Given the permissions, owner and group of a file, what's the algorithm that determines whether a given user can read/write/execute a file? As I understand it, a file has 3 sets of permissions: owner permissions, group permissions, and everybody else permissions. Moreover, the file has is assigned to a owner, and a group.  How linux combines all this information, to actually determine the permissions a given user has over the file?  For example, say a file is:  --- rw- --x  That is, the owner has no permissions, the group can read/write, and everybody else can only execute.  Now user "Joe" comes to this file. Depending on which groups Joe belongs to, and whether Joe is or not the owner of this file, what can he do with it? He could execute the file, because x is set for everybody. But if "Joe" is the owner, x is forbidden for the owner. What takes precedence?
Precedence of user and group owner in file permissions I just ran into something unexpected (for me) regarding file permissions on Linux (Arch Linux). Basically I have:   userX in groupX fileX userX:groupX ---rwx----   What puzzles me: I cannot perform any action (rwx) on fileX. Is this right? Can someone please confirm this is indeed the expected behaviour?  The only actions I can perform are mv and rm because I have write permissions on the parent directory.  The thing is, I always thought these permissions collapse on each other, starting with the most general one (other -> group -> user). In other words, if o=rwx who cares what the persmissions for group and user are? Apparently this is not the case but it doesn't make much sense to me; it seems counterintuitive. The only thing this approach seems to be useful at, is to easily exclude a very specific person / group, which doesn't seem like a smart way to go at it (imho). Besides, the owner (and group?) should be able to chmod anyway right? Any thoughts on this matter?
Generating a DEM and DSM from correct LiDAR point classification I have downloaded classified LAS data from    I am trying to generate accurate DEM and DSM for further analysis. I created a LAS dataset with a projected CRS of  NAD_1983_UTM_Zone_19N in meters and the z CRS in meters as well. My question is on which classifications do I choose for the DEM and DSM. Here is the filter options I have in my dataset:     According to unh LiDAR data report class 2 is ground.     What I have done so far:  DEM I chose the class 2 points and used the las dataset to raster.   DSM In the predefined settings I chose first return and used the las dataset to raster tool.   Is this an accurate way of generating these two rasters? Do I not have to take into account the the unassigned class 1, noise class 7, reserved 11, reserved 17, reserved 18?  Additionally (I can ask this as a separate question if it gets requested to), when using the las dataset to raster tool the sampling value is defaulted to 10. I would like to change it to 2 or 3 (would be meters) to match the LiDAR resolution. I also plan on using the generated DEM and DSM for a least cost path analysis and I want them to be higher resolution. Will making the sampling_value 2 or 3 throw off the results or should I leave it at 10? Do the Imperials know they are evil? I recieve the below error when I am trying to call a Custom Lightning Component in a Visualforce page that is used in Communities.    Unrecognized Content-Security-Policy directive 'reflected-xss'.   logo180.png Failed to load resource: the server responded with a status of 404 (Not Found)   CommunityHomePage:1 Uncaught SyntaxError: Unexpected token w in JSON at position 0     at JSON.parse ()     at XMLHttpRequest.xhr.onreadystatechange (lightning/lightning.out.delegate.js?v=ZCuyRUYzK_kAf4cKCIeS2A:143)   My Component  &lt;aura:component controller="LeadController" implements="forceCommunity:availableForAllPageTypes"&gt;     &lt;aura:attribute name="theLead"          type="Lead"          default="{ 'sobjectType': 'Lead',                    'Rating__c': 2,                    'Company': '',                    'FirstName': '',                    'LastName': '',                    'Email': '' }"/&gt;     &lt;form&gt;          &lt;ui:inputText value="{!v.theLead.Company}" label="Company" class="input"/&gt;         &lt;ui:inputText value="{!v.theLead.FirstName}" label="First" class="input"/&gt;         &lt;ui:inputText value="{!v.theLead.LastName}" label="Last" class="input" /&gt;         &lt;ui:inputEmail value="{!v.theLead.Email}" label="Email" class="input" /&gt;         &lt;ui:button label="Save" press="{!c.save}"/&gt;     &lt;/form&gt; &lt;/aura:component&gt;   My Lightning App is   &lt;aura:application access="GLOBAL" extends="ltng:outApp" implements="forceCommunity:availableForAllPageTypes"&gt;     &lt;aura:dependency resource="c:CommunityChatter"/&gt; &lt;/aura:application&gt;   My VF Page is  &lt;apex:page standardController="Lead"&gt;     &lt;apex:includeScript value="{!$Site.BaseUrl}/lightning/lightning.out.js"/&gt;     &lt;script&gt;         $Lightning.use("c:MyLightApp", function() {             $Lightning.createComponent(                 "c:CommunityChatter",                 {},                 "theLead",                 function(cmp) {                     console.log("Component created!");                     console.log(cmp);                 });             });     &lt;/script&gt;      &lt;div id="theLead"&gt;&lt;/div&gt; &lt;/apex:page&gt; Prove: The positive integers cannot be partitioned into arithmetic sequences (using Complex Analysis) Using url package without hyperref makes link hit boxes erratic I've currently got a url link in a footnote in my document. With the hyperref package, everything works correctly. Because the IEEE PDF Express tool doesn't like having the hyperref package, I've removed it and only left in the url package.  However, some strange behavior occurs as a result of this. Instead of just the link being clickable, entire paragraphs of text before/after end up being clickable and going to the same link. This occurs for both Skim and Preview in Mac OSX.  Does anyone have an inkling of what might be causing this? Is Gauss's law wrong, or is it possible that $\int_s{\vec E} \cdot d\vec{s}=0$ does not imply $\vec E = 0$? This is a question from David J Griffith's Introduction to Electrodynamics.      A specified charge density $\sigma(\theta)=k\cos(\theta) $ is glued over the surface of a spherical shell of radius $R$. Find the resulting potential inside and outside the sphere.   The question was solved using legendre polynomials and the final answer for potential inside the sphere was : $V(r,\theta) = \frac{kr}{3\epsilon_0}cos\theta$  This final answer is confusing because The Electric field inside the sphere is coming out to be dependent on $r$ and $\theta$ whereas electric field inside a shell, no matter what the charge distribution is outside, is $zero$ from gauss's law.      my doubts:         why is the electric field inside non zero?    Can gauss's law explain this, or does it fail here?      Since solving using ordinary surface integral gave me the same result and since the. divergence inside the shell is $zero$, I concluded that legendre polynomials and gauss's law in differential form are correct. So the problem should be with the integral form of gauss's law : $\int_s{\vec E}.d\vec{s} = \frac{q}{\epsilon_0}$  The answer I got for this doubt is that  "since the charges are glued to the surface, and not evenly distributed, electric field inside need not be zero. "     This is not convincing because proof of gauss's law does not expect the charges to be free to move. presence of an exrernal force that would hold the charges in place does not change the theorem. That is    Say only a single charge $q_i$ is present outside      then $\int_s{\vec E_i}.d\vec{s} = \frac{q_{inside}}{\epsilon_0}=0$      Now if there are more charges, following any distribution, net electric field $\vec E = \vec E_1 + \vec E_2+\vec E_3+...$       So the net flux,       $\int_s{\vec E}.d\vec{s} = \int_s{\vec E_1}.d\vec{s}+\int_s{\vec E_2}.d\vec{s}+\int_s{\vec E_3}.d\vec{s}+. . .=0$   Or is it possible that $\int_s{\vec E}.d\vec{s}=0$ does not imply $\vec E = 0$? Closed unit disk homeomorphic to $\mathbb{R}^2$? I've already shown the existence of a homeomorphism between the open unit disc and $\mathbb{R}^2$ and now I'm trying to work out whether the closed unit disc is homeomorphic to $\mathbb{R}^2$ or not. Clearly the only real difference is the fact it includes the points actually on the circle, but because the continuous, invertible, bijective map I defined for the open disc was $\dfrac{x}{1-|x|}$ this clearly is not defined for the points on the line.   Intuitively I'm thinking it's not possible to form a homeomorphism with the closed disk precisely because of these points on the circle but can't really form a decent argument. I was thinking along the lines of showing that the non-open, closed subset $\bar{D}(0,1) \backslash D(0,1)$ (which is just the set of points on the actual circle i.e the boundary/frontier of the closed disk) can't possibly bijectively map to a closed subset of $\mathbb{R}^2$ - which clearly would have to be the case in a homeomorphism.   Any advice would be greatly appreciated. How to fix "Duplicate sources.list entry" warning? Every time I try to do some update (sudo apt-get update) it says:   Reading package lists ... ready W: Duplicate sources.list entry http://archive.canonical.com/ubuntu/ need /partner amd64 Packages (/var/lib/apt/lists/archive.canonical.com_ubuntu_dists_precise_partner_binary-amd64_Packages) W: Duplicate sources.list entry http://archive.canonical.com/ubuntu/ need /partner i386 Packages (/var/lib/apt/lists/archive.canonical.com_ubuntu_dists_precise_partner_binary-i386_Packages) W: You have to run apt-get update to correct these problems   sources.list:   ls /etc/apt/sources.list.d/ as requested:  milton@milton-HuronRiver-Platform:~$ ls /etc/apt/sources.list.d/ emesene-team-emesene-stable-precise.list precise-partner.list precise-partner.list.save upubuntu-com-chat-precise.list upubuntu-com-chat-precise.list.save I do not understand much about mine bitcoins, but I downloaded a program that is like a wallet, but I want to know how I do to mine. Has a calling GUIminder but is for windows, someone knows one that is for ubuntu? Is there a name for an element $z$ such that $\,zx = z = xz\,$ for all $x$? Is there a general name for the following properties, (similar to the properties of existence of an additive identity, existence of multiplicative identity etc):   For any given set, the intersection with the empty set results in the empty set. For any real number, multiplication with zero results in zero. Find all continuous functions satisfying $\int_0^xf=(f(x))^2+C$ for some constant $C \neq 0$. Find all continuous functions $f$ satisfying   $$\int_0^xf=(f(x))^2+C$$ for some constant $C \neq 0$, assuming that $f$ has at most one $0$.  I have a question about the solution to this problem. It says that   Clearly $f^2$ is differentiable everywhere, its derivative at $x$ is $f(x)$ (I'm assuming that this is because the left hand side is differentiable, the right hand side must be differentiable as well). So $f$ is differentiable at $x$ whenever $f(x) \neq 0$, and  $$f(x)=2f(x)f'(x),$$ so $f'(x) = \frac{1}{2}$ at such points. Thus, $f= \frac{1}{2}x+b$ for some $b$ on any interval where it is non-zero; if $f$ has a zero, this gives two possible solutions, with two possible values of $b$, but since $f$ is assumed continuous, they must be the same. So we need $$\int_0^x(\frac{1}{2}t+b)dt=(\frac{1}{2}x+b)^2+C$$  so we must have $b=\sqrt{-C}$ or $-\sqrt{-C}$, leading to two solutions for $C \lt 0$.  I don't understand the bolded statements. First, how does the differentiability of $f^2$ guarantee that $f$ is differentiable, and why only at $x$ where $f(x) \neq 0$?  Next, why are there two possible solutions if $f$ has a zero, but since $f$ is continuous they must be the same?  Finally, does the last statement mean that if $C \gt 0$, then there is no solution, since we're restricted to real numbers here?  I would appreciate it if anyone answers my questions. I have a little problem with the placement of my picture. I want to insert it at the end of the introduction chapter but its place is not where I want.   I think the problem become from the:  \begin{figure} ... \end{figure}   Because when I insert the picture without using \begin{figure}... the picture is at the end of the chapter as I want.   Look the picture below. I was watching some videos on YouTube showing how to get the Duke O' Death in GTA 5, however what I have seen is sort of unclear.  Some people say you must be a returning player on GTA 5 to get it (what does this mean too BTW?), some people don't say that. Some people say you have to be Trevor, some people don't. Some say the time of day matters, some don't. And apparently you can buy it from Warstock website (I can't).   Can someone please tell me how to get it?! GTA 5 came with my PS4 (I didn't play it on PS3) if that helps. Partition 256 GB SSD for dual Boot, Windows 10 + Ubuntu 19.04 I plan on installing Ubuntu 19.04 and give it 100 GB of my 256 GB SSD space and leave the rest for Windows as I would primarily be using Ubuntu.     A. Now, as I plan to install a lot of applications in Ubuntu, should I give more space to the / partition than the home partition? (Or maybe even drop the /home altogether?).    B. I have another 128 GB SD card for files like photos, audio and video files. Please suggest me the optimal partitioning for the use case.    C. Also, I have 8 GB of RAM so what should be the optimal swap partition size?    D. How would the distribution be if I choose "install Ubuntu alongside Windows" option? Train passport control from London to Paris I'm a non-EU citizen, I will be travelling from London to Paris next month, so I was wondering since most countries track entry and leave dates, if I use the train to switch these countries and they don't control it, my UK visa will seem like entry YES but no leaving. Same for the Schengen, I wouldn't have an entry date but I'll be leaving,  Will it be trouble later? Are they controlling this on trains? If not is there anything I should do before? Is Con modifier × level added to HP every level-up? Is colour, as represented using primary colours, accurate only to humans? Slightly biological, hopefully physical enough to be answered.  Suppose a magenta hue is represented by a mix of red and blue pigment. This is all very well for a creature with red and blue photoreceptors, but suppose it was seen by a creature which had a magenta-sensitive receptor, but no red or blue. Would the colour appear the same (insomuch as a qualititave concept can appear the same, I suppose I mean 'Would they interpret it as colour of the same wavelength?')?  The crux of my question is, do the particular bands in which photoreceptors are activated affect vision of additive, as opposed to pure, hues?  Finally, completely off-topic, but if there happens to be a biologist around, do animals on the whole have similar photoreceptors, or are they placed largely randomly?  Thanks, Wyatt Compilation problem with siunitx (returning error regarding ifnum) I'm trying to get siunitx working. For some reason I keep getting this error:  ! Missing = inserted for \ifnum. &lt;to be read again&gt;                     - l.3 \begin           {document}^^M   I have tried a minimal document to make sure it is not some kind of compatibility issue. And I get that same error in the most minimal document possible.  I'm using pdfLaTeX to compile, and have tried both from TeXWorks and from bash. I'm using TeXLive, if that matters. I have also tried reinstalling siunitx, l3packages, and l3kernel. There was an issue with l3kernel before this, due to an apparently old version. But all three packages are now up to date. I've also reinstalled expl3 while trying to debug the original issue.  My minimal document is:  \documentclass{article} \usepackage{siunitx} \begin{document} \end{document}   The output I get is:  This is pdfTeX, Version 3.14159265-2.6-1.40.16 (TeX Live 2015/Debian) (preloaded format=pdflatex) restricted \write18 enabled. entering extended mode (./untitled-2.tex LaTeX2e &lt;2016/02/01&gt; Babel &lt;3.9q&gt; and hyphenation patterns for 81 language(s) loaded. (/usr/share/texlive/texmf-dist/tex/latex/base/article.cls Document Class: article 2014/09/29 v1.4h Standard LaTeX document class (/usr/share/texlive/texmf-dist/tex/latex/base/size10.clo)) (/home/&lt;name&gt;/texmf/tex/latex/siunitx/siunitx.sty (/home/&lt;name&gt;/texmf/tex/latex/l3kernel/expl3.sty (/home/&lt;name&gt;/texmf/tex/latex/l3kernel/expl3-code.tex) (/home/&lt;name&gt;/texmf/tex/latex/l3kernel/l3pdfmode.def)) (/home/&lt;name&gt;/texmf/tex/latex/l3packages/xparse/xparse.sty) (/usr/share/texlive/texmf-dist/tex/latex/amsmath/amstext.sty (/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsgen.sty)) (/usr/share/texlive/texmf-dist/tex/latex/tools/array.sty) (/home/&lt;name&gt;/texmf/tex/latex/l3packages/l3keys2e/l3keys2e.sty) (/usr/share/texlive/texmf-dist/tex/latex/beamer/translator/translator.sty (/usr/share/texlive/texmf-dist/tex/latex/graphics/keyval.sty) (/usr/share/texlive/texmf-dist/tex/latex/beamer/translator/translator-language- mappings.tex))) ! Missing = inserted for \ifnum. &lt;to be read again&gt;                    - l.3 \begin          {document}^^M ?   Does anyone have any idea what might be going wrong here? How to prove reflexivity, symmetry and transitivity for the following relation? Query Activity for ORDER BY xxx DESC LIMIT I'm trying to create a query activity in order to show, from a Data Extension, only the last 5 articles ids. I tried with the formula ORDER BY xxx DESC LIMIT 0,5 as in SQL but it is not working and it is returning this exception:     The ORDER BY clause is invalid in views, inline functions, derived tables, subqueries, and common table expressions, unless TOP or FOR XML is also specified   How can I use ORDER BY in a Data Extension?