How to test if my server is vulnerable to the ShellShock bug?

Question: How can I ensure my Bash installation is not vulnerable to the ShellShock bug anymore after the updates?
Comment: See [Is there a short command to test if my server is secure against the shellshock bash bug?](http://security.stackexchange.com/q/68168)
Comment: Please note there are two other vulnerabilities in bash still unpatched (CVE-2014-7186 and CVE-2014-7187).
Comment: Patches that fix CVE-2014-7186 and CVE-2014-7187 are available as of not long after Deer Hunter posted his comment. If you have a distro provided patch for CVE-2014-7169 you may already have enough to block 7186/7187, test your system with the below commands and see. Also check for any more security updates for your distro.
Answer: To check for the CVE-2014-6271 vulnerability
env x='() { :;}; echo vulnerable' bash -c "echo this is a test"

it should NOT echo back the word vulnerable.

To check for the CVE-2014-7169 vulnerability
(warning: if yours fails it will make or overwrite a file called /tmp/echo that you can delete after, and need to delete before testing again )
cd /tmp; env X='() { (a)=>\' bash -c "echo date"; cat echo

it should say the word date then complain with a message like cat: echo: No such file or directory. If instead it tells you what the current datetime is then your system is vulnerable.

To check for CVE-2014-7186
bash -c 'true <<EOF <<EOF <<EOF <<EOF <<EOF <<EOF <<EOF <<EOF <<EOF <<EOF <<EOF <<EOF <<EOF <<EOF' || echo "CVE-2014-7186 vulnerable, redir_stack"

it should NOT echo back the text CVE-2014-7186 vulnerable, redir_stack.

To check for CVE-2014-7187
(for x in {1..200} ; do echo "for x$x in ; do :"; done; for x in {1..200} ; do echo done ; done) | bash || echo "CVE-2014-7187 vulnerable, word_lineno"

it should NOT echo back the text CVE-2014-7187 vulnerable, word_lineno.

To check for CVE-2014-6277. I'm not 100% sure on this one as it seems to rely on a partially patched system that I no longer have access to.
env HTTP_COOKIE="() { x() { _; }; x() { _; } <<`perl -e '{print "A"x1000}'`; }" bash -c "echo testing CVE-2014-6277"

A pass result on this one is it ONLY echoing back the text testing CVE-2014-6277. If it runs perl or if it complains that perl is not installed that is definitely a fail. I'm not sure on any other failure characteristics as I no longer have any unpatched systems.

To check for CVE-2014-6278. Again, I'm not 100% sure on if this test as I no longer have any unpatched systems.
env HTTP_COOKIE='() { _; } >_[$($())] { echo hi mom; id; }' bash -c "echo testing CVE-2014-6278"

A pass for this test is that it should ONLY echo back the text testing CVE-2014-6278. If yours echoes back hi mom anywhere that is definitely a fail.
Comment: Can we add the general test `foo='() { echo not patched; }' bash -c foo` to this? Until function exports are put in a separate namespace, we won't stop running from one parser bug to the next.
Comment: One point of note: even if the version of BASH is vulnerable, if nothing uses it (i.e. all accounts used by daemons, such as "www" or "cups" or whatever) are configured with BASH as their default shell, and none of your codes calls system() or the like, having the vulnerable version may be less risky, but still, upgrade BASH as soon as possible.
Comment: Does that test have a CVE? Do you have any references to describe this problem? Also this sort of info may belong on one of the other questions about shellshock due to this Q being about how to test the success or failure of existing patches.
Comment: That's from Michal Zalewski's blog post on some upcoming Shellshock CVE's (http://lcamtuf.blogspot.com/2014/09/bash-bug-apply-unofficial-patch-now.html). It's his suggested test for CVE-2014-6278, which is still non-public. It seems I was wrong about the test's generality, though; I've already encountered a case where Zalewski's test passed but the CVE-2014-7187 test failed.
Comment: And here is the full disclosure on CVE-2014-6277 and CVE-2014-6278, along with commands to check for them: http://seclists.org/fulldisclosure/2014/Oct/9
Answer: Export a especially crafted environment variable that will be evaluated automatically by vulnerable versions of Bash:
$ export testbug='() { :;}; echo VULNERABLE'

Now execute a simple echo to see if Bash will evaluate the code in $testbug even though you've not used that variable yourself:
$ bash -c "echo Hello"
VULNERABLE
Hello

If it shows the "VULNERABLE" string, the answer is obvious. Otherwise, you don't need to worry and your patched version of Bash is OK.
Please note multiple patches have been released by the major Linux distributions and sometimes they don't fix the vulnerability completely. Keep checking the security advisories and the CVE entry for this bug.
Comment: In addition to CVE-2014-6271, the incomplete fix from Red Hat in particular has its own that is also worth following: [CVE-2014-7169](https://access.redhat.com/security/cve/CVE-2014-7169).
Comment: One-liner that doesn't pollute your shell env and happens to work even if 'youre using an alternate login shell (which may not know about `export`): `env testbug='() { :;}; echo VULNERABLE' bash -c "echo Hello"`
Comment: There's some Ubuntu specific details here http://askubuntu.com/questions/528101/what-is-the-cve-2014-6271-bash-vulnerability-and-how-do-i-fix-it - personally I had to upgrade from Ubuntu 13.10 to 14.04 to fix the issue
Answer: I wrote a CLI utility called ShellShocker to test your webserver for vulnerabilities on CGI scripts.
To test your site, you'd run:
python shellshocker.py <your-server-address>/<cgi-script-path>

ie
python shellshocker.py http://example.com/cgi-bin/possibly-vulnerable-script.cgi

EDIT: this utility's been taken down, sorry :'(
Comment: Your link is dead
Comment: @SSK Sorry ;) Mistype.
Comment: Your link is still dead.
Comment: Yep, sorry, I took it down. It was being exploited in ways I didn't like.
Answer: ShellShock is practically a conjunction of more than one vulnerabilities of bash, and at this moment there is also malaware that exploits this vulnerability, so ShellShock can be an issue that is still open, there is a thread with updates from RedHat about this issues.
Redhat recommeds the following:
Run command:
$ env 'x=() { :;}; echo vulnerable' 'BASH_FUNC_x()=() { :;}; echo vulnerable' bash -c "echo test"

If output is:
$ env 'x=() { :;}; echo vulnerable' 'BASH_FUNC_x()=() { :;}; echo vulnerable' bash -c "echo test"
vulnerable
bash: BASH_FUNC_x(): line 0: syntax error near unexpected token `)'
bash: BASH_FUNC_x(): line 0: `BASH_FUNC_x() () { :;}; echo vulnerable'
bash: error importing function definition for `BASH_FUNC_x'
test

you don't have any fix.
If output is:
$ env 'x=() { :;}; echo vulnerable' 'BASH_FUNC_x()=() { :;}; echo vulnerable' bash -c "echo test"
bash: warning: x: ignoring function definition attempt
bash: error importing function definition for `x'
bash: error importing function definition for `BASH_FUNC_x()'
test

you have CVE-2014-6271 fix
If your output is:
$ env 'x=() { :;}; echo vulnerable' 'BASH_FUNC_x()=() { :;}; echo vulnerable' bash -c "echo test"
bash: warning: x: ignoring function definition attempt
bash: error importing function definition for `BASH_FUNC_x'
test

you are not vulnerable.
The other part of ShellShock check is the CVE-2014-7169 vulnerability check ensures that the system is protected from the file creation issue. To test if your version of Bash is vulnerable to CVE-2014-7169, run the following command:
$ cd /tmp; rm -f /tmp/echo; env 'x=() { (a)=>\' bash -c "echo date"; cat /tmp/echo
bash: x: line 1: syntax error near unexpected token `='
bash: x: line 1: `'
bash: error importing function definition for `x'
Fri Sep 26 11:49:58 GMT 2014

If your system is vulnerable, the time and date will display and /tmp/echo will be created.
If your system is not vulnerable, you will see output similar to:
$ cd /tmp; rm -f /tmp/echo; env 'x=() { (a)=>\' bash -c "echo date"; cat /tmp/echo
date
cat: /tmp/echo: No such file or directory

Answer: You can submit your CGI URL to this online test:
http://shellshock.iecra.org
Comment: It is polite to provide reasons for downvotes.
Comment: "We log all scans"??? Creepy.  I'd download the python and run it myself.
Comment: @brad at least they're telling you. I'm sure that if I was providing a whitehat security service that offered this service I might well keep a log (if only a counter with no individual details) of how many people blindly entered their site details into a website that said it was going to attempt a penetration test, without knowing much about the authenticity of the site offering the test... and they'd want a log of who tested what in case someone used their service to find vulnerable sites belonging to others, too...
Answer: type env x='() { :;}; echo vulnerable' bash -c "echo this is a test" and if this returns vulnerable and this is a test it means that your OSX/Linux machine is affected.
Remedy is to update to the latest version of bash.
Comment: Why as root? Completely unnecessary.


How can Arduino source code be tested automatically (continuous integration)?

Question: I'd like manage my Arduino source code (projects and libraries) under source control with continuous testing. How can I automatically compile the code with continuous integration tools, to make sure each version compiles cleanly? In the best case one should be able to configure builds for multiple processors, optionally run unit tests and check for maximum binary size.
Comment: The issue with this is it goes against the original purpose of continuous integration: it's meant to push changes and then have it automatically build and deploy within minutes. This allows your customers to get the latest features and fixes as they happen, instead of every two months. For Arduino it's just "cloud making sure it builds." For unit tests you might have to bypass the Arduino libraries to build functions and send example data over the "pins."
Comment: Compiling binary size isn't that hard, but to do unit tests, you would have to structure your code in such a way that it is unit-testable, which is hard enough if you want to keep size small. Besides, you will need to run those test on a chip or in an emulator to get a test that is more or less reliable.
Comment: Other than passing it through Ino and `avr-size`?
Comment: @IgnacioVazquez-Abrams I don't mind which tools to use, but it should run automatically on some cloud hosting or continuous integration service.
Comment: I found https://github.com/kyab/travis-test-arduino but its experimental and a comprehensive answer/tutorial as answer would be better.
Comment: Multiple use cases behind this question + different answers for each. If use case _functional unit tests_, as already suggested you modify your code's function returns, but this isn't foolproof: and downsides if that's embedded into your deliverable.   If your use case is you want to _measure_ integration w/HW, ex: "does Arduino light a LED in response to stimuli, i.e. temperature?"  Be creative. You will need additional hardware and software which can _observe_ what the Arduino under test does, then have a way to pass messages to the test runner (PySerial, etc).
Comment: @AnonymousPenguin `"bypass the Arduino libraries to build functions and send example data over the "pins."` is what I did [in the library discussed in my answer here](https://arduino.stackexchange.com/a/50534/42393).  It enables testing things like `does Arduino light a LED in response to stimuli, i.e. temperature` purely in software.  In other words, it's doing more than just "make sure it builds".
Answer: Newest version of Arduino ide has a command line interface to build and upload code. But you can obviously do it by makefile and avrdude.
Now, you have compiled your code BUT you need testing.
As simulator are complex,incomplete, expansive and.. Just a simulation, and because the chip are relatively cheap, building a board witch will make HW interaction AND check the results its the fastest and easiest way.
On that "special" board you may upload something like an interpreter witch take a test from the PC and execute it, something similar to firmata for arduino.
At least that is how I would build it.
And as far as I know there are no know implementation of this, even if I'm quite sure many industries should and probably do that.
Answer: As the creator of PlatformIO I would recommend you to look into it. It's a cross-platform code builder and missing library manager. It can build the same code for the many popular embedded development platforms and boards.
PlatformIO can be be integrated with many popular Continuous Integration (CI) systems (or your own). See documentation with examples.
Let's look into .travis.yml config/template for Travis CI:
language: python
python:
    - "2.7"

env:
    - PLATFORMIO_CI_SRC=path/to/source/file.c
    - PLATFORMIO_CI_SRC=path/to/source/file.ino
    - PLATFORMIO_CI_SRC=path/to/source/directory

install:
    - python -c "$(curl -fsSL https://raw.githubusercontent.com/platformio/platformio/master/scripts/get-platformio.py)"

script:
    - platformio ci --board=TYPE_1 --board=TYPE_2 --board=TYPE_N

Example
Integration for USB_Host_Shield_2.0 project. The .travis.yml configuration file:
language: python
python:
    - "2.7"

env:
    - PLATFORMIO_CI_SRC=examples/acm/acm_terminal
    - PLATFORMIO_CI_SRC=examples/Bluetooth/WiiIRCamera PLATFORMIO_BUILD_FLAGS="-DWIICAMERA"
    - PLATFORMIO_CI_SRC=examples/ftdi/USBFTDILoopback
    - PLATFORMIO_CI_SRC=examples/Xbox/XBOXUSB
    # - ...

install:
    - python -c "$(curl -fsSL https://raw.githubusercontent.com/platformio/platformio/master/scripts/get-platformio.py)"

    # Libraries from PlatformIO Library Registry
    # http://platformio.org/#!/lib/show/416/TinyGPS
    # http://platformio.org/#!/lib/show/417/SPI4Teensy3
    - platformio lib install 416 417

script:
    - platformio ci --board=uno --board=teensy31 --board=due --lib="."

Configuration file: https://github.com/felis/USB_Host_Shield_2.0/blob/master/.travis.yml
Build History: https://travis-ci.org/felis/USB_Host_Shield_2.0
Comment: If you are affiliated or associated with PlatformIO you should disclose this in your answer, or it may be flagged and removed as spam. Thanks!
Answer: One example of setting up Jenkins continuous integration for Arduino project can be found here: Continuous integration for embedded systems
The example shows how to build and upload image to Arduino and execute Selenium web tests (the system under test is Arduino-based web-server).
Comment: nice because it use some existing software witch is feature rich. but it seems to do only web testing; can you please expand the answer? also link-based answer are bad.
Answer: I wrote this test unittest framework for Arduino, since i could not find proper existing. While i did not write it for CI, it would be good fit for CI job, since it requires no hardware but can be ran on PC.
Running the CI jobs without the hardware has good sides and bad sides, good sides beeing that

No flashing, no hardware needed -> can be runned in parallel -> fast to check for example for every commit
No hardware issues influencing the tests -> no need to worry did this test just fail because my XYZ-hardware component is not stable

On the downside there is:

Its not testing the actual target code, for example your 'int' is 32 bits in your PC and 16bits in AVR.
Comment: "_your 'int' is 64 bits in your PC_": you probably mean "32 bits", or you are using some exotic OS.
Comment: You are right of course, thanks. I edited my answer to fix that.
Comment: note you can set up an in-home CI server with a cheap pc like a raspberry hooked up to an HW board and thus have a piece of the CI infrastructure running on real HW (while maybe keeping the default cloud CI for all that is software)
Answer: I've just put together a decent size writeup as an answer to this related question about an Arduino CI/unit testing framework I wrote that's finally mature enough to start talking publicly about.
The arduino_ci ruby gem supports both local testing and Travis CI integration (e.g. this build job for the Adafruit FONA library).
Some examples of how it integrates:

The DoSomething example library shown above, used to test arduino_ci itself
A practical example, testing a Queue implementation
A complex example, simulating a library that controls an interactive device over a SoftwareSerial connection as part of the Adafruit FONA library

I have an issue created for reporting sketch size but no work has been done on that.  It's also possible that I could parallelize the builds someday, but at the moment I'm not precisely sure how I'd do that.  Right now, the  most time consuming build step on Travis CI is downloading the Arduino IDE... parallel testing won't put much of a dent in that if every job needs to do that step.
Answer: I would advice to use the arduino eclipse plugin named sloeber sloeber.io of which I'm the project lead.
It integrates with version control and allows building on multiple platforms as it supports multiple configurations.
Though it is not yet idiot proof I have documented and demonstrated using unit testing of arduino code on the local pc using the google test framework.
Here is a link to a blog containing a presentation of how you can do it. http://blog.baeyens.it/#post25


Chinese citizen, Canadian permanent resident visiting Taiwan from China, is Hong Kong the only way?

Question: My mother is a permanent resident of Canada and a Chinese citizen. She booked a plane ticket to China. If she gets a visa on her Chinese passport from the Taiwanese consulate in Toronto, then flies to China, and visits Taiwan (for tourism purposes) before flying back to Canada, is going through Hong Kong International Airport virtually her only option in order to accomplish this? For some context, this visitor visa to Taiwan is open only to Chinese citizens with a work permit, study permit, long-term residence visa or permanent resident status in Hong Kong, Macau or a foreign country. It also appears that Chinese citizens are not allowed to take trips from China to Taiwan unless they are travelling as a tourist group as of August 1, 2019.
Answer: Well, technically, you have another option: travelling to Macao (or any third country)... But yes, her only option is to do so.
If you fly to Taiwan from the mainland, the Chinese immigration control will ask for a Taiwan Travel Permit issued by mainland Chinese authorities and a valid exit visa recorded on the permit. If you don't have both of them, you cannot travel to Taiwan from mainland China as a mainland citizen. However, no one really cares if you travel to Taiwan via a third location (that is to say, unless you are suspected of espionage or anything like that). If you travel via Hong Kong then you're fine.


What is the best way to strip weekly and seasonal noise from a time series data set?

Question: What is the best way to strip weekly and seasonal noise from a time series data set?
Any recommendations on different approaches and there relative benefits?
Comment: Because the wording is important in this setting: seasonal patterns and noise are distinct "building" blocks in time series. Often one models trend, season and noise.
Comment: Could you please explain in your question what is `weekly and seasonal noise`?
Answer: What you might actually be looking for is some way to remove the cyclical component in the data from the long term trend.
Any smoothing technique will be able to remove noise and the cyclical component in the data. A simple moving average or exponential smoothing technique is sometimes very useful. The difference between the predicted smoothed value and the actual value is the cyclical component in the data plus noise.
You can use a more complicated techniques such as a Hodrick–Prescott filter (usually applied to business cycles). I image you could also fit some function with a aggressive regularization component to encourage smoothness. The prediction by the smooth model fitted will be the trend component and the difference the seasonal component.
Alternatively, simple technique such as seasonality indexes might be used.
A seasonal index (quarterly sales data) is calculated in the following table.

Calculate what the hypothetical constant demand was in each quarter $i.e 403/4$. Calculate in what ratio the actual demand in quarter was above or below the constant demand $i.e 80/100.75$. Decompose data into the trend component $i.e 80/0.89$ and seasonal component $i.e 80-80/0.89$. If you have a monthly data consider converting the 12 data points per year to 4 data points with a weighted average. Basically taking the average of every three month to compute one data point. Weighing the start and end of season less than the middle of the season.
Alternatively, you can also build a simple OLS regression to separate the effect of each season from the long term trend. One independent variable is time, and other independent variables are dummy variables to indicate the season. Use $y=\alpha + \beta t+\beta_1 d_1+\beta_2 d_2 +\beta_2 d_3$ where $t$ is the time period starting from 1, and $d_1$, $d_2$ and $d_3$ is dummy variables for the quarter 2, 3, 4. Using quoter 1 as the base model, add the  coefficient $\beta_2$ to all data-points in quoter 2, $\beta_3$ to all data-points in quarter 3, and $\beta_4$ to all data-points in quarter 4. All the data points will now effectively be in the same quarter (quarter 1). That is, seasonal component of different quarter has been removed.
The different between approaches comes down to effort and complexity. As in any modelling task, no penance exists. The most appropriate technique can only be chosen after examining the objective of what you are trying to do. A very comprehensive standard for seasonal adjustment of time series data is used in the EU. This document gives some very good guidelines. See ESS guidelines
Comment: Broken link http://www.cmfb.org/pdf/ESS%20Guidelines%20on%20SA.pdf
Answer: I read this question differently than in @entropy's answer.  I see this as a "double seasonality" request: i.e. the poster needs to filter out seasonal noise (e.g. a warm/cold cycle, modeled by week) and a weekly seasonal pattern (stores sell more on Saturday than on Tuesday).
There is a good discussion of this problem by Gould and Vahid-Araghi as chapter 14 in Rob J. Hyndman, A.B Koehler, J.K. Ord and R.D. Snyder's book 'Forecasting with Exponential Smoothing'. (2008).  But the poster may be looking for a simpler approach.
Continuing my example above, convert the data to weeks, and estimate weekly seasonal factors (e.g. by time series decomposition). Use these weekly seasonal factors to deseasonalize the daily data.  Then use this daily data to estimate daily seasonality, and remove that by deseasonalizing.


What happens if you take off with a direct tailwind?

Question: What happens if you take off with a direct tailwind?
Comment: It takes longer.
Comment: Perhaps you can expand your question? Simply repeating the title doesn't give us a good idea of what information you're looking for, and what you know already.
Comment: Do you mean taking off in the same direction that the wind is blowing? This is called taking off with a tailwind.
Comment: You'll break it sooner as you climb.
Comment: @FlorianCastellane Yes, it is. That really belongs more as a [question](https://aviation.stackexchange.com/questions/ask) than as a comment, though.
Comment: [Related](https://aviation.stackexchange.com/q/203/62)
Comment: is it common in airfields to change the direction of takeoff on the runway to get favorable headwind rather than tailwind?
Answer: Given how few bounding criteria you have in your question, the general result is

For fixed wing aircraft: your ground speed will be significantly
higher than if you'd taken off heading into the same wind, and thus
you'll tend to use up more runway before lifting off.
Example: with a take off speed of 100 kts, going into or downwind is the difference between 90 knots or 110 knots ground speed before reaching take off speed when the wind down the runway is 10 knots.  This difference becomes more pronounced as wind speed increases; it's a differential of 2 x wind speed.
With a long enough runway it won't matter in terms of "taking off before running out of runway."  On a short field it may matter a great deal.
For Rotary Wing aircraft: you may need a bit more power to hover when
lifting off with a tail wind.  The FAA has this guidance:

Headwinds are the most desirable as they contribute to the greatest
  increase in performance. {snip} When taking off into a headwind,
  effective trans lational lift is achieved earlier, resulting in more
  lift and a steeper climb angle. When taking off with a tailwind, more
  distance is required to accelerate through translational lift.

For a variety of aircraft types, if the tail wind is high enough your manual will recommend against/prohibit down wind takeoffs, but that varies enough between models and types that a general answer can't encompass all of the variations.
Comment: @Criggie -- "a sudden return to not-flying", nice.  As in, "Oh my god, the engines are on fire!  We are going to suddenly return to not-flying!"
Comment: @Criggie You'll have this effect too when starting against the wind. but off cause it will make the "out of runway" problem worse.
Comment: Add something about the "gustiness" too?  If the wind is varying between 5 and 20, then your effective airspeed at take off might suddenly drop 15 knots leading to a loss of lift and a sudden return to not-flying.
Comment: @Criggie the question as asked is about a direct tail wind.  I don't disagree with your point on gustiness, but won't that have a similar effect into the wind, albeit you'll have lower ground speed (and that runway's end is approaching faster!)
Comment: "For Rotary Wing aircraft: you'll need more power to hover" -- this is not true. The only factors for hover performance in a heli are density altitude, weight, and surface (hard or soft).  Translational lift can occur at any angle to the fuselage, because the (rotary) wing is 360-degrees.
Comment: @rbp Many rotary wing aircraft have a slight forward tilt/bias to the disc.  Lifting off into the wind takes advantage of that as you are getting a free (x) knots progress into the translational lift, however, I am sure there are some twin rotor types (CH-47) where this is all washed out, or insignificant, and others where the bias is less.  T/R helicopters do have some tail wind/rearward flight limitations in their operating manuals, but how much varies.  Is the power differential significant? All other things (the standard factors you mention) being equal, maybe not. Slight edit.
Comment: @rbp Put another way, I often found that flying backwards took a bit more power than forward, which is what taking off with a tail wind amounts to (flying backwards) but that might be very "model dependent" ...
Comment: There are always type differences. I gave the aerodynamic answer.
Comment: @rbp And I gave the practical answer: theory and practice have a neat relationship. :-)
Answer: So I will focus on fixed wing aircraft, as that's all I really know about.
Lift is a factor of your "Indicated Airspeed". So the faster the wind is going over the wing, the more lift the wing can generate. You always need a certain Indicated airspeed to take off. The plane simply won't "go up" until you reach that speed. Depending on the aircraft, the needed speed of the air over the wings changes.
For example in a Cessna Grand Caravan you need about 80 knots of Indicated airspeed to really take off. There are some "rules" in its handbook about short take-offs, but in general you want to be above 80 knots IAS before you start "going up".
Now if the wind is constant, and blowing from the front of the craft to the back at 5 knots, then you already have an IAS of 5 knots. Sitting still your IAS is 5 knots, because the air is passing over your wing at 5 knots.
If that wind is passing from the  back (tail) or the aircraft to the front, then you have a IAS of -5 knots when sitting still.
Now we get into ground speed. Mostly when you're flying (in the air) you don't really care about ground speed, other then efficiency and as a measurement of where you are. If you care about it at all it's way back at the end of the list. You care more about IAS (to keep you up) and True Air speed (the speed of which you're actually moving through the air). But when you're taking off or landing you care quite a bit about ground speed.
So generally 1 knot of IAS would be equal to 1 knot of ground speed. So to get our sample plane off the ground, on a day with no wind, you have to be moving at 80 knots on the ground. That's roughly 92 miles an hour.
With a headwind (from front of the plane to back) of 5 knots you have to be moving at 75 knots ground speed or 86 mph.
With a tailwind (back of plane to front) of 5 knots you have to be moving at 85 knots of ground speed or 97 miles per hour.
Depend on your how your plane is designed, those few knots of ground speed can mean the difference between a good take off, and running out of runway. Or because the wheels are actually on the ground, exceeding the safety of the structure of the landing gear.
Lets take a runway of 2000 feet. There are smaller runways, though to be fair this is a pretty small one. The example plane needs 1,160 feet to take off in a situation with no wind and empty. So we could take off from this airport. There's a "rule of thumb" out there that says "operation with tailwinds up to 10 knots, increase distances by 10% for each two knots [of wind]." So at 5 knots of tailwind I go from needing 1,160 feet to about 1,500 (error on the side of caution). I can still take off, but what about weight? Different weights need different lengths to get up to speed. Another rule of thumb "10% change in weight will cause at least a 20% change in takeoff and landing distances." So for are sample aircraft lets say I have a total weight of 6,000 lbs. The Empty weight is 4,550. That's a weight change of around 31%. So now I need to add on 60% distance to my ground roll.  So I need 1,900 feet to take off (again pad for caution). I'm still good. But let's add in the wind. Now I need 2,375 feet to take off and the runway just isn't that long. So I'm stuck on the ground.
So our example in summary:

With no wind. I can take off
With a headwind, I can take off
But with 5 knots of Tailwind I can not take off.

SUPER IMPORTANT NOTES

Rules of thumb are great, but they're not the POH. Every airplane should come with a POH (and I mean every physical plane should have a POH in it). In that POH are real limits, and real rules/guidelines. Most will contain a table or chart that spells out weight, ground roll and wind speeds in one way or another. Some craft will have safety limits, that should not be exceeded.
The rules of thumb are great for conversations in general but should not be applied to an aircraft in real life. If you're flying a plane you should know the plane's specs and limits. Not just "guess" at them.
The numbers I used in the example are accurate enough for an example, but come from Google.
Runway length is also effected by what it's made of. Grass fields take off "longer" then asphalt.
Runways can be as short as 800 feet, but most larger airports have
runways in the 10,000 feet range. The longest public runway is about
18,000 feet. There are runways that are longer.
While the runways may be bigger the jets that use them need to go faster and take longer to get there, so the problem exists for them, too. More so, in some ways.
A lot more then just IAS goes into a take off there is air density, for one. The slope of the runway, the temperature of the air. This example is really simplified to look at the one aspect.
Comment: *"In that POH are real limits, and real rules/guidelines."* Most of the "limits" regarding wind in POH's are **demonstrated** limits, not absolute limits. So I wouldn't call them "real limits" or "rules". Also, there were a lot of aircraft manufactured that never had POH's. Only other thing I would say is that most larger airports do not have runways 18,000 feet long, about 12,000/13,000 is the largest you'll find on public airfields.
Comment: While I agree that the limits are not as limiting as they sound, I thought all aircraft had to have either a POH or an AFM. Could totally be wrong. Also on runway length, I meant that as a max. I will clarify.
Answer: Two risk factors which have not yet been mentioned:
The higher groundspeed required before airspeed is sufficient for take-off will put higher strain on the landing gear and wheels. Imagine a bump in the runway; hitting it at 80 or 100 mph will make a difference which in the worst case may cause e.g. a wheel puncture.
Also, should you need to abort the take-off, the braking distance before the airplane comes to a stop will be much longer from 90 mph than from 70 mph. The stopping distance will be 1.65x longer, although the speed difference in this case is only 1.28x.
Came to think of a third risk factor too: Wind gradient.
Often the wind blows stronger the higher you get above the runway. This can be significant at small airfields. In a normal take-off with a headwind this helps the airplane climb better as it ascends. But in a tailwind take-off the tailwind increases as the airplane ascends, meaning that the climbing rate is reduced (nose must be held down to achieve sufficient airspeed for climbing). If the airplane has sufficient power this may not be noticeable, but a marginally powered plane may have difficulties if there are obstacles close to the field.
Comment: Very important points.
Answer: You will need more runway. Once airborne, there will be no difference, apart from an unfavorable wind gradient.
Besides, it is not advisable, because, in non-controlled airfields, the pilots consider the runway with a headwind as the active runway.
Comment: Third sentence ought to be in bold. This is vary important in GA.  +1
Answer: The airplane will still fly; it just takes considerably more runway to depart.  Most Pilot's Operating Handbooks (POHs) will use a phraseology in their takeoff roll performance charts such as "increase ground roll 10% for every 2 kts of tailwind" or similar.  Doesn't look too bad but consider now that if you depart in a direct 10 kt tailwind, your ground roll and distance to clear a 50 ft obstacle is now 50% greater than a takeoff in still air.  This become a serious factor on short airstrips and high field elevations and density altitudes.  A Cessna 172 may require 1300 feet of runway to do this at sea level at STP but might be upwards of 5000 feet of runway needed for a 6000 ft field elevation at 30° C.
Answer: Jump-pilots and Ag-pilots regularly take off downwind and/or with strong cross-winds providing of course the runway is long enough.  A dedicated airport is preferred.  If you want to get tremendous experience as a pilot, fly 500 hours taking skydivers up to 11,000 feet.  You are dropping falling bombs that become floating bombs that pass through winds aloft from different directions at different altitudes then land on the drop-zone target.  You'll know you're a respected pilot when the experienced jumpers fall asleep during the climb.  You will learn how to say NO! when your boss pushes you to the limit with weight, weather, and flying with minimum fuel.  Most jump-planes look fairly junky and it's fun to tell first time jumpers when they see the airplane, "if you think the airplane looks bad you should see the parachute!"
Comment: This doesn't really answer the question. The fact that some operations are willing to accept tailwind conditions with a long enough runway and/or a dedicated airport does not describe what happens if you take off with a direct tailwind. The remainder of the commentary is interesting but irrelevant to the question. See more on what to put into an answer [here](https://aviation.stackexchange.com/help/how-to-answer). Welcome to Aviation.SE!
Answer: "Once you lift off, there's nothing to worry about".... The increased ground speed may cause you to believe (optical illusion) you have a faster airspeed and the desire to increase your pitch attitude.(Which may be already high due to the lengthened take off roll and the need to climb). Your climb rate will suffer also. (vertical gain vs. horizontal travel). This goes against the bottom line...." Never regret NOT having the air above or the Runway behind you." My personal minimums will not accept a downwind take off OR landing ( also a major optical illusion) greater than 5 Knots.
Answer: The other answers and comments are ignoring an effect that usually does not show up in practice, but that it exists and I have witnessed first hand: as long as the air flow on the frame is reversed, so is the effect of the commands.
For take off, the effect diminishes as the aircraft gains speed, so it will probably only affect gliders and other light aircraft that rely heavily on the commands since the start of the run. On landing, the effect increases as the ground speed diminishes, and I have witnessed a serious crash (straight against a fence that run at the side of the runway) because of it.
Comment: You'll have reverse airflow over the controls only as long as your groundspeed on the takeoff roll is less than the wind speed
Comment: That's exactly what my answer says. And, as I mentioned, the effect increases when groundspeed decreases, so it can be deadly on landing.
Comment: Good point, but the question is about take off.
Comment: It could still be deadly on take off, on a extreme situation (say, 80km/h tail wind on a J3). Usually, not pilot is crazy enough to try to take-off with a heavy tailwind, but it is certainly possible.
Comment: the controls only reverse with a tailwind when the wheel is on the ground.
Comment: Yes, absolutely: as I said, "as long as theh air flow on the frame is reversed". I saw a friend fight for his life for two months at the hospital because of this.


Will Moore's Law be no longer effective once quantum computers are created?

Question: Moore's law states that computer power doubles in every 18 months (more formally: "the number of transistors in a dense integrated circuit doubles about every two years."). Statistics suggest that this observation should be correct, but aren't quantum computers much more powerful than just double-powered classical computers? More interesting question is, is there even a way to improve the power of quantum computers?
Answer:
but aren't quantum computers much more powerful than just
  double-powered classical computers?

Yes. A universal quantum computer with only 100 qubits (12.5 quantum bytes) can find the ground state of a matrix with $2^{200} = 10^{60}$ elements. Assuming Moore's Law could continue forever (which is not true due to physical limitations), it would take longer than the age of the universe (13.5 billion years) for the "doubling of transistors every 18 months" to bring classical computers to what a quantum computer with one quantum gigabyte can do, for certain problems.

More interesting question is, is there even a way to improve the power of
  quantum computers?

There have been proposals for exploiting certain types of phenomena that would lead to devices even more powerful than quantum computers, but in all cases quantum computers would be a special case of such devices (just like classical computers are a special case of quantum computers, they are quantum computers that just only use classical gates and inputs that are not in any superposition). It is hard enough to build a quantum computer, so building the more generalized devices would be even harder.
Answer: The quantum equivalent of Moore's Law is Rose's Law which states that "the number of qubits in a scalable quantum computing architecture should double every year."
The prediction was made by Geordie Rose of D-Wave circa 2003. See D-Wave's Future of Hardware, this article or this amazing answer for more info.
My understanding is that a quantum computer can make $2^n$ computations per step where n is the number of qubits. With the number of qubits doubling every year this means the computational power of quantum computers will accelerate very quickly.
Answer: Moore's law is not a fundamental law of the nature. It is just a heuristic mentioned by Moore to show the growing importance of computer technology. You should never take it for granted and there is nothing wrong if the actual trend doesn't follow Moore's law.
Secondly, Quantum computers give speed up in only certain kinds of computations. You cannot expect it to give exponential speed up for every classical algorithm. So it is inappropriate to compare a QC with a Classical computer. Classical computers are going to stay even after QC become commercially viable.
Comment: I think Moore's law might be the result a complex interaction of various non-technological, mainly economical effects, too. Like this: the need to have faster CPUs, the invested stock into the CPU development, the length of the timeline until a CPU plan becomes actually manufactured CPUs in the stores, and so on.


Could turbine or compressor stages of a jet engine be switched off to improve fuel efficiency?

Question: Active fuel management is a technology developed by General Motors, which is used to improve engine efficiency in the times when the engine is operating under loads which are considerably less than the rated load, as shown in this link. This technology exploits the property of piston engines where some of the cylinders are turned OFF while only few of them work, and hence improving the overall efficiency of the engine. Can a similar technique be employed on an aircraft's engines, where some of the turbine stages (Compressor or Turbine) are switched off in order to improve the performance efficiency of the engine?
Comment: I don't think your analogy works. A car is powered by multiple identical, indivisible units (cylinders) and the power management system turns some of those off to conserve fuel. A plane is also powered by multiple identical, indivisible units (engines) so the analogous control mechanism would be to turn off some of those units (shut down an engine or two), not to somehow turn off parts of the units.
Comment: First of all, a compressor stage is not turbine's equivalent of a cylinder. This would be the combustor (aka flame holder).
Comment: The second issue is that reciprocating engine's cylinder uses very specific amount of fuel per cycle. Use too much or not enough and you get burn problems. In a car you also have very tight coupling of engine to the wheels: speed of X requires Y rpm which means Z fuel consumption (gearbox helps a bit, but just a bit). You can't dial down the power by reducing to any rpm you like. This problem does not exists on an aircraft: almost every rpm works at any speed (because jet exhaust is always faster than IAS). You can simply dial down the RPM, no need of partial shutdown of the engine.
Answer: You cannot "switch off" a stage of a turbine engine.
As seen elsewhere jet engines are a single block mechanically locked together: all the stages (compressor AND turbine) connected to the same shaft. If the shaft turns, all connected stages turn with it.
You can have designs with multiple shafts, but this increases the complexity (design and maintenance) heavily.
Even if we assume for a moment that you could have 1 shaft per stage, stopping one of these would be generally a bad idea.
For acoustic reasons the number of blades on the stationary part of the stage and those on the rotary part must be prime to each other (example: 37 blades on the stationary side and 39 on the rotary one); this means that when the rotary part stops you cannot align all the blades with the stationary ones, creating drag and losses within the engine, thus reducing the efficiency.

How would efficiency of a Jet Engine change, if we assume for a second that its a possibility, to stop a few stages(turn them into free instead of locked)?

You would still decrease the efficiency: compressor stages are the ones actually pulling the aircraft forward (you would then produce less thrust*) and the turbine stages are the ones extracting energy from the exahust.
*: you could even risk having the flame going upstream if you stop too many compressor stages and not having enough pressure at the combustion chamber inlet.
Comment: More to the point. Additional stages increase Carnot efficiency by more closely approximating adiabatic expansion. The ideal jet engine has infinite stages (obviously not ideal from a manufacturing perspective), as at that limit, we get adiabatic expansion. There is no equivalent in an ICE, as ICEs do not have staged PV cycles.
Comment: Stopping individual cylinders in Active Fuel Management reduces the fuel burn, because otherwise a volume of air & fuel is needed for each revolution.  A jet engine doesn't have this fixed displacement problem; the fuel flow can just be reduced (within limits).  Perhaps you could let some turbine or compressor discs in the engine freewheel by adding extra clutches, but I suspect that would be far too complex mechanically, as well as **add** drag inside the engine...
Comment: Lets say that we have an engine where the stages are attached to the shaft by some mechanism (which is a black box). This mechanism has the ability to turn to **free** and **locked** state. How would efficiency of a Jet Engine change, if we assume for a second that its a possibility, to stop a few stages(turn them into **free** instead of **locked**)?
Answer: Can it be done?
Yes
Has it been done?
Yes
Wait, what?! Where what how?
The Pratt and Whitney J58 was designed to allow partial shutdown of the compressor. It does this by placing a distinctive spike in front of the compressor assembly.
However the purpose of the transition to ramjet that is distinctive of the J58 was to allow it to avoid overheating the turbine during supersonic flight, where the increased inlet velocity translated to additional heating of the air.
However this does not increase the efficiency of the jet engine at all.
Overall you actually want as many stages as possible for subsonic flight. This is because multiple stages allow the gas to compress/expand more adiabatically, leading to better Carnot efficiency.
Comment: I can hardly agree. the PW-J58, as shown in the wiki page you linked, simply reduced the airflow to the turbojet duct. In addition `The gas generator RPM was kept at 100% to maintain maximum thrust.`, hardly "switched off".
Comment: Very interesting - I thought the sr71 spikes were only for reducing airflow through the engine.
Comment: +1. I thought I knew the answer (it does not make sense) but I learned it is possible, and SR71 did that, for reasons linked. Thank you!
Answer: Short answer: No.
Longer answer: Jet engines are designed with multiple compressor and turbine discs mechanically attached to a single shaft, called a spool. Usually, there are 2 (or sometimes 3) of these spools within the engine, due to the need of the high pressure compressor and the main intake fan to spin at different speeds. Each spool spins freely and is driven by the compressed air in the engine core being pushed through the turbine stages attached to that spool.
Diagram of a Turbofan Jet Engine

Source: Wikipedia
There is no way to "shut down" a particular spool. As long as the pressure in the engine core is higher than the pressure behind the nozzle, the turbines will spin and drive the spool. If you detach either one of the turbine stages or one of the compressor stages from a spool such that it 'freewheels,' the turbine discs will likely overspeed due to decreased load. Additionally, an undriven compressor stage would experience compressor stall, which is essentially an aerodynamic stall of the blades of the compressor stage.

Finally, this is entirely unneeded for a couple of reasons:
First, aside from the problems it would cause, there would be nothing to gain from shutting down a compressor stage. As Andy correctly mentioned in a comment, jet engines do not have a constant fuel burn per revolution, unlike piston engines. If a jet engine doesn't need to produce as much power, it can simply inject less fuel in the combustion chamber. As the pressure in the combustion chamber drops, the spools will spin down accordingly on their own (due to less pressure driving the turbine stages.)
Second, the power output profiles of jet aircraft operation are nothing like those of a car. For a car, high engine power is usually used only in brief spurts for acceleration and cruise uses a small fraction of that amount of power. In a jet airplane, on the other hand, the engines will be operated at a rather high percentage of their maximum RPMs for most of the flight. This is because additional power allows them to fly higher, which actually increases efficiency. See the answers to the previous question How far can a 777 fly with just one engine at altitude? Unlike a car, significantly reducing the power during cruise flight actually reduces the fuel efficiency of an airliner.
Comment: "In a jet airplane, on the other hand, the engines will be operated near their maximum performance for most of the flight." That is certainly not true in civil aviation. The thrust in cruise is typically around 25% of the maximum takeoff thrust. I think the answer in link on "flying on one engine" seems somewhat confused.
Comment: @alephzero Thrust or RPMs? Thrust will be lower for the same RPMs due to less dense air (as that answer mentions.) I'll edit my answer to make clear that I mean RPMs here, not thrust.
Answer: If you extend the idea of "switch off" a bit, this is already done in several different ways.
Surveillance aircraft may be designed to loiter over their target area with some engines shut down completely. That is not just a matter of shutting down the engines - for example if you are going to loiter at high altitude for several hours at temperatures below -50C, you are likely to need special systems to heat the oil in the shut-down engines, to avoid damage when you restart them.
Many jet engines contain variable stator vanes in the compressors, which are automatically adjusted to improve the efficiency under different working conditions.
In multi-shaft engines, the relative speeds of the different shafts changes depending on the working conditions. That is more efficient that forcing all the compressor and turbine stages to run at the same speed on a single shaft. In a multi-shaft turbofan, the bypass ratio (i.e. the fraction of the air being compressed in the core engine and used for combustion, rather than just being blown by the fan to generate thrust) will also change.
Answer: Fuel efficiency is not improved by shutting off stages of a compressor or turbine. Fuel efficiency is a function of overall pressure ratio, reduce this and efficiency is reduced.


Gauging tight parking spots

Question: So that I don't keep dinging or putting scratches my front bumper, what is the best way to gauge tight parking spaces ?
Say, if a parking spot is walled in three directions and you are pulling in your car, other than counting on experience how does one gauge if the front bumper will rub against (or not) the wall ? Are there any reference points ?
Answer: One thing I found with myself, after learning to drive on farms at a very young age, is that I seem to naturally "know" or "feel" where the outer limits of my car is. It's strange and I can't fully explain it, but I've personally never had this issue.
However!!
Many people do, you're definitely not alone, and there are a few solutions!
One, if it's your house/carport, I have seen people hang a tennis ball from a string, attached to the ceiling. It'll be put in just the right place, so that when your car is close enough to the wall ahead, the tennis ball is just touching your windshield. That's really helpful if you have a big 4x4 and a little parking space in your house.
Another option, is an ultrasonic beeper. Some cars will have these already installed from the factory, but you can get kits off ebay that have sensors and indicators, and are fairly cheap.
The other option I can think of quickly, is a tried-and-tested method seen on many Japanese cars... Little parking wands. They're just a stick that attaches to the front bumper, and you can easily see where the extremity of the car's nose is. I guess ebay would have them, but I've only ever pulled them off imported cars, never put them on!
Hope that helps!
Comment: Anybody remember the [steel curb feelers](https://s-media-cache-ak0.pinimg.com/736x/72/cd/7d/72cd7decafd0b138febfb1ce973ce478.jpg) that used to be mounted near the tires, down low on fenders?  They were a springy rod about 10" long that would scrape on the curb when you got real close.  They made a loud noise as they got dragged over the concrete curb.  Ha! Thanks for the memories.
Comment: The 'knowing where the corners of your car' comes from practice - it is that simple. After years of driving many, many cars, I can now know the corners of my car with high accuracy after 30 minutes. I can't do the same with a big truck, though - but truck drivers can, so it is obviously practice there as well.
Answer: I'm a bit of a parking elitist, so let me tell you what you should do if you want to be cool, like me :P
When pulling or backing into a spot, I've made a habit of pulling in the minimum distance, just enough that my car is in line (also centered and parallel, because parking snob) with the parking spot paint, which is enough to guarantee you aren't hanging out into the flow of traffic.You can use your mirrors to see when the lines for the packing spot are about equal with the back of your car, or equal to the car next to you, then you don't have to worry about hitting your front bumper unless it's an EXTREMELY tight spot, which is pretty rare, in my experience.
I began parking like this when I drove a little Civic hatchback. I always hated looking for a parking spot in a busy lot, seeing one, pulling up, only to find the spot was occupied by a little car or motorcycle, amd I didn't want to be that guy. It also prevents people from impeding the flow of a busy lot, as they will glace right over my car instead speeding up, slowing down, starting to turn, fist fighting other motorists for the spot etc.
For gauging parallel parking, go practice one day, get yourself parked an acceptable distance from the curb (<6"), then get in the drivers seat and sit in a natural position that you know you can repeat. Find a reference point on your car that lines up well with where the curb meets the ground. I find one of the many ridges/holes in the windshield wipers works the best. You can even put a small notch or mark the spot with a pen. This way, next time you pull up, you can sit in your natural position, look at where your reference point lines up with the ground, and gauge how far you are from the curb.
Comment: "because parking snob", LOL
Answer: Practice in a store carpark with some cones.
Personally, if I'm in a tight spot, I find it easier to reverse in; I can then see all the way down each side of the car using the mirrors (and new cars now generally come with reversing cameras).
You say "other than counting experience" - you can't. You need the experience, so you need to practice where you won't damage your car.
Comment: Another place to practice is in the residential neighboods in downtown Boston.  Get yourself an older car and move there for a year or two.  You'll quickly learn how to park in a tight spot if you want to park anywhere at all.  And Boston is especially good for learners since it is accepted there that parking is a contact sport.

Gauging tight parking spots


Differences between "Klausur", "Prüfung" and "Examen"

Question: Is there any differences in usage between Klausur, Prüfung, Examen, Test*, and (Klassen)arbeit*?
* Edit: added more synonyms based on answers below.
Answer: Let me go through each of them to explain some differences:

Prüfung: The most generic term of all three. A "Klausur" is a kind of "Prüfung", as well as an "Examen".
Examen: This term is in modern times used only with final exams within some educations, especially when the test is conducted by a state authority. Then it is called "Staatsexamen"; examples for this might include final exams for law or medical students. This Wikipedia article lists other examples for "Staatsexamen". If I understand right, "Examen" was once used for every type of (final) exam in higher education.
Klausur:: A written test in universities. The term sometimes* is used for written tests within the last two years of grammar school (Oberstufe).
[*]: At least when I was in grammar school...
Comment: You can delete *sometimes* and thus the [*], too.
Comment: The term *Klausur* was used all the time when I was in school, I think anything from 7th grade ("Quarta") up to Abitur, with the final exams also being *Klausuren*. And the term replaced the term *Klassenarbeit* which was used in the years before. I don't know if that is a regional thing.
Comment: As far as I know in both medicine and law studies, as well as teaching (Lehramt) gibt es das Erste und das Zweite Staatsexams, wobei das 2. noch nach einem praktischen Abschnitt nach dem Studium abgelegt wird.
Answer: AFAIK, Klausur and Examen¹ are only used for theoretical tests, while Prüfung can as well be a practical test, like Führerscheinprüfung (test for driving license) and Materialprüfung.
You couldn't say Materialexamen or Materialklausur. (Well - in German, you're free to combine old words to new ones, so you could say it, but people would raise they eyebrows for this unusual combination).
Test would be another alternative, which is used for practical tests too.
Klausur has a second meaning as in  "Die CSU geht in Wildbadkreuth in Klausur.", which means conclave, and similar: enclosure.
¹) according to Wikipedia (thanks to Hendrik Vogt), Examen is used, for example for musicians, for practical tests too.
Answer: Just want to add the word "Arbeit". At the school I visited, we only used the words "Prüfung" and "Arbeit".
We used "Prüfung" for the "final exams" and "Arbeit" for the normal tests.

Schreiben wir morgen eine Arbeit in Deutsch?
Comment: You may add "Test" too.
Answer: "Prüfung" could be most generally translated as "test".
An oral test, could be a "Mündliche Prüfung", for instance, but there is never a "Mündliche Klausur". It wouldn't make sense, since the word 'Klausur' implies a silent session behind closed doors.
"Examen" implies almost every time a kind of final test, final exam, etc.
Comment: The first sentence is a bold statement. ;p


why my flag is marked as disputed?

Question: not sure why my flag is marked as disputed for Magento 2 - How to add ajax tab on admin user edit page in admin section . Its not an answer but still my flag is marked as disputed.
Answer: The flag was disputed because the community has a mixed feeling about the post.
From the review, 1 "Recommend Deletion", but 2 "Looks OK". Thus, the consensus was that the post deemed "OK" even though it was flagged as "Not an Answer".
From What is a disputed flag?,

Currently, the following scenarios result in a flag being disputed:

[...]
A "not an answer" or "very low quality" flag kicks the post into the Low Quality Posts review queue but the final result of the review was "Looks OK".
Answer: Rahul Makwana, Thanks for raising the concern about the flag.
The answer is not an answer, So right now I am deleting.
Your flag is disputed by Community user means which is a background process.
https://magento.stackexchange.com/users/-1/community?tab=profile

why my flag is marked as disputed?


How do I find people who actually want to play Left 4 Dead survival mode on Xbox live

Question: It seems like about 50% of the time I join a random game of Survival mode on XBox Live I end up with a bunch of 12 year olds who think it's funny to just go around and shoot each other. If I really want to play survival mode how do I find a game where people actually want to play instead of just dick around?
Comment: Get it on the PC?
Answer: I think by searching for player's name that are serious and invite them into your server could be the only way to have what you want.
Search in forums or other gaming website about L4D and you should fine players older than 12. Add their name in your friend list in the Xbox and you're set.
Answer: Ask reddit /r/gaming, or some folks on here and other forum sites for an online meetup.
Or just lobby jump until you find some good players.... good luck though.


Can I configure my Sony A57 screen and viewfinder display to brighten with a manual flash, just like with the popup flash?

Question: When I pop up the built-in flash on my Sony Alpha 57, the LCD and electronic viewfinder brighten up a lot, so I can focus properly in low light situations. However, when I put on my Yongnuo 560 mkII, this doesn't happen. Is there any way to change this behavior or is it standard behavior when an external flash is attached? I looked at the camera settings, but didn't see anything that would appear to affect this and without this effect, I can't see anything on the screen or viewfinder.
Answer: From what I understand, that Yongnuo is a manual flash. While I am not experienced with Sony Alpha cameras, I am assuming that it is unable to simulate any brightening the flash unit may provide through the EVF or LCD because the flash is not communicating any information to the camera. Manual flashes must be manually configured. My best suggestion would be to go into the camera's settings and increase the brightness of the EVF and the LCD to see if that helps.
Answer: Recently, I bought a Sony Alpha α68, and had the same problem. When I use an external non-TTL flash (manual only), the EVF is very dark, and I can't see the model.
But the solution is in the menu of the camera. Follow this procedure to fix the issue:

Go to Menu
Go to the gear icon
Go to second (2) menu
Go to the Live View Display option. The default option is Setting Effect On. Change this option to Setting Effect Off.

This setting changes the EVF to display like a camera with a pentaprism. It works for me on my Sony Alpha α68.
I hope this configuration works for you.
Regards.
Comment: Thank you very much ! I dont know why i didnt think of this myself.


Why is a "squeeze bunt" referred to as such?

Question: This refers to a bunt with the runner on third base. Why isn't a bunt referred to as a squeeze bunt with runners on other bases? Or is it a special type of bunt (e.g. toward the first base line) to maximize the chances of the runner getting from third to home?
Answer:
Why is a "squeeze bunt" referred to as such?

Although not explicitly stated, context could be used to gain insight on the coining of this phrase.
An April 20, 1905 Chicago Tribune article stated:

"[Ducky] Holmes tried to 'squeeze' in the run which would have won the
  game with a bunt, but it went
  foul."(1)

The first use of the term "squeeze play" can be found in the Chicago Tribune five days later when an article stated:

"[New York Highlanders] manager [Clark] Griffith says he has a new one
  called the 'squeeze play,' which is working
  wonders."(1)
(2)

Clark Griffith is credited with coining this phrase. He is also credited for inventing the play, although there have been other claims that the play has been invented by others and used before this 1905 instance.

Why isn't a bunt referred to as a squeeze bunt with runners on other
  bases?

Based on the context of the phrase above, the term "squeeze" is used in relation to scoring a run. Thus, one would not be "squeezing" in a run if a bunt was used to advance base runners not on third base. A bunt with the intention of advancing a base runner (regardless of whether the batter gets on base or not) is known as a "sacrifice bunt." A "squeeze bunt" is a type of "sacrifice bunt."

Or is it a special type of bunt (e.g. toward the first base line) to maximize the chances of the runner getting from third to home?

Looking at the different types of squeeze bunts, the player has the discretion on whether to take his chances, before or during a bunt, to advance home. The placement of the bunt, although a significant factor, does not seem to define a "squeeze bunt" as such. A "squeeze bunt" is defined as such if the overall intention is to advance the base runner from third base.
There are two different kinds of "squeeze bunts":

Safety: The base runner on third base determines when and if to run based on where the ball is bunted. The main factor is the probability of the fielding team able to throw out the base runner at home plate, and this may be further determined by defensive fielding alignment (eg, are the infielders aligned closer to home plate than usual?).
Suicide: The base runner on third base advances for home immediately after the pitch is thrown.
Comment: I'd say that squeeze came from the close grouping of the fielders (C, P, 3B, 1B) fielding the bunt, and the batter and runner all converging on a 'tight squeeze' at the plate.  I've never heard of run scoring called squeezing outside the context of a bunt.


Do aerodynamics scale for model aircraft?

Question: If I wanted to make a scale model plane that looked like a real aircraft, could I just scale down all of the measurements of the actual aircraft to make a model aircraft with similar flight characteristics? If not, what is the reason?
Comment: Relevant concept: https://en.wikipedia.org/wiki/Similitude_(model)
Answer: Aircraft do not scale linearly, for a number of reasons.

Most aerodynamic equations include a speed squared term. If you halve the speed, you only get a quarter of the lift and drag, so models tend to be lighter and less powerful than you'd expect.

If you make a plane with half the wing span, it only has a quarter of the wing area. So now a half size model flying at half speed only has one sixteenth of the lift.

Reynolds number - air flowing over a surface will start with laminar flow but turn turbulent after a while, depending on the speed (and density and viscosity but we can ignore those). A smaller, slower model will see more laminar flow than the full size aircraft. In practice, this is a relatively small effect compared to the previous factors but it's an important consideration for high performance models.

Example
A full size Spitfire had a wing span of 36 ft 10 in (11.23 m), a weight of 5-6000lbs (2-3,000kg) and between 1000hp and 2000hp depending on the variant, with a maximum speed of around 400mph.
If you scaled it linearly, a 1/10th scale model would have a 1.1m span, weigh 200kg, have 100hp and fly at 40mph!
If (as Phil suggests) you scale weight and power by 1000 (10 cubed) it would weigh 5-6lbs and have 1-2hp, which is close but still heavier and more powerful than real models:
A 72" model (1/6th scale) might weigh 15lbs and have 2.5-3KW (4hp) and fly at 100mph.
A 44" model (1/10th scale) might weigh 2-3lb and have 2-300W (1/2hp) and fly at 60mph.
A 36" model (1/12th scale) might weigh about 1lb and have 100W (1/7th hp) and fly at 50mph
Comment: "If you scaled it directly, a 1/10th scale model would have a 1.1m span, weigh 200kg" how do you figure? Ostensibly, the design would be scaled by a factor of 1/10 in three dimensions, resulting in a volume scale factor of (1/10)^3 or 1/1000. Assuming construction with materials of the same density, the mass scale would be the same. And power too, to maintain the same power-to-weight ratio. So, 5 to 6 pounds, and 1 to 2 horsepower.
Comment: Where can I get that 100hp engine that will fit into the nose of a 1/10-scale Spit? :-)
Comment: @PhilFrost is right. Reducing all dimensions of a 3D object to 1/10th of their original size reduces the volume and thus the weight of the scaled object to 1/1000 of the original. It's called the Square Cubed law and it means your model plane would weigh 1/1000 of the original weight, not 1/10th.
Comment: @BobJarvis-ReinstateMonica - I don't know but if you find one, please let me know!
Comment: @PhilFrost - I've added your numbers to the answer.
Answer: Elaborating on @Robin's answer with the full effects of the cube-square law.
If we were to construct a model aircraft at half the length of a full aircraft, the model would:

Have half of the wingspan as the full aircaft
Have  a quarter of the wing area
Have an eighth of the mass

Counter intuitively, this means that the model has more surface area per unit volume eg. more wing area per unit mass.
Where this becomes more difficult is in applying this to gain an understanding about the characteristics of our model aircraft.
As @Robin said,

Most aerodynamic equations include a speed squared term. If you half the speed, you only get a quarter of the lift and drag

But this is a simplistic way of looking at things, consider the full lift equation:

For our model to stay in the air, it needs the same lift to mass ratio as the full size aircraft. But remember the mass has decreased by a factor of 8, so we only require a lift that is an eighth of the original lift force. Assuming the lift coefficient and the density of air stay constant, we need to adjust the speed and wing area.
Mathematically we can show that the required velocity for flight is roughly 70% of the velocity of the aircraft, greater than a clean multiple of a half would suggest.
Comment: 1) For a constant density (eg. using the same materials in both the model and the aircraft), mass scales with the cube of the linear scale factor. 2) You are correct, beam strength scales with the cube of its thickness (second moment of area) and linearly by its width, so theoretically there is a minimum size a model aircraft can be scaled down, since the mass 'increases' relative to beam size.
Comment: Can you scale mass directly with volume? It's been a long time since I studied structures, and I can't remember how beam strength scales, just that there are some cube terms in there!
Answer: For a given constant global density, mass grows with the cube of the linear dimension.
Concerning lift, all other things equal, lift grows linearly with the wing area, and the wing area grows with the square of the linear size. For similar reasons, drag grows with the square of linear size too.
And concerning power required, it grows with the power 3.5 of the linear dimension, because –in general- the power required by any heavier-than-air aircraft is proportional to its weight times its speed. The weight scales with the cube of the linear dimension, and the airspeed is squared in the formula for lift, so the power for the proportionality of lift should be 0.5. Since the the power required is proportional to the product of weight and speed, the exponentes are added, and the result is 3.5
Answer: Yes, but a certain amount of surface area is required for the air to come across the wingbody. As an object decreases in surface area it's propensity for airflow decreases with it, that's why paper airplanes don't fly very far unless the wing surface is sufficient to capture a steady air quantity.


Database of chess games for evaluating ranking systems?

Question: I would like to test my ranking system based on information theory.
I need a database of games with outcomes and ranks of the single players.
Where can I find this?
Answer: There was a Kaggle competition sponsored by the FIDE looking for an alternative to the current ELO system. The link is:
http://www.kaggle.com/c/ChessRatings2
The dataset has over a million actual games covering ~50k players. There's also discussions of the alternative approaches used (the competition itself is now over) and scoreboard of metrics to see how well your ranking system compares.
Answer: There is actually a rather large DB of chess games at http://chesstempo.com.  I'm not sure how open they are with it, but it could be a good starting point.
Answer: You could also try ChessGames.com. There is at least one API for accessing the data: Chess::Games::DotCom on metacapn.


How can I get my 13 month old to eat better and sleep through the night?

Question: My child is 13 months old. She is breast fed, eats solids but doesn't eat a lot during supper time. Apparently she eats well at day care. She wakes 3 to 4 times at night and sometimes every hour. Twice I have ended up force feeding her baby porridge during one of these wakings and then she sleeps through till the next morning. She is definitely hungry. When we eat dinner she nibbles and I can't get her to eat more than she wants to. She has no problem eating biscuits and chips after supper so there is clearly space. I have now taken the chips and biscuits away completely. She refuses to have formula or a bottle of expressed milk - which I could add porridge to. How can I get her to eat more on her own so that she can be full and sleep longer at night without force feeding her?
Comment: Can you cut out (or cut down or make earlier) the afternoon snack so that shes really hungry at dinner time? Also shes old enough to try lots of new foods. Are you putting a small variety in front of her so she can try feeding herself at dinner?
Comment: What kind of solids are you giving her? Regular food?
Comment: Hi Dave & RachelC. Thank you for your replies. She eats with me at night. I make veggies, meat - either chicken or beef, potatoes - either sweet or normal and sometimes rice or couscous, sometimes I make stews. She basically nibbles. I do cut everything into small pieces and if she doesn't want to eat from me, I then put it in front of her to help herself. She still nibbles.
Answer: You must be very tired, and very stressed!
The good news is that I think you might be able to fix this quite quickly and easily.
But first, you mustn't ever try to force-feed your child. No matter how worried or tired you are, this won't work and could cause serious problems.
You don't say that your child is underweight, so I'm going to assume her weight is fine.
Therefore she is getting enough food, period.
Because she has "space" for biscuits, it does not mean your baby is  hungry or needs the nutrition. Most humans will eat sweet, high calorie food at any time if offered - that's probably down to the way we evolved, when it was a sensible strategy!
Unless there's some underlying medical problem, there's no reason your 13 month old now needs food during the night. If your baby is of normal weight, then she's getting enough calories, so there's no reason she needs to feed during the night at this age.
If you think about it, your final question

How can I get her to eat more on her own so that she can be full and sleep longer at night without force feeding her?

doesn't make sense. If she is of normal weight and in the absence of a medical problem, she can't both (a) be hungry and (b) need "force-feeding" in order to sleep. If she doesn't want food during the night, then I think there is no issue of feeding and the problem is entirely one of sleeping.
All humans, just like your baby, wake up several times during the night. If we don't have a sleep problem, we turn over and go back for another cycle, and we don't even remember the partial waking.
The problem is that she's not falling back into deep sleep by herself. My guess from the information you give is that she has a sleep association problem. This is like a habit; expecting something to be a certain, usual way when she goes to sleep. It can be easy to fix!
Therefore I suggest you investigate the sleep problem.
It might simply that your child has an association with something unhelpful, such as

you being there when she falls asleep (unless you are co-sleeping and you want to be)
being nursed or fed to sleep

In particular, if she is used to being nursed or fed to sleep, it might be that she is used to feeding when she wakes during the night, and now hasn't learned how to sleep without this (because you keep trying to feed her!). Since she's not hungry now, since her stomach has grown since she was a baby and she's now getting enough food during the day, that is creating the confusion for her and you.
To sleep independently, she needs to learn to fall asleep by herself so that she can fall asleep after her partial wakings. For more information, read the book by Ferber "Solve your child's sleep problems" which helped me immensely.
Good luck!
Comment: Hi MontyBom. Thank you for your reply. She is under weight. She started daycare around 4.5 months old and had what I thought was flu from about 6 months old till  year old. She stopped picking up weight at the rate she was picking up. The doctors say she is 2kgs under weight. I thought the flu was normal as everyone says she will be sick all the time if she goes to daycare. Anyway, we took her for tests etc in December and it turned out she had Moraxella in her lungs. She is now better now and has picked up 900g in the last month. I will look for the book, thank you.
Comment: I did take her to the doctor a few times while sick and got given antibiotics which seemed to help a bit but not fully.
Comment: Sorry to hear she was sick. Our daughter got very sick too when she first went to daycare. (I think it is very common unfortunately, as you say!) I'm glad to hear she is gaining weight again. Since she is gaining weight, following an illness which is resolved, I believe everything in my answer still applies. (Obviously, first and foremost take the guidance of your doctor.)
Answer: I asked a very similar question here about a year ago
1 year old baby won't eat in day, drinks milk all night
and I got some helpful answers although no-one could really suggest how to get my son to eat more.
A year on, we've had some success trying certain things and I think that just time in itself makes a big difference. It's not very well accepted by society now that extended breastfeeding and children waking up at night is a normal and natural thing. You only need to look at how many questions there are on this site and the internet in general to see it's not at all unusual. Therefore, if you want your daughter to eat more and wake less at night, you can't really expect her to just do it by herself for a while longer yet.
What we did that helped was some fairly  basic and gentle night weaning. There are more structured and stricter versions you can try depending on how much you want to achieve. The idea is to get the baby used to having less milk at night and they will gradually compensate by eating (or drinking) more during the day. Search online for night weaning, you'll get lots of suggestions.
With us, we started with my husband going in for the first night-waking which tended to be around 12:30. He would offer comfort and bottled milk to my son but he didn't take it. He cried what seemed like a lot the first night, but checking the clock it was only about 20 minutes. The second night he cried less and after that he was OK and mostly stopped waking at that time. When he went back to sleep, he slept for as long as he would have if I had breastfed him. This and the fact that he refused bottled milk led us to believe that he wasn't really hungry at this time.
We then moved on to the next waking around 3 am. Occasionally he would drink some milk from the bottle but not as much as breastfeeding and after a while he stopped bothering. We had a good spell where he would sleep until anywhere from 4:30 to 6. I would then breastfeed and stay with him and he'd go back to sleep until it was time to get up. We could probably have cut out this too but I didn't mind it as I work full time, I enjoyed keeping this chance for closeness with him.
My son is gradually starting to enjoy his food more. He's still not a big eater, he's only a small child, but now he can speak he actually tells us he likes a food even if he doesn't eat much of it. We try very hard not to push him to eat although it can be difficult to avoid, especially if you feel that you're going to be up half the night. But the more he can communicate, the more we realise that there's no way to make him eat when he doesn't want to.
Comment: It is not at all clear to me that it is normal and natural or healthy for adults and toddlers to go night after night after night after night without a full uninterrupted night's sleep.  Sleep is IMPORTANT, and a baby waking up 3 times every night probably isn't getting enough.  Tiny babies evolved to feed through the night, but a child that old can get enough food during the day to get a full night's sleep.
Comment: Hi MiniMum. Thank you for your response. My problem is I'm a single mom most of the time but when my husband gets back from his trip, I will try get him to go to my lg. I will stop the force feeding. I've only done it 3 times.
Comment: Hi Leigh22. It will be easier to try this with some help but there are a lot of different ways to do it. There's even some for co-sleeping. One that I was considering trying was Jay Gordon's method. I think it's important to stick to something once you start so if your husband is away a lot then I'd suggest looking for something you can do mostly by yourself. Dr Sears also has some good tips if you want to try a gentle approach.


MacBook Pro sometimes has trouble "waking up" its Internet connection

Question: Several times a day I'll close my MacBook Pro laptop with the power still on, then later I'll open it again, unlock the screen with my admin password and wait for it to reconnect wirelessly to the Internet. (My power settings are set so that it disconnects after being closed for a certain period of time.) 9 times out of 10 it's successful in reconnecting, but every once in awhile it fails to reconnect. Usually when that happens, all I have to do is close and reopen the laptop, unlock the screen again, wait for it to try again and then it works, but that's so annoying. Why does it do that? I should also mention that I've had the computer for 3 years and it's only done this in like the last year. It's possible that it started happening when I upgraded my wireless router to an 802.11n.
Answer: I had the same issue with my previous MacBook Pro (late 2006). One solution was to turn the wifi off, then to turn it on again (faster than closing & opening, you can do it through the menu bar icon).
I guess it's due to some timeout in detecting the surround networks and it may happen especially if there are many of them.
There is probably no fix to that and won't be any in the future.
One of the solution would be to change the time of detection, but as far as I know, there's no way to do that.


federal guidelines for reporting expenses and donations

Question: I'm running for city council in a small town on the platform of transparency... really like 18f api standards, looking to find a schema to describe expenses and donations for the campaign - ie some place to create an endpoint that could be harvested by a 3rd party...  looking for schemas in general - I'm using schema.org for the markup - and could probably come up with something from there?   just curious whether this makes sense as an approach / if someone else is doing something similar
Comment: http://data.influenceexplorer.com/docs/contributions/ was a great answer - that has a nice schema - it's more than sufficient for my needs, thank you!
Comment: You might want to take a page from the FEC's book - they have data at http://www.fec.gov/disclosure.shtml and http://www.fec.gov/finance/disclosure/disclosure_data_search.shtml. The Sunlight Foundation's Influence Explorer might also suit you well for an example of what your data could look like: http://data.influenceexplorer.com/docs/contributions/ and http://data.influenceexplorer.com/contributions/
Answer: The first thing to consider is what data you have and what format is it in.
Whatever it is, you can first make it available in a bulk download. Providing all the data and updating it on a schedule is a vast improvement that doesn't require a lot of overhead.
Then, take stock of what kind of format the data is in. If you have the data in PDFs, focus on a way to get that information into a data base. If the records are being kept in excel, that is at least structured but you would want to upgrade to a database as well.
If the information is in a database, then making an API is not too complicated. I would suggest a json API. Making the field names clear and readable can go a long way. Having good documentation is very important- even the best schema is frustrating if there is poor documentation.
The level of detail that you can give is dependent on the underlying detail in your data.


How can I enable auto-rotate for the home screen?

Question: I have a "handset" with Android 2.3.4, and the "flip" feature works for every app and screen, except the desktop. That is, if I flip my phone any screen or app will flip too, yet the desktop remains fixed. There was an exception when I was playing a game and I pressed the home button: there the desktop was flipped, but it seems it was "forced" to flip by the game. How can I make it flip like any other app or screen?
Answer: If it doesn't work out of the box, which is the case with many Android phones, then you have a  few different options:

A launcher replacement which adds this feature (may not work with all ROMs)
A custom ROM like cyanogen mod, which has this feature built in. You can read more about custom ROMs here
Wait for an official update which adds this feature. (may never happen)
Answer: Old question, but this answer is relevant for other Android versions.

I suffer from the similar problem in my Android 4.2.1 where all apps would follow auto-rotation except the home screen (default Launcher app). I found a solution mentioned here and here.
The device needs to be rooted and Xposed Framework installed. App Settings is the app that did the job in my device.
Instructions

Install, activate and launch App Settings.
Locate and select your default launcher app → slide to ON.
Change Orientation  to Normal rotation if you want orientation to be synced with auto-rotation, or choose other ones based on your needs.
Tap "save" icon next to ON to save settings.
Go back to Launcher, and as per your settings you will notice the orientation in it.
Default Launcher in landscape mode with auto-rotation

App drawer in landscape mode with auto-rotation

We're good to go!


Sources for etymologies of Ancient Greek proper names and placenames?

Question: There are good etymological dictionaries for Ancient Greek: if you're searching for the origin of a word, you'll probably find information in Frisk, Chantraine, or Beekes. But if you're looking for the etymology of the name of a mythological figure, or an island, or a town, with those dictionaries you're usually out of luck. Some proper names have an entry, but most don't, and there doesn't seem to be any method to which ones are included. Google and etymological websites are rarely helpful. Are there any etymological works for Greek that focus on proper names? Specific journals that tend to publish such articles? Does anyone have any other tips for finding proposed etymologies for a name?
Comment: I usually look it up in Brill's New Pauly at first http://referenceworks.brillonline.com/browse/brill-s-new-pauly.
Comment: Would material written in Greek be of any use for you? Ch. Symeonidis has released books dedicated to toponymy and Babiniotis includes a fair amount of common names and their etymology.
Comment: @Midas, yes, assuming the scholarship are reliable, pointers to Modern Greek materials would be helpful! I know of Babiniotis but not Symeonidis.
Comment: @TKR ok, give me some time and I will have a better look on it. This is something of interest for me too.
Comment: @TKR: I've modified my post with some extra material in the last few days.
Answer: Pape–Benseler's 1911 dictionary of proper names is old, and its etymologies maybe disproportionately rely on the etymological guesses of Byzantine lexicographers; but it is comprehensive, and always a good starting point.
Comment: Cool! Good to see you here, and sorry life sidelined me from that blog...
Answer: Babiniotis "Ετυμολογικό Λεξικό τής Νέας Ελληνικής Γλώσσας" is definetely a good source for personal and place names. The title refers to the modern Greek language, but includes etymologies on mythological names, ancient Greek names and placenames. Even biblical names are included. Here is a small sample:

Of course, it's purpose is not to cover all Greek toponymy as that would require a gigantic volume. It is simply a huge etymological dictionary including place and personal names.
For toponyms and their etymology there is a dedicated book which basically covers mainly the modern names. However, since so many places are called by their ancient name it might be of your interest. In some places he explains that place name A is of Slavic origin and then tells you what the ancient name was. It is a huge volume and a bit pricey. You can have a look here: Νεοελληνκά Οικωνύμια (Τοπωνύμια) and for a sample here
There is also this site where under the "Other" tab there is an index of Pre-Greek place names. Of course Pre-Greek means no etymology.
A collection of papers dedicated to personal names: Greek Personal Names: Their Value as Evidence
Possibly one of the best resources on Greek dialectology has a searchable database of personal names as well: ΘΕΤΙΜΑ


Why doesn't Robin appear in the Justice League and Justice League Unlimited animated series?

Question: Robin is part of the DC animated universe, so why doesn't he appear in the Justice League or the follow-up Justice League Unlimited series?  What is the reason behind not including any Robin or Nightwing character in the Justice League series; not even as a special appearance?
Answer: From IMDb:

When the series was expanded from Justice League to Justice League Unlimited, producers considered adding Batman's sidekicks, Robin, Batgirl, and Nightwing.
However, DC Comics turned them down, because the Robin/Dick Grayson role was being used on Teen Titans.

There was/is something called "(Bat)-Embargo":

a decision to keep certain DC characters exclusive to certain shows across the television and film medium.

Bruce Timm, the man behind Justice League and Justice League Unlimited said about the Bat-Embargo:

... to tell you the truth, as much as I […] love those characters, I don't really miss [them] all that much.  It's not like we don't have tons of other interesting characters to play with.
If I were doing an actual Batman show, and not allowed to use those characters, yeah, that'd be pretty galling, but Batman's only one ingredient in the Justice League's brew.  The Bat-clan aren't really essential in any way to the current show ...

although,

At one point during the later series Justice League Unlimited, an episode featuring Batgirl was discussed. ... The episode was never produced as the rights to the Batgirl character were not held over and were being used by the team on The Batman at the time

However, in the episode Grudge Match they sidestepped the Bat-Embargo:

Dick Grayson has a blink-and-you-miss-it cameo as Nightwing, shown watching from a rooftop as Canary and Huntress drive their way into Blüdhaven.

Watch the scene on YouTube
Comment: +1 for nice detailed answer. I previously knew this Nightwing scene but i didn't recognized him that time.
Comment: When I saw that Nightwing clip for the first time I was hoping he would make more of an appearance in the episode.
Answer: At the time Warner Bros., owners of DC Comics and makers of these shows, had a newly-successful Batman film franchise.  As a result, they essentially reserved the Batman "universe" (i.e. his settings, friends, and foes) for those films and for Batman-specific TV series.  The end result was that both the Justice League series and Smallville couldn't make extensive use of Batman, Gotham, Robin, Nightwing, etc.  Other Justice League members didn't have such a limitation, and so the series saw significant use of their rogues galleries.
Comment: But justice league used batman,gotham(not sure but i think they used it),joker,cadmus and many more batman properties.
Comment: Clayface ,Copperhead,Harley Quinn,Clock King etc. Not sure if deadshot can be counted or not.
Comment: Don't forget Terry McGinnis(batman) and alferd.  I f i am not wrong there are few more batman related character but not remember at the moment.
Comment: let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/7915/discussion-between-ankit-sharma-and-keen)
Answer: Blüdhaven appears briefly in the Justice League Unlimited television series episode "Grudge Match" as the backdrop for a meta-human fighting match organized by Roulette in which female Leaguers under mind control (including Fire, Wonder Woman and Black Canary) fight it out. A signboard at the city's entrance says "Welcome to Blüdhaven". In the same scene, the silhouette of Nightwing appears in a cameo. (Source:Wikipedia)
Answer: People don't actually notice but dick grayson and barbara gordon ARE in Justice league 1'st season in the season finale. It's a single minute but if you catch it in the right second. It's when flash, lantern, and wonderwomen are in an alternate reality and Batman is a vigilante rebel against Savages army. Among batmans soldiers you see a couple right before they kiss. A long haired man that resembles Dick and a red headed women resembling Barbara. That isn't a coincidence. You also notice a boy that looks like tim drake and a girl that looks like annie the daughter of clayface. Amazing
Comment: Could you provide an image of the scene you're talking about?
Comment: Alternative time lines, don't really count here imho, but +1 for pointing it out.
Answer: Let's not forget that joker is not in JLU either. The reason neither he nor Tim appears is because by the second series, the whole Joker Junior plot unfurled, which forced Batman to dismiss Tim. This part is confusing because the flashback scene was made before either JL series so Bats was still in his TNBA costume. But judging by Joker appearing in season 2 of JL as well as season 1, he kidnapped Drake by the end of JL and died before JLU