I am learning server stuff and I have one chapter about /etc/passwd  i have this:  root:x:0:0:root:/root:/bin/bash bin:x:2:2:bin:/bin:/bin/sh sys:x:3:3:sys:/dev:/bin/sh sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/bin/sh man:x:6:12:man:/var/cache/man:/bin/sh lp:x:7:7:lp:/var/spool/lpd:/bin/sh mail:x:8:8:mail:/var/mail:/bin/sh news:x:9:9:news:/var/spool/news:/bin/sh uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh proxy:x:13:13:proxy:/bin:/bin/sh ...some otehrs... irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin whoopsie:x:105:114::/nonexistent:/bin/false vmail:x:150:8:Virtual maildir:/var/zpanel/vmail:/sbin/nologin   I want to know what is the difference between /bin/false - /sbin/nologin and /usr/sbin/nologin
I have often heard it recommended that a user account should be disabled by setting its shell to /bin/false. But, on my existing Linux systems, I see that a great number of existing accounts (all of them service accounts) have a shell of /sbin/nologin instead.  I see from the man page that /sbin/nologin prints a message to the user saying the account is disabled, and then exits. Presumably /bin/false would not print anything.  I also see that /sbin/nologin is listed in /etc/shells, while /bin/false is not.  The man page says that FTP will disable access for users with a shell not listed in /etc/shells and implies that other programs may do the same. Does that mean that somebody could FTP in with an account that has /sbin/nologin as its shell?  What is the difference here? Which one of these should I use to disable a user account, and in what circumstances? What other effects does a listing in /etc/shells have?
Sorting references with special characters alphabetically I have a problem within the reference list. Namely I have some references where the authors first surname letter is Š (\v{S}) and when listing them in the references they appear amid those authors whose surname starts with V instead after those whose surname starts with S and those whose starts with T (it should list R, S, Š, T... and not R, S, T, U, V with Š in between)  Here is my minimal working example:   \documentclass{article}  \usepackage{filecontents}  \begin{filecontents}{AA.bib}  @article{simovic13, Author = {\v{S}imovi\'{c}, H. and Deskar-\v{S}krbi\'{c}, M.}, Journal = {Zbornik radova Ekonomskog fakulteta u Rijeci}, Number = {1}, Pages = {55--78}, Title = {Dynamic effects of fiscal policy and fiscal multipliers in {Croatia}}, Volume = {31}, Year = {2013}}  @misc{tenhofen07, Author = {Tenhofen, J. and Wolff, G. B.}, Note = {Deutsche Bundesbank Discussion Paper Series 1: Economic Studies No. 14. Frankfurt am Main: Deutsche Bundesbank}, Title = {Does anticipation of government spending matter? Evidence from an expectation augmented {VAR}}, Year = {2007}}  @misc{spilimbergo09, Author = {Spilimbergo, A. and Symansky, S. and Schindler, M.}, Note = {IMF Staff Position Note No. 11. Washington: International Monetary Fund}, Title = {Fiscal multipliers}, Year = {2009}}  @misc{ver11, Author = {Verhelst, S.}, Note = {Egmont Paper, No. 47, Brussels: Egmont Institute}, Title = {The Reform of European Economic Governance: Towards a Sustainable Monetary Union?}, Year = {2011}}  @article{vuckovic10, Author = {Vu\v{c}kovi\'{c}, V.}, Journal = {Privredna kretanja i ekonomska politika}, Number = {125}, Pages = {61--88}, Title = {Political Business Cycles: Do They Exist in {Croatia?}}, Volume = {20}, Year = {2010}}  \end{filecontents}   \begin{document} \nocite{*}   \bibliographystyle{plain} % works % \bibliographystyle{alpha} % works ... % \bibliographystyle{apalike} % works \bibliography{AA} \end{document}   I am thankful for any help!!!  Ana Unity smooth local rotation around one Axis, oriented toward a target When does Thread.CurrentThread.Join() make sense? Understanding p-value I know that there are lots of materials explaining p-value. However the concept is not easy to grasp firmly without further clarification.  Here is the definition of p-value from Wikipedia:     The p-value is the probability of obtaining a test statistic at least   as extreme as the one that was actually observed, assuming that the   null hypothesis is true. ()   My first question pertains to the expression "at least as extreme as the one that was actually observed." My understanding of the logic underlying the use of p-value is the following: If the p-value is small, it's unlikely that the observation occurred assuming the null hypothesis and we may need an alternative hypothesis to explain the observation. If the p-value is not so small, it is likely that the observation occurred only assuming the null hypothesis and the alternative hypothesis is not necessary to explain the observation. So if someone wants to insist on a hypothesis he/she has to show that the p-value of the null hypothesis is very small. With this view in mind, my understanding of the ambiguous expression is that p-value is $\min[P(X&lt;x),P(x&lt;X)]$, if the PDF of the statistic is unimodal, where $X$ is the test statistic and $x$ is its value obtained from the observation. Is this right? If it is right, is it still applicable to use the bimodal PDF of the statistic? If two peaks of the PDF are separated well and the observed value is somewhere in the low probability density region between the two peaks, which interval does the p-value give the probability of?  The second question is about another definition of p-value from Wolfram MathWorld:     The probability that a variate would assume a value greater than or   equal to the observed value strictly by chance.   ()   I understood that the phrase "strictly by chance" should be interpreted as "assuming a null hypothesis". Is that right?  The third question regards the use of "null hypothesis". Let's assume that someone wants to insist that a coin is fair. He expresses the hypothesis as that relative frequency of heads is 0.5. Then the null hypothesis is "relative frequency of heads is not 0.5." In this case, whereas calculating the p-value of the null hypothesis is difficult, the calculation is easy for the alternative hypothesis. Of course the problem can be resolved by interchanging the role of the two hypotheses. My question is that rejection or acceptance based directly on the p-value of the original alternative hypothesis (without introducing the null hypothesis) is whether it is OK or not. If it is not OK, what is usual workaround for such difficulties when calculating the p-value of a null hypothesis?     I posted a new  that is more clarified based on the discussion in this thread. The search parameter isanswered ignores acceptances Why aren't orbitals symmetric? Carry over long sequence of missing values with Postgres I have a table like this:  create table foo (foo_label text, foo_price int, foo_date date);  insert into foo (           values           ('aaa', 100,  '2017-01-01'),           ('aaa', NULL, '2017-02-01'),           ('aaa', NULL, '2017-03-01'),           ('aaa', NULL, '2017-04-01'),           ('aaa', 140,  '2017-05-01'),           ('aaa', NULL, '2017-06-01'),           ('aaa', 180,  '2017-07-01')         );   As you can see a few values on the foo_price column are missing.  What I need is that missing values get filled up with the "previous" available value in this way:   foo_label | fixed_foo_price | foo_date -----------+-----------------+------------  aaa       | 100             | 2017-01-01  aaa       | 100             | 2017-02-01  aaa       | 100             | 2017-03-01  aaa       | 100             | 2017-04-01  aaa       | 140             | 2017-05-01  aaa       | 140             | 2017-06-01  aaa       | 180             | 2017-07-01   My attempt:  select      foo_label,      (case when foo_price is null then previous_foo_price else foo_price end) as fixed_foo_price,     foo_date from (   select        foo_label,        lag(foo_price) OVER (PARTITION BY foo_label order by foo_date::date) as previous_foo_price,        foo_price,       foo_date       from foo ) T;   As you can see from here:    It doesn't fill completely the '100' series.  Any idea how can I get the wanted result? Kill the [bugs] tag? It seems most of the questions tagged  on Stack Overflow are just intended to indicate "there's something wrong with my program", which would cover probably at least 80% of all questions on Stack Overflow.  There are some questions where it seems to refer to a possible bug in a framework or utility. I'm not sure the tag is really all that useful in that case either.  What does meta think? When I dip a paper towel in a cup of water the water gets drawn up due to . How is this reconciled with conservation of energy, as it would seem on the surface that the potential energy of the system has gone up with no work being done? Limiting Length of Input in JTextField is not working A Basic Question about Gravity, Inertia or Momentum or something along those lines Why is it that if I'm sitting on a seat on a bus or train and its moving quite fast, I am able to throw something in the air and easily catch it? Why is it that I haven't moved 'past' the thing during the time its travelling up and down? How to use the symbol \angle at the section title Crop a big picture into several small size pictures Is there a a way with GIMP editor to crop a big picture into several small equal sized pictures? So when all those small pictures connected in order would make a big picture. I am wondering how to differentiate all these different joins ... Logical volume is not mounted but is in use. Please close all applications using this device (eg iscsi) With constant travel, is it possible to not have a tax residence? I have absolutely no experience with Linux, and I desperately need to get my computer back up and running again with Windows.  How do I remove Ubuntu and reinstall Windows?    Editor's note: many of the answers are about removing Ubuntu from dual-boot but keeping Windows (which is a bit complicated), while other answers are about removing Ubuntu from single-boot (which is easy: basically just format the disk while installing Windows). The question as written is ambiguous between dual-boot or single-boot. Reference: Why are my "special" Unicode characters encoded weird using json_encode? Weird future tense usage I am now reading  book and have noticed a couple of cases of weird (for non-native speaker) future tense usages.   The point of the kata is to train your fingers and your brain. I'll do a kata or two every day, often as part of settling to work. I might do it in Java, or in Ruby, or in Clojure, or in some other language for which I want to maintain my skills.`   The phrase about doing a kata or two every day looks perfect for Present Simple. Why does the authoer use Future Simple instead?   However, a professional also knows that there will be times when he will fail, his risk calculations will be wrong, his abilities will fall short; he'll look in the mirror and see an arrogant fool smiling back at him.   Shouldn't we use Present Simple after when/if in this kind of cases? I am especially curious about this case as sometimes I forget to switch to Present Simple after if/when and I thought it is a critical error (which I didn't expect to see in a book). What do 'real', 'user' and 'sys' mean in the output of time(1)?