Can two mysql SELECT FOR UPDATE FROM mytable WHERE .. IN (..) deadlock?
Are InnoDB Deadlocks exclusive to INSERT/UPDATE/DELETE?
How do I setup user autostart and properly configure systemd user services? On my arch server, I was setting up users restricted to their home directories. I ran:  useradd -m -s /bin/bash username and passwd username  I've read   I figured I should use systemd user services to make each user run a node server on startup. So i logged into one user account su username and created a file ~/.config/systemd/user/serve.service containing:  [Unit] Description=One of the servers  [Service] ExecStart=/usr/bin/node /home/username/server.js  [Install] WantedBy=default.target   then I ran systemctl --user enable serve.service which responded with Failed to connect to bus: Permission denied  As far as I understand I should run systemctl --user ... command logged in as a user and not as root.  So what did I miss in this configuration? How long does it take for a black hole to form for an external observer? The question is $$\text{If }\, p, \ q\in \mathbb{N}, \;1-\frac12+\frac13-\frac14-\dotsb-\frac{1}{1318}+\frac{1}{1319}=\frac{p}{q}.\qquad \text{Prove that } 1979\mid p.$$ So my solution went like this:  $$S=1-\frac12+\frac13-\frac14-\dotsb-\frac{1}{1318}+\frac{1}{1319}\Rightarrow S=\sum_{k=1}^{1319}\frac{1}{k}-2\sum_{k=1}^{659}\frac{1}{2k}=\sum_{k=660}^{1319}\frac{1}{k}$$ Now this is equivalent to finding the sum of the roots of the equation $$\left(x-\frac{1}{660}\right)\left(x-\frac{1}{661}\right)\dots \left(x-\frac{1}{1319}\right)=0$$. Rewriting this equation, we get $(660x-1)(661x-1)\dotsc(1319x-1)=0$ (we can discard the $\displaystyle \frac{1319!}{659!}$ since $1979$ is a prime). Calculating the sum of the roots, we get the required value to be equal to $(1320+659)\times 330$ which is obviously divisible by $1979$ (again discarding the coeffecient of $x^{660}$).  Now my question is: Using the same method of converting the problem into finding the sum of roots of a polynomial, we get from the original equation something like this: $$(x-1)\left(x+\frac{1}{2}\right)\dots \left(x-\frac{1}{1319}\right)=0 \Rightarrow (x-1)(2x+1)\dotsc(1319x-1)=0$$ So, the sum of roots would be $-1+2-3+4-\dotsc+1318-1319=-660$ But this is not divisible by $1979$. Why does the former solution work while the latter doesn't? Is there a flaw in my reasoning? Note: I know that the question can be solved by some other methods. Please only explain my given doubts and don't instead give another solution  I realised my mistake after some hours of pondering over it. (In the 1st equation) To get the required sum I would need to take calculate $\displaystyle -\frac{\text{coeffecient of }x^{659}\,}{\text{coeffecient of }x^{660}}$. However what I've done is calculate this:  $\displaystyle -\frac{\text{ coeffecient of }x}{\text{coeffecient of }x^{660}}$ which is actually equal to $\text{sum of roots taken }659 \text{ at a time} $. It was just a coincidence that the value I calculated was divisible by $1979$. The correct way, indeed, would be through the link supplied Long lay over in Seoul. Do I need a visa as a Filipino citizen? I'm a Filipino immigrant from USA about to visit home in December.  I have a 14-hour lay over in Seoul,  South Korea.  Do I need a visa to leave the airport to do a little sightseeing? How to move the center of scaling Hello. I'm a beginner.  In the model shown, when I select all of the top vertices and then scale them to the center, the center of scaling is not the center of the 3d-model.   How do I move the center of scaling? How do I move the manipulator widget where I want it after selecting? Is selenium webdriver capable of database testing? After reading so many answers and forums it makes me confused. Some people say: Selenium webdriver is a browser automation tool and it has nothing to do with the database. And some other showing JARs and code that how we can connect selenium to the database and we can test database using selenium webdriver. So I would really like to know if we can do database testing using selenium? If yes then which databases tool it supports like Mysql, SQL server, Oracle... And if selenium is not suitable for database testing then please recommend to me the best tool for database testing. Is the op-amp inverting or non-inverting? I am studying the function and characteristic of an op-amp to build a line-following robot with the schematics below. However, in many tutorials, the way to differentiate an inverting and non-inverting op-amp is by looking at the connection to ground via the inverting or non-inverting terminal.  However, in the schematics, the op-amp is considered to have connections to ground, thus in this case, how do I differentiate it then?  I may have understood the whole concept wrongly. Pls help!    EDIT: Please ignore the switch as it may have been drawn wrongly by the supplier. Extending the User model with custom fields in Django Getting the default text editor used in system I have used select-editor and I note that I am using /usr/bin/nano. Is this the default text editor I am using?  When I open text files, It opens with gedit  What command in terminal must be specified to get the default text editor that I am using, and have it returned to e in terminal? Movie/TV series with a scene of spiky, black goo growing out of a lab container? There was a scene from a sci-fi horror video, not animated, don't know if it's a movie or TV series, where there was this black goo in a glass container and some scientists were looking at it under a microscope.   The pitch black goo grew and grew so fast, eventually breaking out of the inner box and the scientists that were inside the "inner lab" were begging to get out but the scientists outside that inner lab refused to open the door. The black goo was spiky (had spikes).  It's not any of the "Alien" movies, "The Blob", "Life", or "The Thing". It's not vintage. It was made after 1990, I'm pretty sure. How to make the window full screen with Javascript (stretching all over the screen) I would like to configure Apache 2 running on Kubuntu to execute Perl CGI scripts. I've tried some steps that I came across by googling, but nothing seems to work.  What is the right way of achieving this? 12 hours delay with ATmega16A I am trying to turn on a LED for 5sec every 12 hours. I tried:  #include &lt;mega16.h&gt; #include &lt;delay.h&gt;  void main(void) {     DDRC.0 = 1;     PORTC.0 = 0;      while(1)     {              unsigned long i;        unsigned long j;        PORTC.0=1;         for(i=1; i&lt;432; i++)        {              delay_ms(100);          }         PORTC.0 = 0;         for(j=1; j&lt;100; j++)        {            delay_ms(50);          }     } }   but the LED was on for about 2 hour every week. Why is median age a better statistic than mean age? If you look at       Or this Wikipedia page      Clearly  seems to be the statistic of choice when it comes to ages.  I am not able to explain to myself why  would be a worse statistic. Why is it so?  Originally posted  because I did not know this site existed. I hope this isn't a silly question but I've been watching TNG and this bothers me.  The transporter 'pad' area is relatively small.  As a guess, maybe 12 people can fit on it.  But the vast majority of times it's being used by 2-3 people.  However, the transporter is able to beam people from anywhere on the ship to anywhere (within some distance I presume).  It's fairly common for them to perform a transport directly to the bridge.  So, why is there an actual room?    If a three man away team is to beam down to the surface of a planet - why do they have to walk all the way to the transporter room, then stand on the pad to get down there?  Why not simply beam them from where they are, to the surface.  The ship's computer is able to locate anyone on board. How does mission progress work in multiplayer? Force NTFS permissions inheritance for newly created files Does anybody know a way to force that all files that get created inside some folder inherit the NTFS permissions of that folder.  The problem is the following:  I have a third party software that is creating PDF files inside a certain folder, but the problem is that those files get created with only the permissions for that user and for the administrators group, the file doesn't inherit the permissions of the folder it is in (Include inheritable permissions... is not marked on the files that get created), which give access to other groups of users also. Assume there is a rigid body in deep space with mass $m$ and moment of inertia $I$. A force that varies with time, $F(t)$, is applied to the body off-center at a distance $r$ from its center of mass. How do I calculate the instantaneous acceleration, rotational acceleration, and trajectory of this object, assuming it starts from rest? My son has been playing Minecraft on our home computer for a couple of years now.  He just got an iPad Mini 2 for his birthday. Is it possible to transfer his game and his saves onto his iPad Mini 2? Prove if $\operatorname{ord}(a)=m$, $\operatorname{ord}(b)=n$, and $\operatorname{gcd}(m,n)=1$, then $\operatorname{ord}(ab)=mn$.   I was reading this and was thinking how this proof would look like. I tried to do it and am not sure if this is correct. Here is what I did:  If $a$ and $b$ commute then $(ab)^{mn} = a^{mn} * b^{mn} = (a^m)^n * (b^n)^m = 1 * 1 = 1.$ So $ord(ab) | mn$.  Now, take $k = \operatorname{ord}(ab) = m^\prime * n^\prime$ where m' is relatively prime with $n$ and $n'$ is relatively prime with $m$. By the result above $m' | m$ and $n' | n$. Now we have $((ab)^k)^{m/m'} = 1$ since $(ab)^k=1$. But on the other hand, by the commutativity:  $$((ab)^k)^(m/m') =$$  $$((ab)^(m' * n'))^(m/m') =$$  $$ a^{n'm} * b^{n'm} = $$  $$(a^m)^{n'} * b^{n'm'}=$$  $$b^{n'm'} = 1$$  This implies that $n' * m'$ is divisible by $n$. But $m'$ is relatively prime with $n$, so we must have $n' = n.$ By symmetry, $m' = m$. So $ord(ab) = mn$.  Just to say this again, I want to prove if $a$ and $b$ commute and $m$ and $n$ are relatively prime then   $$ord(ab)=mn.$$   The comments are vague. I guess this must be the answer then and there probably is not another way to do this.