My linux(ubuntu 14.04) unexpectedly stopped working after reboot. I caught:  error: file '/boot/grub/i386-pc/boot.mod' not found.  Entering rescue mode ...    How to solve this? And what could be a reason for such problem? Ubuntu was loading updates when I initiated reboot.
error: file '/grub/i386-pc/normal.mod' not found. grub rescue&gt;   What can I do? I just sit and stare at it.   I found my old netbook (Dell Inspiron 1010) which I have not used for about four years. I replaced Windows XP with Ubuntu 12.10. I used my bootable USB drive. I installed and rebooted. I got the message that normal.mod is not found.   What should I do? Type exit, reboot, or quit? Should I re-install?
Can I board if my flight arrives 1.5 hours before my UK visa becomes valid? My visa to UK is valid starting from June 25 but my flight to LGW is June 24 10:30 PM (edit: this is landing time not departure based on VCE-LGW flight times presented by easyjet.com). I still have 1.5 hours until my visa becomes valid. I prefer not to change my flight because I don't want to pay extra charges.   Will the EasyJet airlines going to allow me on board? I will be coming from Venice. How long does it take from landing to Immigration in London Gatwick? Can I stay longer in the airport before I pass through Immigration? Can I still see my luggage in the conveyor belt after 1.5 hours? How much time before they take away my luggage from the belt? Generalizing a sequence. Consider a sequence of the form:  $x[n]=-1,-1...,1,1,...,-1,-1...,1,1... \quad n&gt;0$  One can think of this as a square wave ($\pm1$) with a 50 % duty cycle (coming from EE).  For the simplest case of such a series i.e. $-1,+1,-1,+1,-1...$, a general equation is quite trivial ($x[n]=-1^n$).  Can we have e general equation for the other cases i.e. when there are multiple $-1$'s followed by $+1$'s ? Let random vector $x = (x_1,...,x_n)$ follow multivariate normal distribution with mean $m$ and covariance matrix $S$. If $S$ is symmetric and positive definite (which is the usual case) then one can generate random samples from $x$ by first sampling indepently $r_1,...,r_n$ from standard normal and then using formula $m + Lr$, where $L$ is the Cholesky lower factor so that $S=LL^T$ and $r = (r_1,...,r_n)^T$.  What about if one wants samples from singular Gaussian i.e. $S$ is still symmetric but not more positive definite (only positive semi-definite). We can assume also that the variances (diagonal elements of $S$) are strictly positive. Then some elements of $x$ must have linear relationship and the distribution actually lies in lower dimensional space with dimension $&lt;n$, right?  It is obvious that if e.g. $n=2, m = \begin{bmatrix} 0 \\ 0 \end{bmatrix}, S = \begin{bmatrix} 1 &amp; 1 \\ 1 &amp; 1\end{bmatrix}$ then one can generate $x_1 \sim N(0,1)$ and set $x_2=x_1$ since they are fully correlated. However, is there any good methods for generating samples for general case $n&gt;2$? I guess one needs first to be able identify the lower dimensional subspace, then move to that space where one will have valid covariance matrix, then sample from it and finally deduce the values for the linearly dependent variables from this lower-dimensional sample. But what is the best way to that in practice? Can someone point me to books or articles that deal with the topic; I could not find one. In Python, what's the difference between 'except Exception as e' and 'except Exception, e' Prove for any $a&gt;1$ there exist a natural number, $N$, such that $a^n&gt;n$ for all $n \ge N$  My attempt:  By definition, for $N$ to be a natural number $1\le N \le ∞$ for any integer $N$.  By induction, the base case $n=1$ is true because $a^1&gt;1$ which is true.  Now assume that $a^k&gt;k$ is true, then it is also true for $n= k+1$.  Hypothesis  $a^{k+1}&gt;k+1$  Now I am not sure if I am on the right track Let $G$ a group with normal subgroups $M,N$ such that $M\cap N=\{e\}$.   i) Show that for every $m\in M$ and for every $n\in N$, $mn=nm$.   ii) If $G$ is generated by $M\cup N$ then $G\cong M \times N$.   This is an homework question for abstract algebra. I think I can prove $i)$. But I have no idea how to prove $ii)$. Can anybody give me a hint for this one ?    Here my proof for i): Let $n \in N$ and let $m\in M$. Let $x=mnm^{-1}n^{-1}$. As $N$ is normal subgroup, $mnm^{-1} \in N$. Therefore $x \in N$.  As $M$ is normal subgroup , $nmn^{-1} \in M$. Since $m\in M$, then $x=m(nm^{-1}n^{-1})\in M$. This implies that $c\in M \cap N$, then $c\in \{e\}$, then $c=e$, and we get $mn=nm$. 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? Remap Keys in Linux I'd like to switch my Ctrl and Alt keys under Linux (to make it more Mac-like).  How do I do this?  If it helps, I'm running Ubuntu 9.04. ESM is available for 12.04, which enables Advantage customers to keep receiving kernel updates and updates for many user space packages. In our case it's very important to know if we'll be able tot use Ubuntu 14.04 safely after April '19, because it is not possible to upgrade our application and migrate it to say, 16.04. How to upload string as file with jQuery or other js framework If column matches another file, print every line with match (awk/grep) How can I get my external IP address in a shell script? I need to find my external IP address from a shell script. At the moment I use this function:   myip () {      lwp-request -o text checkip.dyndns.org | awk '{ print $NF }' }   But it depends on perl-libwww, perl-html-format, perl-html-tree installed. What other ways can I get my external IP? Proof of $\gcd(a,b)=ax+by\ $ [Bezout's identity] How to order the Ubuntu Phone? Yes, of course, I want that Ubuntu Phone.   Where is the order now button? How many times can an Australian leave and re-enter South Africa (90 days at a time without a visa) in a year, and do they need to be out of the country for a certain period of time before they re-enter?  I want to be in South Africa for as long as I can, however as an Australian without a visa I can only stay for 90 days at a time. What I would like to do is simply leave South Africa and go to another country in Africa for a few days, before returning with a new 90 day allowance.    Is this possible, or must I wait a certain period before re-entering South Africa/is there a limit to the amount of times I can do this in one year? Let $A$ and $B$ be two constant matrices and let $x$ and $ y$ be two random vectors, what is the general formula for $Var(Ax+By)$? I know the formula for when $x$ and $y$ are scalar random variables and $A$ and $B$ are constants, but what about the matrix case? Maximize window shortcut What is the keyboard shortcut to maximize a window on OSX? I'd like to know the shortcut that is equivalent to double clicking on the window title. I do not want to make the window full screen. regular expressions / pattern matching on ubuntu command line Can misused Schema.org hurt SEO? I've inherited a site where I noticed that    there is an excessive use of Schema.org in all navigation elements pages describing products are marked as itemtype="http://schema.org/CreativeWork"   So I'm wondering if these tags are sending the wrong message and not truly optimized. I realize that the nav (1) is done in some themes, but I'm more worried about (2). Can it be a hit SEO-wise to mislabel pages instead of products? How can I find my Apple ID on my iPad? My mum can't find her apple ID on her iPad. I'm not with her at the moment and do not have an iPad so I don't know where to look.  She already has an Apple ID set up on this iPad, so I don't want to set up another one.