I accidentally ran sudo chown -R root:root /usr/ on my ubuntu machine (while playing around with sd-card of my Raspberry Pi. I actually wanted to type sudo chown -R root:root usr/ without slash.)  Now I get this error: sudo: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set.  Is it possible to fix this?  EDIT: I had the wrong command in my post before. I forgot the root:root. Although all files in /usr are owned by root I get the error message.
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 issues should be considered when overriding equals and hashCode in Java? What issues / pitfalls must be considered when overriding equals and hashCode? How to restrict users on changing their wallpapers? I don't want my users to change the system wallpaper. How do I the lock the wallpaper down? Update  Users are changing wallpaper by right clicking the picture and choosing set as wallpaper. How to restrict this behaviour?  Is it possible to remove Backgrounds Tab from Appearance Preferences? If yes how? Ratios in Regression, aka Questions on Kronmal Recently, randomly browsing questions triggered a memory of on off-hand comment from one of my professors a few years back warning about the usage of ratios in regression models. So I started reading up on this, leading eventually to Kronmal 1993.  I want to make sure that I'm correctly interpreting his suggestions on how to model these.   For a model with a ratio with the same denominator on both the dependent and independent side: $ Z^{-1}Y = Z^{-1}1_n\beta_0 + Z^{-1}X\beta_X + \beta_Z + Z^{-1}\epsilon $   Regress dependent ratio on the (inverse) denominator variable in addition to the other ratios Weight by the (inverse) denominator variable  For a model with dependent variable as a ratio: $ Y = \beta_0 + \beta_XX + Z1_n\alpha_0 + ZX\alpha_X + Z^{-1}\epsilon $   Regress numerator by original variables, denominator, and denominator times original variables [what about categorical variables?] Weight by (inverse) denominator  For model with only independent variable ratios: $ Y = \beta_0 + X\beta_X + Z^{-1}1_n\beta_{Z^{-1}} + W\beta_W  + Z^{-1}W\beta_{Z^{-1}W} + \epsilon $   Include numerator and (inverse) denominator as main effects, ratio as interaction term.    Are my interpretations here correct? Evaluate the infinite product $$\lim_{ n\rightarrow\infty }\prod_{k=2}^{n}\left ( 1-\frac{1}{k^2} \right ).$$  I can't see anything in this limit , so help me please. Person falls into radiotelescope and his mind gets transported to the far future I need your help with references. I have 1 main reference section, and I want to include a second list of references as an appendix. For the main reference I use:  \newpage  \bibliographystyle{plainnat}  \bibliography{library}   The problem is that I don't know how to include the second list using a different bib file, and then calling the function \nocite{*} to show every sources inside the file.   I have the appendix part workout. I need your help to design the function to call the second bibliography, and that does't interfere with the main reference:   \newpage  \appendix  \section{Other Sources} \label{app:ReferencesB}   In addition, I will prefer that the word References is not shown after Other Sources.  Thank you so much!! 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. I just came onto a project with a pretty huge code base.   I'm mostly dealing with C++ and a lot of the code they write uses double negation for their boolean logic.    if (!!variable &amp;&amp; (!!api.lookup("some-string"))) {        do_some_stuff();  }                                      I know these guys are intelligent programmers, it's obvious they aren't doing this by accident.   I'm no seasoned C++ expert, my only guess at why they are doing this is that they want to make absolutely positive that the value being evaluated is the actual boolean representation. So they negate it, then negate that again to get it back to its actual boolean value.   Is this correct, or am I missing something? Is it okay to have 100% CPU usage constantly? I often do 3D rendering in the background which consumes 100% of the CPU (I lower the priority of the process so that it does not hinder any tasks I am working on).  My concern/question is whether it is okay to run a computer/laptop with a 100% CPU load constantly.  Could this reduce the lifespan of the system? Proving $f' = - \frac{\partial{F}/\partial{x}}{\partial{F}/\partial{y}}$ Is the universe finite or infinite? How does Cypher exit/enter the Matrix without an operator? In The Matrix, Cypher enters the Matrix to speak with the Agents, then leaves again. We never see if he has an operator, and as he kills Tank and Dozer you might assume he doesn't have one.  If he didn't have an operator how does he jack in/out of the Matrix? Do I need to activate the firewall? I only use Ubuntu for a home desktop use? How to select faces by area I found this documentation:   Under "Face Selection Mode" it says:     Face Selection Mode:      ...        Area   Selects all faces that have a similar area as those already selected.   But I can't figure out where in blender this option is hiding? What are some examples of manifolds that do not have boundaries and are not boundaries of higher dimensional manifolds?  Is any $n$-dimensional closed manifold a boundary of some $(n+1)$-dimensional manifold? As , the retag privilege serves a lot more confusion and a lot less of its benefit due to the suggested edit system. It must be done away with. It will be done away with. ♪  In light of this decided course of action, we're going to need a new snack for the road between "Create Tags" at 300 reputation and "Established User" at 1000 reputation. We'd like your help in thinking about some ideas on what would be a nice privilege to sit at this level. Since we're... a bit dry on our end.  The primary guideline in deciding what kind of privilege to put here is acknowledging its position in the overall hierarchy of privileges. 500 reputation is an early-intermediate user, one who has started to really get the hang of the site and its function. It can be something that provides convenience in how they currently can act on the site, or it could be some new functionality that fits as an early ability (especially considering there's no new abilities until 2000 reputation's "Edit Everywhat" ability).  I look forward to hearing what creative ideas y'all can provide. Programming with Dynamic "ping: unknown host google.com" but IPs works fine Is it possible to dynamically set Views' pager settings? Say for instance, you have a view that displays when viewing a certain node type, but you want the pager settings to be different for each individual node. I was thinking of making a CCK field like "pager setting" and then give it an integer option of x-y. But I don't know if it's possible to somehow dynamically plug that field into the Views' settings. Or is there another way to do this maybe? Generate t distributed random variable in matlab How can we generate t distributed random variables with given mean and covariance in matlab. trnd is a function in matlab but we can get random variable with different degrees of freedom but how to get random variable with given mean and covariance?