Recently my laptop has been unable to boot, I have been having hard drive problems over three past few weeks but I would like to know if I need a new hard drive or not.  When booting I get,  Error: unknown filesystem Entering rescue mode... Grubrescue&gt;   I have tried to fix it by following online guides, knew of Wichita told me to do this,  # on the grub shell do: set root=(hd0,6) set prefix=(hd0,6)/boot/grub insmod normal normal # boot into the system, then in the shell do sudo update-grub sudo grub-install /dev/sda   This failed after insmod normal and it stated error: unknown filesystem  I need some advice about if it's a hard drive fault or if it's fixable and if so how?
I did a dumb thing... I forgot that Ubuntu 10.04 (Lucid Lynx) switched to &nbsp;2 which puts a ton of *.mod files (kernel modules) in /boot/grub. I thought they were soundtrack files put there erroneously, and I moved them. Needless to say, the next reboot was traumatic. I was presented with something I had no memory of ever seeing... a 'grub rescue>' prompt.  With the help of  however, I was able to recover...   I discovered that GRUB rescue does not have 'cd', 'cp' or any other filesystem commands except its own variation of 'ls'. So first I had to find the partition with the /boot directory containing vmlinuz file and other boot image files... (approximation from memory of failed attempts, as well as blank lines for clarity, added 2014-07-10 by docsalvage)    grub rescue&gt;  ls   (hd0,4) (hd0,3) (hd0,2) (hd0,1)    grub rescue&gt;  ls (hd0,4)/boot ... some kind of 'not found' message  grub rescue&gt;  ls (hd0,3)/boot ... some kind of 'not found' message  grub rescue&gt;  ls (hd0,2)/boot ... grub ... initrd.img-2.6.32-33-generic ... vmlinuz-2.6.32-33-generic   I found a /boot directory containing the vmlinuz file vmlinuz-2.6.32-33-generic on partition (hd0,2). Then I manually booted from the 'grub rescue>' prompt. The following commands will...   Set the root to use the /boot directory on partition (hd0,2). Load kernel module linux. Set that module to use the kernel image vmlinuz-2.6.32-33-generic. Set initrd(initialize RAM disk) to use the image initrd.img-2.6.32-33-generic. Boot Linux.  grub rescue&gt;  set root=(hd0,2)/boot   grub rescue&gt;  insmod linux   grub rescue&gt;  linux (hd0,2)/boot/vmlinuz-2.6.32-33-generic root=/dev/sda2 grub rescue&gt;  initrd (hd0,2)/boot/initrd.img-2.6.32-33-generic   grub rescue&gt;  boot    This boots and crashes to the BusyBox prompt which DOES have some rudimentary filesystem commands. Then I moved the *.mod files back to the /boot/grub directory...  busybox&gt;  cd /boot   busybox&gt;  mv mod/* grub busybox&gt;  reboot  The reboot was successful, but that was a lot of work.   Is there an easier way?
C++ single template specialisation with multiple template parameters TikZ \foreach loop with macro-defined list The distance between touching objects What is the distance between, say, a cup of coffee and the table it rests on? What is the distance between two touching hands? Proof of the inequality $(x+y)^n\leq 2^{n-1}(x^n+y^n)$ I have been denied a visa several times in a row. How does one deal with such serial refusals? Usage of “when” or “while” in this context He left the house _ I was still sleeping   Would this sentence be better completed with when or with while? Can you intentionally fail a skill check? This comes up to me in the context of the 3.x/PF/d20 Fly skill, even when I simply read about it: Can you intentionally fail a Fly skill check, or any other skill check for that matter, if you, or your character for that matter, decides that the effects of failing the check are what is desired in the situation?  Example:  Take a a shapeshifted Draconian cruising at high altitude, with a few friends on his back who have some means of breathing air supply, whether it be mundane or magical.  Now lets say that the air supply goes kablooie, similar to a decompression or all-packs-trip in an airliner.  For the sake of the folks on his back -- if not himself, depending on if dragon forms need supplemental air to fly at such high altitudes, the Draconian has to lose altitude, and fast.  Considering that by RAW, a Fly check failure leaves yourself falling, would saying "I initiate a rapid descent" be enough to treat the next Fly check as an intentional failure, or would you have to roll a 'reverse' Fly check, where failing the check gives you the desired outcome of a rapid descent, and succeeding leaves you stuck at altitude?  P.S. I added the rules-as-written tag because a RAW answer is highly desired here, albeit not mandatory.  I can already mostly figure it out from a simulationist standpoint, but that answer involves going in-depth into airline flying and non-normal procedures. Who is responsible for defining a site logo? I mean, there are moderators of the site that define it, or stackexchange defines it? What are your thoughts on writing your text in images?  I'm not saying throughout the whole website... But in certain key locations like image carousels. And I'm not talking about the special cases where you have font types that browsers can't render. I'm talking about text that uses standard fonts and is not too big (3/4 bullets).  Should I embed the text in the images that compose the carousel? Or should I apply the text to the images as "real text" HTML?  What are the advantages/ disadvantages of using text in an image? I was so good with windows, now I’m feeling like a complete idiot.  I have an SSD for ubuntu and want to install the majority of my programs to a separate HDD but I have no clue how. All searches I have tried only turn up with dual-boot installations.   (RESOLVED -> ) I am also having trouble locating "/etc/". Specifically, to modify Conky. Searching for this term only turns up instances where people are telling you to access this file, not how to get to it. Suppose I have some theorem in the paper  Section 1 Theorem 1.1. Let ...  And then later in the paper I want to recall the theorem by reprinting it  Section 4 We recall Theorem 1.1: Theorem 1.1. Let ...  What's the proper way to do this? How unique is the php session id First of all, I know that light does indeed travel slower in a medium like air or water, but that's because the photons are bouncing off of the medium's particles and in different directions so the light beam as a whole is slowed down (or at least that's the classical explanation I've read somewhere).  But my question is about light traveling freely in the vacuum. What if an astronaut during a spacewalk switches on a flashlight towards the opposite direction he is moving. Will that light travel slower than normal?  If not, is there another way to make light move slower? For example, can you make a beam of light move so slow that you can visually perceive it being affected by gravity? Correct way to use include and includeonly when writing a large document like a thesis I am writing a large document with several chapters and I would like to work on each chapter separately. In my main.tex I include the chapters either like   \include{chap1.tex}  \include{chap2.tex}  \include{chap3.tex}   or   \input{chap1.tex}  \input{chap2.tex}  \input{chap3.tex}   I think \include is preferable if I want things to be referenced and cited correctly? but doing it the \include way latex main.tex I don't get any dvi output whereas with \input things compile fine to dvi. What's going wrong here?  I would then like to use \includeonly (or \excludeonly ) to work on individual sections of the document whilst maintaining the referencing etc.  A mwe can be handy:  \documentclass[a4paper,10pt]{article} \includeonly{chap1}  \begin{document}   \include{chap1}   \include{chap2}   \include{chap3} \end{document} In the following code, I need to use +/- where I have used it, and plus/minus where I have used it.  \documentclass{amsart} \usepackage{lipsum} \usepackage{calc} \parindent=0 pt \parskip=12 pt plus 0 pt minus 0 pt \def\headsep{25pt} \newcommand{\LAYOUT}[5]{%   \setlength{\hoffset}{0pt}   \setlength{\voffset}{0pt}   \setlength{\topmargin}{#1 - 1in - \voffset - \headheight - \headsep}    \setlength{\oddsidemargin}{#2 - 1in - \hoffset}   \setlength{\evensidemargin}{\oddsidemargin}   \setlength{\textheight}{#3}   \setlength{\textwidth}{#4}   \setlength{\marginparwidth}{#5} } \newcommand{\FULLPAGE}{\LAYOUT{1in}{1in}{9in}{6.5in}{0.75in}}  \FULLPAGE \begin{document} \lipsum[1-10] \end{document}   If I replace the plus and minus in line 5 with + and - I get an enigmatic  "missing begin{document}" error.    If I replace the minus's in lines 10-11 with "-" I get an equally enigmatic error:  "Missing number, treated as zero. Illegal unit of measure (pt inserted)."   Can somebody please explain when one can use +/- and when one can use plus/minus?  Presumably there's a good reason why latex's error messages are so completely mystifying, and why inconsistencies like these keep appearing? It's really hard to explain to my coauthors, who regularly complain that latex is the most infuriating program ever devised by mankind.  Thanks very much for any advice!   Leo Difference between standard error and standard deviation I'm struggling to understand the difference between the standard error and the standard deviation. How are they different and why do you need to measure the standard error? While I was looking at the values of the zeta function for the first natural numbers, I noticed that the sum of the values minus $1$, converge to $1$. Better put: $$\sum_{n=2}^{\infty} \left(\zeta(n)-1\right) = 1 $$ Furthermore, if you use only the even numbers for the zeta function, the sum will converge to $\frac{3}{4}$, or $$\sum_{n=1}^{\infty} \left(\zeta(2n)-1\right) = \frac{3}{4}$$  Leaving $$\sum_{n=2}^{\infty} \left(\zeta(2n-1)-1 \right)= \frac{1}{4}$$  This is probably common knowledge among mathematicians, but I couldn't find much about it on the internet. Is there a proof of this or perhaps even a simple explanation why this is so? Prove if $\operatorname{ord}(a)=m$, $\operatorname{ord}(b)=n$, and $\operatorname{gcd}(m,n)=1$, then $\operatorname{ord}(ab)=mn$.   I was reading this and was thinking how this proof would look like. I tried to do it and am not sure if this is correct. Here is what I did:  If $a$ and $b$ commute then $(ab)^{mn} = a^{mn} * b^{mn} = (a^m)^n * (b^n)^m = 1 * 1 = 1.$ So $ord(ab) | mn$.  Now, take $k = \operatorname{ord}(ab) = m^\prime * n^\prime$ where m' is relatively prime with $n$ and $n'$ is relatively prime with $m$. By the result above $m' | m$ and $n' | n$. Now we have $((ab)^k)^{m/m'} = 1$ since $(ab)^k=1$. But on the other hand, by the commutativity:  $$((ab)^k)^(m/m') =$$  $$((ab)^(m' * n'))^(m/m') =$$  $$ a^{n'm} * b^{n'm} = $$  $$(a^m)^{n'} * b^{n'm'}=$$  $$b^{n'm'} = 1$$  This implies that $n' * m'$ is divisible by $n$. But $m'$ is relatively prime with $n$, so we must have $n' = n.$ By symmetry, $m' = m$. So $ord(ab) = mn$.  Just to say this again, I want to prove if $a$ and $b$ commute and $m$ and $n$ are relatively prime then   $$ord(ab)=mn.$$   The comments are vague. I guess this must be the answer then and there probably is not another way to do this. Can newsletters take into account a user's ignored tags on that site? I have seen several questions that discuss using your "Favorite" tags to construct a newsletter.   I'm looking for a similar request - but for ignored tags.  I figure it might make sense to split this request from the "favorite" requests because it has different implementation.  Can we exclude questions on the "ignore" tags lists in the newsletter?   For example, I subscribe to the Board and Card Games newsletter.   Currently (and frequently) 6 of the 7 questions are about magic-the-gathering, a tag I have in my ignored list.     I now get a newsletter where at best 1/7 questions is interesting and worth clicking on.  Related questions about using "Favorites": Nested sequence of non-empty compact subsets - intersection differs from empty set I have the following proposition:  "If $(S_n)$ is a sequence of compact subsets of a metric space such that  $S_1 \supseteq S_2 \supseteq ... \supseteq S_n$  Then $\bigcap^\infty_{i=1} S_i$ $\neq$ $\emptyset$"  My lecture notes provide the following proof, whose last step I don't understand:    Proof: Assume by way of contradiction that $\bigcap^\infty_{i=1} S_i$ = $\emptyset$. Let $V_n := (S_n)^c$ for each $n$. The class $\mathbb{C} :=\{V_n: n \in \mathbb{N} \}$ is an open covering of $S_1$. Since $S_1$ is compact, $\exists I$ finite, $I \subset \mathbb{N}$, s.t $\{V_i: i \in I \}$ covers $S_1$. Let $n:=max(I)$. The class $\{V_1, ..., V_n \}$ also covers $S_1$ and we get the following contradiction   $\emptyset = \bigcap^n_{i=1} S_i = S_n$    So, I don't get the part from "Let $n:=max(I)$..." onwards, especially the contradiction. I have tried applying DeMorgan's Law and the only way the last equalities makes sense is if the union of $\{V_1, ..., V_n \}$ equals the whole metric space, a property I haven't been able to understand from the steps of the proof. This is a corollary to the finite intersection property, so it must have a connection but again I can't quite get it.  Thanks in advance