There is no /etc/default/rcS anymore on my ubuntu 18.04 server (no GUI)  I had set TMPTIME=20 and after the upgrade from 16.04 this seems to be reverted to a much shorter time. How can I customize the cleanup of /tmp ?    There where also other variables in rcS like UTC=yes or FSCKFIX=yes. Where have those gone?
How is the /tmp directory cleaned up? Is it automatic? If so, how frequently is it cleaned up?
What is the difference between "Redirection" and "Pipe"? This question may sound a bit stupid, but I can not really see the difference between redirection and pipes.  Redirection is used to redirect the stdout/stdin/stderr, e.g. ls &gt; log.txt.  Pipes are used to give the output of a command as input to another command, e.g. ls | grep file.txt.  But why are there two operators for the same thing?  Why not just write ls &gt; grep to pass the output through, isn't this just a kind of redirection also? What I am missing? QGIS corrupting shapefiles? I'm hoping someone out there might be able to help or suggest some tests to try and resolve some very odd QGIS behaviour of late...  Our core GIS team of 4 users has been testing v2.10 prior to roll-out for the remainder of the organization.  In the past couple of weeks we have had some very odd shapefile corruption things happening and are yet to isolate or identify a potential cause...  These have included:   Editing one line (using the scissor tool to split into two records) and having the resulting records attributes completely replaced by attributes from another geometry no-where near the edited row (spatially or in the attribute dbf) Line geometries completely disappear while their attributes get associated with an unrelated geometry  Line geometry get partially deleted and replaced with a vertice in infinity (line visually extends beyond the dataset and no matter how far zoomed out you never see the end)   The above is happening in a polyline layer, that we did discover has some multi-line geometries..? Perhaps this is impacting... but never saw this issue with v2.8 and the same layer. The layer has undergone MANY save-as's in the past week and many verify geometry checks as we thought invalid geometry may have been the cause...  In another separate layer yesterday, to a separate user (me) i created a layer with approx 30 polygons... adding, deleting some and doing some 'avoid intersection' to remove overlaps. Layer looks fine in qgis, saved and also a save-as to a completely new file but when i load into ArcGIS online (and later is ArcMap as a test) some of the overlaps and deleted objects are still there. Close and reopen qgis,  reopen the file and they are definitely not.  The project was created in v2.8 that i was editing in (but had been saved in 2.10).  Does anyone have any ideas/suggestions.  We do still have 2.8 installed as well as 2.10? We have never encountered issues like this when testing other new qgis versions while still running old ones? Is it okay to board only the second flight of a return ticket? The return ticket is much cheaper than buying one way I was browsing flight price at Singapore Airlines website, and a one-way flight from SIN to SFO cost this much:    That's quite expensive. I tried browsing around and found that a return flight from SFO to SIN and back to SFO cost much cheaper:    It's really weird because the second ticket includes the exact same flight that cost 1900+, but it's almost half the price. The reason for this counter-intuitive situation is explained in the answers this question   If I am located in Singapore and my intention is to fly one-way to SFO, is it safe to book the flight in the second picture and only board SFO-SIN leg? Will they deny me because I miss the SIN-SFO flight? I'm looking for mathematics books, courses + exercises for high school level. My daughter was high school certificated but she has stopped her studies for 5 years. She would like to be involved in new educational program but she needs to restore her mathematic capabilities.  Could you help me to identify which mathematics books can help her?  Thanks a lot for your reply,  FR. What are integers $x$ and $n$ such as $ x^4+x^3+x^2+x+1 = n^2$? What are the integer numbers $x$ such as $x^4+x^3+x^2+x+1$ is the square of an integer?  $0$ and $-1$ are obvious answers, but how many are there? Using a function in two different ways Let f be an r-cycle in $S_n$. Given any $h \in S_n$, show that $hfh^{-1} = (h(x_1), h(x_2), \dots, h(x_r))$ How can I combine two render layers? I would like to know which nodes can I combine this two render layers  width?    I've made this with alpha over node and transparent rendering. I want such an image but I don't want to lose the background (Sky texture).    Thanks for helping! :) So, I got some laptop charger from my neighbor and I was thinking about to do something with it. Then one day I feel tiny shock from the output of the charger. I thought ac to dc filtering mechanism maybe shorted. Then I had tested other remaining charger to see if there was any AC current going on. And they all do the same. Is it normal to have flow some AC through DC ? Can I do something about it ? make it safer for work ? It does not feel like comfortable. I need to add a coloured line before my caption; this is what I used:  \usepackage[labelfont=bf]{caption}  \DeclareCaptionFormat{myformat}{\hrulefill #1  #2 #3} \captionsetup[figure]{format=myformat}   but the figure turns out to be line this:    and not a horinzontal line which what I want  2) I want the line to be coloured RGB [152 204 204] with thickness about the same as \top rule. Can anyone show me how to do this? I'm working on a project that requires me to get some of the position and rotation values to give to an Arduino via pyserial, but after sifting through the Blender documentation I can't find how to get them through script. Is it wrong to write:  class A { public:     virtual ~A() = 0; };   for an abstract base class?  At least that compiles in MSVC... Will it crash at run time? Earlier I asked a question about  and got the answer that while it is only necessary for anonymous types, that it is used nonetheless to make writing code 'quicker'/easier and 'just because'.  Following  I saw that var gets compiled down to the correct type in the IL (you will see it about midway down article).  My question is how much more, if any, IL code does using the var keyword take, and would it be even close to having a measurable level on the performance of the code if it was used everywhere? Office 2016 Advanced Setup I would like to set a maximum execution time for sql queries like set_time_limit() in php. How can I do ? Numbering in algorithmicx I have simple code:  \documentclass{article}  \usepackage{algorithm}  \usepackage{algpseudocode}  \begin{document}  \begin{algorithm}   \caption{Examples}\label{alg:Examples}   \begin{algorithmic}[1]   \State $X=45$   \State $X=45$   \State $X=45$   \State $X=45$   \State $X=45$    \end{algorithmic} \end{algorithm}          \end{document}     How to put a point after the number of the algorithm? I use chapters in report:  \documentclass[a4paper,12pt]{report}  \usepackage{algorithm}  \usepackage{algpseudocode}  \begin{document}  \chapter{Chapter 1}  \begin{equation} X_2=4 \end{equation}  \begin{algorithm}   \caption{Examples}\label{alg:Examples}   \begin{algorithmic}[1]   \State $X=45$   \State $X=45$   \State $X=45$   \State $X=45$   \State $X=45$    \end{algorithmic} \end{algorithm}  \end{document}     How to change the numbering to take into account the chapters? Multiple simultaneous downloads using Wget? Show that if terms of a series have ratio less than the ratio of convergent series, then the series converges We have two infinite series $\sum a_n $ and $\sum b_n$, such that $a_n &gt; 0,\ b_n &gt; 0$ and $a_{n + 1}/a_n \leq b_{n + 1}/b_n$ for all $n$. Show that if $\sum b_n$ converges, then $\sum a_n$ also converges.   Any hints on how to prove this? I can sort of picture why this must be true, but I'm not sure how to prove this rigorously. I'm not sure using the ratio test would help here.. What happens if I use RAM of a faster speed than the CPU supports? Looking at the  CPU, under Memory types it says "DDR3-1333/1600". My question is, in what way does the CPU limit the RAM speed? What would happen if I put in a DDR3-2133 RAM chip together with the CPU, if the motherboard supports the faster RAM speed? Would it be better to get a RAM chip that is DDR3-1600 so it matches the CPU's listed frequency? Computing $\lim_{(x,y)\to (0,0)}\frac{x+y}{\sqrt{x^2+y^2}}$ What is the result of  $\lim_{(x,y)\to (0,0)}\frac{x+y}{\sqrt{x^2+y^2}}$ . I tried to do couple of algebraic manipulations, but I didn't reach to any conclusion.  Thanks a lot.