Ubuntu wont start after trying to fix brightness issue I'm running Ubuntu 18.04.2 LTS.  I had brightness issues in my Ubuntu so checked out a few forums. From  forum, I followed the instructions and did:  Opened the file /etc/default/grub using gedit or any other text editor. Found below line:  GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"    Changed above line to:  GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"   Also created the file /usr/share/X11/xorg.conf.d/80-backlight.conf with contents:  Section "Device"     Identifier  "Intel Graphics"     Driver      "intel"     Option      "AccelMethod"     "sna"     Option      "Backlight"       "acpi_video0"     BusID       "PCI:0:2:0" EndSection   Now Ubuntu won't start. It shows a black screen with the following boot messages.  [   2.601256] VFS: Cannot open root device "mapper/ubuntu--vg-root" on unknown-block(0,0) [   2.601308] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.15.0-48-generic #51~Ubuntu [   2.601336] Hardware name: Acer Aspire 47362 / Aspire 47362 BIOS V1.08 08/14/2009 [   2.601375] Call trace: [   2.601412]  dump_stack+0x58/0x81 [   2.601446]  panic+0x94/0x1e6 [   2.601479]  mount_block_root+0x199/0x234 [   2.601514]  ? calibrate_delay+190/0x4e0 [   2.601546]  ? create_dev.constrprop.7+0x3a/0x53 [   2.601581]  mount_root+0x33/0x35 [   2.601612]  prepare_namespace+0x11b/0x167 [   2.601645]  kernel_init_freeable+0x1b3/0x1c5 [   2.601679]  ? rest_init+0xa0/0xa0 [   2.601711]  kernel_init+0xd/0x100 [   2.601744]   ret_from_fork+0x2e/0x38 [   2.601795]  Kernel Offset: 0x3d000000 from 8x1a000000 from 8xc1000000 (relocation range: 8xc100000-0xf17dfdfff) [   2.601836]  ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on    unknown-block(0,0)
Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) Upon trying to upgrade from 10.10 to 11.04 all seemed to go well until the restart. This error message is what comes up:  Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)   How do we fix that?
Ubuntu 14.04 Wireless not working: no network interface. Atheros [168c:003e] device How to get bright concert photos? I've been starting to shoot some live music recently and have been doing an okay job and see an improvement with each time I shoot. However recently I was shooting and all of my photos have come out very dark, too dark to use really. I was shooting in manual with 1/100 shutter speed aperture as wide as possible and a 6400 iso. Any advice is welcome. Thanks in advance. Induction: Prove that $4^{n+1}+5^{2 n - 1}$ is divisible by 21 for all $n \geq 1$. Induction: Prove that $4^{n+1}+5^{2 n - 1}$ is divisible by 21 for all $n \geq 1$. I have this picture:  (I have the original in Pixen and could export it to several different formats. I went with PNG though since it's lossless.)  When I open my picture in Preview (OS X) and zoom in, it looks fine. The characters have extremely sharp boarders between them and the background. However, when I put it into my LaTeX document, compile it to a PDF (using TeXShop) and then zoom in, it suddenly have gotten blurry (see screenshot: ).  Minimal working example:  \documentclass[12pt]{article} \usepackage{graphicx} \begin{document} \includegraphics[scale=1]{fig1.png} \end{document}   In the end, I would like to be able to scale the picture freely without there being any blurring at all. I've read that it is possible to add a method to an existing object (i.e., not in the class definition) in Python.   I understand that it's not always good to do so. But how might one do this? Is errno thread-safe? Is voltage the speed of electrons? Why is this sentence correct? “She suggested that he go to the cinema.” Why is this sentence correct?     She suggested that he go to the cinema.   I would definitely use goes instead of go. MySQL sort after argument in IN() Prove that $\lim_{t\to \infty} t\mu(\{x:f(x)\geq t\})=0$ Problem  Suppose $f$ is a non-negative integrable function on a measure space $(X,\mathcal{A},\mu).$ Prove that $$\lim_{t\to \infty} t\mu(\{x:f(x)\geq t\})=0$$  Attempt  Let $E_t=\{x:f(x)\geq t\}$ Note that $f\chi_{E_t}\leq f$. Since $f$ is integrable, the Lebesgue dominated convergence theorem tells us that $$\lim_{t\to\infty} \int f\chi_{E_t}\rightarrow \int \lim_{t\to\infty} f\chi_{E_t}=0,$$ since $\lim_{t\to\infty} f\chi_{E_t}=0$ a.e. $\ ^{(1)}$ The result follows from the fact that $$t\mu(E_t)\leq\int f\chi_{E_t}.$$  Question  I am having trouble proving $(1)$. That is, how can I show that $f\chi_{E_t}\rightarrow 0$ a.e? $f(z)=\frac{z}{1+|z|} $ Is 1-1? How do I deal with a bored or distracted player bringing down the group? My group have been playing various D&amp;D style games for a few years,  I have one player however that often will drift off and start playing on his phone  and several times has actually fallen asleep (with his character having to be "nudged" along by his fellow players).  He insists he's "just tired" and "isn't bored" — and besides, he keeps insisting we all get together for D&amp;D and wants to play.  Unfortunately we're all pretty busy, so if I'm to get the group together at all it's usually late on a Sunday. After talking to the player he insists it's not the game, or the story, he just happens to be tired. But, it's the same excuse every week, and the odd times we've played at different times or situations, the falling asleep has happened.  How do I cope with:   The morale destroying (for me) idea of your players falling asleep through a campaign and story you've put lots of work into. The general tone of the room when this player loses interest. (Occasionally a couple of others zone out into Facebook when they're not "active" because the players have split up / gone unconscious).   Given that it's an "all or nothing" situation with the group (there are only 3 players and they won't play unless all 3 are around), how do I best deal with it? C# object references and Action types long long implementation in 32 bit machine As per c99 standard, size of long long should be minimum 64 bits. How is this implemented in a 32 bit machine (eg. addition or multiplication of 2 long longs). Also, What is the equivalent of long long in C++. This question, , seems to indicate $$\nabla_a \sqrt{g}=0.$$ Why is this the case? I've always learned that $$\nabla_a f= \partial_a f,$$ hence surely $$\nabla_a \sqrt{g}=  \partial_a\sqrt{g} \neq 0. $$  Where's the hole in my logic? Prove that a limit doesn't exist In my assignment I have to prove that the following function doesn't have a limit:  $$f(x)=\frac{x}{x-\lfloor{\sin x}\rfloor}$$ when $${x \to 0}$$  In other words, I have to prove that for every $\delta$ such that $0&lt;|x-{x_0}|&lt;\delta,$ $|f(x)-L|&gt;\epsilon$.  In fact, I don't even know how to start. Do I choose my $\delta$? I know that the sin function has certain values that's supposed to help me. How do I use it?  I have to prove this by definition, so I can't use limit arithmetic for example  Thanks. Can't Open files from a directory in python Why do electrons occupy the space around nuclei, and not collide with them? We all learn in grade school that electrons are negatively-charged particles that inhabit the space around the nucleus of an atom, that protons are positively-charged and are embedded within the nucleus along with neutrons, which have no charge. I have read a little about electron orbitals and some of the quantum mechanics behind why electrons only occupy certain energy levels. However...  How does the electromagnetic force work in maintaining the positions of the electrons? Since positive and negative charges attract each other, why is it that the electrons don't collide with the protons in the nucleus? Are there ever instances where electrons and protons do collide, and, if so, what occurs? How can I make 3D Text in Russian? I've seen a similar question on BSE about entering foreign languages into 3D Text, but it doesn't help. I've tried using two different fonts (both of which support Russian). I've tried enabling International Fonts in Blender's User Preferences, but it doesn't work as well. It either types English text with Greek letters or displays empty vertical rectangles.   If anyone has been able to add text in any foreign language, please let me know.  I actually found out that it can be easily done through Text Editor, which would be probably the best way for me since I would prefer to paste my text. Can anyone perhaps guide me through? I wanted to switch to Xfce (I had KDE and GNOME installed), and I did this :    sudo apt-get install xubuntu-desktop sudo apt-get remove kubuntu-desktop sudo apt-get remove ubuntu-desktop sudo apt-get autoremove   but to my surprise, I could still pick gnome, kde plasma, etc during the log in.  So, how do I completely remove KDE and GNOME desktops?