SQL injection attacks -- syntax issue
How can I prevent SQL injection in PHP?
I want to buy a new notebook in the near future to play games on it. I'm looking forward for the new Steam for Linux client. My question is that where does the Steam install the games, on the home partition, or in the usr folder, or somewhere else? I do not use pre-release (i.e. beta) versions of either Steam or Ubuntu. Calculate Euler equations of fluid dynamics without division? I'm working on the calculation of the  with the . Unfortunately I'm not allowed to do a division. So I'm wondering if there's a form which does not need a division.  At the moment the Euler equations look like this:  $$ \frac{\partial}{\partial t} \begin{pmatrix} \rho \\ \rho v_1 \\ \rho v_2 \\ \rho v_3 \\ \rho E \end{pmatrix} = -\mathrm{div} \begin{pmatrix} \rho v_1 &amp; \rho v_2 &amp; \rho v_3 \\  \rho v_1^2 + p &amp; \rho v_1 v_2 &amp; \rho v_1 v_3 \\  \rho v_2 v_1 &amp; \rho v_2^2 + p &amp; \rho v_2 v_3 \\  \rho v_3 v_1 &amp; \rho v_3 v_2 &amp; \rho v_3^2 + p \\  (\rho E + p) v_1 &amp; (\rho E + p) v_2 &amp; (\rho E + p) v_3 \end{pmatrix} $$  As you can see, I first need to calculate $\frac{\rho v_1}{\rho}$ to get $v_1$ so I can calculate e.g. $\rho v_1^2$ I have a Lenovo T570 with Xubuntu 18.04 LTS. My current issue is that my cpu speed stepping is kind of going nuts and does what ever it thinks its best.  Sample: when I run my IDE and cpu load increases during build time, the governor changes automatically. I caught the moment during compiling my project with the following call:  martin@martin-ThinkPad-T570:~$ while cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor; do sleep 1; done powersave powersave performance performance   cpufreq-info tells me this:  martin@martin-ThinkPad-T570:~$ cpufreq-info  cpufrequtils 008: cpufreq-info (C) Dominik Brodowski 2004-2009 Report errors and bugs to cpufreq@vger.kernel.org, please. analyzing CPU 0:   driver: intel_pstate   CPUs which run at the same hardware frequency: 0   CPUs which need to have their frequency coordinated by software: 0   maximum transition latency: 4294.55 ms.   hardware limits: 400 MHz - 3.50 GHz   available cpufreq governors: performance, powersave   current policy: frequency should be within 3.50 GHz and 3.50 GHz.                   The governor "performance" may decide which speed to use                   within this range.   current CPU frequency is 3.25 GHz. analyzing CPU 1:   driver: intel_pstate   CPUs which run at the same hardware frequency: 1   CPUs which need to have their frequency coordinated by software: 1   maximum transition latency: 4294.55 ms.   hardware limits: 400 MHz - 3.50 GHz   available cpufreq governors: performance, powersave   current policy: frequency should be within 3.50 GHz and 3.50 GHz.                   The governor "performance" may decide which speed to use                   within this range.   current CPU frequency is 3.36 GHz. analyzing CPU 2:   driver: intel_pstate   CPUs which run at the same hardware frequency: 2   CPUs which need to have their frequency coordinated by software: 2   maximum transition latency: 4294.55 ms.   hardware limits: 400 MHz - 3.50 GHz   available cpufreq governors: performance, powersave   current policy: frequency should be within 3.50 GHz and 3.50 GHz.                   The governor "performance" may decide which speed to use                   within this range.   current CPU frequency is 3.26 GHz. analyzing CPU 3:   driver: intel_pstate   CPUs which run at the same hardware frequency: 3   CPUs which need to have their frequency coordinated by software: 3   maximum transition latency: 4294.55 ms.   hardware limits: 400 MHz - 3.50 GHz   available cpufreq governors: performance, powersave   current policy: frequency should be within 3.50 GHz and 3.50 GHz.                   The governor "performance" may decide which speed to use                   within this range.   current CPU frequency is 3.36 GHz.   Please take a look at     current policy: frequency should be within 3.50 GHz and 3.50 GHz.       The governor "performance" may decide which speed to use   Afterwards to go back to powersave I use my little script:  martin@martin-ThinkPad-T570:~$ cat cpu_freq_save.sh  #!/bin/bash sudo cpufreq-set -g powersave -c 0 --min 400MHz sudo cpufreq-set -g powersave -c 1 --min 400MHz sudo cpufreq-set -g powersave -c 2 --min 400MHz sudo cpufreq-set -g powersave -c 3 --min 400MHz   Which resets the min frequency and the governor but as soon as I compile again with my IDE every time the governor and the min frequency changes again.  Any idea how I can disable that automatic change?  PS: If you need more details, just tell me where to find them and I will provide them Can black holes actually merge? If time stops at the event horizon, can we ever detect two black holes merging? In other words, if you are a short distance away, would you encounter a spherically symmetric gravitational field, or a dipole field? The center of the dihedral group How to prove that the center of the dihedral group $D_{2n}$ is $\{1,r^{n}\}$ and the center of $D_{2n-1}$ is $\{1\}$?  I don't know how to prove it in this general case. Why are there non-visible objects in my final render? Have Blender on about 4 machines rendering animations. Just spotted on one of the machines its rendering something different from the actual scene that I have setup.    Top window shows a different set of layers objects to whats actually being rendered in the rendering window below.  In my scene contents, layers objects 1-5 are not visible, but these are the ones that look like they are being rendered.  The only thing I can assume is that perhaps it might be because I did not save the document before clicking render, but I would not have expected that behaviour (you dont need to save your word document before printing it).  Can anyone confirm why this is happening? I'm trying to determine if there is a best practice for typesetting the "evaluated at" bar for derivatives. The three possibilities I'm thinking of are shown in the code excerpt below:  \begin{gather*} 5 + \frac{df}{dt} \Bigr\rvert_{t = 0} \\ 5 + \frac{df}{dt} \biggr\rvert_{t = 0} \\ 5 + \left. \frac{df}{dt} \right\rvert_{t = 0} \\ \end{gather*}     The \Bigr option doesn't quite reach the top and bottom of the fraction. The \biggr option overshoots the top and bottom of the fraction by a little bit. And the \left...\right option has the same height as the \biggr option, but it introduces a little extra space between the + and the fraction. I'm having trouble deciding between these options. Is there a best practice for typesetting this? Show that quotient rings are not isomorphic I've been given a homework problem that requires me to show that the rings $\mathbb{C}[x,y]/(y - x^2)$ and $\mathbb{C}[x,y]/(xy-1)$ are not isomorphic.    This is my attempt at a solution:  For $\mathbb{C}[x,y]/(y - x^2)$, we can parametrize in the following way: $x = t$ and $y = t^2$. Then this ring is isomorphic to $\mathbb{C}[t]$.  For $\mathbb{C}[x,y]/(xy-1)$, we can parametrize $x = t$ and $ y = 1/t$. Then this is isomorphic to $\mathbb{C}[t, 1/t]$.   But $\mathbb{C}[t, 1/t]$ is not isomorphic to $\mathbb{C}[t]$.  Am I on the right track? If not, any helpful hints? How far can one get in analysis without leaving $\mathbb{Q}$? Suppose you're trying to teach analysis to a stubborn algebraist who refuses to acknowledge the existence of any characteristic $0$ field other than $\mathbb{Q}$.  How ugly are things going to get for him?  The algebraist argues that the real numbers are a silly construction because any real number can be approximated to arbitrarily high precision by the rational numbers - i.e., given any real number $r$ and any $\epsilon&gt;0$, the set $\left\{x\in\mathbb{Q}:\left|x-r\right|&lt;\epsilon\right\}$ is nonempty, thus sating the mad gods of algebra.  As @J.M. and @75064 pointed out to me in chat, we do start having some topology problems, for example that $f(x)=x^2$ and $g(x)=2$ are nonintersecting functions in $\mathbb{Q}$.  They do, however, come arbitrarily close to intersecting, i.e. given any $\epsilon&gt;0$ there exist rational solutions to $\left|2-x^2\right|&lt;\epsilon$.  The algebraist doesn't find this totally unsatisfying.     Where is this guy really going to start running into trouble?  Are there definitions in analysis which simply can't be reasonably formulated without leaving the rational numbers?  Which concepts would be particularly difficult to understand without the rest of the reals? How can you reduce ambient noise from servers? Does borrowing from my 401(k) make sense in my specific circumstance? I know the standard answer and understand that I will be losing out on that compound interest, but I am young and only need to borrow a few thousand. here are some more details:   Need to borrow $6500 to pay off a car and two student loans ($300/month in payments combined) I am 22 and work full time, making about $70K annually I contribute 8% of my income with a 4% company match I increase that by 2% every year The loan would be over 48 months ($140/month) I live very frugally and have almost no discretionary spending that can be cut (don't eat out all the time, no gym membership/ Netflix/ Apple music etc.) I'm cash-poor: 90% of my salary is going to mortgage, groceries, students loans, car payment, newborn baby medical expenses, and commute. These are not my only debts, just the ones I am seeking to pay off in the short term. I work two jobs, one full and one part time. I started a business, and my wife has two jobs. Working more is not a good answer to the original question.   It seems to me that I would be reducing middle to high interest debt while also saving myself $150 per month.   Loans:     Student loan 1: $1200 @ 5%   Student loan 2: $1100 @ 4.25%   Car Loan: $4000 @ 6% Find all functions $f(x)$ such that $f\left(x^2+f(y)\right)$=$y+(f(x))^2$ Let $\mathbb R$ denote the set of all real numbers. Find all function $f: R\to \ R$ such that   $$f\left(x^2+f(y)\right)=y+(f(x))^2$$   It is the problem. I tried to it by putting many at the place of $x$ and $y$ but I can't proceed. Please somebody help me. Trouble creating 3TB ext4 partition due to msdos-partition-table-imposed error Imported object shows aligned to the wrong axis I was doing fine with importing an obj I made in Marvelous Designer into Blender for rigging.  The dress would settle nicely on my SL avi.    Now when I import the object; it is perpendicular to my avi and I have spent a week trying to figure out what I did...  Is there a keystroke or setting that I need to make sure is correct so that my dress fits my avatar again? Why is there a file called [ in my /usr/bin directory? Recently back to Linux from another operating system I noticed a file called [ which seems strange to me.  What is it for?  $ ls -l /usr/bin | head -2 -rwxr-xr-x 1 root root       39552 Nov  3 14:44 [   I'm using Ubuntu 15.04 How can I install packages without starting their associated services? As you're probably aware, by default when you install a package on a Debian or Ubuntu based system, if the package contains a service, that service will generally be enabled and started automatically when you install the package.  This is a problem for me.  I've found myself needing to manage templates for building LXC containers. There are several containers, each corresponding to a Debian or Ubuntu release. (There are also Red Hat-based containers, but they aren't relevant here.)  /var/lib/libvirt/filesystems/debian6_template /var/lib/libvirt/filesystems/debian7_template /var/lib/libvirt/filesystems/ubuntu1004_template /var/lib/libvirt/filesystems/ubuntu1204_template   Occasionally I will find that the templates have a missing package or need some other change, so I will chroot into them to install the package. Unfortunately when I do that, I wind up with several copies of the package's service running!  By way of example, I found the templates didn't have a syslog daemon, so I installed one:  for template in /var/lib/libvirt/filesystems/{debian,ubuntu}*_template; do     chroot $template apt-get install rsyslog done   And promptly wound up with four copies of rsyslog running. Not to mention two copies of exim4. Oops!    I read somewhere (though I can't find it again now) that it's not supposed to start services when running in a chroot, but that clearly isn't happening here.  One potentially viable  calls for temporarily replacing the various commands which actually start services, such as start-stop-daemon and initctl, though this is a lot more work than I really wanted to do. If I have no other choice, though...  The ideal solution here would be for Debian-based systems to stop doing this crap, but failing that, perhaps an obscure or undocumented command line option for apt-get?  In case it wasn't clear, I really want to keep anything related to managing the templates outside the templates, if possible. I have thus far avoided the nightmare that is testing multi-threaded code since it just seems like too much of a minefield.  I'd like to ask how people have gone about testing code that relies on threads for successful execution, or just how people have gone about testing those kinds of issues that only show up when two threads interact in a given manner?  This seems like a really key problem for programmers today, it would be useful to pool our knowledge on this one imho. Python, Unicode, and the Windows console Can I travel to Schengen countries that were not on my itinerary when I applied? How to pass parameters to an alias? For bash script, I can use "$@" to access arguments. What's the equivalent when I use an alias?