GRUB booting error I am getting this grub rescue error no filesystem thing. I have read a lot of threads on this issue, but those solutions are not working. I tried live CD, and changed the booting option from hard disk to CD ROM, but still I get the same grub rescue error.   I have two operating systems, the other one is Windows 7. I formatted some part of my hard drive during which GRUB might have lost some files. I get that, but now what should I do? Please tell me how to deal with this thing:   Error: unknown filesystem. grub rescue&gt;
How to fix "error: unknown filesystem. grub rescue> I get this error:  Error: unknown filesystem. grub rescue&gt;   I'm not exactly sure what I did. I believe I installed Ubuntu over Windows on my Acer netbook. I then tried to install , but it wouldn't start installing.  I turned the netbook off and back on. Now I get the error.  I have read a lot of other questions like this, but in my case I cannot boot a CD. If I put a Ubuntu CD or a Linux Mint CD into my external CD/DVD drive and change my BIOS to boot the CD-ROM first, it just gives me the same error screen.  Update copied from comment dated 2012-05-26 02:54:29Z  Here are some results from my commands:   grub rescue&gt;ls (hd0) (hd0,msdos5) (hd0,msdos1)  grub rescue&gt;ls (hd0,msdos5) unknown filesystem  grub rescue&gt;ls (hd0,msdos1) unknown filesystem  grub rescue&gt;ls (hd0) unknown filesystem
Why do variable names often start with the letter 'm'? Let $a$ and $b$ be two integers such that $\left(a,b\right) = 1$. Prove that $\left(a+b, ab\right) = 1$.   $(a,b)=1$ means $a$ and $b$ have no prime factors in common  $ab$ is simply the product of factors of $a$ and factors of $b$.  Let's say $k\mid a+b$ where $k$ is some factor of $a$.  Then $ka=a+b$ and $ka-a=b$ and $a(k-l)=b$.  So $a(k-l)=b, \  a\mid a(k-1)$ [$a$ divides the left hand side] therefore $a\mid b$ [the right hand side].  But $(a,b)=1$ so $a$ cannot divide $b$.  We have a similar argument for $b$.  So $a+b$ is not divisible by any factors of $ab$.  Therefore, $(a+b, ab)=1$.  Would this be correct? Am I missing anything? I was trying to do some of these questions to check my understanding about the topic, but I'm not sure if they're correct. Here are my answers.   1) Suppose $f$ is continuous on $[0,1]$. Must there be a nondegenerate closed subinterval $[a,b]$ of $[0,1]$ for which the restriction of $f$ to $[a,b]$ is of bounded variation?   No, because $f(x)$ might be a constant function. In this case, $f(x)$ will not be the difference of two increasing functions...and so will not be of bounded variation.  2) Let $f$ be the Dirichlet function, the characteristic function of the rationals in $[0,1]$. Is $f$ of bounded variation on $[0,1]$?   No, because we cannot express it as the difference of two increasing functions.  3) Let $f$ be a step function on $[a,b]$. Find a formula for its total variation.  If we partition $[a,b]$ in such a way that for each $[x_{i-1}, x_i]$ (which is part of the partition), $x_{i-1}$ and $x_i$ each correspond to the midpoint of a step. I know this is not a formal answer, but I'm just trying to check my understanding. Why, historically, do we multiply matrices as we do? Multiplication of matrices &mdash; taking the dot product of the $i$th row of the first matrix and the $j$th column of the second to yield the $ij$th entry of the product &mdash; is not a very intuitive operation: if you were to ask someone how to mutliply two matrices, he probably would not think of that method. Of course, it turns out to be very useful: matrix multiplication is precisely the operation that represents composition of transformations. But it's not intuitive. So my question is where it came from. Who thought of multiplying matrices in that way, and why? (Was it perhaps multiplication of a matrix and a vector first? If so, who thought of multiplying them in that way, and why?) My question is intact no matter whether matrix multiplication was done this way only after it was used as representation of composition of transformations, or whether, on the contrary, matrix multiplication came first. (Again, I'm not asking about the utility of multiplying matrices as we do: this is clear to me. I'm asking a question about history.) This is a  about IPv6 Subnetting.      Related:               I know a lot about , and as I prepare to (deploy|work on) an IPv6 network I need to know how much of this knowledge is transferable and what I still need to learn. IPv6 seems at first glance to be much more complex than IPv4. So I would like to know:   IPv6 is 128 bits, so why is /64 the smallest recommended subnet for hosts? Related to this:   Why is it recommended to use /127 for point to point links between routers, and why was it recommended against in the past? Should I change existing router links to use /127? Why would virtual machines be provisioned with less than a /64 worth of addresses? Are there other situations in which I would use a subnet smaller than /64?  Can I map directly from IPv4 subnets to IPv6 subnets? For instance, does an IPv4 /24 correspond directly to an IPv6 /56 or /120? My interfaces have several IPv6 addresses. Must the subnet be the same for all of them? Why do I sometimes see a % rather than a / in an IPv6 address and what does it mean? Am I wasting too many subnets? Aren't we just going to run out again? In what other major ways is IPv6 subnetting different from IPv4 subnetting? Configuring ADB for Nexus 4 on Ubuntu 11.10 I'm trying to find the probability of getting 8 trials in a row correct in a block of 25 trials, you have 8 total blocks (of 25 trials) to get 8 trials correct in a row. The probability of getting any trial correct based on guessing is 1/3, after getting 8 in a row correct the blocks will end (so getting more than 8 in a row correct is technically not possible). How would I go about finding the probability of this occurring? I've been thinking along the lines of using (1/3)^8 as the probability of getting 8 in a row correct, there are 17 possible chances to get 8 in a row in a block of 25 trials, if I multiply 17 possibilities * 8 blocks I get 136, would 1-(1-(1/3)^8)^136 give me the likelihood of getting 8 in a row correct in this situation or am I missing something fundamental here? find examples of two series $\sum a_n$ and $\sum b_n$ both of which diverge but for which $\sum \min(a_n, b_n)$ converges Find examples of two series $\sum a_n$ and $\sum b_n$ both of which diverge but for which $\sum \min(a_n, b_n)$ converges. To make it more challenging, produce examples where $a_n$ and $b_n$ are positive and decreasing.  Edit: This problem is taken verbatim from Exercise 2.7.11 on page 68 of Abbott's Understanding analysis. Steady-State Current I am in the process of completing some homework and have come across a question that says: "What is the steady-state current?" It is asking in reference to a circuit that includes two capacitors in parrallel and a DC source of 24V and an AC source given by $\epsilon = 20 \cos(120 \pi t)\ \text{V}$, where $t$ is in seconds. I assume that it is asking when the current is constant. Because naturally the current is not constant due to the AC source, would I just consider the DC source for this? How can I store and retrieve a custom list in a blend file? I am trying to create a script that will allow me to generate a list and store it in the blend file. The list starts out blank and then strings get added to the list, resulting in: [&quot;test1&quot;,&quot;test2&quot;,&quot;test3&quot;] I create a PropertyGroup Class for the enum, define a new scene property as a CollectionProperty type with access to that enum Class, before appending a new item into the enum: import bpy  class item_set(bpy.types.PropertyGroup):     myItems = []     enums = bpy.props.EnumProperty(name=&quot;My Items&quot;, items=myItems) bpy.utils.register_class(item_set)  bpy.types.Scene.myItemSet = bpy.props.CollectionProperty(type=item_set)      newItem = bpy.context.scene.myItemSet.add() newItem.myItems.append(&quot;test&quot;)    I need to be able to add items to the list, save the blend file, re-open the file, run the script again and retrieve the list from the scene. However, the  states:  One thing to keep in mind is that after saving and reloading your blend-file, your new property will have disappeared...    ...To make the values you assigned in a previous session available again, you need to redefine the property. So after reopening the blend-file you need to rerun: bpy.types.Object.myProperty = bpy.props.StringProperty()   I can do the appending into and retrieval of the property values absolutely fine upon an initial run, but as the documentation states, the property is unavailable when trying to view it's contents on a reload of the file (after having run the script, saved and re-opened the file), but I am unsure how to redefine it without clearing all it's values. If I redefined the scene property, it would presumably also need the enum Class to be available, which would currently set myItems back to [] (empty). Do I need to change the way I am initially setting the items in the class or am I on entirely the wrong track with all of this? All I need to do is store a list in the blend file, so if there is a better way please let me know. Thanks. (I would hope, eventually, to be able to store sub lists [[&quot;a&quot;,&quot;b&quot;],[&quot;c&quot;,&quot;d&quot;],[&quot;e&quot;,&quot;f&quot;]], I'm just trying to get normal lists to work first.) How can I delete my account? I'm setting up a Cronjob that will backup a MySQL database I have in my server, but I don't want it to keep overwriting the same file over and over again. Instead, I want to have an array of backups to choose from, done automatically. For example:  ## Cronjob, run May 21st, 2011: mysqldump -u username -ppasword database &gt; /path/to/file/21-03-2011.sql  ## SAME Conjob, run May 28th, 2011: mysqldump -u username -ppasword database &gt; /path/to/file/28-03-2011.sql   And so on.  Is there any way that I can use the system date and/or time as some kind of variable in my Cronjob? If not, what are your suggestions to accomplish the same? How can I recover from a "AMD-Action:downloadProduct:SP" during installation of macOS? Just wiped my hard drive on my MacBook Pro from 2013. Went to install a new copy of MacOS Sierra. I get the following error:  AMD-Action:downloadProduct:SP   I looked online and tried change the date using the Utility Terminal and the following command:  date mmddHHMMyy   Then did   csrutil enable csrutil clear   Then I tried clearing the NVRAM using command + option + P + R on startup.  Still no luck. Still getting the same error message. Apple support told me to go to a "computer repair store".  Any advice? Which is more appropriate in the following sentence?     "I asked him to not judge her according to (or: based on) her beauty"   vs     "I asked him not to judge her according to (or:based on) her beauty"   or maybe you wouldn't choose either of the above, but something else? Is there a way in blender or an addon that allows me to select a bunch of faces (or verts) and evenly distributes (or relaxes) them into quads clean quads.  Without screwing up the vert ID/order.  Edit: I would like to have the shapes of my quads to turn into perfect squares while maintaining the volume of the object and the vertex order. Does the sum of reciprocals of primes converge? Is this series known to converge, and if so, what does it converge to (if known)?  Where $p_n$ is prime number $n$, and $p_1 = 2$,  $$\sum\limits_{n=1}^\infty \frac{1}{p_n}$$ Evaluation order of Button's action How many non-negative integer solutions does the equation $3x + y + z = 24$ have? Constant Amortized Time What is meant by "Constant Amortized Time" when talking about time complexity of an algorithm? Standard error of regression coefficient without raw data