I have gone though man apt.conf. I feel the information there is quite overwhelming and difficult to understand for beginners moving to Ubuntu/Debinan Platforms. Could some one explain in simple english what is the use of this file and how it can benefit an apt user. Further this file seems be not setup on my machine - so I think it's not required for normal usage, but I am trying to understand advanced usage. so want to dig in to it. ll /etc/apt/apt.conf ls: cannot access '/etc/apt/apt.conf': No such file or directory  Edit: I feel trying to understand the apt conf part on a whole makes sense as every thing should be some or the other way related. On going to /etc/apt and doing an ls -l /etc/apt$ ll total 72 drwxr-xr-x   7 root root  4096 Aug 28 23:46 ./ drwxr-xr-x 144 root root 12288 Sep  1 15:53 ../ drwxr-xr-x   2 root root  4096 Sep  1 15:53 apt.conf.d/ drwxr-xr-x   2 root root  4096 Apr  9 15:51 auth.conf.d/ drwxr-xr-x   2 root root  4096 Apr  9 15:51 preferences.d/ -rw-r--r--   1 root root  3412 Aug 31 20:35 sources.list drwxr-xr-x   2 root root  4096 Aug 31 20:34 sources.list.d/ -rw-r--r--   1 root root  3410 Aug 31 20:35 sources.list.save -rw-r--r--   1 root root 14771 Aug 28 23:46 trusted.gpg -rw-r--r--   1 root root  8497 Aug 27 01:28 trusted.gpg~ drwxr-xr-x   2 root root  4096 Aug 28 23:46 trusted.gpg.d/  Evey thing here is understandable after bit of digging. Except for apt.conf.d/ (and  auth.conf.d/, which seems to be empty and I am not bothered about this in this Q). Now on entering - apt.conf.d/ and doing ll you see bunch of more files - /etc/apt/apt.conf.d$ ll total 96 drwxr-xr-x 2 root root 4096 Sep  1 15:53 ./ drwxr-xr-x 7 root root 4096 Aug 28 23:46 ../ -rw-r--r-- 1 root root   49 Aug 18 01:22 00aptitude -rw-r--r-- 1 root root   40 Aug 18 01:21 00trustcdrom -rw-r--r-- 1 root root  630 Apr  9 15:51 01autoremove -r--r--r-- 1 root root 1349 Sep  1 15:53 01autoremove-kernels -rw-r--r-- 1 root root   92 Apr  9 15:51 01-vendor-ubuntu -rw-r--r-- 1 root root  168 Aug 31 20:32 10periodic -rw-r--r-- 1 root root  108 Apr  2 16:55 15update-stamp -rw-r--r-- 1 root root   85 Apr  2 16:55 20archive -rw-r--r-- 1 root root  168 Aug 31 20:32 20auto-upgrades -rw-r--r-- 1 root root  243 Dec 16  2009 20dbus -rw-r--r-- 1 root root 1040 Mar 12 18:50 20packagekit -rw-r--r-- 1 root root  114 Jun  5 18:43 20snapd.conf -rw-r--r-- 1 root root 2592 Jan 18  2020 50appstream -rw-r--r-- 1 root root 2164 Feb  9  2019 50apt-file.conf -rw-r--r-- 1 root root  625 Oct  7  2019 50command-not-found -rw-r--r-- 1 root root 5459 Apr 14 04:07 50unattended-upgrades -rw-r--r-- 1 root root  435 Jan 18  2020 60icons -rw-r--r-- 1 root root  251 Jan 18  2020 60icons-hidpi -rw-r--r-- 1 root root  182 Aug  3  2019 70debconf -rw-r--r-- 1 root root   32 Aug 28 12:34 99synaptic -rw-r--r-- 1 root root  305 Apr  2 16:55 99update-notifier  So through this Q, I am looking for answers regarding the significance of apt.conf and the set of files in apt.conf.d/ - what kind of configurations does these files enable ( and of course man apt.conf is not quite understandable at least for beginners) Second Edit following user535733 response - How are the files in the apt.conf.d named. Do they follow some naming convention that simplifies understanding what config aspects go where.
I was browsing through the apt folder to try my proxy settings and I was unable to find the apt.conf file in Ubuntu 11.04. Is there any alternative file for it?  Adding proxy settings to 99-synaptic in apt.conf.d does not help as it gets overwritten everytime I restart the system.
What does the register keyword do in C language?  I have read that it is used for optimizing but is not clearly defined in any standard.  Is it still relevant and if so, when would you use it? How to apply a macro to each column of a table Can Objective C determine the caller object reference at runtime (reflection)? Can you cast Mirror Image twice on successive turns and have 6 duplicates of yourself instead of 3? (PHB, pg. 260) is a spell that has a casting time of 1 action, and a duration of 1 minute. My question is, can you cast Mirror image twice on successive turns, gaining 6 images by turn 2?  Sample Turns:  Turn 1: Mirror Image (3 images)  Turn 2: Mirror Image again (6 images, with 3 of them lasting 1 turn less)  Since Mirror Image doesn't require concentration, there should be no interference between the 2 casts in terms of concentration. I know that this could be up to DM Fiat, but I was wondering if there was a proper interpretation of the printed rules for this situation. How do I fix a "Problem with MergeList" or "status file could not be parsed" error when trying to do an update? How do I reset my Unity configuration? I've been messing around with Unity and broke something, how do I "start over"? Employment office encounters an alien masquerading as a human I'm looking for a story where a guy who has done job interviews for years is approached by an applicant, and because of his experience talking to people (I remember he specifically mentions having done something like 250,000 interviews), he immediately is able to tell the applicant is actually an alien in human form.  He goes on to help the alien understand human emotions &amp; teaches him how to fit in. A more succinct expression for "The day before yesterday" Is there a more succinct expression for "the day before yesterday"?   In German for example, gestern = 'yesterday.' The prefix vor roughly means before, so logically, vorgestern means 'the day before yesterday.'   Similarly, morgen = 'tomorrow', the prefix über roughly means over, so again, übermorgen means 'the day after tomorrow.'  (In Mandarin Chinese also you have respectively 前天 &amp; 後天.)  Presumably, there are also similarly logical ways to say "the page after the next" or "the paragraph before the last", etc.   Are there no similarly succinct, and graceful, expressions in English? Time-ordered operator in Srednicki , "Note that the operators are in time order...we can insert $T$ without changing anything". This I agree with. But then on the next paragraph he states "The time order operator $T$, moves all...where they annihilate...". How correct is this paragraph? Is equation (5.14) always valid? Is equation (5.14) the reason why the time-ordering symbol $T$ appears all over the place in QFT?  The equations I'm referring to are (braket package available?):   $$\langle f|i\rangle = \langle0|~a_{1'}(+\infty)a_{2'}(+\infty)a_{1}^\dagger(-\infty)a_{2}^\dagger(-\infty)~|0\rangle \tag{5.13} $$  and since time goes from right to left inside the braket we put the $T$-symbol  $$\langle f|i\rangle = \langle 0|T ~a_{1'}(+\infty)a_{2'}(+\infty)a_{1}^\dagger(-\infty)a_{2}^\dagger(-\infty)~|0\rangle \tag{5.14} $$   without changing anything.   After this, the $T$-symbol appears everywhere! What are the units of entropy of a normal distribution? I have a random process that follows a normal distribution. It's parameters are mean = 35 units, std.dev. = 8 units. I've seen from the  for the normal distribution that there is a formula to calculate the entropy. So plugging in the figures as:- $$     .5\log\left(2\pi e^1 8\cdot 8\right) $$ I get a value of 1.52, which I take to be  per sample.  My question is what are these units?  What thing do I have 1.52 of?    is (typically) measured in units of bits, after Claude Shannon's definition.  So can I take it that each sample generates 1.52 bits of entropy?  Clearly recording those samples generates information and therefore occupies a real and discrete amount of storage space. Ergo entropy cannot be unit less. Calling Java from MATLAB? Clicking links in pdfs opened with Okular opens Abiword (instead of the default browser) I work with Xubuntu 12.04 and use Okular (version 0.14.3) to view pdf files. If I click a web link in a pdf file (created with "pdflatex" using the "hyperref" package), "Abiword" (It's a word-processing software, like Libreoffice writer) is opened instead of my default browser google-chrome. How can I change this behavior? The settings in Okular do not seem to provide a solution.   (Note that I set google-chrome as the preferred application for web browsing under Settings -> Preferred Applications, so that's not the problem). How to draw arrows between circled coefficients of polynomials using tikz How tipe are this series?  $$\sum_{n=2}^\infty \frac 1 {n^2\ln n}$$ But $$\sum_{n=2}^\infty \frac 1 {n\ln n\ln(\ln n)}$$ I used Condensation Test, but I stack after that. Thanks! I need to be able to compare some month names I have in an array.  It would be nice if there were some direct way like:  Month.toInt("January") &gt; Month.toInt("May")   My Google searching seems to suggest the only way is to write your own method, but this seems like a common enough problem that I would think it would have been already implemented in .Net, anyone done this before? Aggregate Rating not displayed in Google search results What is the meaning of this "let there be light" joke? I've added many PPAs using the add-apt-repository command. Is there a simple way to remove these PPAs? I've checked in /etc/apt/sources.list for the appropriate deb lines but they aren't there.   This is on a server system so a command line solution would be great! When hyperref is loaded I receive the following error:     TeX capacity exceeded, sorry [input stack size=5000].   However, when I remove hyperref package it compiles successfully. I traced it back and found that \maketitle causes the error but don't know how to fix it. Is there any way to use hyperref in my setup.   Code:       %!TEX TS-program = xelatex     \documentclass[journal,transmag,]{IEEEtran}      \usepackage[hyphens]{url}     \usepackage{hyperref}      \usepackage{xunicode}      \usepackage{fontspec}      \usepackage{polyglossia}     \setmainlanguage{english}     \setotherlanguage{arabic}     \newfontfamily\arabicfont[Script = Arabic]{Amiri} % Replace 'Simplified Arabic' with a font from your system       \begin{document}     \title{A Very Nice Title}      \author{\IEEEauthorblockN{             John Doe\IEEEauthorrefmark{1}}%,~\IEEEmembership{Member,~IEEE}         \IEEEauthorblockA{\IEEEauthorrefmark{1}My address}         % &lt;-this % stops an unwanted space         \thanks{Manuscript received mm dd, 20xx; revised mm dd, 20xx.               }     }      % The paper headers     \markboth{headers...}%     {Shell \MakeLowercase{\textit{et al.}}: Bare Demo of IEEEtran.cls for IEEE Transactions on Magnetics Journals}      \IEEEtitleabstractindextext{%         \begin{abstract}My Abstract.\end{abstract}          % Note that keywords are not normally used for peerreview papers.         \begin{IEEEkeywords}             Key 1, Key 2     \end{IEEEkeywords}}      \maketitle       \IEEEdisplaynontitleabstractindextext     % \IEEEdisplaynontitleabstractindextext has no effect when using     \IEEEpeerreviewmaketitle       \section{Introduction}     English Text      \begin{Arabic}      السَلَامُ عَلَيكُمْ     \end{Arabic}       \end{document} Nonzero nilpotent elements in Zn So I've been stuck on this proof for the past threes days now. I keep going back and forth and making no progress.     Let $n\in \mathbb{Z}_{\geq 2}$. Show that $\mathbb{Z}/n\mathbb{Z}$ has a nonzero nilpotent element iff there is a prime $p$ s.t. $p^2$ divides $n$.   $(\Rightarrow)$ I know $a$ can be factored into distinct primes, so $a=p_1^{e_1}\cdot ...\cdot p_m^{e_m}$ then $a^k=p_1^{e_1k}\cdot ...\cdot p_m^{e_mk}$.  Also since $n|a^k$ so $a^k=nd$ for some $d\in \mathbb{Z}$.  $a^k=p_1^{e_1k}\cdot ...\cdot p_m^{e_mk}=nd$. So $nd$ has that distinct prime factorization.  Then I get lost on what to do.