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• What is the point of dynamic allocation in C++?

  - by Aerovistae

  I really have never understood it at all. I can do it, but I just don't get why I would want to. For instance, I was programming a game yesterday, and I set up an array of pointers to dynamically allocated little enemies in the game, then passed it to a function which updates their positions. When I ran the game, I got one of those nondescript assertion errors, something about a memory block not existing, I don't know. It was a run-time error, so it didn't say where the problem was. So I just said screw it and rewrote it with static instantiation, i.e.: while(n<4) { Enemy tempEnemy = Enemy(3, 4); enemyVector.push_back(tempEnemy); n++; } updatePositions(&enemyVector); And it immediately worked perfectly. Now sure, some of you may be thinking something to the effect of "Maybe if you knew what you were doing," or perhaps "n00b can't use pointers L0L," but frankly, you really can't deny that they make things way overcomplicated, hence most modern languages have done away with them entirely. But please-- someone -- What IS the point of dynamic allocation? What advantage does it afford? Why would I ever not do what I just did in the above example?

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• ffmpeg add two audio streams to video

  - by Tossin Hausen

  I tried this: ffmpeg -i /sdcard/video/transcode/video.avi -map 0:0,0 -i /sdcard/video/transcode/first.mp3 -map 1:0,1 -i /sdcard/video/transcode/second.mp3 -map 2:0,2 -acodec copy -vcodec py /sdcard/video/transcode/Output.avi to add two audio streams to one video file. But ffmpeg says the number of mappings should match the number of output streams. What is wrong here? I'm trying to work with an Android build of FFmepg "ffmpeg for android beta". "Does not work" means that this uncommunicative Android build of FFmpeg just stops without giving any error message. The -codec copy option does not work with this build. Now I tried the same set of files with the FFmpeg called command line tool that comes with Ubuntu 10. Something (can't say where it is from). The -codec copy option does not work with this FFmpeg too. Here the complete output: m30x:~/movie/Film$ ffmpeg -i input.avi -i first.mp3 -i second.mp3 -map 0 -map 1 -map 2 -acodec copy -vcodec copy output.avi FFmpeg version SVN-r0.5.9-4:0.5.9-0ubuntu0.10.04.1, Copyright (c) 2000-2009 Fabrice Bellard, et al. configuration: --extra-version=4:0.5.9-0ubuntu0.10.04.1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --disable-stripping --disable-vhook --enable-runtime-cpudetect --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --enable-shared --disable-static libavutil 49.15. 0 / 49.15. 0 libavcodec 52.20. 1 / 52.20. 1 libavformat 52.31. 0 / 52.31. 0 libavdevice 52. 1. 0 / 52. 1. 0 libavfilter 0. 4. 0 / 0. 4. 0 libswscale 0. 7. 1 / 0. 7. 1 libpostproc 51. 2. 0 / 51. 2. 0 built on Jun 12 2012 16:27:34, gcc: 4.4.3 [NULL @ 0x93cfd10]looks like this file was encoded with (divx4/(old)xvid/opendivx) -> forcing low_delay flag Seems stream 0 codec frame rate differs from container frame rate: 30000.00 (30000/1) -> 25.00 (25/1) Input #0, avi, from 'input.avi': Duration: 01:30:33.00, start: 0.000000, bitrate: 901 kb/s Stream #0.0: Video: mpeg4, yuv420p, 576x432, 25 tbr, 25 tbn, 30k tbc Input #1, mp3, from 'first.mp3': Duration: 01:30:32.84, start: 0.000000, bitrate: 63 kb/s Stream #1.0: Audio: mp3, 22050 Hz, stereo, s16, 64 kb/s Input #2, mp3, from 'second.mp3': Duration: 01:30:32.84, start: 0.000000, bitrate: 63 kb/s Stream #2.0: Audio: mp3, 22050 Hz, stereo, s16, 64 kb/s Number of stream maps must match number of output streams Merging only one audio stream with the video stream works with Ubuntu and Android version of FFmpeg. Here the complete output: ffmpeg -i input.avi -i first.mp3 -map 0 -map 1 -acodec copy -vcodec copy output.avi FFmpeg version SVN-r0.5.9-4:0.5.9-0ubuntu0.10.04.1, Copyright (c) 2000-2009 Fabrice Bellard, et al. configuration: --extra-version=4:0.5.9-0ubuntu0.10.04.1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --disable-stripping --disable-vhook --enable-runtime-cpudetect --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --enable-shared --disable-static libavutil 49.15. 0 / 49.15. 0 libavcodec 52.20. 1 / 52.20. 1 libavformat 52.31. 0 / 52.31. 0 libavdevice 52. 1. 0 / 52. 1. 0 libavfilter 0. 4. 0 / 0. 4. 0 libswscale 0. 7. 1 / 0. 7. 1 libpostproc 51. 2. 0 / 51. 2. 0 built on Jun 12 2012 16:27:34, gcc: 4.4.3 [NULL @ 0x9bfad10]looks like this file was encoded with (divx4/(old)xvid/opendivx) -> forcing low_delay flag Seems stream 0 codec frame rate differs from container frame rate: 30000.00 (30000/1) -> 25.00 (25/1) Input #0, avi, from 'input.avi': Duration: 01:30:33.00, start: 0.000000, bitrate: 901 kb/s Stream #0.0: Video: mpeg4, yuv420p, 576x432, 25 tbr, 25 tbn, 30k tbc Input #1, mp3, from 'first.mp3': Duration: 01:30:32.84, start: 0.000000, bitrate: 63 kb/s Stream #1.0: Audio: mp3, 22050 Hz, stereo, s16, 64 kb/s Output #0, avi, to 'output.avi': Stream #0.0: Video: mpeg4, yuv420p, 576x432, q=2-31, 90k tbn, 25 tbc Stream #0.1: Audio: libmp3lame, 22050 Hz, stereo, s16, 64 kb/s Stream mapping: Stream #0.0 -> #0.0 Stream #1.0 -> #0.1 Press [q] to stop encoding frame= 6157 fps=6156 q=-1.0 size= 31667kB time=246.28 bitrate=1053.3kbits/s Do you have an idea why it does not work with two audio streams? By the way, ffmpeg -i input_with_first_audio_stream.avi -i second.mp3 -acodec copy -vcodec copy output_two_audio_streams.avi -newaudio works with both versions of ffmpeg that I use, but the first audio stream is played too fast (x10 or more), while the second audio stream is played correct. Many thanks in advance and sorry for my unconventional question and outdated versions of ffmpeg. But I am a lamer and it is not so easy for me to compile from the source (especially for the Android version). I will try to compile an up to date version of ffmpeg with Ubuntu, but I don't have much free time.

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• What is the safest and least expensive way to store 10 terabytes of data?

  - by Josh T

  I'm a member of a production company and we're preparing for our first feature film. We've been discussing methods of data storage to keep all of our original content safe (for as long as possible). While we understand data is never 100% safe, we'd like to find the safest solution for us. We've considered: 16TB NAS for on-site storage 4-5 2TB hard drives (cheap, but not redundant), copy original footage to drives then seal in static free bag Burn data to Blu-Ray disks (time consuming and expensive: 200 disks == $5000) Tape drive(s)? I know the least about tape drives, except the fact that they're more reliable than disks. Any experience/knowledge with this amount of data is hugely appreciated.

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• Functional testing in the verification

  - by user970696

  Yesterday my question How come verification does not include actual testing? created a lot of controversy, yet did not reveal the answer for related and very important question: does black box functional testing done by testers belong to verification or validation? ISO 12207:12208 here mentiones testing explicitly only as a validation activity, however, it speaks about validation of requirements of the intended use. For me its more high level, like UAT test cases written by business users ISO mentioned above does not mention any specific verification (7.2.4.3.2)except for Requirement verification, Design verification, Document and Code & Integration verification. The last two can be probably thought as unit and integrated testing. But where is then the regular testing done by testers at the end of the phase? The book I mentioned in the original question mentiones that verification is done by static techniques, yet on the V model graph it describes System testing against high level description as a verification, mentioning it includes all kinds of testing like functional, load etc. In the IEEE standard for V&V, you can read this: Even though the tests and evaluations are not part of the V&V processes, the techniques described in this standard may be useful in performing them. So that is different than in ISO, where validation mentiones testing as the activity. Not to mention a lot of contradicting information on the net. I would really appreciate a reference to e.g. a standard in the answer or explanation of what I missed in the ISO. For me, I am unable to tell where the testers work belong.

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• How to do dependency Injection and conditional object creation based on type?

  - by Pradeep

  I have a service endpoint initialized using DI. It is of the following style. This end point is used across the app. public class CustomerService : ICustomerService { private IValidationService ValidationService { get; set; } private ICustomerRepository Repository { get; set; } public CustomerService(IValidationService validationService,ICustomerRepository repository) { ValidationService = validationService; Repository = repository; } public void Save(CustomerDTO customer) { if (ValidationService.Valid(customer)) Repository.Save(customer); } Now, With the changing requirements, there are going to be different types of customers (Legacy/Regular). The requirement is based on the type of the customer I have to validate and persist the customer in a different way (e.g. if Legacy customer persist to LegacyRepository). The wrong way to do this will be to break DI and do somthing like public void Save(CustomerDTO customer) { if(customer.Type == CustomerTypes.Legacy) { if (LegacyValidationService.Valid(customer)) LegacyRepository.Save(customer); } else { if (ValidationService.Valid(customer)) Repository.Save(customer); } } My options to me seems like DI all possible IValidationService and ICustomerRepository and switch based on type, which seems wrong. The other is to change the service signature to Save(IValidationService validation, ICustomerRepository repository, CustomerDTO customer) which is an invasive change. Break DI. Use the Strategy pattern approach for each type and do something like: validation= CustomerValidationServiceFactory.GetStratedgy(customer.Type); validation.Valid(customer) but now I have a static method which needs to know how to initialize different services. I am sure this is a very common problem, What is the right way to solve this without changing service signatures or breaking DI?

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• Library Organization in .NET

  - by Greg Ros

  I've written a .NET bitwise operations library as part of my projects (stuff ranging from get MSB set to some more complicated bitwise transformations) and I mean to release it as free software. I'm a bit confused about a design aspect of the library, though. Many of the methods/transformations in the library come with different endianness. A simple example is a getBitAt method that regards index 0 as the least significant bit, or the most significant bit, depending on the version used. In practice, I've found that using separate functions for different endianness results in much more comprehensible and reusable code than assuming all operations are little-endian or something. I'm really stumped regarding how best to package the library. Should I have methods that have LE and BE versions take an enum parameter in their signature, e.g. Endianness.Little, Endianness.Big? Should I have different static classes with identically named methods? such as MSB.GetBit and LSB.GetBit On a much wider note, is there a standard I could use in cases like this? Some guide? Is my design issue trivial? I have a perfectionist bent, and I sometimes get stuck on tricky design issues like this... Note: I've sort of realized I'm using endianness somewhat colloquially to refer to the order/place value of digital component parts (be they bits, bytes, or words) in a larger whole, in any setting. I'm not talking about machine-level endianness or serial transmission endianness. Just about place-value semantics in general. So there isn't a context of targeting different machines/transmission techniques or something.

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• Unity Launcher only runs once - requires lightdm restart before it runs again

  - by Don

  I have an intermittent problem that just started showing up several days ago. I am running 11.10 and all updates are current. I first saw the symptom with a custom version of the "Home" nautilus-home.desktop file I created in ~/.local.share/applications. I added a few static shortcuts to specific folders. What I found was, clikcing the icon once would open up my home folder, but after closing that nautilus window, clicking the icon again did nothing (did not even show icon backlight animation). However, I could right click on the same icon and access my short cuts as many times as I want. Symptom persisted until restarting lightdm. Just yesterday I saw the same sort of symptom happen with a custom launcher I created for a chromium-borwser to open a specific URL (with a few short cuts to other URLs). Click the icon - it works once. Then never again. Right click the icon and I can use the short cuts over and over - no problem. Note - at one point I assumed I might have a problem with my custom .desktop file, so I did a test by removing my custom nautilus-home.desktop. However, even after restarting lightdm, and verifying the home icon was the standard one from /opt/share/applications (all my custom shortcuts were gone) I saw the same symptom re-appear - it runs once and then not again until restarting lightdm. It seems to be intermittent and seems to move between various launchers. Not sure what to do or even what background data to gather. Attempt to improve question after the first answer: I tried the following: 1) remove all custom launchers 2) reboot 3) add custom lauchers back 4) reboot 5) attempt to use .... still have "runs once and never again" symptom with several launchers

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• Why does explorer restart automatically when I kill it with Process.Kill?

  - by Thomas Levesque

  If I kill explorer.exe like this: private static void KillExplorer() { var processes = Process.GetProcessesByName("explorer"); Console.Write("Killing Explorer... "); foreach (var process in processes) { process.Kill(); process.WaitForExit(); } Console.WriteLine("Done"); } It restarts immediately. But if I use taskkill /F /IM explorer.exe, or kill it from the task manager, it doesn't restart. Why is that? What's the difference? How can I close explorer.exe from code without restarting it? Sure, I could call taskkill from my code, but I was hoping for a cleaner solution...

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• Designing Content-Based ETL Process with .NET and SFDC

  - by Patrick

  As my firm makes the transition to using SFDC as our main operational system, we've spun together a couple of SFDC portals where we can post customer-specific documents to be viewed at will. As such, we've had the need for pseudo-ETL applications to be implemented that are able to extract metadata from the documents our analysts generate internally (most are industry-standard PDFs, XML, or MS Office formats) and place in networked "queue" folders. From there, our applications scoop of the queued documents and upload them to the appropriate SFDC CRM Content Library along with some select pieces of metadata. I've mostly used DbAmp to broker communication with SFDC (DbAmp is a Linked Server provider that allows you to use SQL conventions to interact with your SFDC Org data). I've been able to create [console] applications in C# that work pretty well, and they're usually structured something like this: static void Main() { // Load parameters from app.config. // Get documents from queue. var files = someInterface.GetFiles(someFilterOrRegexPattern); foreach (var file in files) { // Extract metadata from the file. // Validate some attributes of the file; add any validation errors to an in-memory // structure (e.g. List<ValidationErrors>). if (isValid) { // Upload using some wrapper for an ORM an someInterface.Upload(meta.Param1, meta.Param2, ...); } else { // Bounce the file } } // Report any validation errors (via message bus or SMTP or some such). } And that's pretty much it. Most of the time I wrap all these operations in a "Worker" class that takes the needed interfaces as constructor parameters. This approach has worked reasonably well, but I just get this feeling in my gut that there's something awful about it and would love some feedback. Is writing an ETL process as a C# Console app a bad idea? I'm also wondering if there are some design patterns that would be useful in this scenario that I'm clearly overlooking. Thanks in advance!

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• How to fill in the network line in the ubuntu interfaces config file?

  - by matnagel

  I have to configure an ubuntu hardy server network interface. The service hoster told me that this is the network data for the machine: IP Range: 111.111.200.74 to 111.111.200.78 Netmask: 255.255.255.248 Broadcast: 111.111.200.79 Gateway: 111.111.200.73 Subnet: 111.111.200.72/29 I am only using the first IP address. I will update the /etc/hosts file with 111.111.200.74, but I am still unsure how the /etc/network/interfaces file should be. This is my plan: auto lo iface lo inet loopback auto eth0 iface eth0 inet static address 111.111.200.74 netmask 255.255.255.248 network 111.111.200.??? broadcast 111.111.200.79 gateway 111.111.200.73 As you can see I don't know how to build the network line. How would I calculate the data for the network line and what is the result? (I changed the first 2 octets of the subnet, they are not "111.111" in the real setup.)

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• datacenter network change control best practices

  - by jpolache

  I have been tasked with compiling a list of possible network equipment changes at a data center. The task includes tagging which changes need change control and which don't. Does anyone know of a "best practices" list that I can start from? The methods for doing change control at this data center are well established. The list would be of specific configuration items that should or should not be included in the change control process, of example; static route entries switch port assignments firewall rule additions/changes etc.

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• Cannot execute Java program: UnsupportedClassVersionError

  - by Ricko Devian

  I have installed JDK 6, but I can't execute a Java program. For example, I have made test.java. I compile it with javac tes.java and there's no error when I compile it, but when I want to execute that program it always displays an error. I execute the Java program with java tes. Exception in thread "main" java.lang.UnsupportedClassVersionError: tes : Unsupported major.minor version 51.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:634) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:277) at java.net.URLClassLoader.access$000(URLClassLoader.java:73) at java.net.URLClassLoader$1.run(URLClassLoader.java:212) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:205) at java.lang.ClassLoader.loadClass(ClassLoader.java:321) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294) at java.lang.ClassLoader.loadClass(ClassLoader.java:266) Could not find the main class: tes. Program will exit. My javac version is 1.7.0, my java version is 1.6.0. Here is my tes.java code: class tes{ public static void main(String[]args){ System.out.println("hello"); } }

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• Hyper-V Server hvremote.wsf Script - ns lookup for DNS Verification test fails

  - by Vazgen

  I'm trying to connect my Hyper-V Server to a Windows 8 client for remote management. I have: Joined server to WORKGROUP Enabled Remote Management Set the server name Set a static IP Set the DNS servers to my ISPs DNS Servers (same as default DNS Servers on my Windows 8 remote management client) Set the correct time zone Created net user on server (net user /add admin password) Added user to special Administrators group on server (hvremote /add:admin) Granted anonymous dcom access on client using hvremote However, the "ns lookup for DNS verification" fails on both the client and server with the same error: Server: my.isps.server.name.net Address: 111.222.333.1 *** my.isps.server.name.net can't find 192.168.1.3: Non-existent domain Thanks for the help.

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• Cannot mount USB drive -- FSTAB error

  - by user107646

  Recently, one of my desktops seems to have developed a problem with the fstab and mounting USB drives. The specific error I receive is... Unable to mount TRAVELDRIVE Error mounting: mount exited with exit code 1: helper failed with: Unprivileged user can not mount NTFS block devices using the external FUSE library. Either mount the volume as root, or rebuild NTFS-3G with integrated FUSE support and make it setuid root. Please see more information at http://tuxera.com/community/ntfs-3g-faq/#unprivileged The contents of my fstab are... /etc/fstab: static file system information. # # <file system> <mount point> <type> <options> <dump> <pass> proc /proc proc nodev,noexec,nosuid 0 0 #Entry for /dev/sdc1 : UUID=7e3431cd-522f-4e35-b286-4300fa702d4a / ext4 errors=remount-ro 0 1 #Entry for /dev/sda1 : UUID=60684D08684CDE82 /media/Archive ntfs-3g defaults,locale=en_US.UTF-8 0 0 #Entry for /dev/sdc5 : UUID=cd166221-4b1d-40f7-b9de-785208990587 none swap sw 0 0 /dev/sdd1 /media/sdd1 ntfs nls=iso8859-1,ro,users,umask=000,user 0 0 /dev/sdd5 /media/PS3 (fat32) vfat users,user 0 0 /dev/sdd5 /media/sdd5 vfat uid=m3talhead,users,user 0 0 I'm guessing its a problem with the duplicate /dev/sdd5 entries (?), but being the *nix noob I am, I'm not certain. What am I missing? Any assist is greatly appreciated!

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• Is there any viable alternative to using a linux/unix/BSD firewall/router/vpn?

  - by ObligatoryMoniker

  I am trying to purchase something to replace our Vyatta router that is running in a virtual machine on Hyper V (having the whole network go down when the host has to reboot is not convenient and I am getting the sense that this configuration may not be stable). Most posts on this topic suggest using Linux/OpenBSD/FreeBSD/etc with some recommendations to use appliances from vendors for specific purposes like firewall and VPN. We are a windows shop and it has been a stretch for us to make use of Vyatta but since it was free and straightforward to use we decided to use it. Now we need something that is easier for our team to (re)deploy and manage. I would rather purchase something windows based or an appliance that can do all of the following things: DHCP server (reservations, specified gateway, dns, etc) Static Routes that route traffic across three interfaces Easily Reproducible (Powershell script, Puppet, Chef, etc) Intuitive interface (Decent web interface would be fine but I don't want them to have to go to CLI) Does any one have any recommendations on what I should be looking at that might meet our needs?

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• How to choose a web server for a Python application?

  - by Phil

  Information and prerequisites: I have a project which is, at its core, a basic CRUD application. It doesn't have long running background processes which it forks at the beginning and talks to later on, nor does it have long running queries or kept alive connection requirements. It receives a request, makes some queries to the database and then responds. In order to serve static files and cachable files fast, I am going to use Varnish in all cases. Here is my question: After reading about various Python web application servers, I have seen that they all have their "fans" for certain, usually "personal" reasons, which got me confused since each usecase differs from the next. How can I learn about the core differentiating factors of Python web servers (in order) to decide how suitable they are for my project and if one would be better than the other? What are your (technically provable) thoughts on the matter? How should I choose a Python web server? Thank you.

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• Using Google App Engine to Perform World Updates vs an Authoritative Server

  - by Error 454

  I am considering different game server architectures that use GAE. The types of games I am considering are turn-based where the world status would need to be updated about once per minute. I am looking for an answer that persuades me to either perform the world update on the google servers OR an authoritative server that syncs with the datastore. The main goal here would be to minimize GAE daily quotas. For some rough numbers, I am assuming 10,000 entities requiring updates. Each entity update would require: Reading 5 private entity variables (fetched from datastore) Fetching as many as 20 static variables (from datastore or persisted in server memory) Writing 5 entity variables Clients of the game would authenticate and set state directly against GAE as well as pull the latest world state from GAE. Running the update on GAE would consist of a cron job launched every minute. This would update all of the entities and save the results to the datastore. This would be more CPU intensive for GAE. Running the update on an authoritative server would consist of fetching entity data from the GAE datastore, calculating the new entity states and pushing the new state variables back to the datastore. This would be more bandwidth intensive for the datastore.

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• Accessing through VPN, which internet connection would be used

  - by Sriram

  I've a data card which has a limit of 2 GB up/download traffic per month. I've an office internet line which has an unlimited up/download. I've successfully connected to VPN using my data card and by changing certain configurations like DNS etc., have also been able to use my office line for internet (verified by doing a IP check - returns the static IP of our office). Now to my question - is it just a NAT which is happening or am I actually using my office line for all communication. Which one would reflect the usage/trace. The data card usage log at this moment does not reflect any usage (which is confusing since the VPN is over the data card connection). Further more (theoretically), would the net be any faster if my office line is let us say 8Mbps and the data card is 512kbps by doing this as against directly connecting the internet using the data card.

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• Status code in nginx try_files directive

  - by Hamish

  Is it possible to use the current status code as a parameter in try_files? For example, we try to provide a host specific 503 static response, or a server-wide fallback if it wasn't found: error_page 503 @error503; location @error503 { root /path_to_static_root/; try_files /$host/503.html /503.html =503; } There are a number of these directives, so it would be convenient to do something like: error_page 404 @error error_page 500 @error error_page 503 @error location @error { root /path_to_static_root/; try_files /$host/$status.html /$status.html =$status; } But the Variables documentation doesn't list anything that we could use to do this. Is it possible, or is there an alternative way to do this?

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• How does Router know where to forward packet

  - by kornelijepetak

  If several computers with local addresses (192.168.0.#) are connected to a router and each computer opens a web browser and requests a page over HTTP, when these TCP:80 packets are sent out, the router switches the local address with the static IP of the router (i.e. Provider given IP) so the server can reply to the appropriate address. But how does the router know to which computer to forward the HTTP reply, since the TCP header does not contain the local IP address (does it?), and all computers are using port 80? Does this have anything to do with the MAC addresses? How exactly does this work?

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• Dynamic procmail filters

  - by WombaT

  i need procmail to place incoming mail into specific folder depending on some set of rules. I know how i can accomplish this, but i need to write static set of rules in a specific file. What i really need is to configure procmail to use rules stored in mysql database. How i can do this? I've read a bit about that and one solution i found is to pipe message to a php/perl script and return a folder name to place message. But i have completely no i idea how to use php script as a rule and then use its return value.

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• Having to check collisions twice per game tic

  - by user22241

  I have vertically moving elevators (3 solid tiles wide) and static solid tiles. Each are separate entities and therefore have their own respective collision routines (to check for, and resolve, collisions with the main character) I check my vertical collisions after characters vertical movements and then horizontal collisions after horizontal movements. The problem is that I want my platform to kill the player if it squashes him from the top, and also if he's on a moving platform (that is moving up) that squashes him into a solid block. Correct behaviour, player on solid blocks being squashed from above by decending elevator Here is what happens. Gravity pushes character into solid block, solid block collision routine corrects characters position and sits him on the solid block which pushes him into the moving elevator, elevator routine then checks for collision and kills player. This assumes I am checking solid blocks first, then elevator collisions. However, if it's the other way around, this happens.... Incorrect behaviour, player on accending elevator gets pushed into solid blocks above Player is on an elevator moving up, gravity pushes him into the elevator, solid block CD routine detects no collision, no action taken. Elevator CD routine detects character has been pushed into elevator by gravity, corrects this by moving character up and sitting him on the elevator and pushes him into the solid blocks above, however the solid block vertical routine has now already run for this tic, so the game continues and the next solid block collision that is encountered is the horizontal routine. This detects a collision and moves the character out of the collision to the left or right of the block which looks odd to say the least (character should get killed here). The only way I've managed to get this working correctly is by running the solid block CD, then the elevator CD, then the solid block CD again straight after. This is clearly wasteful but I can't figure out how else to do this. Any help would be appreciated.

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• Bridging LXC containers to host eth0 so they can have a public IP

  - by Vianney Stroebel

  UPDATE: I found the solution there: http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge#No_traffic_gets_trough_.28except_ARP_and_STP.29 # cd /proc/sys/net/bridge # ls bridge-nf-call-arptables bridge-nf-call-iptables bridge-nf-call-ip6tables bridge-nf-filter-vlan-tagged # for f in bridge-nf-*; do echo 0 $f; done But I'd like to have expert opinions on this: is it safe to disable all bridge-nf-*? What are they here for? END OF UPDATE I need to bridge LXC containers to the physical interface (eth0) of my host, reading numerous tutorials, documents and blog posts on the subject. I need the containers to have their own public IP (which I've previously done KVM/libvirt). After two days of searching and trying, I still can't make it work with LXC containers. The host runs a freshly installed Ubuntu Server Quantal (12.10) with only libvirt (which I'm not using here) and lxc installed. I created the containers with : lxc-create -t ubuntu -n mycontainer So they also run Ubuntu 12.10. Content of /var/lib/lxc/mycontainer/config is: lxc.utsname = mycontainer lxc.mount = /var/lib/lxc/test/fstab lxc.rootfs = /var/lib/lxc/test/rootfs lxc.network.type = veth lxc.network.flags = up lxc.network.link = br0 lxc.network.name = eth0 lxc.network.veth.pair = vethmycontainer lxc.network.ipv4 = 179.43.46.233 lxc.network.hwaddr= 02:00:00:86:5b:11 lxc.devttydir = lxc lxc.tty = 4 lxc.pts = 1024 lxc.arch = amd64 lxc.cap.drop = sys_module mac_admin mac_override lxc.pivotdir = lxc_putold # uncomment the next line to run the container unconfined: #lxc.aa_profile = unconfined lxc.cgroup.devices.deny = a # Allow any mknod (but not using the node) lxc.cgroup.devices.allow = c *:* m lxc.cgroup.devices.allow = b *:* m # /dev/null and zero lxc.cgroup.devices.allow = c 1:3 rwm lxc.cgroup.devices.allow = c 1:5 rwm # consoles lxc.cgroup.devices.allow = c 5:1 rwm lxc.cgroup.devices.allow = c 5:0 rwm #lxc.cgroup.devices.allow = c 4:0 rwm #lxc.cgroup.devices.allow = c 4:1 rwm # /dev/{,u}random lxc.cgroup.devices.allow = c 1:9 rwm lxc.cgroup.devices.allow = c 1:8 rwm lxc.cgroup.devices.allow = c 136:* rwm lxc.cgroup.devices.allow = c 5:2 rwm # rtc lxc.cgroup.devices.allow = c 254:0 rwm #fuse lxc.cgroup.devices.allow = c 10:229 rwm #tun lxc.cgroup.devices.allow = c 10:200 rwm #full lxc.cgroup.devices.allow = c 1:7 rwm #hpet lxc.cgroup.devices.allow = c 10:228 rwm #kvm lxc.cgroup.devices.allow = c 10:232 rwm Then I changed my host /etc/network/interfaces to: auto lo iface lo inet loopback auto br0 iface br0 inet static bridge_ports eth0 bridge_fd 0 address 92.281.86.226 netmask 255.255.255.0 network 92.281.86.0 broadcast 92.281.86.255 gateway 92.281.86.254 dns-nameservers 213.186.33.99 dns-search ovh.net When I try command line configuration ("brctl addif", "ifconfig eth0", etc.) my remote host becomes inaccessible and I have to hard reboot it. I changed the content of /var/lib/lxc/mycontainer/rootfs/etc/network/interfaces to: auto lo iface lo inet loopback auto eth0 iface eth0 inet static address 179.43.46.233 netmask 255.255.255.255 broadcast 178.33.40.233 gateway 92.281.86.254 It takes several minutes for mycontainer to start (lxc-start -n mycontainer). I tried replacing gateway 92.281.86.254 by : post-up route add 92.281.86.254 dev eth0 post-up route add default gw 92.281.86.254 post-down route del 92.281.86.254 dev eth0 post-down route del default gw 92.281.86.254 My container then starts instantly. But whatever configuration I set in /var/lib/lxc/mycontainer/rootfs/etc/network/interfaces, I cannot ping from mycontainer to any IP (including the host's) : ubuntu@mycontainer:~$ ping 92.281.86.226 PING 92.281.86.226 (92.281.86.226) 56(84) bytes of data. ^C --- 92.281.86.226 ping statistics --- 6 packets transmitted, 0 received, 100% packet loss, time 5031ms And my host cannot ping the container: root@host:~# ping 179.43.46.233 PING 179.43.46.233 (179.43.46.233) 56(84) bytes of data. ^C --- 179.43.46.233 ping statistics --- 5 packets transmitted, 0 received, 100% packet loss, time 4000ms My container's ifconfig: ubuntu@mycontainer:~$ ifconfig eth0 Link encap:Ethernet HWaddr 02:00:00:86:5b:11 inet addr:179.43.46.233 Bcast:255.255.255.255 Mask:0.0.0.0 inet6 addr: fe80::ff:fe79:5a31/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:64 errors:0 dropped:6 overruns:0 frame:0 TX packets:54 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:4070 (4.0 KB) TX bytes:4168 (4.1 KB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:32 errors:0 dropped:0 overruns:0 frame:0 TX packets:32 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:2496 (2.4 KB) TX bytes:2496 (2.4 KB) My host's ifconfig: root@host:~# ifconfig br0 Link encap:Ethernet HWaddr 4c:72:b9:43:65:2b inet addr:92.281.86.226 Bcast:91.121.67.255 Mask:255.255.255.0 inet6 addr: fe80::4e72:b9ff:fe43:652b/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1453 errors:0 dropped:18 overruns:0 frame:0 TX packets:1630 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:145125 (145.1 KB) TX bytes:299943 (299.9 KB) eth0 Link encap:Ethernet HWaddr 4c:72:b9:43:65:2b UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:3178 errors:0 dropped:0 overruns:0 frame:0 TX packets:1637 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:298263 (298.2 KB) TX bytes:309167 (309.1 KB) Interrupt:20 Memory:fe500000-fe520000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:6 errors:0 dropped:0 overruns:0 frame:0 TX packets:6 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:300 (300.0 B) TX bytes:300 (300.0 B) vethtest Link encap:Ethernet HWaddr fe:0d:7f:3e:70:88 inet6 addr: fe80::fc0d:7fff:fe3e:7088/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:54 errors:0 dropped:0 overruns:0 frame:0 TX packets:67 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:4168 (4.1 KB) TX bytes:4250 (4.2 KB) virbr0 Link encap:Ethernet HWaddr de:49:c5:66:cf:84 inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0 UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) I have disabled lxcbr0 (USE_LXC_BRIDGE="false" in /etc/default/lxc). root@host:~# brctl show bridge name bridge id STP enabled interfaces br0 8000.4c72b943652b no eth0 vethtest I have configured the IP 179.43.46.233 to point to 02:00:00:86:5b:11 in my hosting provider (OVH) config panel. (The IPs in this post are not the real ones.) Thanks for reading this long question! :-) Vianney

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• nginx is not using gzip to talk to backend servers

  - by Michael Gorsuch

  Our web servers are running IIS 7 and are configured to compress dynamic and static content. When I hit these servers directly, gzip compression works. I recently placed nginx in front of them, and gzip compression has stopped. I was able to work around this by explicitly enabling gzip compression on nginx itself, but that seems a little inefficient considering I have half a dozen backends and only one active nginx box. It appears that nginx is stripping out the Accept-Encoding header. Does anyone have any advice for how to 'correct' this behavior? A sample configuration: upstream backend { server 127.0.0.1:8080; } server { listen 80; proxy_set_header Host $host; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; location / { proxy_pass http://backend; } }

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• Code contracts and inheritance

  - by DigiMortal

  In my last posting about code contracts I introduced you how to force code contracts to classes through interfaces. In this posting I will go step further and I will show you how code contracts work in the case of inherited classes. As a first thing let’s take a look at my interface and code contracts. [ContractClass(typeof(ProductContracts))] public interface IProduct {     int Id { get; set; }     string Name { get; set; }     decimal Weight { get; set; }     decimal Price { get; set; } }   [ContractClassFor(typeof(IProduct))] internal sealed class ProductContracts : IProduct {     private ProductContracts() { }       int IProduct.Id     {         get         {             return default(int);         }         set         {             Contract.Requires(value > 0);         }     }       string IProduct.Name     {         get         {             return default(string);         }         set         {             Contract.Requires(!string.IsNullOrWhiteSpace(value));             Contract.Requires(value.Length <= 25);         }     }       decimal IProduct.Weight     {         get         {             return default(decimal);         }         set         {             Contract.Requires(value > 3);             Contract.Requires(value < 100);         }     }       decimal IProduct.Price     {         get         {             return default(decimal);         }         set         {             Contract.Requires(value > 0);             Contract.Requires(value < 100);         }     } } And here is the product class that inherits IProduct interface. public class Product : IProduct {     public int Id { get; set; }     public string Name { get; set; }     public virtual decimal Weight { get; set; }     public decimal Price { get; set; } } if we run this code and violate the code contract set to Id we will get ContractException. public class Program {     static void Main(string[] args)     {         var product = new Product();         product.Id = -100;     } }   Now let’s make Product to be abstract class and let’s define new class called Food that adds one more contract to Weight property. public class Food : Product {     public override decimal Weight     {         get         {             return base.Weight;         }         set         {             Contract.Requires(value > 1);             Contract.Requires(value < 10);               base.Weight = value;         }     } } Now we should have the following rules at place for Food: weight must be greater than 1, weight must be greater than 3, weight must be less than 100, weight must be less than 10. Interesting part is what happens when we try to violate the lower and upper limits of Food weight. To see what happens let’s try to violate rules #2 and #4. Just comment one of the last lines out in the following method to test another assignment. public class Program {     static void Main(string[] args)     {         var food = new Food();         food.Weight = 12;         food.Weight = 2;     } } And here are the results as pictures to see where exceptions are thrown. Click on images to see them at original size. Violation of lower limit. Violation of upper limit. As you can see for both violations we get ContractException like expected. Code contracts inheritance is powerful and at same time dangerous feature. Although you can always narrow down the conditions that come from more general classes it is possible to define impossible or conflicting contracts at different points in inheritance hierarchy.

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