CentOS7 Can't install VBoxGuestAdditions because kernel headers not found
Want to install VirtualBox Guest Additions on CentOS 7 but get a header mismatch
Is is possible to convert a .vdi file into a .iso that can be burned to a cd or dvd and make it like an installer. Or Is it possible to convert virtual machines to physical environments? Continuously Differentiable Curves in $\mathbb{R}^{d}$ and their Lebesgue Measure Show that the image of the curve $\Gamma\in\mathscr{C}^{1}\left([a,b]\to\mathbb{R}^{d}\right)$ has d-dimensional Lebesgue measure zero (of course, $d\geq2$).  This can be proved using the absolute continuity of $\Gamma'$ (since $[a,b]$ is compact and $\Gamma'$ is assumed continuous, hence in $L^{1}([a,b])$) together with the fundamental theorem of calculus to obtain an $\epsilon$-small cover of $\Gamma$ by balls.  But I am trying to prove this using more elementary means (i.e. without integration).  Intuitively, since $\Gamma$ is smooth, we ought to (for fine enough partitions) be able to cover $\Gamma$ by boxes which arise from its tangent line.  And by taking the partition of $[a,b]$ to be finer and finer, the "tangent box" cover ought to also get smaller and smaller.  More rigorously, the vector-version of the mean value theorem can be applied: $$|\Gamma(t_{i-1})-\Gamma(t_{i})|\leq(t_{i}-t_{i-1})|\Gamma'(t_{i}^{\star})|\leq M_{i}\Delta t$$ where $t_{i}^{\star}\in(t_{i-1},t_{i})$ and $M_{i}=\sup_{t\in[t_{i-1},t_{i}]}|\Gamma'(t)|$ which exists and is finite since $\Gamma'$ is continuous.  But to me, it's not quite clear how to rigorously construct a cover by boxes from here.  NOTE:  In the proof I mentioned (using integration), essentially you sum the left hand side over all partition intervals of uniform length $\delta$ (which depends on the $\Gamma'$), and "integrate" the right hand side.  Actually, to be more specific, for each $\epsilon&gt;0$ there exists a $\delta&gt;0$ such that $||P||&lt;\delta$ implies $\int_{t_{i-1}}^{t_{i}}|\Gamma'(t)|dt&lt;\epsilon$ (e.g. absolute continuity).  This allows you to define numbers $\epsilon_{i}=\sup_{t,\bar{t}\in[t_{i-1},t_{i}]}|\Gamma(t)-\Gamma(\bar{t})|\leq\epsilon$ so that $\sum_{i=1}^{\#P}\epsilon_{i}\leq||\Gamma'||_{L^{1}([a,b])}$.  Then you can use these $\epsilon_{i}$ to put balls at each point $\Gamma(t_{i})$ of radius (say) $2\epsilon_{i}$, thus giving you an $\epsilon$-small cover.  Again though, this is harder to establish without integration theory. In PHP 5, what is the difference between using self and $this?  When is each appropriate? How to run an executable on boot and keep it running? I have an executable build from a ndk-build program. I want to run it on a rooted Android device. How much is the possibility that Android will kill my executable?  Using adb shell, I am able to execute my executable using following commands:  adb push executable /sdcard adb shell device:/ $ su device:/ # cd /system device:/system # mount -o rw,remount /system device:/system # mv /sdcard/executable . device:/system # ./executable   My requirement is to run this executable on device boot.  I have tried following:   Write ./executable in init.rc.   On reboot init.rc reset to its original contents. I figured out that Magisk done this.  Write commands in /system/etc/init/bootstat.rc   ./executable service custom /system/executable on boot  ./system/dhandler/diag_revealer    None of the above thing is working. I have thus far avoided the nightmare that is testing multi-threaded code since it just seems like too much of a minefield.  I'd like to ask how people have gone about testing code that relies on threads for successful execution, or just how people have gone about testing those kinds of issues that only show up when two threads interact in a given manner?  This seems like a really key problem for programmers today, it would be useful to pool our knowledge on this one imho. How to adapt the color of a label using pgfplots I created this style that shifts the labels and put them on the bottom of the ybars.  However, I have a problem with the bars that have too short length (for example, see the 8.7 and 5.1 in the example below). I want to check if the values are less than some threshold, or the length of the bar is shorter than the label (number) then change its color.  How can I overlay another label on top of the one in white when the bar is shorter? or maybe change the color of the label to a gradient color? or just overlay the part that is outside of the bar?    \documentclass{standalone}  \usepackage{tikz} \usepackage{pgfplots} \usepackage{pgfplotstable} \usetikzlibrary{calc}  \begin{document} \makeatletter \begin{tikzpicture} \begin{axis}[ ybar, every node near coord/.style={   check for zero/.code={ % If meta=0, make the node a coordinate (which doesn't have text)     \pgfmathfloatifflags{\pgfplotspointmeta}{0}{         \pgfkeys{/tikz/coordinate}     }{}   },   check for zero, color=white, text opacity=1, font=\footnotesize, inner ysep=0.5pt, },% % Bottom nodes  calculate full offset/.code={     \pgfkeys{/pgf/fpu=true,/pgf/fpu/output format=fixed}     \pgfmathsetmacro\testmacro{((\pgfplotspointmeta-\pgfkeysvalueof{/pgfplots/ymin})*10^\pgfplots@data@scale@trafo@EXPONENT@y)*\pgfplots@y@veclength}     \pgfkeys{/pgf/fpu=false} },% nodes near coords bottom/.style={     every node near coord/.append style={         /pgfplots/calculate full offset,         yshift=-\testmacro,         rotate=90, anchor=west,%I need the rotate text here and not in the          %general style, as the ybar redefines the style     } },% ymin=0, nodes near coords={\pgfmathprintnumber[fixed zerofill,precision=1]{\pgfplotspointmeta}}, nodes near coords bottom, ] \pgfplotstableread{ % set real imag mag 1 8.7 2 5.1 3 91.8367  }\mydata \addplot table[x index=0,y index=1,header=false] {\mydata}; \end{axis} \end{tikzpicture} \makeatother \end{document}   * EDIT *  I need to create some special gradient on each label that is below the bar height. For example, I need to adapt something like  to each label that is not showing. However, I cannot find a way to put the macro in the style section of the codes. Or is there any equivalent solution? The effect of gravitational & Coulomb forces on free electrons in a conductor In a metal, why don’t the free electrons fall to the bottom of the metal due to gravity?  Also, charges in a conductor are supposed to reside on the surface so why don’t the free electrons all go to the surface?   Regarding the first question, my hunch is that it is due to the electric force which is greater than the gravitational force and electric force act along the length of the conductor.  I don't have any intuition for the second. If $f(x)=x-\int^{\frac{\pi}{2}}_0f(x)\sin(x)dx$ find the explicit function for $f(x)$ in its simplest form Supernatural sites on Stack Exchange Is there any Q&amp;A site under the Stack Exchange network where we can discuss about supernatural incidents? If not, then whom should I petition to create it? I want to argue that argue that $\pi(\alpha)=\alpha^3+3\alpha+3$ is an irreducible polynomial over the finite field with 5 elements $\mathbb{F}_5$. My approach was just to check that $\pi$ has no roots in $\mathbb{F}_5$. Is this right? How can I use a command to delete all files in Downloads whose dates added are greater than 1 year? I am using a Mac. How can I use a command to delete all files in ~/Downloads whose dates added are greater than 1 year? Does a multiple-entry Schengen visa allow visiting other Schengen countries later, without going via the issuing country? My wife was just issued a multiple entry visa by France, which is good for one year.  Our first trip will be to France, the issuing country.  My question is: after we leave the EU and return, must future trips also start in France? Or may we go directly to (say) Greece from the US on a later visit? Definitions and usage of Covariant, Form-invariant & Invariant? Just wondering about the definitions and usage of these three terms.  To my understanding so far, "covariant" and "form-invariant" are used when referring to physical laws, and these words are synonyms?  "Invariant" on the other hand refers to physical quantities?  Would you ever use "invariant" when talking about a law? I ask as I'm slightly confused over a sentence in my undergrad modern physics textbook:     "In general, Newton's laws must be replaced by Einstein's relativistic laws...which hold for all speeds and are invariant, as are all physical laws, under the Lorentz transformations." [emphasis added]      ~ Serway, Moses &amp; Moyer. Modern Physics, 3rd ed.   Did they just use the wrong word? Can I become leader of the Thieves' Guild without finishing the main chain and is there any benefits from being the leader anyway? I completed the quest where you get the Skeleton Key and I don't really want to continue the chain until I've done a lot of the other stuff in the game, since the key is so useful. Brynjolf said before that I would become leader of the guild after everything was over.  Can I become the leader anyway without finishing the Nightingales quest chain? Are there any bonuses for being the leader? Get full path of the files in PowerShell Linearlayout order is reversed on some devices How can I get ssh-agent working over ssh and in tmux (on OS X)? I have a private key set up for my github account, the passphrase to which is, I believe, stored in OS X's keychain. I certainly don't have to type it in when I open a terminal window and enter ssh git@github.com.  However, when I'm running bash over an ssh session, or locally inside a tmux session, I have to type in the passphrase every single time I attempt to ssh to github.   suggests that a similar problem exists with screen, but I don't really understand the issue well enough to fix it in tmux. There's also  which includes a fairly complicated solution, but for zsh.  EDIT:  In response to , from a local terminal I get the following output:  [~] $ echo $SSH_AUTH_SOCK /tmp/launch-S4HBD6/Listeners [~]  $ ssh-add -l 2048 [my key fingerprint] /Users/richie/.ssh/id_rsa (RSA) [~] $ typeset -p SSH_AUTH_SOCK declare -x SSH_AUTH_SOCK="/tmp/launch-S4HBD6/Listeners"   Whereas over ssh or in tmux I get:  [~] $ echo $SSH_AUTH_SOCK  [~] $ ssh-add -l Could not open a connection to your authentication agent. [~] $ typeset -p SSH_AUTH_SOCK bash: typeset: SSH_AUTH_SOCK: not found   echo $SSH_AGENT_PID returns nothing whatever shell I run it from. I computed the homology groups of the torus, can someone tell me if this is correct? The calculation, not the result that is. Thanks!  The cells of $T^2$ are $e^0, e^1_a, e^1_b, e^2$  The chain groups are  $$ C_0(T^2) = \{ k e^0 |&#160;k \in \mathbb{Z} \} = \mathbb{Z}$$  $$ C_1(T^2) = \{&#160;k_1 e^1_a + k_2 e^1_b |&#160;k_1 , k_2 \in \mathbb{Z} \} = \mathbb{Z} \oplus \mathbb{Z}$$  $$ C_2(T^2) = \mathbb{Z}$$  $$ C_k(T^2) = \{ 0 \} , k &gt; 2$$  Now the homology groups:  $$ H_0(T^2) = \ker \partial_0 / im \partial_1 = \mathbb{Z} / 0 = \mathbb{Z}$$  where $im \partial_1 = 0$ because there is no chain in $C_1(T^2)$ whose boundary is a zero-chain in $C_0(T^2)$. (Is this reasoning correct?)  $$ H_1(T^2) = \ker \partial_1 / im \partial_2 = \mathbb{Z} \oplus \mathbb{Z}$$  where $\ker \partial_1 =  \mathbb{Z} \oplus \mathbb{Z} $, i.e. again everything maps to zero because there is no element in $C_1$ whose boundary maps to an element in $C_0$.  $im \partial_2 = 0$ again because there is no element in $C_2$ whose boundary is an element of $C_1$.  I don't want to use Hurewicz to do $H_1$.  $$ H_2(T^2) = \mathbb{Z}$$ using similar arguments as above.  Thanks for your help.  Edit  I posted the computations as an answer below. I got two up votes but I don't know by who so I'm not yet sure I can trust them... How to get ongoing notifications of unread texts? One of my family members texts me at night when they are having nightmares. I want to know when they text me at 4 am instead of sleeping through it.  Is there a way to make text notifications keep going off until read? Storable Action - System.LimitException: Too many DML statements: 1 @AuraEnabled(cacheable=true) public static String  deleteContacts(List&lt;String&gt; contactIds) {     List&lt;Contact&gt; returnList = new List&lt;Contact&gt; ();     String query = ' SELECT Id,Name, LastName,Department,MobilePhone, Email FROM Contact WHERE id IN : contactIds ';     for (Contact thisContact:  Database.Query(query)) {          returnList.add(thisContact);     }     try {       delete returnList;       return'deleted successfully';     }     catch(Exception ex){        return 'Problem occoured';     }  }  JS Method deleteSelected(){     deleteContacts({         contactIds :this.selectedIds     })      .then(result =&gt; {         this.dispatchEvent(             new ShowToastEvent({                 title: 'Success',                 message: result,                 variant: 'success',             }),         );         return refreshApex(this.getContactList, { searchKeyWord: '$searchKeyWord' });     })     .catch(error =&gt; {         this.error = error;     });