I accidentally deleted the /usr/bin/sudo file. How can I restore it?  I have found , but it seems to be not solved.
This seems to be a chicken-egg problem. The most common task using sudo is installing and removing software.  sudo apt-get purge &lt;appname&gt;   But sudo itself can be removed.  sudo apt-get purge sudo # Do not run this command on production computers!   This is where the fun comes  ubuntu@ubuntu:~$ sudo bash: /usr/bin/sudo: No such file or directory   Although it's obvious that no person in his right mind will purge sudo (other than me), someone can be fooled to run this command (not directly, in its hex mode, or whatever it's called) or a person could SSH in disguised as tech guru and do the mess.  So is there a way of reinstalling sudo?
Can I use a one-way ticket to come to the UK? Or do I need to show a return ticket to be able to get in? Model selection with low N? I've got a study which is kinda messed up by the design...Turns out I ended up with about 50 patients of which 80% have the outcome and 20% don't (binary outcome).  I've been turning in my bed for the last month trying to figure out what to do with this. The only real answer is "don't" but I have to deliver something in the next days as it's part of a master's thesis.  I have about 10 predictors of interest for the outcome (various variable types) and the research question is whether any of these predictors can predict the outcome. Some already have an established correlation in the literature while some are original hypothesis. Several are significant with a univariate logistic regression, but it doesn't look good in any other way than the actual p-value.  Now obviously I'm not going to be able to answer this research question sufficiently but if you were in my shoes, what sort of statistical analysis would you perform to relay to your supervisors?  EDIT: Link to my (anonymized) data (CSV): Positive and negative complex numbers? Can there be such a thing as positive and negative complex numbers? Why or why not?   What about positive or negative imaginary numbers?   It seems very tempting to say $+5i$ is a positive number while $-2i$ is a negative number. On an Argand diagram (complex plane) $+5i$ would be represented by a point above the horizontal axis while $-2i$ is a point below the horizontal axis. I have a dataset that has both continuous and categorical data. I am analyzing by using PCA and am wondering if it is fine to include the categorical variables as a part of the analysis. My understanding is that PCA can only be applied to continuous variables. Is that correct? If it cannot be used for categorical data, what alternatives exist for their analysis? How can I generate PDF metadata from LaTeX? I am writing a document using LaTeX and generating PDF.  Can anybody tell me how I can generate the PDF metadata, e.g. author or title, from LaTeX?  On Windows XP, I am using MikTex's texify to generate the PDF.  On linux, I am using pdflatex to generate the PDF.  Any answers for either platform would be much appreciated! I would like the user to have full rights on this folder (as well as all sub-directories and files in it):  ~/.blabla   currently owned by root.  I have found numerous posts (in this forum and elsewhere) on how to do this for files but I can't find a way to do it for whole folders. I would like to toggle the Do Not Disturb in the notification center with a keyboard shortcut.  I am using BetterTouchTool for some extra keyboard shortcuts but it does not support enabling/disabling the notifications in the default options.  It has an option for executing a terminal command so I'm asking here how to enable/disable Do Not Disturb from the terminal?  I found  and I tried to run the commands but it didn't seem to work. How to automate SSH login with password? How to automate SSH login with password? I'm configuring my test VM, so heavy security is not considered. SSH chosen for acceptable security with minimal configuration.  ex)  echo password | ssh id@server   This doesn't work.  I remember I did this with some tricks somebody guided me, but I can't remember now the trick I used... Rewrite Sharepoint URL (Sharepoint 2013) I'd like to rewrite all my site urls in the way the the user can't figure out the exact name of the the page his viewing. let's say that my site is "www.justarandomsite.com"  and may page is "page.aspx" I' like to have instead of "www.justarandomsite.com/pages/page.aspx" sothing like this: "www.justarandomsite.com/skdhfjksdgfjksdgfjdsgvdjhsgfjdsdsjfgkdsjgfkdsgfjdsgfjkdsg" When I type uname -a, it gives the following output.  Linux mars 2.6.9-67.0.15.ELsmp #1 SMP Tue Apr 22 13:50:33 EDT 2008 i686 i686 i386 GNU/Linux   How can I know from this that the given OS is 32 or 64 bit?  This is useful when writing configure scripts, for example: what architecture am I building for? Let $a,b$ be positive integers.  When $$k = \frac{a^2 + b^2}{ab+1}$$ is an integer, it is a square.    Proof 1: (Ngô Bảo Châu): Rearrange to get $a^2-akb+b^2-k=0$, as a quadratic in $a$ this has two values: $a$ and $kb - a = (b^2-k)/a$. (The second root is determined in two different ways from the expansion $(x-r_1)(x-r_2) = x^2 - (r_1 + r_2)x + r_1 r_2$.)  Now suppose we have $a,b$ such that $k$ is an integer but not a square, by the investigation about roots we have that the second root is a nonzero integer since $k,b,a$ are integers and $k \not = b^2$, futhermore it is positive which is easily seen from its defining equation.  WLOG assume $a \ge b$ so that the second root is strictly smaller than $a$. This leads to a decent, replacing $a$ with the second root.    Proof 2 (Don Zagier): Apply reduction theory (specifically, Sätze 1 and 2 of Section 13 of my book on quadratic fields) to the quadratic form $x^2 + kxy + y^2$, which is the unique reduced quadratic form in its equivalence class.    Note that Proof 2 is pretty much the same as Proof 1 when written out in explicit detail, but I could not read Zagier's book because I cannot read German.  I would like to know more approaches to this and other alternative proofs of this result if possible! Thanks in advance.  I would also be interested in related problems (especially easier ones of a similar nature) and texts which cover the reduction theory in English. Find and replace multiple values within selected cells I want to run a find and replace on multiple values within a range in excel with values from 2 columns: A with the original word; B with the translation. I already found the VBA code to get this working for 50%, but this code runs it on the whole worskheet.  Ideally I would like to be able to run it on just the range I selected. An added bonus would be if I could also select the lookup range.  This is what I'm using this far. Thanks for your help!  Sub abbrev()             Dim abvtab() As Variant             Dim ltsheet As Worksheet             Dim datasheet As Worksheet             Dim lt As Range              'Change Lookup to the sheet name with your lookup table.             Set ltsheet = Sheets("Lookup")              'Change Data to the sheet name with your data.             Set datasheet = Sheets("Data")              'Change A2 to the top left cell (not the header) in your lookup table.             'Change B2 to top right cell.             Set lt = ltsheet.Range("A1", ltsheet.Range("B1").End(xlDown))              abvtab = lt              For i = 1 To UBound(abvtab)                 datasheet.Cells.Replace What:=abvtab(i, 1), Replacement:=abvtab(i, 2), LookAt:=xlPart, _                     SearchOrder:=xlByRows, MatchCase:=True, SearchFormat:=False, _                     ReplaceFormat:=False             Next i End Sub Remove all attributes from html tags Prove that $\left(1+\dfrac{1}{1^3}\right)\left(1+\dfrac{1}{2^3}\right)\cdots\left(1+\dfrac{1}{n^3}\right)&lt;3$   for all positive integers $n$   This problem is copied from Math Olympiad Treasures by Titu Andreescu and Bogdan Enescu.They start by stating that induction wouldn't directly work here since the right hand side stays constant while the left increases.They get rid of this problem by strengthening the hypothesis.$$\left(1+\dfrac{1}{1^3}\right)\left(1+\dfrac{1}{2^3}\right)\cdots\left(1+\dfrac{1}{n^3}\right)\le3-\dfrac{1}{n}$$ and then proceed by induction.  The problem is that I can't find a motivation for the above change.I mean,we could have subtracted a lot of things from the RHS but what should nudge us to try $\dfrac{1}{n}$?The rest of the proof is quite standard,but I can't see how I am supposed to have thought of it.Is it just experience?Or is it a standard technique?A little guidance and motivation will be appreciated. Why are there no line numbers in the code listings? Would it make discussing code easier if you could simply refer to a particular line or range, or am I wrong? $M$ finitely generated if submodule and quotient are finitely generated. I know this must be easy. I'm new to modules, so perhaps I must be missing  something important.     Let $M$ be an $R$-module. Show that if there exists a submodule $N$ such that $N$ and $M/N$ are finitely generated, then $M$ is finitely generated.   If the exact sequence $0 \longrightarrow N \longrightarrow M \longrightarrow M/N \longrightarrow 0 $ (where the second and third arrows are inclusion and projection respectively) splits then $M$ would be isomorphic to the direct sum of $M$ and $M/N$ and the conclusion would follow (I think). But I can't show that it splits.  Thank you. MySQL strip non-numeric characters to compare I'm looking to find records in a table that match a specific number that the user enters.  So, the user may enter 12345, but this could be 123zz4-5 in the database. I imagine something like this would work, if PHP functions worked in MySQL. SELECT * FROM foo WHERE preg_replace(&quot;/[^0-9]/&quot;,&quot;&quot;,bar) = '12345'  What's the equivalent function or way to do this with just MySQL? Speed is not important. I have a layer of georeferenced points, and a layer of vectorized borders. Is there a way I can use QGIS to calculate how many points fall within each area of the borders layer? Is it possible to configure a TP_Link ADSL router to work with a cable connection? Counting points in shapefile within polygons of another shapefile using ArcGIS Desktop? I'm creating a map with two shapefiles:   A polygon of counties Points of cities   I used the function Intersect to group the cities in each county.  I'm trying to get the number of cities in each county to show up in the legend.    For example, in county A there are 16 cities, in county B there are 7 cities and so on.  I'm trying to create a choropleth map that shows the number of cities in each county.