I am running Ubuntu 19.10. The gcc binary installed is  &gt; ls -laht /usr/bin | grep gcc ... lrwxrwxrwx  1 root root       12 Apr  8 17:38 x86_64-linux-gnu-gcc-ranlib -&gt; gcc-ranlib-9 lrwxrwxrwx  1 root root        8 Apr  8 17:38 x86_64-linux-gnu-gcc-ar -&gt; gcc-ar-9 lrwxrwxrwx  1 root root        8 Apr  8 17:38 x86_64-linux-gnu-gcc-nm -&gt; gcc-nm-9 lrwxrwxrwx  1 root root        5 Apr  8 17:38 x86_64-linux-gnu-gcc -&gt; gcc-9 lrwxrwxrwx  1 root root        5 Apr  8 17:38 gcc -&gt; gcc-9 lrwxrwxrwx  1 root root       22 Apr  8 17:38 gcc-9 -&gt; x86_64-linux-gnu-gcc-9 lrwxrwxrwx  1 root root        8 Apr  8 17:38 gcc-ar -&gt; gcc-ar-9 lrwxrwxrwx  1 root root       25 Apr  8 17:38 gcc-ar-9 -&gt; x86_64-linux-gnu-gcc-ar-9 lrwxrwxrwx  1 root root        8 Apr  8 17:38 gcc-nm -&gt; gcc-nm-9 lrwxrwxrwx  1 root root       25 Apr  8 17:38 gcc-nm-9 -&gt; x86_64-linux-gnu-gcc-nm-9 lrwxrwxrwx  1 root root       12 Apr  8 17:38 gcc-ranlib -&gt; gcc-ranlib-9 lrwxrwxrwx  1 root root       29 Apr  8 17:38 gcc-ranlib-9 -&gt; x86_64-linux-gnu-gcc-ranlib-9 -rwxr-xr-x  1 root root     1.2M Oct 10  2019 x86_64-linux-gnu-gcc-9 -rwxr-xr-x  1 root root      35K Oct 10  2019 x86_64-linux-gnu-gcc-ar-9 -rwxr-xr-x  1 root root      35K Oct 10  2019 x86_64-linux-gnu-gcc-nm-9 -rwxr-xr-x  1 root root      35K Oct 10  2019 x86_64-linux-gnu-gcc-ranlib-9 -rwxr-xr-x  1 root root      454 Apr 11  2011 c99-gcc -rwxr-xr-x  1 root root      428 May  7  2006 c89-gcc ...   I want to install gcc-8 for some specific uses only. I can install gcc by running  sudo apt update &amp;&amp; sudo apt install gcc-8   but I am worried that it will mess up everything in my /usr/bin directory, as well as other dependencies on gcc-9.  What is the safest way to install gcc-8 without having to build it myself?
I have gcc 7.3.0 on Ubuntu 18.04. But I am working on a project where I need gcc less than version 6. When I tried to install gcc 5.4 using sudo apt install gcc-5.4, I got this error:  Reading package lists... Done Building dependency tree        Reading state information... Done E: Unable to locate package gcc-5.4 E: Couldn't find any package by glob 'gcc-5.4' E: Couldn't find any package by regex 'gcc-5.4'     What is the appropriate way to install gcc 5.4?
Suppose that $a_1,a_2, \cdots, a_n$ are $n$ different integers. Then $[(x-a_1)(x-a_2) \cdots (x-a_n)]^2 +1$ is irreducible over $\mathbb Q$.   I've no idea why it is true. Thanks very much. My exterior door deadbolt has gotten stuck - it'll open with the lever but not the key. By spraying WD-40 inside the lock, I've been able to get it to work but it's very stiff. I'd like to remove the lock and inspect the inside, either to clean/lube it or replace it. But I can't figure out how to remove the lock; there's no obvious way to do this. (I'm used to seeing two screws on the inside of the deadbolt, usually under the lever arms when it's horizontal.)    How do I remove this? I can loosen the cover plate on the inside but it doesn't do anything other than rotate a few degrees. Constants of integration in integration by parts Is it possible to redirect a command's output to cd? For example, I searched for a directory using locate and got the path to it. Now, instead of writing a cd path, can I redirect the locate output to cd?  I tried this:  $ locate Descargas | grep Descargas$ /home/oliver/Descargas $ locate Descargas | grep Descargas$ | cd $ locate Descargas | grep Descargas$ &gt; cd $ locate Descargas | grep Descargas$ &lt; cd /home/oliver/Descargas $    No luck. This probably isn't particularly useful, but I'm curious. Package incompatibilites: etoolbox, hyperref, and bm, standalone? I am trying to transition to using the etoolbox package, but seem to have run into some difficulties and they appear related to the hyperref and bm packages which to me seem totally unrelated.  The MWE example compiles since \RemoveEToolbox is defined and shows that there is no apparent problem before etoolbox was used.    Commenting out the \def\RemoveEToolbox{} line produces two problems:   With both the \renewcommand, and the usepackage{hyperref} commented, this results in "Runaway argument? Paragraph ended before \bm@test@token was complete". Including the usepackage{hyperref} (with \renewcommand commented) results in "Undefined control  sequence. \Call@AtVeryEndDocument ...cumentHook \@undefined"   But if uncomment the \renewcommand{\bm}{#1} line (effectively doing without any \bm), then this seems to compile.  I have been using this for a while now and things appeared to have been working fine, but now that I attempt to use etoolbox I seem to run into problems.  \documentclass{standalone} \def\RemoveEToolbox{}% Shows that this works fine without {etoolbox}  \usepackage{amsmath} \usepackage{xcolor} \usepackage{bm}  \ifdefined\RemoveEToolbox     \newcommand*{\iftoggle}[3]{#2}% Default to true value of "if" \else     \usepackage{etoolbox}     \newtoggle{paper}     \toggletrue{paper}      %\renewcommand{\bm}[1]{#1}% Why can't I have a normal \bm with {etoolbox}? \fi  % \usepackage{hyperref}  \begin{document}  This document is intended for  \iftoggle{paper}{paper}{electronic} distribution.  \bm{\textcolor{blue}{Solve $x^2-1=0$}}  \begin{align*}     a &amp;= b\\     \iftoggle{paper}{         c &amp;= d\\     }{}     e &amp;= f\\ \end{align*} \end{document} Why does Unix store timestamps in a signed integer? Why is a signed integer used to represent timestamps? There is a clearly defined start at 1970 that's represented as 0, so why would we need numbers before that? Are negative timestamps used anywhere? Similar to this question posted in August 2014:       Has the fact that  (as  in The Fires of Pompeii, and  in Torchwood’s Children of Earth season) yet been addressed/explained either in, or out of universe? How to interleave the lines of two or more files? I have tried to get the 2 files output in a single file.  I have tried below command:  cat file1 file2   but here file2 data is appending to file1.  What I need is file1 1st line followed by file2 first line, and file1 second line followed by file2 second line etc.  Can anybody tell me how to do this in a simple way? What does "Ubuntu" mean, and why did they choose that particular name? How do I check OS with a preprocessor directive? I have a cheap Chinese made tablet from Dubai called the Crony Dubai (www.cronydubai.com). It has a micro B, mini HDMI and a USB labeled as "Host" as well as a micro SD slot. It came with a micro B to USB adapter in box, and its running Ice Cream Sandwich. Is there a way to load Ubuntu on it? Also the tablet is very buggy and crashes often, would that be due to the tablet or the OS? Should a math paper use non-alphabetical ordering of authors' names for unequal contributions? Using alphabetical ordering for authors' names is a long established tradition in mathematics. In the situations of extremely unequal contributions, is it reasonable to break from this tradition?  Has there been any examples?  If it is common, what is the threshold for breaking from alphabetical ordering? Gravitational shielding and equivalence principle CDN: How is it possible that my DNS delivers a different IP depending on the visitors location? I found  how a CDN works. But there is one thing I don't really understand. Let's assume I setup multiple DNS servers at my location and they use the nameserver domains dns1.example.com, dns2.example.com and dns3.example.com. This DNS servers are able to deliver a server IP depending on the visitors location (ping, geo database, browser language or whatever). Now I update this nameserver settings for my domain www.example.org at the registry.  Now, the very first request on www.example.org with an expired TTL tries to resolve the domain. It asks:   the local .hosts/DNS, if TTL expired: the internet providers DNS, if TTL expired: the root DNS, if TTL expired: my local dns1.example.com   But if I understand it correct, the new IP is then added to all these nameserver caches until the TTL expires again. So how is it possible to send other IPs to the visitor depending on his location?  In  theandym said the request is "forwarded", but I don't think this is how a CDN works, because "forwarding" means lengthen the transmission way resulting a longer loading time. Or does a CDN require zero TTL for the domain?  Update1 Through  I found  describing how they optimized CDN performance. It did not explain how the CDN works in general, but there were interesting explanations like the following:     Thereafter, whenever a client attempts to fetch content hosted on the   CDN, the client is redirected to the node determined to have the least   latency to its prefix. This redirection however is based on the prefix   corresponding to the IP address of the DNS nameserver that resolves   the URL of the content on the client’s behalf, which is typically   co-located with the client.   This means Google checks at first the latency of all IP prefixes and defines a DNS resolution table (?) for all available prefixes. And if a visitor has the IP 198.51.100.231 the Google server IP is used, that is set for the prefix 198.51.100.0. But again: How does Google's DNS know which IP the visitor is using? Most visitors resolve Google's domain through their internet provider and by that the resolving is done through those external DNS servers or not?  As an additional example: If I start a DNS resolution for the domain facebook.com with different online tools (hosted in different countries) it is resolved to different IPs with different domains like:   31.13.92.36 Reverse: edge-star-mini-shv-01-frt3.facebook.com 31.13.76.68 Reverse: edge-star-mini-shv-01-sea1.facebook.com 31.13.69.228 Reverse: edge-star-mini-shv-01-iad3.facebook.com 157.240.2.35 Reverse: edge-star-mini-shv-01-ort2.facebook.com   After that I thought it could depend on the DNS server location used by the visitor, but I tried my own (Deutsche Telekom, Germany), Google's (8.8.8.8) and a major one from France (Orange) and they all returned for facebook.com the IP 31.13.92.36. Word for Negatively Surprising I'm searching for a word representing "Negatively surprising", or "Negatively amused" in an appropriate form. Example: Someone who proclaims he aims to do things in the right way has done something in the completely opposite way.    How could you have done such a thing? That action is very ___.   Said with the purpose of showing the contrast between the expected and the actual, and asking for change to adhere with his set goals, instead of just pointing out disappointment.  It is different from  because it asks there about surprise of being affected by the disappointment. The meaning of surprise here is different. Apply a modifier as a shapekey into existing shapekey or merge shapekeys? I am making a shapekey of a model shrinkwrapped to another model. The shrinkmap modifier is too inaccurate to wrap to the model alone. So, my first step was to roughly hand position the geometry around of the first model around the second, then use shrinkwrap. The rough positioning was done as a shape key. I can then apply shrinkwrap, but its as a separate shapekey. The two do not work well together. I need them to be the same shapekey. How do I apply a modifier to an existing shapekey, or merge/combine/join the two shapekeys? Very simply put:  I have a class that consists mostly of static public members, so I can group similar functions together that still have to be called from other classes/functions.  Anyway, I have defined two static unsigned char variables in my class public scope, when I try to modify these values in the same class' constructor, I am getting an "unresolved external symbol" error at compilation.  class test  { public:     static unsigned char X;     static unsigned char Y;      ...      test(); };  test::test()  {     X = 1;     Y = 2; }   I'm new to C++ so go easy on me. Why can't I do this? Repair disk from single user mode (fsck fails) A  is formed when a raindrop refracts light, but why then does the whole sky not become a huge rainbow when it rains? Would the light not be dispersed into ordinary white light? What causes it to look as if each end is nearly touching the ground? How can I share files over a Windows network? I have a media computer which I recently reformatted to Ubuntu 10.04. I am probably just missing something obvious but I can't figure out how to share folders and files, so that I can browse to them on my Windows computers in order to copy files to/from the computer.  How do I do this?