Who washed the Prophet's(PBUH) Janaza?

Question:
Who were the persons(sahabas)R.A washed the Prophet's(PBUH)
Janasa(deadbody)?
Who was the Imam for the funeral prayer of Prophet(PBUH)?
Answer: If you are an arabic reader check this article from IslamWeb(which can also be translated to English) that states that the persons who washed the Prophet were: the prophet's family members who were: Al-Abbas, Ali, Al-Fadl and Kuthm (Al Abbas' sons), Shakran (the prophet's servant), Usama bin Zaid, and Aous bin Khawlah. However they washed him wearing his clothes, they didn't put his clothes off, then they enshrouded him by three clothes.
The answer to the prayer is also found in the above link, there was no Imam who prayed, the Muslims prayed each one alone on the Prophet (PBUH); the men, then the women, then the children. After that they buried him where he died.
Comment: I think this answer is from the Shia perspective, wasn't Abu Bakr (RA) the one that shrouded Prophet (PBUH)?
Answer: Imam Ali a.s. washed him directly but companions of Imam Ali a.s. helped him in pouring water and etc. also the first one who offered the Janasa prayer was Imam Ali a.s. and then male Sahaba and then female Sahaba. The Prophet SAWW was buried in his own home and the room was small few persons could enter and offer prayer and all could not pray together.
Reference:
www.andisheqom.com
Answer: When the Janazah of the Prophet (صلي الله عليه وسلم) was ready, then people came in groups and read the Janazah Salaah. Because the Janazah was inside the Hujrah Mubaarak, only few people at a time entered and read the Janazah Salaah and left, then others followed, but there was no Imam. [Madarijun Nabuiwat]
Ahmed Raza Khan رضي الله عنه states as follows in the fourth volume of his world renowned encyclopaedia Fatawa-e-Razviyah:

The Ulama have differences on the issue of the Janazah Salaah of the Prophet صلي الله عليه وسلم. One Jama'at says that the Janazah Namaaz did not really occur. Small groups came in and sent Durood and Salaams and then left, followed by others.
There are also many Ulama who accept this Namaaz Maroof. Imam Qaazi Iyaaz رضي الله عنه rectified this. Hazrat Abu Bakr Siddique رضي الله عنه was engrossed in giving hope to the Muslims and taking care of the needs of the Ummah. At this time, the allegiance had not been taken on his hands. People came in huge and small groups and continued to pray the Janazah Salaah of Rasoolullah صلي الله عليه وسلم.When the Allegiance was taken on the hands of Hazrat Abu Bakr Siddique رضي الله عنه and his Guardianship was confirmed, He prayed the Janazah Salaah, and after him non other prayed, as mentioned by Imam Shamsul Ulama Sarkhasi رضي الله عنه.
  [Fatawa Razvia vol.4. pg 54 - New Edition of Fatawa Razvia Vol.9 pg.286]

Who washed the Prophet's(PBUH) Janaza?


How to give error feedback during a drag operation?

Question: I am trying to give some visual feedback to the user during a drag/drop operation.  The feedback I'm struggling with is in the case where the drag target is somehow invalid for the type of data being dragged.  I'd like there to be some feedback (during the drag) which displays a small message as to why the drag would be invalid.
I am trying to implement this by adding an adorner to the target, and have this display some message when enabled.  This seems to work ok, but isn't great.  The adorner seems like quite a low level way of doing this, as I need to implement the OnRender function.  I would prefer if my adorner simply contained normal WPF controls (like text labels, etc), rather than have to define my own rendering.
Is there a way of adding normal WPF controls to an adorner instead of overriding OnRender?
Is there something I should be using instead of adorners to give feedback to the user during a drag operation?
Answer: You can use a Popup. It could contain any number of WPF controls in it.


Should I use an arithmetic or a geometric calculation for the Sharpe Ratio?

Question: What are the advantages/disadvantages of using the arithmetic Sharpe Ratio vs the geometric Sharpe Ratio?  Is one more correct?  Or is one better in certain circumstances?
Comment: It's a matter of keeping your units straight, IMO. If you use arithmetic Sharpe, make sure you're using logarithmic returns. If you are using geometric returns, make sure you take exponent of logarithmic standard deviation. I use log returns when prototyping (due to computational ease) and geometric returns when presenting.
Answer: In addition to John's answer and just to make things clear:
The arithmetic mean is given by
$$\mu_a = \frac{1}{n} \sum_{i=1}^n x_i$$
The geometric mean is given by
$$\mu_g = \sqrt[n]{\prod_{i=1}^n (1+x_i)} -1$$
And we have that
$$\mu_g \leq \mu_a$$
So not only would the geometric sharp ratio be taking into account the "actual" return of the portfolio, but it is also a more conservative measure.
Comment: Would it ever make sense to consider the Harmonic mean?
Comment: Where can I find a demonstration that $$\mu_g \leq \mu_a$$
Comment: @MarcoDemaio You can find it on Wikipedia: https://en.wikipedia.org/wiki/Inequality_of_arithmetic_and_geometric_means#Proofs_of_the_AM.E2.80.93GM_inequality
Comment: Assuming that you calculate the nominator of sharpe ratio using geometric mean, how do you calculate the denominator and annualize it properly? For the mean annualization procedure is clear and done by adjusting the root.
Answer: I'm not sure it makes sense to think of one as more correct than another. However, they do have significant differences. It may help to distinguish between ex-post evaluation of a strategy and ex-ante prediction of what the strategy's performance will be.
For simplicity, let's assume the log returns of the strategy are approximately i.i.d. univariate normal and the risk-free rate is a constant. If you were a mean-variance investor deciding between the risk-free rate and the strategy, you would estimate the mean and variance of the log returns, project it to the investor's horizon, and convert the normal to lognormal to obtain the arithmetic returns. So if you were calculating a Sharpe ratio that is consistent with the way it was originated in financial theory, i.e. the slope of the efficient frontier, would be this arithmetic ex ante expected Sharpe ratio.
However, the Sharpe ratio is also used in performance evaluation in different ways. I think one major reason that the geometric version is used is that the numerator will correspond with what the investor actually earned, the CAGR. This might be useful to some people, but personally I prefer to look at the CAGR by itself rather than in the Sharpe ratio. Further, the CAGR is the median of the lognormal distribution under some assumptions. I find it more intuitive to use the mean and keep ex-post consistent with ex-ante, which would bring me back to the arithmetic Sharpe.
Another reason to use the geometric version might be that it avoids the distributional issues with the lognormal distribution (since it has skewness/kurtosis). However, Opdyke (2007) provides the asympototic distribution of the Sharpe ratio under fairly general assumptions.
Answer: I think this is a no-brainer. Only log-returns make sense. The average return can only be computed by averaging the sum of individual log returns. Taking the average of standard (relative) returns does not give you an average of the individual returns. Consider a simple case where the value of an investment alternates between 100 and 50 an odd number of times. The standard return series would be: -0.5, 1, -0.5, …1 (-50% and +100%). The average of that sum gives us 0.25 (25%) – nonsense for an investment whose final value is the same as what we started with. The log returns, on the other hand give us alternating log returns of -0.6931, +0.6931, whose average is 0.
The difference between log returns and standard returns goes to zero as we shorten the period over which we evaluate the value of an investment: LN(P(n)/P(n-1)) is approximately equal to P(n)/P(n-1) – 1. Thus there would not be much difference between standard and log returns (and the computed Sharpe Ratio) if daily measurements were made. The scaling of that Sharpe Ratio from daily returns to annual returns is performed by the sqrt of the number of trade days (252), but that, of course assumes the return distribution is iid, which is not really the case.
Andrew W. Lo has a nice paper that considers the scaling of the Sharpe ratio when the return series is correlated ("The Statistics of Sharpe Ratios")
Answer: There are many variants proposed; some useful, some not so much. As an investor, the most important thing is to compare the exact same ratio, calculated in the exact same way, for each prospect. As the prospect/fund the most important thing is to be clear about the statistic you are reporting so your investors make well informed decisions. So let's start with some definitions specific to your question.
Sharpe ratio, sometimes called the "Modified Sharpe" ratio, is the arithmetic average of excess returns divided by the standard deviation of those returns, $r_t\in R$.
$Sharpe Ratio = \frac{E[R_t - R_{free}]}{\sigma}$  where  $R_t\in[-1,\infty)$, which is a percentage, and $R_{free}$ is the risk-free return rate, typically taken as the current T-Bill rate.
It is commonly calculated over annual periods, but monthly, or daily periods are common too. It is a class of signal-to-noise ratio indicating the expected reward per unit of risk. This is the most commonly cited variant and is the measure proposed by professor Sharpe in 1994.
The Geometric Sharpe ratio is the geometric average of compounded excess returns divided by the standard deviation of those compounded returns. This is equivalent to the arithmetic average and standard deviation of $log(1+r_t)$, which is the more convienient calculation.
The difference is mostly in the use of the average of the excess returns for the period or the compounded returns. Because the log returns are generally smaller, the "Geometric Sharpe ratios" generally suggests a higher number; about 12.5% higher for samples from a uniform distribution. Naturally, it is completely bogus to compare dissimilar ratios...so be sure you know which measure you are digesting.
Answer: The correct answer is "arithmetic mean, because Bill Sharpe says so". He invented the thing, and he's pretty clear on which one he was looking at.
If you use the geometric mean, which is lower the higher the volatility in the returns, and then you divide by standard deviation, you have essentially discounted your result TWICE for volatility.
Answer: The only correct way is using log returns.
To keep everything consistent, take a arithmetic mean of log returns.
Then calculate it net of the risk free (how do you subtract properly using geometric returns?).
Then divide (how do you do this properly using geometric returns?)
by the standard deviation (how would you calculate this properly with geometric returns?).
A geometric mean is just the tip of the iceberg. Geometric returns implies a bunch of new calculations which are far from standard.
Log returns are the only way to go with time series analysis.
Answer: For any real world applications, the difference between the arithmetic and geometric Sharpe ratios is likely to 'fall under the noise floor', i.e. be smaller, typically much smaller, than a standard error. This is even under the generous assumptions of stationarity and absence of omitted variables.
Answer: As a practical example, I have generated a sequence of returns where mean log returns are -12%, while the arithmetic mean is +1.1%.
This can happen with very heavy tailed distributions and, e.g. in evaluating hedge fund performance, the arithmetic return will mask this.
A glance at an equity curve would also highlight the issue so in reality no-one is likely to be fooled.
For unleveraged investing in stocks and indices it will make very little difference, but the arithmetic version is clearly wrong in some cases as it will give a positive sharpe for a series of returns resulting in a large loss of capital.
Comment: Can you post the return series which you are referring to?
Answer: The arithmetic average of +100% in Year 1 and -100% in Year 2 is 0%, but I we all know the result is not a 0% return. So arithmetic returns are absurd to use in any real life context. Maybe in another universe they can serve some purpose.
Answer: I didn't understand this either but after some googleing I understood the importance of geometric mean returns! The most stuff on the internet is in text form which is not easy to understand. So I visualized this discrepancy
Answer: Putting it succintly: It will depend if the returns are arithmetic or logarithmic in the first place.
If they are arithmetic returns, then the geometric mean will have to be used.
If they are logarithmic returns, then the arithmetic mean has to be used.


Does everyone see the same Pokémon?

Question: I was wondering if everyone sees the same Pokémon on the map. If I catch all the Pokémon around me will others be unable to get any?
Answer: From this reddit post I found out:

Same Pokémon spawns for every player in the same place.
Every player can catch it.
Once it is caught by one of the players, other players who faced it can still catch it.
Combat Power depends on the respective player's level.

Intensive playing of the game proved those facts. Incense might bring different results as it has only impact for the user.
Comment: There is an exception to this rule: Pokemon that appear as a result of using Incense will *only appear for you*. Nobody else will see them. Pokemon that appear at Lure Modules however are visible to everyone.
Comment: Not only one, we are like 100 people there and im sure most of them got the game so i thought they constantly grab all the pokemon :) edit: i have a theory that if you see them at the same time both can catch it but if someone catches it and you log on later its gone. No idea if thats the way it works though
Comment: So I'm wondering if they key here is "... other players who faced it can still catch it." Is it if you initiate against a pokemon before being captured, you can all get it?
Comment: Ok thats interesting. The thing is at our workplace there seem to be no pokemon at all since everyone plays it there. Not sure if this is just coincidence though.
Comment: So other people around you also benefit from your incense or is that an exception?
Comment: Ok now that I have some experience playing with a friend and going for a few walks I can say this: When we encountered a pokemon we can **both** catch it. It then stays on the map for a while. It only happened rarely that one could catch it and the other one was too slow (cause his app was closed) I assume this is because the Pokemon get cleared every X Minutes. If your app is open at the same time you should be safe though.
Comment: @Gigala So you assumed a stealthy trainer who catched 'em all? :P
Comment: Today at a park, there was a couple playing and I heard out-loud one of them ask the other if they had caught it. However, there was no Pokemon on my screen at all. Would it be possible that the Android and Apple in-game worlds are actually different instances?
Comment: Can you edit this to make it clearer that it doesn't matter if you faced it or not before someone else catches it? Everyone can catch it until it despawns, end of story,
Answer: I went for a walk with my gf.
We found the exact same Pokemon on the same spot and we could both catch them
Comment: yeah i observed the same thing when walking around with a friend yesterday. I guess its like this: If you see the same pokemon you can both catch it but if someone else catches the pokemon and you go there much later than him you dont get to catch it.
Answer: h0ch5tr4355 gave a great, detailed answer, which I wanted to expand upon with interesting facts. In addition to being in the same place for every player, certain attributes like size and weight are the same before capturing. While HP is dependent on CP, which is dependent on player level, the following are the same for all players:

Size (weight and height)
Moves

I did an experiment (5 Players, Same Pokemon) using 5 accounts, catching the same Pidgey in the same location on all of them. Three of the accounts were level 8, while the other two were level 7. Interestingly, the lvl 8 accounts all got a 92CP Pidgey with 27HP. The lvl 7 accounts got a 109CP Pidgey with 30HP. Usually, higher player levels result in higher CP wild Pokemon, but it was kind of randomized in this experiment. I know 5 players is a sample size, but assuming this is true for all cases, here's what we can deduce from the experiment:

A Pokemon's size and moveset are predetermined when it spawns (prior to capture)
Upon capture, players of the same level will be given the same randomized CP (e.g. 92)

I also remember one time when a kid and I of the same level (6) caught an Arcanine, it was both 301CP exactly, but 838CP for a level 16 guy. So I am pretty confident that my experiment wasn't flawed. But feel free to comment if you have had the same experience or different.
EDIT: From this reddit post, it has been confirmed that IV ranges are also predetermined. By "ranges", I mean that the distribution of IVs for Attack, Defense, and Stamina have multiple possible combinations, but they roughly equal the same number total when added.
Comment: @TimMalone My 3 accounts were level 8 and the other 2 were level 7, all with the same moveset (Quick Attack / Aerial Ace). So regardless of level, the moveset will still be the same.
Comment: Thanks for your answer. I was wondering if spawned Pokemon have the same IVs for anyone who catches them and this answers that. You didn't directly mention the basis for your conclusion on move sets; I assume you did compare these and they were the same for all players? Or just all players on the same level?
Comment: IVs are fixed as well, Pokemon level is random, but always the same for a specific trainer level (and can generally be higher for lower level trainers as long as it's no higher than trainer level +2). Since CP are calculated based on base stats, IVs and pokemon level, they are also identical for trainers of the same level. So basically, everything about the pokemon is fixed when it spawns, except for the level, which is determined randomly for each trainer level.
Comment: The EDIT portion is now outdated.
Answer: The Pokemon only stay in place for short amount of time, regardless of if they've been caught. At work, somebody will announce that they caught something & the rest of us will log in and catch it. It doesn't disappear before we log in. Looks like you just work somewhere where there aren't a lot spawning
Answer: the last answer is accurate. my husband will walk down the street then come back home stating which pokemom he caught. i will then walk/drive to get to the same location and log on, and l the same pokemon is always there if i get there within atleast 5mins...if i go like 10mins after then it wont be there, but i know if get there within 5 mins it will be there. There have been a few occasions where we will be walking tpgether and his screen with show a pokemom and mine will not..this is bc different phones have quicker and slower server connections but most of the time when one is on his screen, i will wait 10seconds, and then the same one will show up on mine. There have been a few times where a pokemom will show up on his and not on mine at all...this goes back to the server on each phone... my phone must have had a server "jump" or "spaz" if you will so it will not locate that pokemon. Hope this helps!
Comment: Not sure why the downvotes. Answer is correct and helpful (if anecdotal). +1.
Answer: Pokemon spawned into the world normally or by lure modules will be visible and catchable by everyone in that area (good thing too, or there would be fights over rare ones!)
However, pokemon attracted by incense (the item that attracts pokemon to your location) will only be visible and catchable by the person who used the incense.
If you are out with a group and they find a pokemon you don't, take a few steps in every direction, or simply wait a few moments. It's likely just a matter of you loading it into your game a little more slowly.
Answer: in short, if everyone is at the same spot where a pokemon is they will all see it unless 1) there phone has had a server "jump"/"spaz" where it did not pick up that pokemon or 2) if the pokemon at that spot dissappears before you can log on.
Pokemon usually stay in one spot for atleast 15minutes. i have not tested past this time.
*if you click on the list of pokemon in the bottom right corner, this will pull up the pokemon near you. if you are with someone else, or a few people for that matter, and eveyone pulls up that list it is most likely that everyones will look a bit different. this is because everyones phones are constantly updating and connecting to the pokemon go sever at different times so one phone might update and connect to the server slightly quicker and one might be super slow so i wouldnt worry to much about your list matching someone elses. if you are both, or all, going after the same pokemon and are walking/driving closer and closer to it everyone will eventually see that pokemon on their screen and all have a chance to catch it. i usually let my husband find the pokemon and then when he does i open my app and log on to get the same pokemon so i dont have to waste my battery :D

Does everyone see the same Pokémon?


Has the world run out of quants?

Question: What is going on with 70-80% of the most recently (like 3-4 months) asked questions? I remember when I joined the first time, most questions really excited me and looked interesting from an intellectual standpoint. Nowadays, its all about "where can I get freebie data", gimme this, gimme that...has another website sprung up which where other quant geeks gather or has the world run out of quants, or have all questions been answered? ;-)
Answer: Nothing's changed; there have always been non-quants looking for free data online. There's been a recent surge in this, yes, but it's a lot better than what it was two years ago when every question was, "What should I learn to become a quant?"
This site will always be small. We're a highly specialized topic (like Theoretical Computer Science) with the added bonus of extreme secrecy as the industry norm. So it's hard to find knowledgeable people who will openly post about things that aren't even proprietary.
Compounding this problem, of course, is the sheer volume of outsiders looking in. This is what you've noticed. The extreme version of this is Quora, where every question is, "What programming language do quants use?" The moderators have been pretty vigilant to stop this, but there's really no way to change human behavior. People who want to post on a site they have no business posting on are going to do it whether we tell them to or not. My solution has been to readily suspend the repeat offenders.
Comment: Fair points made, thanks for sharing. And I notice that you put in a lot of your time to moderate. My comment only touched on my impression of the majority of new incoming questions. I like the site a lot and appreciate that you go to quite some effort to continue to hold up the site and its content to a fairly high standard.
Answer: Why don't you set an example by asking a couple of new model, iconic, awe-inspiring, carved-in-stone-for-future-quants-generations questions? For, it's better to light a single candle than to curse the darkness...
More seriously, there was an excellent (though short-lived) initiative by @Tal Fishman some time ago, i.e. the Weekly Topic Challenge. Might be worth rebooting imo.
Comment: Re your former thought, there isn't just those two extremes. But it is noticeable that the prior frequent derivative related questions have all but disappeared. I myself ask quite a lot of questions at Stackoverflow and compensate by trying to answer questions here. To each his own. Re the latter part, I like the idea of a weekly topic, that there must be a challenge to decide on the topic is perhaps a little over the top just to adhere to the purest form of democracy. I mean you sometimes make a judgement call whether to close a question or not so why not just setting the topic for each week
Comment: To add to your comment, I am well aware that everyone comes here with a different background. I myself am not a "hardcore" quant, I come from the trading side and believe I can add value in terms of issues surrounding managing risk and generating and analyzing ideas in a probabilistic and highly unknown environment of future states. On the other hand I deepen my knowledge on the programming side at the moment and thus tend to ask more on Stackoverflow and answer more here. Purely a function of knowledge domain and learning pursuits. I just voiced the impression of a drop in question quality...
Comment: The weekly challenge idea works well, in my experience.  Two notes: 1. Someone has to take the ball and run with the idea or it won't ever get started.  2. It can be discouraging to have a week or two with minimal response.  Fight through it and I'm sure you'll see better questions.

Has the world run out of quants?


What's the logic behind 3-10 UST yield inversion predicting recession?

Question: Is there causality, behavioral or logical explanation behind this indicator or is it just purely an observation based on correlation? My guess is that there are existing derivatives with clauses that force them to take action that results in inverting the curve because it makes no sense to receive less for 10s than 3s.
Comment: the real interest rate measures the rate at which consumption () is expected to grow over a given horizon. A high 1-year yield signals that growth is expected to be high over a one-year horizon. A high 10-year yield signals that annual growth is expected, on average, to be high over a ten-year horizon. If the difference in the 10-year and 1-year yield is positive, then growth is expected to accelerate. If the difference is negative--i.e., if the real yield curve inverts--then growth is expected to decelerate. https://andolfatto.blogspot.com/2018/09/what-is-yield-curve-forecasting.html
Answer: When the market enters a risk-off period the investors proceed to a rotation between more risk assets (commodities, equities etc...) to the less risky ones. At this point there is just a lot of supply/demand imbalance on the bonds which drives the yield of the 10y down
When investors proceed to "flight to quality" they want to protect themselves against volatility which government debt offers however they do not necessarily want to get exposed to the long end of the curve (because they do not want to be exposed to long term inflation expectation moves) nor to the short end (because they do not want to be exposed to short term Fed policy changes). So this explains why in the end the demand tends to happen more in the "belly" of the curve (5->10y sector).
Answer: I have also heard it said (but never researched myself) that the reason it leads to recession is because when the yield curve inverts, banks prefer the higher yields they can get by investing their capital towards the lower end of the curve (instead of tying it up for longer and lower). In other words, bank lending on the long end drys up, and creates a drag on economic growth.
Answer: Your scepticism is warranted.  Although there is correlation, the causality runs in reverse;  When the market's get a wiff of the growth cycle peaking then this gets priced into the long end of the yield curve (as lower expectations of future growth and inflation pressure drives down expectations of poicy rate levels), causing inversion.


Is it possible to integrate Google Cloud Connect with SharePoint?

Question: I am on SharePoint 2010 for Internet Sites. I need to know whether it is possible to integrate Google Cloud Connect with SharePoint 2010. If yes, how to do it?
Comment: What type of integration are you looking for?
Comment: Something like editing documents within SharePoint with GCC at backend.
Answer: Why would you want to do this?
The idea of Google Cloud Connect is to provide SharePoint-like functionality with Google Docs without using SharePoint.
With that said, there are no known solutions to integrate the two.  And I don't think there would be a benefit of such anyway.
Answer: It is technically feasible, but extremely unlikely to happen.  Microsoft has published an open API for software companies so that they can have their client interface directly with SharePoint for creating and editing content or using the version control system.  Even after 10 years have used it.  This would be something the Google team would need to do on their end, and I doubt they have any interest in integration with SharePoint.


Non interactive zero knowledge proof with common reference string

Question: I would like to have some explanations about Non Interactive Zero Knowledge Proof. I saw with an example how to use the Fiat-Shamir transformation on Schnorr identification scheme to get a NIZK and I understood how it works in the random oracle model.
What I don't understand is how does a NIKZ work in the common reference string model (CRS). If I understand it right, the principe is that the CRS is generated in a trusted way and is used by the prover and the verifier to establish the truth of a statement.
Without worrying about the generation of this CRS, I would like to know how an algorithm works with a concrete example. I found lots of examples in the random oracle model but I didn't find any with a CRS. Can someone explain to me or give me some links that illustrate this concept in a more practical way, for example with a demo implemented in some language or from a library ?
Comment: https://medium.com/qed-it/the-incredible-machine-4d1270d7363a
Answer: A NIZK in the CRS model consists of algorithms $(\operatorname{Setup}, \operatorname{Prove}, \operatorname{Verify})$ where
$$\operatorname{Setup}(1^\lambda)\rightarrow (\sigma, \tau)$$
generates a public CRS $\sigma$ and a verification state $\tau$. The proving algorithm $$\operatorname{Prove}(\sigma, x, w)\rightarrow \pi$$ uses the CRS, a statement and a witness to produce a proof $\pi$, which the verifier can check using the verification state
$$\operatorname{Verify}(\tau, x, \pi) \rightarrow 0/1.$$
Such NIZK systems exist for virtually any statement you could be interested in, namely for any $\textbf{NP}$ relation. You can find an implementation of a NIZK for Boolean circuit satisfiability here: https://github.com/scipr-lab/libsnark
Comment: What I wanted to know was more what's in the Prove and Verify algorithms. But I will look at your link. Thank you
Answer: Recently it is shown that prover does not need to trust CRS generator/s to get ZK property, you may read more details on https://eprint.iacr.org/2017/599 and https://eprint.iacr.org/2017/587.
Regard to an instance of NIZK proofs, I would recommend Pinocchio, a succinct NIZK system in the CRS model, which has a nice example and implementation. More on, https://www.microsoft.com/en-us/research/publication/pinocchio-nearly-practical-verifiable-computation/
By the way, Pinocchio has focused on verifiable computations and particularly in this NIZK system, CRS elements are generated by verifier which is not the case in general.
Answer: Check out the notes for lectures 11-13 here: http://www.cs.umd.edu/~jkatz/gradcrypto2/scribes.html
The notes explain how NIZK proofs can be constructed in the CRS model based on trapdoor permutations.
Comment: Could you please [edit] your answer to provide an overview / a summary of how the linked resource answers the question in case the resource goes down?


How do PC/Mac games detect piracy?

Question: I was recently reading an article about clever ways programmers have protected their games from pirates, such as the creators of Game Dev Tycoon. This made me curious: how do they detect that the copy of the game running is in fact a pirated version on a technical level? The closest answer I was able to find through some research was how SNES cartridges can detect if they're pirated, but that tactic obviously doesn't apply to PCs.
Comment: @Byte56 I agree that the question is rather broad, but I think it's still a good question.  An ideal answer might provide a common piracy-detection method, and perhaps links to sources that explain other known solutions.
Comment: Probably the best ever possible way to avoid piracy is to do what Blizzard have done for Diablo III : the client do rendering and such but most of the game rules and logic are only stored at Blizzard servers side (eg: how much gold you receive when you open a chest in room X with player at level Y). It is not possible to defeat this unless you stole Blizzard binaries/source for the server part (which is very unlikely). Some people have created emulators, but because its not same rules (they are approximations), it does not give same game experience at all.
Comment: I think this question is too broad. There are a number of ways that games detect piracy, and many of them are specific to each game.
Answer: First thing first: there is no way for a computer to know whether a file is pirated or not. Piracy is a legal/moral term, and as so, it has no meaning on a file, which is only composed of ones and zeroes.
That said, piracy prevention and countermeasures usually focus on finding out whether or not a user has something (usually an object) which can only be obtained if a copy of the game was purchased, and make that difficult to duplicate. There are tons of ways to do this, each one with advantages as well as flaws. I'll mention a few:

Early games asked users to input a word from the game manual, which you should only get if you bought a game box. A photocopier or a scanner easily defeats this technique though.
More recently, media checks are more common. The idea is that you require the game CD to be in the drive for the game to run. To implement this, you can for example access critical data files from the CD without which the game cannot run, or simply check for the existence of a file in the CD. This worked pretty well when CDs were difficult to duplicate, but CD copiers, and more recently drive emulators can be used to easily defeat these technique.
However, CD copies are not perfect, so many other techniques focus on detecting whether the CD is the original pressed CD, or a copy. To implement this, a game can check for non-standard elements that are inserted on the game disc during press time, but cannot be easily and reliably replicated by a CD burner, on a CD-R. Some common ways to do this are:

Creating dummy "ghost" files in the CD during mastering, which are not accessible from the CD filesystem, but do exist, and can be read if you know where to find them. This data is absent on file-by-file disc copies. Copying the entire disc image will copy these files though.
Another way is to intentionally insert errors in the disc. CDs contain error correction codes. By inserting errors in the data, which can be transparently corrected by a disc reader, the disc will work normally, but the errors won't be copied to the CD-R. By looking for these intentional errors, a game can consider a CD to be an original pressed copy. RAW disc image copies defeat this though.
Inserting twin sectors, with the same address but different data will yield different results when seeking data forward and backward. Checking for the existence of this is possible, and duplicating a CD with these twin sectors is very difficult.
Measuring the actual position of the pits in the CD. Once again, duplicating a CD with the pits in the same positions is very difficult.

However, many CD emulators, like Daemon Tools, or Alcohol 120% can actually emulate these features. Because of this, many publishers choose to include a CD emulator detection step, and prevent the game from running if an emulator is detected. The implementation of an emulator detector is outside of the scope of this answer though.
Instead of, or in addition to checking for a physical CD, a game can request the user to input some data, like a product key. Some ways to use product keys are:

Checking for mathematical features in the key. However, this doesn't prevent key duplication, and if the checking algorithm is discovered or reverse-engineered, a pirate may be able to create new keys at will which will appear to be legitimate to the game. Software that creates keys at will are called "keygens".
Generating a hash based on the user's hardware, send this hash and the product key (usually a combination, called the "installation key") to a server owned by the game company, and based on the hash and serial, create an activation key. Using one-way numeric methods (like modular arithmetic, or some methods with elliptic curves), a game can see if the activation key matches the hash and serial code, and only run if they match. This technique is called "activation".

With activation, a server may refuse to provide activation keys for multiple hardware hashes with the same serial code. Because of this, even if the serial code, and activation key are copied, the activation key won't match and the game won't run on other computers.

All of these measures are meant to find whether or not the user owns a purchased copy of the game. However, implementing them requires program code that checks for this. It is possible for a pirate to modify the game code to disable or bypass the checks instead of attacking the copy protection mechanisms themselves. The act of modifying game binaries to remove anti-piracy checks is called "cracking".
Cracking can simply consist of disassembling the game executable, finding the place where the relevant checks are made, modifying it to disable the checks, or ignore the results, and reassembling it. Some ways to counter cracking are:

Checking the binary with some hash. However, there must be a program that checks the hash, which can in turn be cracked as well.
Encrypting the program, or simply the check routine, and decrypting it in runtime. This makes disassembly more difficult, as it involves one or more additional decryption steps. IF the decryption key is included in the program (as it must be, because without it, the game cannot be decrypted), then the pirate can reverse engineer the decryption, find the routine, and crack the copy protection.
Because of this, as a game publisher, you want to make the key as hard to find as possible, and optionally make the decryption algorithm hard to understand. Some ways to make the key hard to find are:

Obscure it by creating it in strange ways. This simply slows the cracking process.
Create per-machine master keys similar to the serial protection mentioned above.

However, regardless of the method you use to create your keys, the keys themselves will be in memory while decryption is in progress. Memory inspectors, debuggers and emulators can help a pirate find and copy the key while it is in memory. Memory peeking can be attacked in several ways:

Having a privileged service that detects memory accesses in the specified region, and redirect the addressing somewhere else. As this requires ring 0 access, and programs that do this are more commonly used for not-so-legitimate purposes, antivirus software usually block them. (this is why many games and other software ask to turn off virus protection when running). Writing software that correctly does this is extremely difficult, and can easily compromise the stability and security of the host OS. The XCP scandal is a good example of an implementation of this method gone wrong.
Modern hardware and operating systems provide some tools, like memory curtains, secure media paths and TP modules, to make it easier to make a program that decrypts data, while being resistant to memory inspection.

There are many many more techniques to attack piracy, ranging from the trivial to the esoteric. Unfortunately, it is possible for all of these techniques to fail to recognize a genuine copy, and it's usually the more aggressive techniques that have higher false positive ratios.
As a game publisher, you usually want to choose a set of techniques whose cost of implementation, expected cracking time, and false positive ratio are in line with your expectations.
It is a common misconception that piracy protection is meant to be completely unbreakable. Most game sales happen in the first few months after release, so a piracy protection scheme is usually considered effective if breaking it consumes enough time for the game publisher to collect a large amount of profits before it gets broken.
Regarding Game Dev Tycoon, they did not use any anti-piracy technologies. They simply created a "broken" build, and distributed it over BitTorrent, as is stated in the beginning of the article you mentioned.
Comment: Even having a competing answer I need to down my hat to your answer, better presentation and obviously more time put in it. Better technique coverage also, and I must say that I never heard of "memory curtains, secure media paths and TP modules". What is that ??
Comment: @v.oddou: These are elements that can be used for hardware supported DRM. A TP module is a cryptographic processor chip. Many modern (2007 and later) computers include a TPM. A memory curtain lets you create write-only memory sections which are not readable even to the OS, specifically to store keys for the TPM to use. A secure media path is a system in which content travels encrypted from end to end (even all the way to the display). Using these technologies correctly is far from trivial though...
Comment: Just as a tiny add-on, there's a great article about the Spyro copy protection that discusses a lot of this stuff as applied to one game, along with some rationale and an interesting story: http://www.gamasutra.com/view/feature/3030/keeping_the_pirates_at_bay.php
Comment: This answer is completely erroneous. https://www.youtube.com/watch?v=FVVx5WYmO2s Flagging for moderator intervention.
Comment: @Krythic how about you write your own and then?
Answer: It is pretty easy, you just have to run a MD5 or SHA256 on your own executable, then, when you detect the signature has changed from what you hardcoded into the binary after you built the final release, then its clear somebody hacked your executable.
Then most companies, don't just show a popup anymore (it was the case before) that says "broken PE" or "virus detected" and then exit the game, because this will be counter-cracked very fast be hackers. Because the game is paused on the message loop of the dialog so it is immediate to see because of what branch the dialog was poped up, and just bypass the branch by changing the code at the condition check.
Today, companies use very subtle change in gameplay, like multiply the life of monsters to make the game unplayable, or incredibly cleverly integrated in this management game, where you run a game company and you loose eventually because too many players were pirating your game. Nice mise en abyme in this case.
Sometimes it just gets you a red flag uploaded on the company servers, and when you want to call them for support you get a speech, or trapped into revealing your identity.
but this is all of topic, the technique is hashing. and these checks can be run in many places in the binary so that if hackers find one and clear it, its not enough.
EDIT:
If you just copy the game as-is, it may work if the game has no anti-piracy measure at all. It was working with very old games, pre CD burners era.
That is why, most of the time, the game has to be installed to run, not just the installation folder copied. This involves hidden files put a bit everywhere in the system, and registry keys.
The game checks the presence of these things, which can only be created by the installer.
And the installer, can only be run from the CD, which is not copiable because of erratic bits that do not respect the error-correction code system at the first bytes of the disc, which kills most CD player drivers.
Some copy software, like nero of alcohol, proposes you to ignore the errors but what they burn is then a corrected copy, the installer detects that and there you go again.
EDIT2:

Q: how to hash a file then insert the hash into the file which changes
  the hash ?

@Byte56:
Damn we are getting intelligent comments here :) Yes it is a paradox and it cannot be solved. So the hash has to be made on the part of the binary that does not contain the hash. And the check code has to know that, to exclude that zone when hashing to self check. I have seen people using tags, like ~~#### [put hash here] ####~~ to enclose their hash and do the exclusion. But it has the flaw of being easy to spot for hackers, so the hash has to be scrambled, and scattered in multiple locations. Even encrypted why not, and the same camouflaging operation goes to store the private key.
Comment: What if the game files are copied as-is? Won't the hash validate in this case?
Comment: @PandaPajama : excellent remark. i'm doing an edit.
Comment: How do they deal with hashing an executable then hard coding that hash in the executable, thereby changing the hash?
Comment: @Byte56 : edited again :)
Comment: @MickLH : I have to say that I liked your answer for the reason that I agree with the experience should move people to naturally give money out of sheer awe. Too bad it didnt really answer the question and you got downvoted (naturally one could say). You are being too absolute on the private key. This private key is worth nothing more than hash encryption, it hasnt a great value like credit card database for example. But if you insist then the checksum could be sent on the network for check on server. But security is only as strong as its weakest point, and this has a serious flaw, a hacker
Comment: can just hack the function that sends the check to the network to make it send the original network message frames, without having to know even what is the content, and voila you get validated by the server. Hard rules like you mention makes no sense in general. Also I would really love to improve the answer if you think something is impossible please speak some details so everybody can win here. think of future googl-ers.
Comment: You can trivially calculate the public key given the private key (hence "private" vs "public") making the key pair useless if the private key is _ever_ shared. If you want a hash use a hash function. -- Next, your exact hacker argument applies to that hash solution which is why I call it impossible. A hacker can always just disable the hash function and replace it with something that always returns the "correct" hash. -- Finally, the solution with network relies on the game server to check with the master server if a client is legit (like steam), there is no way to stop local piracy. period.
Comment: This should be the accepted answer.
Answer: cant they just put a ext partition on a mac game
macs cant read ext
Comment: If there was a file on the partition that was needed, the game couldn't execute.  If solely the existence of the partition was "proof" that it was a legit copy, it would be INCREDIBLY easy to replicate.

How do PC/Mac games detect piracy?


What precautions should I take for storing a DSLR camera at home?

Question: I often take pictures at home and just store it on a shelf. Is it ok to store a dslr camera this way or should I always put it in a bag, drawer etc ?
Comment: You shouldn't. Cameras are for using not for observing as display pieces.
Comment: I leave my camera lying around on a shelf; lens attached, batteries charged, memory card inside.
Comment: @dpollitt what are you prattling on about. No one has said that want to use it as an ornament
Comment: gently toss it in the corner, it will be fine.
Answer: Most important factor to consider when storing a camera; is to ensure the area is dry, moisture free and it is a dust free environment. otherwise, you can breed Fungus spores.
I collect old camera and they are all kept inside a Velvet Lined wooden box with Silica Gel pouches chucked in the box to ensure that any unexpected moisture is absorbed.
Cameras that I use on a more frequent basis, I never store inside a bag, box, cupboard or shelf.
They sit constantly mounted on a tripod, in a corner and out of the way. I just throw a dust proof cover over them when finished and pull the draw string at the bottom.
As the room where they are kept is dry with no humidity, I have nothing to worry about. In fact, I may even keep a camera on the shelf in the same room if all tripods are used up.
This includes cameras that I take outdoors for a shoot, when I come back, the lenses which are always inside their own protective cases each with silica gel, (which I do change from time to time), go on a shelf and I generally leave one camera with a Kit lens of 28-70mm on the body mounted on the tripod, always parked in "P", as you say, for convenience and also speed of requirement! you never know what the kids may do next or the cat decides to do something equally amusing!
Keep your cameras away from Dust, Humidity and moisture and they will be fine.
Answer: 1.) Keep it away from the tiny hands of a 2-year old.
2.) Store in a bright, dry place that has protection from dust.
Answer: If you are storing camera at home, you could do the following to keep it safe:

Find a dry place to store the camera. If you are keeping inside a box, put a small puch of silica gel, just in case there are any moistures.
Keep them at a place or a locked cupboard so that it does not fall off.
Definitely keep it away from dust areas.

HTH.
Answer: The two key issues are:

Dust. If the shelf is in a dust free environment then it makes no difference in this regard. Most shelves in most houses, however, are not in a dust free environment.
Risk of physical damage If there is no risk of something falling on the camera or knocking it off the shelf then there is no additional risk. Otherwise the damage from an impact can be much more severe if the camera is not in a protective case.
Answer: If you store your camera with the lens attached it needs to be somewhere away from dampness as well as safe.
I've got mine in a basket that sits inside a bedside cabinet with a dry tea towel loosely draped over it, and I have the silica gel sachets littered about the basket. The silica gel sachets are well worth the money(as has been stressed in these other answers ) click on this link  http://www.ebay.co.uk/itm/Silica-Gel-Sachets-Desiccant-Pouches-1g-sachet-UK-Based-Craft-Company-/161299617316?pt=LH_DefaultDomain_3&var=&hash=item258e34d624
where you can order them for a couple of pounds delivered.
Answer: Basically I would keep it dry (as suggested already) and prevent it from direct sunlight.
Taking out classical batteries may also be a good idea; maybe even rechargeable ones to avoid deep discharge.
For cameras with a mechanical shutter (the old non-electronic ones) you might also want to release the shutter to relieve the spring moving the shutter.
Answer: Also: If you storage area is anywhere near where cooking and/or tobacco smoking happens, religiously protect any lenses or valuable filters with caps, cheap/old UV filters, boxes, etc. Even when they are in a cupboard/cabinet. Grease and smoke love to condense on glass.
Answer: Lock the camera in a safe. Don't make it easy for a burglar to snatch your DSLR.
Comment: I guess if you live in a super-high crime area. Otherwise this seems like a recipe for dropping out of photography entirely.


Resetting Ubuntu to factory settings

Question: I've had a lot of problems lately and now I'm having problems logging in at the login screen. I'm giving up and just want to reset and start over. How can I "factory reset" Ubuntu, in this situation, or, for future reference, in general?
Comment: @Rinzwind perhaps another option would be for the OP to install an alternate desktop (such as LXDE) from the CLI and then log in to *that* to make a new USB
Comment: can you get use a terminal (control alt f1) and log in? If so  and answer might be provided where you use wget to download an ubuntu iso and command line to write it to an USB (not seen one yet though ;) )
Comment: @Rinzwind yes I can
Comment: @Rinzwind ok we could try this I'm not too familiar with wget at all though
Comment: @steeldriver if I did this do you mind giving me a few steps of the process
Answer: I can see a couple of options but they depend on you being able to get to a command prompt with a working internet connection.

Install another desktop.
Burn a new USB installer from command line.

Install another desktop

This does not guarantee a working desktop though. Your problem might be something related to video card and also present in other desktops. Drop to a command line and start of with this:
sudo apt-get update

and then pick ONE of these (to install that specific desktop):
xubuntu-desktop
lubuntu-desktop
ubuntu-mate-desktop

I only listed a few (you could also install kUbuntu but for just getting a desktop to be able to make an installation disk might be overkill).

Burn a new USB installer from command line

Download Ubuntu from command line with
wget http://releases.ubuntu.com/14.04/ubuntu-14.04-desktop-amd64.iso

(change the url to a release you want. see http://releases.ubuntu.com and the directories below that for what you need). It will show something like this:
~/Downloads$ wget http://releases.ubuntu.com/14.04/ubuntu-14.04-desktop-amd64.iso
--2015-02-28 21:09:59--  http://releases.ubuntu.com/14.04/ubuntu-14.04-desktop-amd64.iso
Resolving releases.ubuntu.com (releases.ubuntu.com)...
18.104.22.168, 2001:67c:1360:8c01::1e
Connecting to releases.ubuntu.com (releases.ubuntu.com)|
18.104.22.168|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 1010827264 (964M) [application/x-iso9660-image]
Saving to: 'ubuntu-14.04-desktop-amd64.iso   6%  58,05M  1,36MB/s   eta 7m 47s

and then "dd" the ISO to the USB flash drive. Pay extra attention to the device name. If you mess this up you could overwrite your current install... I tend to use dmesg:
[26005.823077] sd 7:0:0:0: Attached scsi generic sg3 type 0
[26006.953612] sd 7:0:0:0: [sdc] 30299520 512-byte logical blocks: (15.5 GB/14.4 GiB)
[26006.954291] sd 7:0:0:0: [sdc] Write Protect is off
[26006.954298] sd 7:0:0:0: [sdc] Mode Sense: 23 00 00 00
[26006.954912] sd 7:0:0:0: [sdc] No Caching mode page found
[26006.954918] sd 7:0:0:0: [sdc] Assuming drive cache: write through
[26006.972919]  sdc: sdc1
[26006.976297] sd 7:0:0:0: [sdc] Attached SCSI removable disk

So that would be "sdc". This will burn it (skip the 1st one if you are still in Downloads, skip the 2nd one if it is already installed):
cd ~/Downloads
sudo apt-get install gddrescue
sudo ddrescue -d -D --force ubuntu-14.04-desktop-amd64.iso /dev/sdc

Results:
GNU ddrescue 1.19
Press Ctrl-C to interrupt
rescued:    63504 kB,  errsize:     230 B,  current rate:     196 kB/s
   ipos:    63504 kB,   errors:       1,    average rate:   12700 kB/s
   opos:    63504 kB, run time:       5 s,  successful read:       0 s ago
Finished

and an image of the freshly created USB ISO:
Comment: than you so much I almost got it to work but I had a faulty usb so I went and got a new one and when I run dmesg I get--"sd 6:0:0:0: [sdb] Write Cache: diabled, read cache: enabled, doesn't support DPO or FUA. That's the only thing that differs from your code should I just continue or do I need to do another step?
Comment: that is fine. all you should need is the device name
Comment: which is sdb and not sdc in his case
Answer: From Factory reset - Wikipedia:

Computer factory resets will restore the computer to the computer's original operating system and delete all of the user data stored on the computer.

This can be achieved either by re-installation of the OS or using a factory reset option. But in Linux, there is no option for factory reset inbuilt. So, it is required to look for alternatives which can achieve above said things.
While re-installation of the OS is the preferred method in order to remove users, user files and user applications but it is somewhat a tedious task. There is a tool called Resetter which would make "resetting Ubuntu" easier and will do what factory resets usually do.
Introduction:
Resetter is a tool which is used to reset Ubuntu installation to factory default. The Ubuntu system will go back to the state when it was installed for the first time. It finds all applications which are installed after Ubuntu fresh installation and delete them. Not just applications, it also deletes the users too. Deleting users means deleting their home too which means all user files and configurations. You don't have to install everything from the beginning. Just reset your Ubuntu to its factory defaults and start installing everything else.
Installation:

Download the latest release of Resetter and add-apt-key_versionX.deb from GitHub or use wget to direct download. At the time of posting this answer v3.0.0 was the latest release. To download using wget use:
wget https://github.com/gaining/Resetter/releases/download/v3.0.0-stable/resetter_3.0.0-stable_all.deb
wget https://github.com/gaining/Resetter/releases/download/v3.0.0-stable/add-apt-key_1.0-0.5_all.deb

Install some dependencies:
sudo apt install libqt5clucene5 libqt5designer5 libqt5help5 python3-psutil python3-pyqt5 python3-pyqt5.qtsvg python3-sip

Install downloaded .deb packages:
sudo dpkg -i package1.deb package2.deb

Using Resetter:

Open Resetter from Dash and authenticate. Authentication is required to perform administrative tasks.

To reset Ubuntu, click on Automatic Reset. But if you want to remove multiple packages at once click on custom reset.

Click "Yes" to confirm. You'll get a dialog which would list all the packages which would be removed.

Click "OK" to start. The factory reset will begin:

A new user will be created to access the system using administrative privileges. A dialog will appear which would show details about that newly created user. After that confirmation for Reboot will appear.

If your Ubuntu boots into TTY mode (command line/console mode), login with the credentials of new user and install desktop environment again.
sudo apt install ubuntu-desktop
sudo reboot

Use previously provided password to login.

Modify Username and Password as per convenience.
Comment: @rtaft Actually most of the question which deals with resetting Ubuntu are closed as duplicate of this. Example: [How to completely reset Ubuntu and all installed applications to its original setting?](https://askubuntu.com/q/594930/816190). This answer would help users who can at least use their GUI. I believe this question is widely applicable and can be expanded towards more generalization. After all, Q&A aren't meant for OP only. :)
Comment: They cannot login to the desktop to use the UI, these instructions require logging in.
Comment: @rtaft rightly or wrongly, many questions asking how to "factory reset" Ubuntu are closed against this one. I've therefore decided to edit the question to make it more general. I should have done this before offering the bounty, oops.
Answer: Reinstalling can mean erasing everything, reformatting the partition, loosing all data and installing Ubuntu with a brand new /home/user directory. This is the common result when doing a google search.
This answer is about reinstalling Ubuntu and keeping /home/user directory. The following is from: Ubuntu Reinstallation

Ubuntu Reinstallation
Introduction
Sometimes reinstalling is the quickest way to solve a problem, for example if an upgrade failed or if your graphics driver is broken. When reinstalling, you're most likely want to preserve two things:

/home folder with your files and settings
Entries in boot menu (if you have multiple OS installed)

How To Reinstall Ubuntu
Since Hardy it is possible to reinstall Ubuntu without losing the content of the /home folder (the folder that contains program settings, internet bookmarks, emails and all your documents, music, videos and other user files). This can be done even if /home is not on a separate partition (which is the case by default if you did not manually separate it when installing Ubuntu originally). This tutorial can also be used to upgrade Ubuntu (eg 11.04 -> 12.04 from a 12.04 live-CD).
Before doing anything
This operation should not damage your documents but, for security, backup your documents and settings (including /home hidden files) on external disk or DVDs. (eg via CloneZilla) Note: Some special applications settings may be in system folders, eg LAMP, see below in the thread.
Run the Ubuntu installer

Run the UbuntuInstaller
Follow the prompts until the "Installation type" (or "Allocate disk space") menu
Choose the right option as described below:

Choose the right option
There are two possibilities - choose the one that fits what the installer is showing:

If an "Upgrade 1X.XX to 1Y.YY" option is available (like in the screenshot below), choose it.

Or, if the above option is not available, choose manual partitioning ("Something-else" option), then select Ubuntu system partition, set its mount point as "/". Be sure to keep the same format type, the same size, and untick the "Format" checkbox or all data on "/" will be deleted!. Also set other partitions (/boot, /home... see DiskSpace) if needed.

Then finish the installation process. (this may take several hours, like a normal install)
After reinstalling
After reinstalling, user accounts must be re-created with the same login and password.
See also

Discussion on the forum

Create a Live USB

How to Create a Bootable Linux USB Flash Drive, the Easy Way
Answer: No standard factory reset for Ubuntu

There is no standard explicit factory reset standard for Ubuntu, but there are several methods that can produce the same or similar results.

Your personal files

Even if the current system does not work, you can probably copy or recover many or all of your personal files, when you boot from another drive, for example an Ubuntu live drive (USB pendrive or DVD disk).
With a good backup routine you will have peace of mind, even if the drive crashes physically.
Maybe your system drive or the file system(s) of your Ubuntu is damaged. You can check that and maybe repair the file system(s) according to this link.

Re-installation

A complete re-installation of Ubuntu is much faster than the corresponding installation of Windows. Re-install into

the same partition(s) as before or
different partition(s) or
the whole drive (if you no longer want to dual boot or multi boot).

A limited re-installation of Ubuntu can make things easier.

The most typical case is to preserve the /home directory, easiest using a separate 'home' partition.
Maybe you want to preserve some system files, that you think are good, from the /etc directory tree.

There are already good and detailed answers here describing re-installation.

Fresh installation

If there are problems, a fresh installation can be a good alternative to 'factory reset'.
The [re-]installation can be to the original version and flavour of Ubuntu, but it can also be to new version or community flavour, a fresh installation. Please notice that you should stay with the same flavour of Ubuntu and use the same userIDs and names, if you want to keep /home.
Compared to upgrading with do-release-upgrade it is often a reliable and efficient method to install a newer version, for example the most current 'first point release', 16.04.1 LTS, 18.04.1 LTS ... with long time support.
But sometimes there are problems with hardware drivers, so you had better 'Try Ubuntu without installing', try live from a USB drive or DVD disk, before installing a newer version.

Resetter

Using the tool 'Resetter' is described in an answer here.

Make an early backup. You may need it in the future

Think ahead and backup your Ubuntu system when it is new (or maybe the whole drive if a dual boot system). There are several backup tools. A full backup can be a cloned [compressed] image of the whole drive made with
Clonezilla.
When you want to reset your system, restore it using this backup.

Restore points or snapshots

You can create several backups and use them as possible 'restore points' or 'snapshots' of the system, maybe once or twice per year.
But you should also have a more frequent (daily or weekly) backup routine for your personal files, at least 'everything that you cannot afford to lose'.
Comment: @Zanna, You are welcome :-) I'm glad that I was able to make what you asked for. -- I think you are good at reviving/improving old threads with questions that are useful for many people.
Comment: Thanks a lot :) this is the answer I think this question needs most, though I appreciate the other answers posted too.

Resetting Ubuntu to factory settings


External forum dedicated to tikz/pgf

Question: More and more questions are related to tikz/pgf and not tex in here: should not the creators of this site think of a dedicated tikz/pgf forum?
Comment: I don't think Tikz/Pgf questions, in a way, "pollute" the forum. It is just because graphics are becoming indispensible in any kind of TeX document, which were long confined to the `\includegraphics{}` command (slight exaggeration of course). What you can do is amazing with them. Besides, you see a lot of other types of questions also if you turn off the "TikZ/Pgf" filter ;)
Comment: @pluton: Yep, that didn't work as a joke I guess. What I wanted to say is that Pgf/TikZ are becoming a strong internal mechanism for La/TeXing and many questions appear on the site having content interlinked with some x package + Pgf problem. Then there would appear the difficulty of classification of these problems.
Comment: @percusse, @pluton: TeX.SX is not a forum!
Comment: @pluton: This clearly belongs on meta.tex.sx because it is a question about the site. I migrated it there now.
Comment: @percusse: I'm not talking about pollution of any kind. I just think it could be more efficient for (potential) tikzs user to have a dedicated forum even though I know this tool has strong links with tex. For an improved organization of the forum and as a non (yet) tikz user, I just think that two separate forums are relevant.
Comment: @Martin: ok thanks, I was not sure about where to ask the question.
Comment: @pluton: Do we need to give the same privilege to PSTricks? :)
Comment: @Martin: Why cannot `*.stackexchange.com | stackoverflow.com`  be called/categorized as a forum?
Comment: @xport: It all depends what you understand under "forum" of course. In general a forum has a much less strict format and have often a tree like structure in their threads, i.e. people post replies on the posts of other people. This generates a much lower signal-to-noise ratio then on a stricter Q&A site like this. This results in a better quality and is a main reason why e.g. Google lists us very high. We don't won't (new) people to think that this site is just another forum to avoid non-answers and other unwanted things.
Answer: I disagree.  Firstly, with regard to the "pollution".  I'm not usually an advocate of tags, but this is one case where I think that the tag system works.  TikZ/PGF questions are easily identifiable as such and usually correctly tagged, so using the ignore or follow features of tags should actually work here.
Secondly, with regard to having a separate forum, I don't see any advantages to this.  The main point is that there is no clear separation of users.  I answer quite a lot of TikZ questions, but I ask quite a lot of non-TikZ questions (and sometimes answer if they're easy enough).  For both, I'm in the same "mental state".  If I see a TikZ question and I'm thinking about TeX-related stuff, then I don't have to "shift gears" mentally to think about the TikZ question, and vice versa.  On the other hand, if I was browsing MathOverflow and came across a TeX question then I would have to do that mental shift, showing that TeX questions don't belong there.
Lastly, I think that TikZ/PGF questions benefit the site.  I don't think it is big enough to lose a large section of its questions, and they do draw people here.  They also provide a showcase of things that might just make dull papers a little more interesting to read.  Think of it as a "Look what I can do!" (in the nicest possible way, of course).
Comment: I agree with these points.  Many questions have the form "how do I draw X in (la)tex", and people often give a tikz solution, but these are not tikz questions per se.  I actually think the perspective "tikz is not tex" is really wrong -- rather, tikz is among the best parts of the (la)tex ecosystem currently.
Comment: Full ACK. In addition I don't like the phrasing "related to tikz/pgf and not tex". TikZ/PGF is written in (La)TeX for (La)TeX and is therefore part of (La)TeX.
Answer: If you mean with forum a site like TeX.SX (which is not a forum but a Q&A site) then you should know the following:
All stackexchange sites need to be officially proposed on http://area51.stackexchange.com/ where they need a certain number of supporters to get the site into the beta stage. Once the beta site shows enough activity it is elevated to a full site or shut down otherwise. It isn't very easy to get so far if you don't have the right amount of supporters and your proposal can be closed as a duplicate similar to questions here. Because TikZ/PGF is for LaTeX and there is already a site for that, I can basically guarantee that such a proposal will be closed quickly.

There is already a "PGF/TikZ forum" in form of a mailing list which is accessible under http://old.nabble.com/PGF-and-TikZ-f3582.html. Also http://www.texample.net/tikz/resources/ is a dedicated TikZ website.
Comment: There is a forum entitled Graphics, Figures and Tables at LaTeX Community (http://www.latex-community.org/forum/viewforum.php?f=45), another one at sourceforge's pgf place and the pgf-users mail list also at sourceforge. I'm subscribed to this one and visit the first from time to time. I think tex.stackexchange is the most active one.
Answer: (After the migration, I rephrased (and also changed my point of view))
At first I agreed with the statement because there are several pgf/tikz post in this Q&A which are not stricly on TeX; but then, reading all other answers, I realized that the good use of tags may itself be a good alternative to a dedicated Q&A, as suggested in the question, which will indeed add a bit of noise to the whole system.

External forum dedicated to tikz/pgf


Is there a difference between Rurouni Kenshin & Samurai X?

Question: I was told there was a difference between Rurouni Kenshin & Samurai X but I've only seen Rurouni Kenshin. Are they really different and if so can you explain how?
Answer: No, there's no difference.
From Wikipedia:

In 1999 Sony tried and failed to market the series in the United States as Samurai X via an existing company. The TV series was later licensed in North America by Media Blasters, who split it up into "seasons", and released on DVD.

The Wikipedia article links an Anime News Network article from the same time period, which says:

Similarly, EX Online is reporting that Sony's plans to market Ruroni Kenshin in the US as "Samurai X" by means of an existing company have fallen through. However, since Sony's raid on fansubbers carrying the series, no new plans or partnerships have been announced by anyone. ANN will be asking around about this and come to a conclusion about this one at Project A-kon this year (by process of elimination, we hope), but meanwhile, or contact at Sony has stopped returning our e-mails.

So Samurai X was just the name Sony came up with when it was trying to do a US release of Rurouni Kenshin in 1999. Media Blasters called the series Rurouni Kenshin for its US release, but ADV later reused the Samurai X name when it released the Rurouni Kenshin OVAS and movies:

The English-language versions of the OVAs, as well as the film, were originally released as Samurai X in North America, although the original name was included on the later DVD and Blu-ray Disc releases.

Later on in the same article:

ADV Films released the series on two VHS or DVD sets in 2000 under their Samurai X name in North America, and the film version in 2003.

Sony actually did produce a dub of the series under the name Samurai X:

Sony Pictures Television International created an English-language version of the series, titled Samurai X, that airs outside of the United States.

The Wikipedia article includes links to Animax Asia and Animax Latin America for Samurai X, though the links are down now.
Answer: No, there isn't. It called a localisation editing.

Localisation is an essential process in releasing anime outside of Japan. It can cover a range of different processes depending on the individual title and the desired result. At its most basic level, the localisation process is responsible for deciding on romanised character and term names, as well as episode titles
Answer: They are different as long as you are talking about Samurai X trust because of the fact that Samurai X is the story before the events of Rurouni Kenshin as Kenshin Himura was Batosai the Manslayer
Comment: Did you mean [*Samurai X: Trust & Betrayal*](https://en.wikipedia.org/wiki/Rurouni_Kenshin:_Trust_%26_Betrayal), which is known as *Rurouni Kenshin: Meiji Swordsman Romantic Story – Recollection or Reminiscence Chapter* in Japan? Were you probably mixing the localized title with the Japanese title?


Is an incorrect address on a W2 a problem?

Question: I worked at a company in 2011, with address A, and in 2012, came back to the Company with Address B. There were no overlaps with the addresses from 2011 to 2012. However, payroll didn't update my address when I came back in 2012. So basically, 100% of my income earned in 2012 was at Address B, but my W2 lists Address A. Is this going to be a problem on my taxes, or will it raise an Audit flag in the future? If so, is it possible to correct a W2, or is the printed one final?
Answer: You do not need a corrected W2 because the address is wrong. No-one cares about the address, its just where the form is being mailed to.
Re the tax calculations, since W2 is a summary of payments already done, if your withholding was incorrect because the employer thought you're in State A, but you're really in State B (county, city, whatever) - then its your problem to fix. The employer will not retroactively pay taxes on your behalf, and it is your responsibility to update the address when it changes. So if this is the case, calculate the taxes due and pay ASAP to the entity you should be paying, and file a claim for refund to the entity you shouldn't be paying. You may get hit with penalties. Ask the payroll if they can help you with this, but they probably won't. If they don't - no need to correct W2. Corrected W2 is a problem for the payroll, and makes a lot of additional significant work. They won't do it unless they have to.
If you're within the same tax jurisdiction, just moved a couple of blocks away - no-one cares.
Answer: If both addresses are in the same state (Ohio?), there should be no problem with Federal income tax or state income tax as long as the taxpayer ID is correct. There might be
issues with county income tax or city income tax, if any, and especially if the
tax withholding for these is incorrect. But, assuming these nonFederal
issues are not relevant, you could ask your payroll office about
issuing a corrected W-2 but they might drag their feet on the matter since it will mean
work for them (and expense to the company) without any effect on the substantive issues.
You should, of course, insist on them correcting your address in your files (for the
2013 W-2).


Post the Area51 announcement on the SF blog

Question: Now that Area51 has been announced on the SO blog, could you also post it on the SF blog.  In the case that people are following the SF blog and not the SO blog and understanding that that might be a pretty small set of people.  But still, how 'bout some SF love?
Answer: It is my understanding that the SF blog is not meant for that sort of stuff.
The SF blog is in place to document the the Server Fault related topics that the team has to deal with.

Hardware Upgrades
Database Config stuff
Load balancing
Speed Optimizations

This is what was posted about the serverfault blog:

You can expect to find blog posts there related to us documenting our own efforts of running and scaling our network of websites — the same sort of stuff you've come to expect from the server category on this blog. We want to actively give back to the community by documenting everything we're doing on the sysadmin front — both by discussing it on the blog, and asking (and answering!) relevant questions about it on Server Fault whenever possible.
Comment: Wasn't the impression that I got.
Comment: Still is reasonable to assume that "a blog specific to Serverfault" will have non-intersecting sets of users.
Comment: @squillman check out my edit to my answer


Print came out like a wafer

Question: I'm not sure how else to describe it. There's probably a name for this but I just don't know it. But the bottom few layers came out great, but the rest came out kind of like a triscuit. Below are pics of my print and settings. I am using a delta style printer. Can someone tell me what this issue is called and how to fix it?
Answer: The phenomenon you experience is called under-extrusion. Under-extrusion is the effect of extruding lesser filament than required for the print. The result of under-extrusion (depending on the amount of under-extrusion) can be described as spongy prints, gaps in prints/layers, failed prints, etc. As the amount of plastic flow is less than required for the print, the quality and print strength is much lower than that of a normal filament flow printed part.
Most severe under-extrusion is usually caused by incorrect filament diameter setting. E.g. Ultimaker Cura (to date, April 2019, the version is 4.0) is notorious for resetting the filament diameter to 2.85 mm after you upgraded to a newer version (because that is the diameter of the filament the Ultimaker machines use) while most people use 1.75 mm diameter filament.
From the settings if appears you have set the correct filament diameter (i.e. if you use 1.75 mm filament). Please measure the filament over a few meters and determine the average filament diameter to be sure.
In your case it must be something else!
A higher temperature causes filament to be more fluid (do check if the temperature you use fits the type of filament you use), so an increased temperature should help against under-extrusion (less friction for the extruder to push the filament through the nozzle). Please do check the extruder stepper; is it skipping?, is the tension the extruder gear exerts on the filament enough to prevent slipping?
Finally, blockage of the nozzle; partial blockage of the nozzle can prevent consistent flow from the nozzle. It is advised to rigorously clean the nozzle (e.g. using the atomic cleaning method where you heat up the nozzle insert filament and turn off the heat to pull the filament out when temperature is about 30 °C lower than the printing temperature of the filament) or replace the nozzle.

To complete the answer, another source for under extrusion that is seen from the beginning of 2020 of Marlin firmware operated 3D printers is that instead of normal extrusion (where E in the G-code file denotes extrusion of filament movement in units of length), the printer assumes it is volumetric displacement. From the Marlin menu of the graphical controller you can change volumetric displacement to length displacement by disabling volumetric flow.
Comment: I upgraded Cura (I got the version from the support page of my printer https://gearrev.com/pages/support). You are correct in the filament issue diameter too. I had this set to 1.75, when i opened it, it was at 2.85 which i figured was a mistake because i remember setting it to 1.75 before print. So i changed it for the screen shot figuring it maybe reset when I shut down cura last time.

Then I checked the nozzle, which was fine, the heatbreak however; That needed some work. The teflon tube was warped. Printing now and even the raft looks better.

I appreciate the answer!
Comment: The Cura issue seems to be that they moved filament diameter to a per-extruder setting when adding multi-extruder support, and now the default is wrong and needs to be fixed for each extruder.
Answer: Underextrusion.

I suggest upgrading to Cura 3, as you are working with a version 1.5.
If you print PLA, you print WAY too hot (190-200 °C Nozzle, 60 °C Bed), if it is ABS, knock down the temperature a little.
Check for a clogged nozzle.
*
Comment: I have no idea why the heat is at 245. I didn't catch that. The filament box says PLA+ 205-225 so i used 212. I think this old Cura version was an issue. Weird because I got it from the support page of the printer (https://gearrev.com/pages/support). Upgraded and also found that the filament diameter reset itself to 2.85 and the heatbreak's teflon insert was broken.

Also appreciate the term for this because when googling for "triscuit 3d print", i didn't quite get what i was looking for lol
Comment: Yeeea, filament resetting to 2.85 mm is an old bug. PLA+ is printed higher than normal PLA, so 210-220 sounds ok-ish.
Answer: Just to add to the already made answers:
Check out heat-creep!
When heat from the hot-end creeps up in the filament, it melts and blocks the extrusion (more or less severely), and under extrusion results.
It's basic characteristic is that the print starts out great, and then some time in, under extrusion happens.
The solution is to cool down the cold part of the hot-end which is usually done with a small fan directed onto the cold part, e.g the top part where the filament enters the hot-end.
Most hot-ends have a heat sink on the cold part, but in my experience this is not enough and for me a fan has always been needed.
Comment: Good addition! Usually it stops extrusion as a whole, but indeed sometimes heat creep could cause partial blocking.

Print came out like a wafer


Ubuntu touch availability on TF101

Question: I would like to ask if there is any plan or indicative timeline if an installation would be made available for Asus Transformer TF101 device.
Answer: check out this link
http://forum.xda-developers.com/showthread.php?t=2168473
this is still a pre-alapha build, so it will be extremely unstable and a lot of the features are still not working, so i would wait until it has at least reached a a stage where most of the features are working.
PLEASE TRY AT YOUR OWN RISK!!!
All credit goes to raymanfx, Canonical, and jholtom.

Ubuntu touch availability on TF101


Questions and Answers missing

Question: List of my  questions and  my answers have disappeared in the new updated version today, though the data about how long I have been member, my location etc are intact. The reputation points have come down from 700 plus to 596.
Answer: So far as I can tell, your questions and answers are still intact; note that only 5 of each are displayed on your profile summary, but you can view all of them by clicking through to the questions and answers tabs.
Your reputation dropped a bit - like most everyone's did - because the reputation rules have changed a bit and is now recalculated continuously (so deleted posts don't count towards / against it). For details on the new reputation rules, see: https://mathoverflow.net/help/whats-reputation
Comment: Thanks. Yes, now they have reappeared magically!

Questions and Answers missing


Does Nietzsche's Free Death apply to God?

Question: Nietzsche's philosophy is notorious for its famous pronouncement that "God is dead. And we have killed him. Yet his shadow still looms. How shall we comfort ourselves, the murderers of all murderers?" (The Gay Science--Kaufmann, Section 125). When Nietzsche deals with death in the general sense he speaks of the "art of dying at the right time", very similar to Heidegger's notion of "authentic resoluteness." A free death is one where the dying chose or take death as one's ownmost possibility, to put it in Heidegger's Sein und Zeit language. According to Nietzsche, this autonomy and resolve of the will serves as an inspiration to others to be courageous in the midst of such existential Angst. Yet what remains bothersome is how come this free death does not apply to God, or, for example, to the case of Jesus which Nietzsche admits died too young (as a historical figure and not as an agent of the Christian religion). It seems that this possibility would be especially more prevalent in the case of the divine. Does this reveal that Nietzsche's philosophy is not atheistic, but certainly remains theophobic?
Comment: I admit I don't quite understand your reasoning. Any sort of "free death" would certainly need not apply to God; Nietzsche doesn't think God exists, thus how would God even determine a free death for himself? As for Jesus, again I don't see the line of argument - just because Nietzsche considers a certain sort of death more, say, *significant*, that is no reason to claim that Jesus (who is definitely an outlier) should have experienced it. I think the logical steps in your question could use some further explanation.
Comment: Nietzsche is not an atheist like I said. It is more accurate to say he is a polytheist or even a transtheist; it's a brand of theological finitism. Religions for the herd are what Nietzsche is after, which is why he writes: "I cannot believe in a God who wants to be praised all the time." Nietzsche was God obsessed, "Anti-Christ." So it does beg the question is a "free death" the mark of a God. Also, historical divine-human encounters cannot be reduced to psychological projections in Feuerbach's sense. Is not the transvaluation of values an internalization of divine transcendence?
Comment: The greatest theophobes are theists themselves. They fear the punishment from God.
Answer: It's easy to overstate the relevance of Nietzsche's pronunciation to the terms of classical Theology.  When Nietzsche talks about God, he talks about God as a cornerstone of Western Culture, not God as the character of a Christian story.  From section 343 of TGS, Nietzsche spells out his intended meaning:

The greatest recent event - that God is dead, that the belief in the Christian god
  has become unbelievable - is already beginning to cast its first shadows over Europe.

Throughout Western history, belief in Christianity was not merely seen as True but as a necessary prerequisite to any kind of civilized culture.  It might seem hard for us to think now, given that we seem rather accustomed to a kind of capitalism-driven hollowness underlying the notions of Globalization, but Europe and its colonies was very much founded on the idea of a principled providence, that the West carried the truth about God and that its spread across the globe is that of Divine Right.  Sure, this made empires very wealthy, but that was proposed to be simply reward for the elect and confirmation of their faith, rather than the purpose behind a protracted and vicious campaign of motivated subjection of others who lacked their technologies of power.
Nietzsche addresses the death of God in such terms - namely that given the mass of evil and suffering that has befallen the world in the actions of a humanity spurred on in this way, there can be nothing left of Him now.  Whatever Christian theology might claim of or about God in metaphysical terms is not specifically his concern, because the evidence is clear - we are monsters, and whatever abstract right to rule that we proposed God bequeathed upon us as his servants has clearly been jettisoned in our rush to bring the sword.
In the process of the Enlightenment, of Secularism and Science, the truth of this has started to become clear, and the utter fallacy of Christian imperialism leaves us in a state of not merely uncertainty but of profound ending and absence.  The Christianity that grounded our world's actions is what we do in fact believe about God, and the Redemption and ultimate Salvation that it offered us is part of why we as a society did what we did to the rest of the world.  We have to face up to the reality of what we have done, and to claim that either that self-same God lives on or that he forgives us is an act of escape and pretense; our task is to try now to find some way to live on past it in the cold void of a God that no longer defends or supports our collective action.
Can we say that God's death was freely chosen?  Christ, perhaps, took his choices into his own hands and acted with authenticity, but God's death seems to have been violent and long drawn out by a Christian West that scraped his bones dry for every ounce of empowerment we could find.
Comment: I've always understood the Father/Son relation in that sense as another and incredibly powerful aspect of the technology, though that's very much influenced by my own readings of the psychoanalysts and some of the interesting material on Nietzsche's writings about fatherhood more generally rather than his responses to nihilism as such.  Ben-Ami Scharfstein has a very interesting (albeit maybe a little speculative) take on Nietzsche in his book on the lives of key Western philosophers: http://books.google.co.uk/books?id=FWGAnPaQgvkC
Comment: Great answer, Paul! As a side note, I was not sure how Nietzsche deals with Jesus as the Son in relation to the Father. Does it become a matter of Christian propaganda to have Jesus promise us "many rooms in my father's house"? The beginning of your answer looks very similar to Schelling's "history of eternity" and his philosophy of mythology, but he accepts God as the "ideal person" who we as persons seek to be in actual relation. He claimed the process of polytheism (relative monotheism) was a necessary step on the way to absolute monotheism.
Comment: As far as Schelling goes, I'm not familiar with his work I'm afraid, but great philosophers often leave traces of themselves in others who read them - I'm quite influenced by, among others, Karen Armstrong's "A History of God", which does a great job of looking at the human side of the refinement and changes in our concept of the divine.
Comment: I'm definitely going to check out Scharfstein's book; it does look real interesting. Yes, I really like Armstrong's book I think she does a compelling job, especially in the final chapter. I'm very appreciative for the info and anything you can add please let me know!
Answer: I think it is a bit too easy to characterise Nietzsche as an athiest or theophobic. Its possibly the simplest first move one can take when approaching his work. There can be little doubt that he was God-obsessed. Even his move away from religion was to an other - that of Dionysius.
His awareness of the bright attraction of majesty,  power and  violence in this world chimes with Blakes in his song of experience:

Tyger, Tyger burning bright
In the forests of the night

Who himself was deeply influenced by both Christianity and the Greek classics.
Mary Midgeley, in her book Science & Poetry wrote that it is a mistake to treat God as a common criminal that one can haul up in front of a court to be judged. To do this already reduces him to our stature, our scale. This is not to say that a critique cannot be made. If one takes Platos conception of the soul seriously: introspection of the self leads to an introspection of the city - secular and spiritual.
In these terms one cannot say that God can chose a free death.
Is then the death of God chosen freely by the Christian West? One certainly recognises the similariy of the father and the Son here.


Can I change the passphrase of a private key that has been encrypted?

Question: When importing the secret key for the fundraiser I was asked to enter a passphrase, is it possible to change it, if so, how can I do that?
Answer: The passphrase set during the fundraiser can not be changed. After you have entered the fundraiser details, some wallets will store your private key in a keystore file encrypted with a password. In this case the password can always be changed. If there is no built-in function for this you can always enter your fundraiser details again and create a new keystore file with a new password. Your wallet can now be accessed from both keystore files, so the old keystore file can be removed.
The reason that you are asked for the password for every action is that the wallet does not store your private key unencrypted, so it will sometimes need you to enter the password in order to decrypt the private key.
Answer: The passphrase used for fundraiser wallets contribute to the makeup of the secret key, so it's impossible to change it (these passwords aren't actually used for encryption). If you believe your wallet details may have been compromised, you should create a new key and transfer your XTZ.
Comment: No, I mean, after importing the fundraiser key I was asked 2 times for a new passphrase to encrypt my secret keys if I can remember. Every action asks me about this passphrase.
Comment: Are you using a tezos-client or another wallet - please clarify? You can change the encryption password/passphrase with relative ease but the method differs depending on what you are using as a wallet.
Comment: I am using the tezos-client, but I think I would reimport the founder key to change the keystore file. thanks anyway


Entering Chinese characters on Mac OS X

Question: I am running Mac OS X 10.5. How can I enter Chinese characters using Ping Yin?
Do I need to install some software?
Answer: Go to System Preferences > Personal > International > Input Menu and check the appropriate input method(s).  You can then use the menu bar or Cmd-Spacebar to switch input methods.  (Corrected for Leopard names.)
You may need to use the install DVD to install the appropriate fonts and input methods, although IIRC they are installed by default.
Answer: An alternative option to what @geekosaur suggested would be using IMKQIM. It costs 19,99$ but lets you typeset 10000 hanzi for free (if I remember it right).
For an overview on what else can be set up specific to the chinese language on Mac OS X, also have a look at the excellent [chinese mac] website of Yale university.
Also, if you happen to work on a recent MacBook Pro model, you could enable writing on the Trackpad as an input method in the system preferences.
Answer: You should try out the FIT input method (see http://funinput.com/) (It's Chinese though). I personally think it's better than Mac OS X's default/built-in Chinese input method.

Entering Chinese characters on Mac OS X


What is the prescribed time to start fasting from?

Question: What is the prescribed time to start fasting from? I have heard that when azan is listened, sahri time is not ended yet. Thanks
Comment: That depends on your location, as if you have a correct adhan/azhan of fajr than that's the exact timing and you shouldn't go further. In some places there are several adhans for example one 30 min before fajr to wake people up. So this is depending on the customs. In places where your adhan time is based on calculation only you should chose the best and more accurate calculation as fajr and 'isha timing are the most inaccurate ones according this http://islam.stackexchange.com/questions/32643/figuring-out-right-calculation-method-of-prayer-time
Answer: All perfect praise be to Allah
The ASOOL is, that sehri time ends when it does(when dawn breaks), it is not restricted with azaan...
So, you should follow a credible source of suhoor timing and end sahr before that end time.
Now at some or most of the places, fajr azaans are called exactly on the time of end of sahr, in which case if you are sure they make sure they call azaan at proper time, than you can follow the azaan, the thing is you have to make sure you are following the sahr timming.
And during azaan you must not eat, but as of some ahadees, if you are drinking water lets say or you are eating something and a little is remaining and you are still hungry, than you should finish that thing. Prophet ﷺ said:

It was narrated that Abu Hurayrah (may Allaah be pleased with him)
  said: The Messenger of Allaah (peace and blessings of Allaah be upon
  him) said: "If one of you hears the call (to prayer) and the vessel is
  still in his hand, let him not put it down until he finished with it."
Narrated by Ahmad, 10251; Abu Dawood. 2350;

Also have a look at: https://islam.stackexchange.com/a/1776/15642
Allah knows best