Asking because of curiosity. :)  When I type   sudo su   It asks for my user password. And when I type just   su   It asks for the root user password. But both the commands directs me to the root terminal. Then why is there such a difference?
I already read it from manual but I can't see difference..  su - change user ID or become superuser  sudo -s [command]   The -s (shell) option runs the shell specified by the SHELL environment variable if it is set or the shell as specified in passwd(5).  If a                    command is specified, it is passed to the shell for execution.  Otherwise, an interactive shell is executed.  sudo -i disappear description in manual
Add an alert when answering a question that has at least a close vote as duplicate I have one feature-request with the objective of having duplicate questions with no answers:   To (try to) avoid people answering duplicate questions, add an alert that says the question has a probable duplicate if it has a close vote as Exact duplicate, asking the answerer to go to the original and answer there.   What do you think? My objective is letting the duplicate question exist for search purposes, but the answers centralized in the root question. I spotted a  (10k-only by now) and when I went to flag it, the flag dialog told me that I'd already flagged it as VLQ:    The thing is, I'd never seen this post before. And a look at the flag history in my user profile confirms that I haven't flagged a post since yesterday:    Certainly, well before the 2015-02-04 05:36:21Z time of Mr. Miracle's post.  I was able to reproduce this on SO from the VLQ review queue: when you're presented with an answer, click on link at the right side of the page, then click flag. You get the "you have already raised this type of flag" message on either the "it is not an answer" or "it is very low quality" options, I gather depending on the original flag that pushed the post into the VLQ queue. Whats the simplest way to edit and add files to "/var/www"? Having installed the web server is there a simple way to set a user able to use the graphic interface to copy files and directories to the local web server /var/www  I gave myself administrative privileges in Ubuntu but it still doesn't allow copies. What if robots.txt disallows itself? How do I choose between "while" and "whilst"? When should whilst be used instead of while?  For example, should I use the first or the second sentence?      They don't do this whilst they do that.   They don't do this while they do that.   Which would be correct? Is (rest) mass conserved in special relativity? I don't understand why it is said that the (rest) mass of a system is not conserved in relativity. I mean, the momentum of a system is conserved (i.e.: it remains constant in a frame of reference without any external influence). Also the energy of a system is conserved in relativity: it doesn't change without any external agency  and the (rest) mass of a system is just  $$m^2=E^2-p^2$$  $E$ is constant, $p$ is constant, how can $m$ change?  For example, entropy is not conserved in a system, that means that the entropy of the system will increase spontaneously with time, which is really the case. But, is this true for mass?   here is the problem from Griffiths and exact solution as given in the Griffiths,  Two lumps of clay, each of rest mass $m$, collide head-on at $3c/5$ and they stick together. Question: what is the rest mass $M$ of the composite lump?  Solution: In this case conservation of momentum is trivial it is zero before and zero after. The energy of each lump prior to the collision is $$mc^2/\sqrt{1-v^2/c^2} =5mc^2/4.$$ The energy of the composite lump after the collision is $Mc^2$ (since its at rest). so the conservation of energy says: $5mc^2/4 + 5mc^2/4 =Mc^2$ and hence $M=5m/2$.  Notice that this is greater than the sum of the initial masses! Mass was not conserved in this collision; kinetic energy was converted into rest energy, so the rest mass increased. Send values from one form to another form Customise date-time format in Windows Is it possible to customize data (or date-time) format in Windows (I am using Windows&nbsp;XP)?  The current format which is followed by the OS [to show date-modified, etc.] is MM/DD/YYYY or M/D/YYYY, whereas I have been comfortable with DD/MM/YYYY or D/M/YYYY format. I am finding it hard to refer Date-modified [which I use often] of files and folders. How can I safely create a nested directory in Python? What is the most elegant way to check if the directory a file is going to be written to exists, and if not, create the directory using Python? Here is what I tried:  import os  file_path = "/my/directory/filename.txt" directory = os.path.dirname(file_path)  try:     os.stat(directory) except:     os.mkdir(directory)         f = file(filename)   Somehow, I missed os.path.exists (thanks kanja, Blair, and Douglas). This is what I have now:  def ensure_dir(file_path):     directory = os.path.dirname(file_path)     if not os.path.exists(directory):         os.makedirs(directory)   Is there a flag for "open", that makes this happen automatically? Hibernate computer with a timeout from command line on Windows 7 I am trying to hibernate my computer from the command. I was using shutdown /s /t 20 to shutdown the the computer. I change /s to /h to hibernate and now it just returns the usage text as if it doesn't recognise what I have entered. In this is does say  /h         Hibernate the local computer.   Is there something else that I need to use with /h to get it to hibernate? Open a window on a remote X display (why "Cannot open display")? Once upon a time,  DISPLAY=:0.0 totem /path/to/movie.avi   after ssh 'ing into my desktop from my laptop would cause totem to play movie.avi on my desktop.  Now it gives the error:   No protocol specified Cannot open display:    I reinstalled Debian squeeze when it went stable on both computers, and I guess I broke the config.   I've googled on this, and cannot for the life of me figure out what I'm supposed to be doing.   (VLC has an HTTP interface that works, but it isn't as convenient as ssh.)  The same problem arises when I try to run this from a cron job. Redirecting stdout to a file you don't have write permission on My laptop running Windows 7 Ultimate (non OEM) died on me today and it has tonnes of stuff on it - my projects, Visual Studio and office installations, etc. etc.  I am getting a new laptop from somewhere and was wondering if I could just unplug the hard disk from my original (dead) machine and plug it into the new one.  I remember trying this once with Windows Xp (on a desktop) and the OS crashed on boot and I had to reinstall everything again.  I have read about  but by the looks of it, it can be used only when the host computer is alive and kicking -- which mine isn't.  My old laptop was a Compaq Pressario v3000 (3 years old) on an AMD and the new one is going to be a new dual core Intel HP laptop.  Any ideas?  Thanks! Proof that no term (of a language of predicate logic) is a (non-empty) initial segment of another I want to make my appexchange app available in multiple language like Spanish, dutch etc. so that depend on the language of the user they can access the app.  Is it possible in any way..  any help will be appreciated.. Thanks How do I prove that $x^p-x+a$ is irreducible in a field with $p$ elements when $a\neq 0$? Let $p$ be a prime. How do I prove that $x^p-x+a$ is irreducible in a field with $p$ elements when $a\neq 0$?   Right now I'm able to prove that it has no roots and that it is separable, but I have not a clue as to how to prove it is irreducible. Any ideas? Find the integer which is closest to the value of   $\frac{1}{\sqrt[6]{5^6+1}- \sqrt[6]{5^6-1}}$  I have tried putting them between n and n+1 and tried manipulating  n but I cant seem to find a strategy. How to prevent system applications (like the Software Center) from asking for password? Are there any countable Hausdorff connected spaces? Do countable Hausdorff connected topological spaces exist? What is $\mathbb{E}[W(s)\mathrm{e}^{W(S)}]$ where W(S) is a standard Brownian Motion? I know that since it is a Brownian motion that $W(s)\sim{N(0,s)}$. One approach I tried, was to see that $W(s)-W(0)\sim N(0,1)$ and to let $X = W(s)$ and then solve $\mathbb{E}[X\mathrm{e}^X]$ but I end up with some awful integral. I was wondering whether there was an easier way? Or perhaps a simple way to solve this integral: $\int_{-\infty}^{\infty} \frac{1}{\sqrt{2{\pi}s}}x\mathbb{e}^{x}\mathbb{e}^{-\frac{x^2}{2s}}$