I wanted to copy many files in /var folder and it made me slow to use the console (because the owner is root) so I changed the owner of /var folder and all if its subfolder to my user.  After restarting my system, my system can't start and throw low graphic error and it said none of your devices can not be detected. So I go to terminal and try to install my graphic driver but while installing I got these error:  /usr/bin/mandb: can't chmod /var/cache/man/nl/CACHEDIR.TAG :operation not permitted   How should I solve this? I use sudo to install driver
I accidently ran  sudo chmod 755 -R /   instead of  sudo chmod 755 -R ./   I stopped it after few seconds, but now there is some problems such as  sudo: must be setuid root   How can I revert permissions back?
What are some grandiloquent, or simply better, ways of expressing "an idea/thought suddenly came to me", or "an idea/thought struck me", or "I was struck by an idea/thought"? How do I create tools with multiple properties? I'm trying to create an item that can break certain blocks, but also has a colored name in 1.13.2   Here's the command I'm using.  /give iAugust minecraft:shears{display:{Name:"[{\"text\":\"Arcane Shears\",\"color\":\"aqua\",\"italic\":false,\"bold\":false}]CanDestroy:[minecraft:iron_bars]"}}   But it only has a colored name, and it can't break specific blocks. How to open and convert CHM documents? I have some documents that are in a .chm format. I wondered if there is a file format that can be easier to navigate, supported and of equal file size in Ubuntu?  If there is, I would like to start converting all those books and probably using them with less hassle on all my Ubuntu PCs and my Android phone. Why more (and varying number of) logical reads with read ahead (prefetch)? After creating tpch database in my SQL Server, I tried below query:      set statistics io on     DBCC DROPCLEANBUFFERS;             select top 100 * from dbo.lineitem order by l_partkey;   The table lineitem has a non-clustered index on l_partkey. I issued the above queries for several times and found out that the logical reads vary each time:      Table 'lineitem'. Scan count 1, logical reads 1019, physical reads 4, read-ahead reads 1760, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.     Table 'lineitem'. Scan count 1, logical reads 1007, physical reads 4, read-ahead reads 1720, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.     Table 'lineitem'. Scan count 1, logical reads 1030, physical reads 4, read-ahead reads 1792, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.   From the post here: , I know it could be caused by read ahead behavior.  BUT exactly why read ahead could cause more logical reads? How does it change the SQL Server behavior? Like SQL Server may read more index page since it's in cache anyway?  Anyway, I disabled read ahead and issue the above query again. Now it reports the same amount of logical reads each time. BUT the logical reads is much smaller!!      Table 'lineitem'. Scan count 1, logical reads 404, physical reads 160, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.   So my question is, why the read ahead feature could cause many more and various logical reads count?  Out of curiosity, I tried another query without the "order by":      select top 100 * from dbo.lineitem   Here's the result without read ahead:      Table 'lineitem'. Scan count 1, logical reads 5, physical reads 3, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.   Here's the result with read ahead:      Table 'lineitem'. Scan count 1, logical reads 15, physical reads 2, read-ahead reads 3416, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.   The one with read ahead still has more logical reads. So, why? ID for Contact portion of Person Account Is it possible to get the ID of a Contact which is part of a Person Account?  I have a custom object which has a custom field referencing the Person Account, though it seems to be referencing the Contact directly. I have created a button which I am using to pass the ID into a Visualforce Page.  With the Insert Field drop-down on the create/edit button page I can put in {!Account.Id} or {!Contact.Id} but neither of these work. The Account ID is placed in the URL but is not the correct ID and the Contact ID is blank, which I assume is because the button is on a Person Account page and not a Contact Page. While drawing a simple 3D (fake 3D in fact) cube, I realized that the corners end up with unwanted extensions of the line. I understand this is related to the width of the lines themselves, but how can I remove them? An alternative solution of drawing the desired figure is also welcomed.  Example:  \documentclass{article} \usepackage{tikz}   \begin{document} \begin{tikzpicture}  \draw[draw=black,fill=gray!20] (0,0) --(4.8,0)-- (4.8,5)--(0, 5)--cycle; \draw[draw=black,fill=gray!20] (4.8,5) -- (4.9,4.8)--(4.9,-0.1)--(4.8,0)--cycle; \draw[draw=black,fill=gray!20] (0,0) -- (0.1,-0.1)--(4.9,-0.1)--(4.8,0)--cycle; \draw[dashed,draw=black] (4.8,5) -- (4.9,4.8)--(0.1,4.8)--(0.,5)--cycle; \draw[dashed,draw=black] (0.1,-0.1)--(0.1,4.8)--(0.,5)--(0,0)--cycle; \end{tikzpicture} \end{document} jQuery select and wrap textNode Call C++ library in C# I have a lot of libraries written in C++. I want to call these libraries from C#, however, I have met many problems. I want to know if there is a book or guideline to tell me how to do that. $ \tan 1^\circ \cdot \tan 2^\circ \cdot \tan 3^\circ \cdots \tan 89^\circ$ How can I find the following product using elementary trigonometry?     $$ \tan 1^\circ \cdot \tan 2^\circ \cdot \tan 3^\circ \cdots \tan 89^\circ.$$   I have tried using a substitution, but nothing has worked. I would like to change the caption in the List of Tables in a way it is different from the caption in the corresponding table. How can I do that? Does there exist a command to do that? Why is a different dll produced after a clean build, with no code changes? When I do a clean build my C# project, the produced dll is different then the previously built one (which I saved separately). No code changes were made, just clean and rebuild.   Diff shows some bytes in the DLL have changes -- few near the beginning and few near the end, but I can't figure out what these represent. Does anybody have insights on why this is happening and how to prevent it?   This is using Visual Studio 2005 / WinForms.  Update: Not using automatic version incrementing, or signing the assembly. If it's a timestamp of some sort, how to I prevent VS from writing it?   Update: After looking in Ildasm/diff, it seems like the following items are different:   Two bytes in PE header at the start of the file. &lt;PrivateImplementationDetails&gt;{guid} section  Cryptic part of the string table near the end (wonder why, I did not change the strings) Parts of assembly info at the end of file.   No idea how to eliminate any of these, if at all possible... I need to find node voltage at A. This seems like a trivial question, but when I set up the resistive voltage divider equations they are not equal to each other. Am I doing something wrong?  My equations are \$V_A = V_1(R3/(R3+R1)) = V_2(R3/(R3+R2))\$      I tried solving this problem with an LTSpice simulation and with the superposition method, but my answers did not match (although very close to each other). Is this because the simulator uses an approximation? Can someone compare results? Bind an element to two sources I currently have two text boxes which accept any number. I have a text block that takes the two numbers entered and calculates the average.   I was wondering if there was a way I could bind this text block to both text boxes and utilize a custom converter to calculate the average? I currently am catching the text changed events on both text boxes and calculating the average that way, but I am under the assumption data binding would be more efficient and easier. How can I change GNOME Shell theme? I've installed the GNOME Shell in Ubuntu 12.04 and I want to change the "Shell Theme", But it doesn't allow me to do that.  The alert says something like: "The GNOME-Shell extension is not activated", and I want to install it with the console, But it returns me an error.  How can I solve this problem? Array of Matrices in MATLAB I am looking for a way to store a large variable number of matrixes in an array in MATLAB.  Are there any ways to achieve this?  Example:  for i: 1:unknown   myArray(i) = zeros(500,800); end   Where unknown is the varied length of the array, I can revise with additional info if needed.  Update: Performance is the main reason I am trying to accomplish this.  I had it before where it would grab the data as a single matrix, show it in real time and then proceed to process the next set of data.  I attempted it using multidimensional arrays as suggested below by Rocco, however my data is so large that I ran out of Memory, I might have to look into another alternative for my case.  Will update as I attempt other suggestions.  Update 2:  Thank you all for suggestions, however I should have specified beforehand, precision AND speed are both an integral factor here, I may have to look into going back to my original method before trying 3-d arrays and re-evaluate the method for importing the data. How can I install Celestia on Ubuntu 18.04.1? Like the title said, I want to install Celestia. I already downloaded the packages  and then, I tried all the things that I found on some posts (also, they're outdated, cause the last one is for Ubuntu 16.04) but nothing works.  How can I install it on Ubuntu 18.04.1? Installing a 16-bit Windows 95 game on 64-bit Windows 7 Home Premium When should \cdot be used to indicate multiplication? Is this purely personal style, or are the generally accepted guidelines? Clearly, when dealing with numbers either $2 \cdot 2$ or $2 \times 2$ is needed, but within formulae where an absence of an operator implies multiplication, when should a \cdot be used? I tend to use it only sparingly if it aids in grouping. (Of course, barring the cases where it's required, e.g. a dot product.) Any help would be appreciated.  If $n$ is a natural number $\ge 2$ how do I prove that any graph with $n$ vertices has at least two vertices of the same degree? How to iterate over arguments in a Bash script