Today I installed Ubuntu alongside windows 8 (option was first, without making partition). Everything was Ok but when the system restart there was no option to choose Ubuntu. By default it always start with my existing OS 8. Please Help me.  Thnx Lalit Kumar
I installed Windows 7, which ate Ubuntu's boot file. When starting up the computer, it now goes straight to Windows, without giving me the option of booting Ubuntu.   How can I get Ubuntu back?
The photon sphere is a spherical region in space where photons are forced to travel in an orbit at $r = \frac{3GM}{c^{2}}$.   Is it possible to detect these spheres?  What happens if I fall through it? What happens to a photon that tangentially hits the event horizon, wouldn't this also lead to a photon orbiting the black hole? EDIT Since neutron stars also might have a , do we know neutron stars that should have such a sphere? Can you make an opportunity attack against a moving object? Intuitive analysis of gradient, divergence, curl How can I make sure texts from friends with iPhones don't go to iMessage instead of my Android phone? I have always used an Android phone, but text messages from certain friends get hijacked by iMessage. How do I prevent iPhones and MacOS Messages from sending me iMessages? I need all messages to be SMS or MMS. Some friends with iPhones will text me, but I don't receive the message. Today I noticed the Message app on my Mac had notifications. I never open this app since I don't use iMessage, but I looked today, and found multiple &quot;lost&quot; messages from several weeks ago. Please note that this is NOT the same question as . My Android phone is not, and has never been, registered with iMessage, and I have already followed those instructions. Another poster () had the same question as me----but it was closed, being deemed as the same as the Removing phone number question. It's actually fairly different. I have tried:  Leaving my Messages app closed on my Mac. But somehow messages from these people get hijacked. Deregistering my mobile number using Apple's online Deregister iMessage tool. When I attempted this, I got the message &quot;Your phone number is not registered with iMessage.&quot; Finding a setting on my Android phone that addresses this. The problem is apparently (and logically seems to be) on the Apple end.  Things  says he tried:   Closing Messages.app. I still get macOS notifications of messages. In Messages &gt; Preferences… &gt; Accounts &gt; [my email address], untick &quot;Enable this account&quot;. Then my friends messages disappear and I never see them at all, at least until I reenable in Messages.app. Looking in System Preferences and on icloud.com and appleid.apple.com    to see if there is some setting I can disable—but I've not found    anything relevant. Using Apple's Deregister iMessage tool to unregister my mobile    number. When I attempted this it gave me the message &quot;Your phone number is not registered with iMessage.&quot; The "Spell Storing" ability of the Shield Guardian says:     To do so, the wearer must cast the spell on the guardian.  The spell has no effect but is stored within the guardian.   This seems to indicate you cannot cast, for instance, Fire Shield on the Guardian, because that has a range of Self.  This seems different than what is intended, as the wording for a ring of spell storing is:     This ring stores spells cast into it, holding them until the attuned   wearer uses them....Any creature can cast a spell of 1st through 5th   level into the ring by touching the ring as the spell is cast.  The spell has no effect, other than to be stored in the   ring.   The use of the word "into," which does not seem to indicate any range, versus the use of the word "on," which seems to mean the guardian is a target of the spell.    Which is the correct interpretation, grammatically, versus what is the RAI? Find the sum of angles without trigonometry? Why is the relationship between atomic number and density not linear? Generating list of manually installed packages and querying individual packages I'd like to get a list of packages installed manually by apt or aptitude and be able to find out whether a foobar package was installed manually or automatically. Is there any neat way of doing that from the command line? Why is free will a widely discussed, established concept? Does this concept emerge from religious / spiritual doctrine? Why is there so much interest in this topic?  If a neural-network based AI machine with a certain high degree of complexity scores a perfect 100 every run in a turing test, have we not already refuted the idea of free will? In fact, let me extend this reasoning, if ANY machine scores a single point in a turing test (and not 100), have we not already disproved (or alternatively put in great doubt the existence of) free will? If we already created a machine that can master a certain degree of human interaction, have we not then demonstrated that human interaction is programmable? (given enough time for the creation of a complex or more appropriately elaborative neural system).   From the perspective of an external observer, such a machine would be qualitatively human although intrinsically quantitative behind a stream of 1's and 0's. It would exhibit a type of decision making indistinguishable from that of a human. Does this not reduce the type of decision making we understand to be "free will" to something quantitative, deterministic, materialist? How long are the life phases of a dragon? Better understanding of Drupal behaviors I read about Drupal behaviors today, and I tried writing the following code.  (function ($) {    Drupal.behaviors.mymodule = {     attach: function (context, settings) {       $('#mymodule_id', context).change(function () {         alert('Handler for .change() called.');       });     }   };  }(jQuery));    Is Drupal.behaviors.mymodule the namespace? What are the context and settings parameters passed to the Drupal behavior? Is this the equivalent of document.ready()?   Can I attach any number of functions?  Can I define JavaScript functions which will be called somewhere? For $x$ and $\lambda$ complex, if $|x| \gt \frac{1}{2} + \sqrt{\frac{5}{4} + |\lambda|}$ then $|x^2+\lambda| \gt |x| +1$ Where does gravitational waves' energy go? How to convert an MKV to AVI with minimal loss To convert an MKV to AVI, I do two things. The first thing I do is this:  ffmpeg -i filename.mkv -vcodec copy -acodec copy output.avi   or this:  ffmpeg -i filename.mkv -sameq -acodec copy output.avi   Either of these will convert the MKV to an AVI, but the problem is that the video does not play smoothly for some reason. That's fine though, because if I do one more thing it gets fixed:  ffmpeg -i output.avi -vcodec mpeg4 -b 4000k -acodec mp2 -ab 320k converted.avi   After I do this then the file plays without problem. I had success doing it this way for one file, but then I tried it on another file, and there is a slight, but noticeable loss in video quality. This is the output I get when doing the second step:  FFmpeg version 0.6.1, Copyright (c) 2000-2010 the FFmpeg developers   built on Dec 29 2010 18:02:10 with gcc 4.2.1 (Apple Inc. build 5664)   configuration:    libavutil     50.15. 1 / 50.15. 1   libavcodec    52.72. 2 / 52.72. 2   libavformat   52.64. 2 / 52.64. 2   libavdevice   52. 2. 0 / 52. 2. 0   libswscale     0.11. 0 /  0.11. 0  Seems stream 0 codec frame rate differs from container frame rate: 359.00 (359/1) -&gt; 29.92 (359/12) Input #0, avi, from 'output.avi':   Metadata:     ISFT            : Lavf52.64.2   Duration: 00:04:17.21, start: 0.000000, bitrate: 3074 kb/s     Stream #0.0: Video: mpeg4, yuv420p, 704x480 [PAR 229:189 DAR 5038:2835], 29.92 fps, 29.92 tbr, 29.92 tbn, 359 tbc     Stream #0.1: Audio: vorbis, 48000 Hz, stereo, s16 Output #0, avi, to 'converted.avi':   Metadata:     ISFT            : Lavf52.64.2     Stream #0.0: Video: mpeg4, yuv420p, 704x480 [PAR 229:189 DAR 5038:2835], q=2-31, 4000 kb/s, 29.92 tbn, 29.92 tbc     Stream #0.1: Audio: mp2, 48000 Hz, stereo, s16, 320 kb/s Stream mapping:   Stream #0.0 -&gt; #0.0   Stream #0.1 -&gt; #0.1   I just used arbitrarily large settings on the second step and it worked nicely before but not in this case. What settings should I use? I am a new user, who has just been told to run / execute a command. The answer has some text with a grey background like this text here or  sometimes this text here.   However, I don't know what "run" or "command" means in relation to Ubuntu.  How do I do this?    This is intended for use as a Q&amp;A you can link to when you tell someone to run a command. Upgrading my Wubi 11.04 to 11.10 I want to upgrade my current Wubi installation (Ubuntu 11.04) to Ubuntu 11.10. Is this possible to do inside Wubi? Or do I have delete Wubi from Windows, therefore deleting my current Ubuntu installation; and then install 11.10 via the Wubi installer?  Thanks Is there an equivalent in mathematical language to the modulo (or mod) function in computing? Could someone please explain? I couldn't find anything on the internet, everything talks about how to go about it in some way, but nothing says exactly what it is.   Also, what is a fully trusted assembly and how do they differ from one another?  I have a MS certification exam and this is the only topic that I just don't understand.  EDIT: Thanks guys. Now I have a better understanding of security in .NET. I was able to pass my certification exam. How to look up a symbol or identify a letter from a math alphabet or other character? I know what my symbol or character looks like, but I don't know what the command is or which math alphabet it came from. How do I go about finding this out? How do I forward/NAT all traffic to one interface/IP to a remote IP? I have one "server A" that has multiple IPs attached to it, like so:  eth0:0 1.1.1.1 eth0:1 1.1.1.2 eth0:2 1.1.1.3   I have another "server B" that also has multiple IPs attached to it, like so:  eth0:0 2.2.2.1 eth0:1 2.2.2.2 eth0:2 2.2.2.3   Now, I want to setup iptables on "Server A" to forward/NAT all incomming traffic on "eth0:2" to IP 2.2.2.3 on "Server B".  I have verified that "Server A" is able to "talk" to "Server B" on IP 2.2.2.3. Ping and telnet to open ports works just fine and I have the forward-flag turned on (net.ipv4.ip_forward=1)  I have tried multiple different ways, DNAT, SNAT, MASQUERADE etc, but I cannot get anything to work.  This line works fine if I try to forward traffic between IPs on the SAME server:  iptables -t nat -A PREROUTING -d 1.1.1.3 -j DNAT --to-destination 1.1.1.2   But if I switch out the "1.1.1.2" for "2.2.2.3", it does not work.  I assume that I need a second iptable rule to solve it. I have tried with the following POSTROUTING rules without any luck (not at the same time):  iptables -t nat -A POSTROUTING -d 2.2.2.3 -j MASQUERADE iptables -t nat -A POSTROUTING -d 2.2.2.3 -j SNAT --to 1.1.1.3 iptables -t nat -A POSTROUTING -j MASQUERADE   What am I missing?  EDIT 1:  I finally got it to work by using the following:  net.bridge.bridge-nf-call-iptables=0  iptables -t nat -A PREROUTING -d 1.1.1.3 -j DNAT --to-destination 2.2.2.3 iptables -t nat -A POSTROUTING -d 2.2.2.3 -j SNAT --to 1.1.1.3   However, now another problem appeared. All logs etc on server 2.2.2.3 shows that ALL traffic now comes from 1.1.1.3, like apache logs, mail logs etc. I assume this is the nature of NAT.   However, when I do standard port forwarding on my home-router to my laptop that is running apache, I see the original "requester IP" in the logs. So, how does the router do this? And how can I do the same on my server setup?  Bottom line, I want to forward all traffic from Server A (1.1.1.3) to Server B (2.2.2.3), BUT I also want to be able to see where the traffic came from on Server B (2.2.2.3), i.e the apache logs should show the original IP of the requester.  I assume I should use some other way than NAT to make this happen, and it should be possible, as even my simple home-router is able to do this.  One extra thing, the IPs attached to Server A and Server B is LOCKED to each respective server. Thus, Server A is NOT able to send out traffic FROM IP 2.2.2.3. It is locked by my provider in the router.