error with the grub package, but I don't really know how grub works. I noticed that this update also included 'firmware', not sure if that could be related. Is my best bet just to boot from a live CD and see if I can roll back the update to grub somehow? Edited to add: OK, thanks to lots of people ! Here's what I think I now understand.  On 'non-UEFI' systems, grub is installed in two separate parts. The first, most basic, part is the part that is started on bootup. But for most of it's functionality, it needs the second part. These parts must be aligned - neither part must require any functionality from the other part which is not actually there. The visible, run-time problem occurs when these parts are not aligned, and the function grub_calloc is not supplied. It's not 100% clear to me if grub_calloc belongs in the second, larger part or the first. I would have expected the second, but the grub build system is a work of considerable art, so I don't know :).  The root cause of the problem is that the grub update has not ensured that both parts have been updated. Ideally, failure to do this should cause grub installation to fail, and the system should be reverted to a safe state. This does not happen. This is actually still a bit of a mystery to me. All that the update needs to do by default is put each part where the current parts are, because obviously that worked. If the install locations/drives are configuration - driven, and one of these locations can't be reached, then somehow a mismatch has arisen between that configuration data and reality. This might not show up as a problem as long as no new dependency was introduced between the parts.   All flavours of solution involve reinstalling grub to ensure that the two parts are aligned. It's not actually necessary to go back to the previous version ( although that will work ), because it's not the grub runtime per se that is broken. There are numerous ways to achieve this, depending on your environment, but running the Boot-repair live disk worked for me. It may be useful, for the purpose of avoiding such a misalignment in future, to ensure that the grub installer on your system is configured to install to the correct devices. This update resolves some important bugs (). If you have reverted grub to resolve this problem, be aware that you are exposed to these issues. Write18: capturing shell (script) output as command/variable? Let's say I compile the following file with pdflatex -shell-escape test.tex:   \documentclass{minimal}  \begin{document}  File listing is:  \immediate\write18{ls /usr}  \end{document}   This will send the output of the command ls /usr to report/log of pdflatex (primarily to stdout).   There are then two cases I'd like to utilize:    The output of ls /usr being included directly in the document (LaTeX stream). The output of ls /usr becoming the contents of a \newcommand (by this I mean, that I'd like the script to be executed when the \newcommand is executed first - and upon subsequent calls to the new command, the shell code should not be executed anew).    I have read through , but I'm not sure if this "pipe input" can be applied to \newcommand.   I have also read through  - and it seems that Tex' file I/O should be used; but I'm quite disliking the fact that I'd still have to redirect the script output (actually, in this case, the ls /usr output) to a file, and then read it in, to have it as contents of a command.   So, is there an easier way to achieve what I'd want (hopefully, illustrated through an example based on the above code)?     EDIT: Ehm, I should have asked one more question earlier :) I'll try with an edit here, although it will probably get missed .. :)   I originally asked for a \newcommand that will execute shell code only upon its definition (i.e., in a sense it is "cached"); and the answer from @egreg does exactly that. But then - would it be possible to have a different \newcommand definition, such that each time this newcommand is called, the shell command is executed anew? I.e. executing something like \@@input|"cat tempfile" (which cannot be executed as such), where tempfile changes between calls? Difference between information and knowledge? As far as I think projection of data unto subject mind is information for the subject whereas indentation or impressions accumulated owing to projection of data unto subject mind is knowledge for the subject. I want to know am I right? Or can someone provide a more rigorous answer! Proving a three variables inequality What happens to the Windows 7 key when upgrading to Windows 8? Microsoft is offering "Microsoft Windows 8 Professional Upgrade" at a discounted price compared to the OEM version. However it states:     If you currently have a personal computer running Windows 7, Windows XP or Windows Vista then you can upgrade to Windows 8 Pro (Professional).   My question is what happens to the Windows 7 key that I use to upgrade? Will it become the Windows 8 key or will it generate a new Windows 8 key?  Basically if I upgrade using my Windows 7 key from my laptop for my desktop will I be able to continue using the laptop on Windows 7 while concurrently using Windows 8 upgrade on my Desktop? He who must not be named? (aka Anyone can ping everyone in chat) For some or other reason, typing @ᔕᖺᘎᕊ in a chat room pings everyone who's been in that chat room for the last 7 days...    Seems to work in all chat rooms (I only tested 2 as I don't want to upset too many people...)  How should we proceed? Find a tangent to two quadratic bezier curves I have two quadratic bezier curves and I want to find whether they have a common tangent, and if so where it is.  If the first bezier is defined by points $(x_1, y_1)$, $(x_2, y_2)$, $(x_3, y_3)$, then the points on the curve have coordinates:  $x = (x_1 - 2x_2 + x_3)t^2 + (2x_2 - 2x_1)t + x_1 \\ y = (y_1 - 2y_2 + y_3)t^2 + (2y_2 - 2y_1)t + y_1$  Or to simplify things:  $x = A_xt^2 + B_xt + C_x \\ y = A_yt^2 + B_yt + C_y$  Likewise, I can get an equation for the second bezier:  $x = D_xs^2 + E_xs + F_x \\ y = D_ys^2 + E_ys + F_y$  The gradient of the tangent, $m$, to the first curve at $t$ is $\dfrac{2A_yt + B_y}{2A_xt + B_x}$,  which must be equal to the tangent to the second curve at $s$, $\dfrac{2D_ys + E_y}{2D_xs + E_x}$.  So $m = \dfrac{2A_yt + B_y}{2A_xt + B_x} = \dfrac{2D_ys + E_y}{2D_xs + E_x}$  Which I rearranged to get:  $t = \dfrac{2(B_yD_x - D_yB_x)s + B_yE_x - B_xE_y}{4(A_xD_y - A_yD_x)s + 2(A_xE_y - A_yE_x)}$  The gradient of the tangent is also equal to the difference in the y-coordinates over the difference in x-coordinates:  $m = \dfrac{D_ys^2 + E_ys + F_y - (A_yt^2 + B_yt + C_y)}{D_xs^2 + E_xs + F_x - (A_xt^2 + B_xt + C_x)}$  But that's as far as I got. The algebra looks too messy from here. Can anyone solve this, or is there a better approach? Is $(x^2+y^2+z^2) \ \sin \frac{1}{\sqrt{x^2+y^2+z^2}}$ Differentiable in $(0,0,0)$? Unbounded continuous function on non-compact metric space Suppose $(S,d)$ is a non-compact metric space. Is it possible to construct an unbounded continuous function from $S$ to $\mathbb{R}$? If it is possible, please show the construction method :)  Here's my attempt to solve this problem: Because $S$ is not compact, we can find a neighborhood assignment function $N(x)$ so that a finite cover is not possible. Then each time we can find an uncovered point from the union of neighborhoods before, and change the function by $f(x):=max\{f(x),\text{a function which equals to the indice of this point at that point and gradually vanishes at further points from the selected point}\}$. However I'm concerned that while this function is unbounded, there may be some invalid points for this function (goes to infinity)...  EDIT: As I found out there is a duplicate question, however the elementary solution is not presented in that question, so I still wish to know about this problem. :) I changed my hostname, why is my bash PS1 prompt unchanged? Bounding lines around tax nodes I am trying to draw lines around a number of nodes. I very much like the definition of \convexpath definition given , but it is not working well on my setup (MacTex 2014 with all available updates).   I tried to compile , but what I get is the following, which is clearly not what I should be getting. Any ideas would be much appreciated. The easiest way to explain this question is with a thought experiment:  Consider God, the ultimate of everything, who is wholly omnipotent (all-powerful) and omniscient (all-knowing). Let's just say, hypothetically, that he wanted  (this is a totally random example I just happened to be reading about; I could have just as easily said He wanted Bob to score a free-throw in basketball 3 times in a row tomorrow, or Sally to knit a blue sweater on Sunday, November 4th, 2012).  But anyways, one way He could do this (get X group of people to save a man from a burning car) is: At the beginning of time, God could instantly plan out the future and set in motion a massive chain of events, from the creation of light and stars, the creation of Earth and the creatures, mankind, then civilization with all the conflicts and progress and glory that comes with it, such that one day, a few people would come from out of nowhere—complete strangers to each other—and save this man (also a stranger) from under a burning car. God need not intervene at all this whole time, He merely "ignited" the chain of events from day 1 and watched it unfold exactly as He planned. Let's call this Universe A.  He could also, being all-powerful, just freeze time for a bit and skip a few steps, creating the world and universe instantly, with all the civilizations and animals and things in place, putting all the strangers there together next to a car which is already on fire and the man trapped under it. Then press play, and presto, you have the exact same scenario, without billions of years of buildup. Let's refer to this as Universe B.  God is obviously capable of doing both. My question thus is whether there is an  (really any difference at all) between Universe A and Universe B. Personally, I don't think this kind of power is outside of God's capability; he should, after all, have no problem with creating identical universes which match up exactly once they reach "biker under the car" moment where He unfroze time in Universe B. At that moment, Universe A and Universe B are exactly the same, right? Or is there somethinge special about Universe A, with all it's buildup, that separates it intrinsically from Universe B? In other words, is it outside of God's ability to make them exactly equivalent? The blackboard bold font in the AMSFonts package only has capital letters.  I sometimes wish to use a blackboard bold "1", for which I can use \usepackage{bbold}. But this changes the entire blackboard bold font, and I like the original AMSFonts versions of the capital letters better.  Is there a simple way for me to get \mathbb{1} from one package and the blackboard bold capitals from another? Prove $(a+b)^\frac{1}{n} \le a^\frac{1}{n} + b^\frac{1}{n}$ Prove: $$ (a+b)^\frac{1}{n} \le a^\frac{1}{n} + b^\frac{1}{n}, \qquad \forall n \in \mathbb{N} $$ I have have tried using the triangle inequlity $ |a + b| \le |a| + |b| $,  without any success. Fast way of copying IMAP to IMAP on CentOS I'm trying to copy of IMAP emails from one server to my new server but after Googling for hours and trying several tools, nothing is working. Is there a tool that actually works?  I am copying hundreds of thousands of emails so using a email client is out of the question, I tried it, and at the rate of a email per 2 seconds, it would take a few weeks or months!  www.linux-france.org/prj/imapsync/ is commonly mentioned, however, the tool is no longer available.  I tried www.athensfbc.com/imap_tools/ which just hangs and does nothing.  Any migration tools that work?