In Unix, when exec  If Real user ID is not same with file owner, and Set user ID bit is on, then, effective user id is changed to file owner's, and saved set user ID too. Because Effective user ID is copied to Saved set user ID when exec.     At this moment, Why saved set userID is needed?   Because of security problem? if it is right, especially what case?
Real UID, effective UID, and some systems even have a "saved UID". What's the purpose of all these, especially the last one?
When is $\phi(n)$ a prime number? I was thinking about this problem today. If $p$ divides $n$, then $p-1$ must divide $\phi(n)$. But $p-1$ is even for all primes greater than $2$, so must $\phi(n) = 2$ - the only even prime? I feel like this argument is shaky and not very rigorous! I am using tufte-latex package, which uses mathpazo with old style numerals. To make figures (plots) I would like to use lining numbers.  The problem is that the figures are converted from svg to pdf using inkscape and the numbers are not in mathmode (In math mode the numbers are lining numerals by default).  I think of two possible solutions:  a) Is there any command similar to \oldstylenums that does the opposite work?  b) inkscape put the text of the figure in \smash{-22.22} commands. Is any way,  using sed, awk, perl,... to change that to \smash{$-22.22}? Do Stack Exchange sites allow editing of comments and posts from other users? Possible Duplicate:         Is this normal behavior in Stack Exchange sites that after just signing up one can edit not only his/her own comments / posts, but also others' comments / posts?  If so, then the Q&amp;A does not look safe to me. Imagine someone maliciously modifying a post and bringing bad reputation on a Q&amp;A member.  Can you check this and perhaps fix it? Based on newtons third law If an elephant can apply 250N force and a rabbit can apply 25N force , and if they are pulling each other , then elephant will pull with 250N force and according to newtons third law the rabbit should also pull the elephant with 250N force.then from where do the rabbit got the extra 225N i.e.(250-25=225) force??? can anyone please explain. It looks like we'll be adding  support to Stack Overflow. This is necessary to prevent bots, spammers, and other malicious scripted activity. We only want human beings to post or edit things here!  We'll be using a JavaScript (jQuery) CAPTCHA as a first line of defense:    The advantage of this approach is that, for most people, the CAPTCHA won't ever be visible!  However, for people with JavaScript disabled, we still need a fallback and this is where it gets tricky.  I have written a  which we can re-use.    However, I'd prefer to go with something textual to avoid the overhead of creating all these images on the server with each request.  I've seen things like..   ASCII text captcha: \/\/(_)\/\/ math puzzles: what is 7 minus 3 times 2? trivia questions: what tastes better, a toad or a popsicle?   Maybe I'm just tilting at windmills here, but I'd like to have a less resource intensive, non-image based &lt;noscript&gt; compatible CAPTCHA if possible.  Ideas? How do I change the icon for a particular file type? I'm trying to change the icon for application/x-hwp files. I've added the icons to the proper places, and checked it with assoGiate (after reading ). It shows that my desired icon is associated with the file type. Nevertheless, Nautilus is still showing the old icon. How can I make Nautilus show the correct icon? How can I report bugs with or request features for the Stack Exchange mobile apps? "along the river" vs "alongside the river"? In a question on "along" vs "alongside", I have seen this question and the correct answer on the web site makes me confused.      The question is: I enjoyed my walk _________________ the river.  a) along b) alongside  I selected "...along the river" as the correct answer, but on the web site it is shown as wrong and the correct answer is "alongside".  How can that be? I still do not agree, because I have studied the difference between the two. "along" is just the right preposition for thin and long places like road, path, street, beach etc".   So, why would the correct answer be "alongside" which simply means "next to"? Do you not think "along" seems to be better fitting?  Regards,  Note: I would be more than gratefull, if somebody show it to me in a video, like "a walk along the river" and "a walk alongside the river". Maybe I can understand the how "a walk along the river" and "a walk alongside the river" would take place. Probability of a 2 pair in poker What is wrong with my method of find the probability of a 2 pair?  For the first card we have 52 choices, one this is picked( call it A) we have 3 choices(different suite than A but this same value) for the second card, ( lets call this card B). Now we have AB, to we have to throw away 2 more cards so we don't have 3 of a kind or a four of a kind. Therefore one our third card we have 48 choices and on our fourth card we have 3 choices again similar to above.  On our last card we only have 44 choices left. So the probablity of getting a 2 pair should be (52*3*48*3*44)/(52 choose 5).  But this isn't correct.     Note: I edited this to "2 pair"; the original version was wrong. MySQL Insert query doesn't work with WHERE clause What is the advantage to crushed garlic over minced garlic beyond texture? I use a lot of garlic in my cooking, especially minced garlic.  But lately I've been doing some more recipes with crushed garlic and while I love the texture of cooked garlic, I can't see how it could be better than minced garlic for the overall taste.  Is there an advantage to crushed garlic over minced garlic, beyond texture? What is Uplay? Can I play Ubisoft games without it? Heroes of Might and Magic VI seems to have installed a program called "Uplay", which it uses to launch (in addition to Steam, mind!)  What exactly is Uplay supposed to be? I notice that when I stop playing, it captchalogs the highlights of my past session (achievements earned, etc.) - which is kinda cool, but also kinda creepy and big-brotherish. Given that I value my privacy, is there anyway to play Uplay games without using Uplay?  Is this just Ubisoft's infamous "always-on" DRM? How do I change the email address associated with my Stack Exchange OpenID? I registered my Stack Overflow account using the Stack Exchange OpenID provider. I later changed my e-mail, but I cannot change the e-mail address associated with my OpenID for some reason. Why is that, and how do I change it? I logged in to Stack Exchange and it lets me change my password, but never my e-mail. Clearing Recently used coordinate reference systems using QGIS? After using some non usual SRC for demonstration purpose, I wish to clear my  "Recently used coordinate reference systems" list for the sake of praticity.  Is it possible?   I am using QGIS 2.10.1. Determine group G as cyclic If $G$ has no proper subgroup, prove that $G$ is cyclic of order $p$, where $p$ is a prime number.     I know that since $G $is a group with no proper subgroups, $g \in G$ is not just the identity. I don't know where to go from there. How do I copy vertex groups from one object to another? So, I decided that a previous project contained exactly what I needed to expedite a new project, so I appended the appropriate objects form the previous project to the new one. This was great, because I didn't have to define new materials, &amp;c.   Regrettably, though, I found out that when it came to vertex groups, where it would have been as helpful to be able to copy vertex groups from one object to another as it was to copy materials, I couldn't figure out how to do so.   Am I looking for a feature which does not yet exist?  NOTE: I did not expect the vertex groups to have assignments in the target objects, but it would have been handy not to have had to retype 25 names. java.lang.OutOfMemoryError: PermGen space Exception How can timelapse sequences be shot without having in-camera support for it?  Which third-party tools are recommended? I want to prove this:  Prove that if $a \in \mathbb{Z}$ is divisible by $4$, then there exist $b$ and $c$ where $b,c \in \mathbb{Z}$ such that $a = b^2 - c^2$  I want to prove this directily:  $4\mid a $,  $a\in \mathbb{Z} \implies \exists b,c \in \mathbb{Z}, \quad$ s.t. $a=b^2-c^2$  Let $k\in \mathbb{Z}$. Then $4=a\cdot k$ and $k$ can divide $4$. Hence,  $\frac{4}{k} =b^2 - c^2 = (b-c)(b+c) \implies \dfrac{4}{k\cdot(b-c)} = b+c$  Is this proof correct? Urdu language not listed in my ubuntu 16.04 LTS I am a new user of Ubuntu 16.04 LTS. To my surprise it does not have Urdu Language in language support widow. Kindly help.   The given answer to  is not helping me.