My 4TB Seagate Backup plus works externally, not internally
Why is my USB drive showing corrupted data when plugged as an internal SATA drive?
What are the use cases of SO_REUSEADDR? I have used SO_REUSEADDR to have my server which got terminated to restart with out complaining that the socket is already is in use. I was wondering if there are other uses of SO_REUSEADDR? Have anyone used the socket option for other than the said purpose? How can I install Ubuntu without removing Windows? I need my pre-installed version of Windows 7 (or any other version of Windows), how could I install Ubuntu without erasing it? Proving $v(s,p)=2^{p-1}(2s-1)$ is a bijection of natural numbers and $f(s)=2s-1$ is a bijection between natural numbers and odd numbers. How do I prove this function is bijective? $$ v(s,p)=2^{p-1}(2s-1). $$ The domain is natural numbers and the codomain is also the natural numbers.  And this one: $$ f(s)=2s-1. $$ The domain is the natural numbers, and the codomain is the odd numbers in the natural numbers.  With this one I would do this to show it's injective: $$ \begin{align} v(s)&amp;=v(s_1)\\ \implies 2s-1&amp;=2s_1-1\\ \implies (2s_1)/2&amp;=(2s_2)/2\\ \implies s=s_1 \end{align} $$ So it's injective since if $v(s)=v(s_1)$ then $s=s_1$.  And to show it's surjective $f(s)=y$: $$ \begin{align} y&amp;=2s-1\\ \implies s&amp;=(y+1)/2 \end{align} $$ Then the function must be surjective since every $y$ is the same as the codomain for $f$.  Am I correct? How can I re-enter the US after time in Canada on the VWP? I am an Australian citizen, currently studying in Canada.   I entered the United States In July 22nd for 3 days, where I stayed in Seattle before leaving to return to Vancouver. I then again entered the states on 11th of October and returned on the 18th of October.  On October 19th my original and first Electronic System for Travel Authorization (ESTA), expired. I was under the impression that if I was to travel into the United States again I would have to apply for another ESTA and start the 90 days again, which I was planning on around December the 10th. In addition to this I am flying into Los Angeles on the 17th of December 2014 (where I plan to travel around the USA until flying out of Los Angeles again on 18th of January back to Australia).  However, after speaking to friends and looking at the website I have become confused on what my next course of action should be.  I am told that I cannot apply for another ESTA and be granted another 90 days visit into the USA, whilst I am in Canada and thus not be able to take any of my flights.  What would be the most appropriate action so that I can take my flights leaving North America and also travel the United States? "Inspirational" quote at start of chapter A clock in freefall Time dilation  using Schwarzschild metric for a non rotating spherical body is: $$t_0=t_f\sqrt{1-\frac{2GM}{rc^2}}$$  For such a non rotating spherical body, what would the time dilation of a clock in vacuum free-falling from infinity be?  (If the answer is non-trivial; a high level outline of the calculation would suffice / be appreciated)  Edit: I am currently working on an iOS app that is trying to model the mechanism underpinning relativity.  So, far the mechanism that I have created is shockingly simple and shockingly good at conforming to Relativity.  However, I am trying to break it.  I am trying to find any possible areas where the two may diverge.  I have noted that using my model a clock in freefall will experience no time dilation, i.e. $t_0=t_f$ and I want to make sure Relativity agrees.  I have noted the gravitational component of time dilation above.  Since my clock is moving one might also expect a kinematic time dilation.  I can calculate the velocity of my clock: $$E_k=\frac{1}{2}mv^2$$ $$E_p=\frac{-GMm}{r}$$ $$v=\sqrt{\frac{2GM}{r}}$$ Plugging this velocity into the kinematic time dilation equation: $$\Delta t'=\frac{\Delta t}{\sqrt{1-\frac{v^2}{c^2}}}$$ $$\Delta t'=\frac{\Delta t}{\sqrt{1-\frac{2GM}{rc^2}}}$$  At this point one might make the observation that the kinematic dilation is the inverse of the gravitational dilation and therefore conclude that: $$t_0=t_f$$ How do I install PowerShell? Not long ago I read something on Microsoft's website about PowerShell being available for Ubuntu.   How would I go about the install of PowerShell?  I'd appreciate guidance for both Xenial &amp; Trusty.   Any installation method is fine, whether compiling source or relying on a package-manager.  Source-compiling methods should contain beginner-level detail. Prove that , any primitive root $r$ of $p^n$ is also a primitive root of $p$ Is there a way to view &amp; modify the code of standard lightning components that are visible when editing the Napili template in the community builder. I was wondering if I could modify some of the code and use it as lightning out. Footnote, non-inline syntax? I would like to use footnotes without cluttering the container paragraph. Something like:  This is a very long complex\footnote[a] sentence.  \foottext[a]{So complex that I would prefer to pull out the footnote text.}   The idea comes from the [linktext][1], [1]: http://url.com markdown syntax. ext4 partition size / free space discrepancies While creating a 250GiB backup partition for my data, I have noticed lots of discrepancies between reported partition size and free space in Nautilus, gParted, df, tune2fs, etc.  At first I thought it was a GiB / GB confusion. It was not.  Then I thought it could be ext4's reserved blocks. It was not.  Im completely puzzled. Here are some images. Here are the steps:   First, NTFS. 524288000 sectors x 512 bytes/sector = 268435456000 bytes = 268.4 GB = 250 GiB.      Nautilus say "Total Capacity: 250.0 GB" (even though its actually GiB, not GB). Apart from that minor mislabeling, so far, so good   Now, same partition, formated as ext4 with gparted:     First, Last and Total sectors are the same. It IS the same 250GiB partition. Used size is 4.11GiB (reserved blocks maybe?)    Nope. Looks like reserved blocks are 12.7 GiB (~5%. ouch!). But... why Total Capacity is now only 246.1 GiB ???. That difference (sort of) matches the 4.11 GiB reported by gparted. But... if its not from reserved blocks, what is it? And why gparted didnt report that 12.7GiB of used space?  $ df -h /dev/sda5 Filesystem            Size  Used Avail Use% Mounted on /dev/sda5             247G  188M  234G   1% /media/BACKUP   df matches Nautilus in reported free space. But.. only 188M used? Shouldnt it be ~12GB? And total capacity is still wrong. So i ran tune2fs to find some clues. (irrelevant output is ommited)  $ sudo tune2fs -l /dev/sda5 tune2fs 1.41.12 (17-May-2010) Filesystem volume name:   BACKUP Filesystem UUID:          613d592e-47f5-4206-96a7-210090d340ef Filesystem features:      has_journal ext_attr resize_inode dir_index filetype extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize Filesystem flags:         signed_directory_hash  Filesystem state:         clean Filesystem OS type:       Linux Block count:              65536000 Reserved block count:     3276800 Free blocks:              64459851 First block:              0 Block size:               4096   65536000 total blocks * 4096 bytes/block = 268435456000 bytes = 268.4 GB = 250 GiB. It matches gparted.  3276800 reserved blocks = 13421772800 bytes = 13.4 GB = 12.5 GiB. It (again, sort of) matches Nautilus.  64459851 free blocks = 264027549696 bytes = 264.0 GB = 245.9 GiB. Why? Shouldnt it be either 250-12.5 = 237.5 (or 250-(12.5+4.11)=~233) ?  Removing reserved blocks:  $ sudo tune2fs -m 0 /dev/sda5 tune2fs 1.41.12 (17-May-2010) Setting reserved blocks percentage to 0% (0 blocks)  $ sudo tune2fs -l /dev/sda5 tune2fs 1.41.12 (17-May-2010) Filesystem volume name:   BACKUP Filesystem UUID:          613d592e-47f5-4206-96a7-210090d340ef Filesystem features:      has_journal ext_attr resize_inode dir_index filetype extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize Filesystem flags:         signed_directory_hash  Filesystem state:         clean Filesystem OS type:       Linux Block count:              65536000 Reserved block count:     0 Free blocks:              64459851 Block size:               4096   As expected, same block count, 0 reserved blocks, but... same free blocks? Didnt I just freed 12.5 GiB ?  $ df -h /dev/sda5 Filesystem            Size  Used Avail Use% Mounted on /dev/sda5             247G  188M  246G   1% /media/BACKUP     Looks like I did. Avaliable space went up from 233 to 245.9 GiB. gparted didnt care at all, showing exactly same info! (useless to post an identical screenshot)  What a huge mess!  I tried to document it as best as I could... So, please can someone give me any clue on what's going on here?   What are those misterious 4.11 GiB missing from NTFS -> ext4 formatting? Why there are so many discrepancies between gparted, Nautilus, tune2fs, df? What is wrong with my math? (questions in bold scattered this post)   Any help is appreciated. While I can not figure what is going on, I am serilously considering giving up on ext4 in favor of NTFS for everything but my / partition.  Thanks! Add Item to Finder Sidebar Method always returns true? Finding inverse of polynomial in a field I'm having trouble with the procedure to find an inverse of a polynomial in a field. For example, take:     In $\frac{\mathbb{Z}_3[x]}{m(x)}$, where $m(x) = x^3 + 2x +1$, find the inverse of $x^2 + 1$.   My understanding is that one needs to use the (Extended?) Euclidean Algorithm and Bezout's Identity. Here's what I currently have:  Proceeding with Euclid's algorithm:  $$ x^3 + 2x + 1  =(x^2 + 1)(x) + (x + 1) \\\\   x^2 + 1 = (x + 1)(2 + x) + 2$$  We stop here because 2 is invertible in $\mathbb{Z}_3[x]$. We rewrite it using a congruence:  $$(x+1)(2+x) \equiv 2 \mod{(x^2+1)}$$  I don't understand the high level concepts sufficiently well and I'm lost from here. Thoughts?  Wikipedia has a page on this we a , but it's still not clear in my mind.  Note that  has almost the same title, but it's a level of abstraction higher. It doesn't help me, as I don't understand the basic concepts.  Thanks. We're in the process of deploying a private openstack instance but don't have the Swift object storage service available yet. Can juju bootstrap launch a utility instance without swift? I see that the openstack configuration control-bucket is a container id. I just flagged a comment as "obsolete" in . To my surprise, it was deleted immediately, just after pressing "Flag Comment".  Now I see it in my flag summary as helpful:        Does this mean that obsolete flags are somehow handled automatically? I went through  but could not find any description on this. What is the time complexity of conjugate gradient method? I have been trying to figure out the time complexity of the conjugate gradient method.  I have to solve a system of linear equations given by  $$Ax=b$$  where $A$ is a sparse, symmetric, positive definite matrix.  What would be the time complexity of the conjugate gradient method? What does this red icon on my panel mean? This red icon.... It showed up after I upgraded to Ubuntu 12.04LTS; I can't figure out how to ditch it. It seems to be a notification thing.  I am at a loss.  The icon is this one:      I clicked it and read this:     An error occurred, please run Package Manager from the right-click menu or apt-get in a terminal to see what is wrong. The error message was:  'Error: BrokenCount&gt;0'.        This usually means that your installed packages have unmet dependencies. How to read dash files Effective way to find any file's Encoding