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  • Is this a File Header / Magic Number?

    - by Hammer Bro.
    I've got 120,000 files (way more, actually; this is just an arbitrary subset) of an unknown type. Linux file does not identify them (not that they're necessarily Linux files), nor do any other methods I've tried. There are only two hints about them that I currently have. One is that I suspect some compression is employed -- I have metadata that claims the file sizes are always some amount larger than what I observe. The other is that in 100,000 of these files, the first 16 bytes are always: ff ee ee dd 00 00 00 00 01 00 00 00 00 00 00 00 That really looks like a file header/magic number to me, but I just can't place it. Does anyone know what kind of files this would indicate? Alternatively, can anyone convince me that these suspiciously common bytes certainly do not indicate a specific file type? UPDATE I don't know the exact reverse-engineering details, but most of the files in our case are zips after the first 29(? or so) bytes are ignored. So in practice the problem is solved (we know how to process the files) but in theory the question is still unanswered -- I don't know which application routinely prepends about 29 bytes to its zips. [I'm not sure if I should leave the question open or not at this point.]

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  • Zero downtime uploads / Rollback in IIS

    - by NickatUship
    I'm not sure if this is the right way to ask this question, but here's basically what i'd like to do: 1.) Push a changeset to a site in IIS. 2.) Don't interrupt the users. 3.) Be able to roll back effortlessly. So, there are a few things that I know have to happen: 1.) Out of Proc session - handled 2.) Out of Proc cache - handled So the questions that remain: 1.) How do i keep from interrupting the users? If i just upload the files to bin, the app recycles and takes 10+ seconds to come back online 2.) How do i roll back effortlessly? I was thinking a possible solution would be to have two sites set up in IIS, one public and one private. Uploads go to private and get warmed up. After warmup, the sites are swapped. A rollback only entails swapping to private without an upload. This seems sound in theory, but Im not sure of the mechanics. Any ideas?

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  • Strange IIS hits originating from Trend Micro

    - by TesterTurnedDeveloper
    I'm trying to trace thru an error on a extranet site I maintain. I've had a look thru the logs, and I'm seeing hits originate from these IP addresses: 216.104.15.130 216.104.15.138 216.104.15.142 216.104.15.13 150.70.84.49 150.70.84.44 Network-tools.com gives 'TREND MICRO INCORPORATED' as the owner of all these IPs. The hits fail as they aren't sending any cookies (therefore aren't considered logged in). The hits are to pages containing URLs that only the logged in user would see, i.e. ImageEdit.aspx?ImageId=467424. I.e. the server isn't guessing these URLs, someone would have to log into the site to know these URLs exist. Theory: the Trend Antivirus client grabs URLs and sends them to the server for 'extra processing'? Googling around gives me this: http://www.forumpostersunion.com/showthread.php?p=51272 - where people are reporting comment spam from these addresses. The articles says their servers have been hacked (a few months ago, presumably fixed now?). A hacked server wouldn't explain how the URLs have been plucked off the user's PCs. Has anyone seen this before? Anything nefarious going on here?

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  • Ruby Passeger + Nginx or lighthttpi + fgci for shared hosting

    - by devnull
    I have set up a passenger + nginx setup and I plan to offer a free non-commercial hosting (or in fact on the fly deployment) for rack-based frameworks (e.g. camping, sinatra). I am facing an "issue" with passenger. For each application you need to configure nginx.conf (it would be the same with apache so it is not an nginx issue) with: server { ... passenger_base_uri /app1; passenger_base_uri /app2; passenger_base_uri /app3; } Now this is not inherently bad as, in theory, I could allow a user to run just one app on his webspace but even in this case I need to create a new server directory on nginx e.g. (user.domain.com). As this will mainly be used to deploy apps the behavior I am looking at is more the possibility to auto map several apps (e.g. app1, app2, app3, app4) under the same server (your app.com/app1 yourapp.com/app2) without having to update the nginx or apache file each time. This seems to be a limitation in passenger. As such I am thinking about an alternative with lighttpd and fastcgi. Would this allow immediate deployment without touching the lighttpd config file e.g. I create a new directory with app2 and it will run immediately ? What is your experience in performance difference between passenger + nginx vs. lighttpd + fastcgi ? thanks in advance scenario details: on nginx + passenger - user cannot add a new sub-folder and run another sinatra/camping app without declaring the path on nginx.conf and restarting the server; wished behavior with the new setup: - user can add a new folder with a new app and it would run on lighttpd+fcgi without any extra configuration of the web server;

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  • Shortest-path algorithms which use a space-time tradeoff?

    - by Chris Mounce
    I need to find shortest paths in an unweighted, undirected graph. There are algorithms which can find a shortest path between two nodes, but this can take time. There are also algorithms for computing shortest paths for all pairs of nodes in the graph, but storing such a lookup table would take lots of disk space. What I'm wondering: Is there an algorithm which offers a space-time tradeoff that's somewhere between these two extremes? In other words, is there a way to speed up a shortest-path search, while using less disk space than would be occupied by an all-pairs shortest-path table? I know there are ways to efficiently store lookup tables for this problem, and I already have a couple of ideas for speeding up shortest-path searches using precomputed data. But I don't want to reinvent the wheel if there's already some established algorithm that solves this problem.

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  • Default Browser hangs (IE, Chrome)

    - by Craig Hinrichs
    IE was my default browser about three months ago when I started experiencing this issue. Intermittent hangs would occur when I would open a new main page or new tab to a site I know would be up. What I mean by a hang: The browser would open and say "Waiting for site " and do nothing more. If I closed the window and reopened it it would immediatly connect. Over time I would have to close and reopen the window to get to the page. This would happen to any page including Google. I finally got sick of it and started using chrome and I will never go back. I recently upgraded my anti-virus and now I am experiencing the same issue with Chrome. I use AVG for my antivirus. Empirically it seems if I don't make Chrome my default browser I don't experience the issue. I tested this theory for over two hours yesterday. Possible issues I have found this coudl be but not confirmed yet: MTU settings are not correct. I am infected but my antivirus has not caught it (unlikely but possible) ?? I would like to think this is related to my antivirus but I am unsure how to verify. I don't like the idea of killing my antivirus if #2 is a possibility. I am looking for tips on how I can trouble shoot possible issues. I am on Windows XP SP3 Thanks in advance.

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  • [java] Efficiency of while(true) ServerSocket Listen

    - by Submerged
    I am wondering if a typical while(true) ServerSocket listen loop takes an entire core to wait and accept a client connection (Even when implementing runnable and using Thread .start()) I am implementing a type of distributed computing cluster and each computer needs every core it has for computation. A Master node needs to communicate with these computers (invoking static methods that modify the algorithm's functioning). The reason I need to use sockets is due to the cross platform / cross language capabilities. In some cases, PHP will be invoking these java static methods. I used a java profiler (YourKit) and I can see my running ServerSocket listen thread and it never sleeps and it's always running. Is there a better approach to do what I want? Or, will the performance hit be negligible? Please, feel free to offer any suggestion if you can think of a better way (I've tried RMI, but it isn't supported cross-language. Thanks everyone

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  • Entry Level Programming Jobs with Applied Math Degree

    - by Mark
    I am about to finish my B.Sc. in Applied Math. I started out in CS a few years back had a bit of a change of heart and decided to go the math route. Now that I am looking for career options finishing up and I'm just wonder how my Applied Math degree will look when applying for programming jobs. I have taken CS courses in C++/Java/C and done 2 semester of Scientific Computing with MATLAB/Mathematica and the like, so I feel like i at least know how to program. Of course I am lacking some of the theoretical courses on the CS. I'd very much like to know how I stack up for a programming job as a math major. Thanks.

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  • IE9 apprears to be ignoring RewriteRule in htaccess file

    - by mouli
    I have a site that uses SEF URLs and htaccess RewriteRules to serve up the pages. This has worked fine for several years until the arrival of IE9. Now it appears that the links are not being rewritten and the site is dead in the water. I have tried different compatabilty modes, to no avail, and I've played with the Rewrite Rules over and over, tried different doctypes and a few other browser settings. I agree that it cannot in theory be a browser specific problem if the problem is with the htaccess file but this site works in IE8, firefox and chrome. I have run the rewriterule through a validator and it looks fine. Any ideas would be appreciated as I am running out of ideas. The site is www.marlboroughsounds.co.nz a sample link is http://www.marlboroughsounds.co.nz/walking/freedom-walk-queen-charlotte-track/4dfw and the rewrite rule thats not working looks like this: RewriteRule ^walking/.*/([a-z0-9_]*)/?$ /walking.php?act_code=$1 [L] The link fails and it serves up a browser 404 page, not even the custom 404 I have for the site. Any ideas would be much appreciated as I am stumped.

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  • NFS Server in Java

    - by dmeister
    I search an implementation of a network (or distributed) file system like NFS in Java. The goal is to extend it and do some research stuff with it. On the web I found some implementation e.g. DJ NFS, but the open question is how mature and fast they are. Can anyone purpose a good starting point, has anyone experience with such things? P.S. I know Hadoop DFS and I used it for some projects, but Hadoop is not a good fit for the things I want to do here. --EDIT-- Hadoop is really focused on highly scalable, high throughput computing without the possibilities to overwrite parts of a file and so an. The goal is you could use the filesystem e.g. for user home directories. --EDIT-- More Details: The idea is to modify such a implementation so that the files are not stored directly on a local filesystem, but to apply data de-duplication.

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  • Best language to learn complementing java

    - by danielrutledge
    Hi all, I'm a somewhat experienced java ee developer, and I wish to complement my background by learning a newish language. I'm recently out of school where I did a ton of scientific computing and some functional programming, so I'm pretty comfortable with those families of languages. If at all possible, I'd like to pick a language with some market value, though I know this is tough to gauge. After snooping around a bit, the consensus seems to be one of Python/Ruby/Perl; how would each of these work with java in a web application environment, and in your opinion which complements it best? Any other suggestions for languages would also be welcome.

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  • Precompile Lambda Expression Tree conversions as constants?

    - by Nathan
    It is fairly common to take an Expression tree, and convert it to some other form, such as a string representation (for example this question and this question, and I suspect Linq2Sql does something similar). In many cases, perhaps even most cases, the Expression tree conversion will always be the same, i.e. if I have a function public string GenerateSomeSql(Expression<Func<TResult, TProperty>> expression) then any call with the same argument will always return the same result for example: GenerateSomeSql(x => x.Age) //suppose this will always return "select Age from Person" GenerateSomeSql(x => x.Ssn) //suppose this will always return "select Ssn from Person" So, in essence, the function call with a particular argument is really just a constant, except time is wasted at runtime re-computing it continuously. Assuming, for the sake of argument, that the conversion was sufficiently complex to cause a noticeable performance hit, is there any way to pre-compile the function call into an actual constant?

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  • How do I give MacPorts privileges?

    - by cojadate
    I tried to install PostgreSQL server development libraries using MacPorts and got the following: Warning: MacPorts running without privileges. You may be unable to complete certain actions (e.g. install). ---> Computing dependencies for postgresql-server-devel ---> Dependencies to be installed: postgresql-devel ---> Building postgresql-devel Error: Target org.macports.build returned: shell command failed Error: The following dependencies failed to build: postgresql-devel Error: Status 1 encountered during processing. To report a bug, see <http://guide.macports.org/#project.tickets> So I guess that means I need to running MacPorts with privileges and try again. Unfortunately I've no idea how to give MacPorts privileges. I'm running OS X 10.6.3

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  • Formatting a barcode with hyphens in between - Assignment question

    - by capex
    Hi, The assignment at my first year uni computing course says my program should read a barcode number, and then display the same 13 digit barcode number separated by hyphens. For example, 9300675016902 should look like 930-067501-690-1. The restrictions say I can't use the following: No arrays No strings No functions. Any directions on this? (So far I have done this: part1 = barcode/10000000000; which gives me the first three digits, and this: part4 = barcode%10; which gives me the last digit. Thanks in advance!

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  • Real benefits of tcp TIME-WAIT and implications in production environment

    - by user64204
    SOME THEORY I've been doing some reading on tcp TIME-WAIT (here and there) and what I read is that it's a value set to 2 x MSL (maximum segment life) which keeps a connection in the "connection table" for a while to guarantee that, "before your allowed to create a connection with the same tuple, all the packets belonging to previous incarnations of that tuple will be dead". Since segments received (apart from SYN under specific circumstances) while a connection is either in TIME-WAIT or no longer existing would be discarded, why not close the connection right away? Q1: Is it because there is less processing involved in dealing with segments from old connections and less processing to create a new connection on the same tuple when in TIME-WAIT (i.e. are there performance benefits)? If the above explanation doesn't stand, the only reason I see the TIME-WAIT being useful would be if a client sends a SYN for a connection before it sends remaining segments for an old connection on the same tuple in which case the receiver would re-open the connection but then get bad segments and and would have to terminate it. Q2: Is this analysis correct? Q3: Are there other benefits to using TIME-WAIT? SOME PRACTICE I've been looking at the munin graphs on a production server that I administrate. Here is one: As you can see there are more connections in TIME-WAIT than ESTABLISHED, around twice as many most of the time, on some occasions four times as many. Q4: Does this have an impact on performance? Q5: If so, is it wise/recommended to reduce the TIME-WAIT value (and what to)? Q6: Is this ratio of TIME-WAIT / ESTABLISHED connections normal? Could this be related to malicious connection attempts?

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  • Make case-sensitive SMB share case-insensitive

    - by fungs
    I am running a legacy XP app that I would like to move on a network share. It is very simple and works in theory but the server providing the share is based on Linux (cannot configure) and the software does not work correctly because it is programmed case-insensitively, it seems. After some research, network shares behave like the filesystem they use underneath. This is normal. Unfortunately I cannot fix the software myself. Is there any way to turn the case-sensitivity into case-insensitivity for a Windows network drive on the client side? I fould two approaches: First, something like icasefile (http://wnd.katei.fi/icasefile/) that wraps around the program and intercepts the file I/O. This is for UNIX only. Secondly, a proxy virtual file system (e. g. something using Dokan). Unfortunately I couldn't find any suitable fs, the only possibility would be to put a case-insensitive filesystem on an image file and put this on the share using for example lmdisk (http://www.ltr-data.se/opencode.html/#ImDisk). Do you have any better ideas?

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  • Need details about applications that are running on Windows Azure

    - by veda
    I have an application which requires large amount of data storage (say some PB) and computing resources. Instead of going for clusters, I am planning to propose to use Windows Azure Cloud for this application. I have gone through white papers of Windows Azure and have collected some details about Azure. But I feel that is not substantial. I need to do some case study about applications that are running on the azure and that uses azure storage efficiently. I looked for several research paper in related to performance of the applications in Windows Azure. But as Azure was quite new, I wasn't able to find any. Now, I am looking for some white papers/details regarding application that uses azure storage to substantiate my proposal. I also need to understand the windows azure storage architecture and virtual machine architecture. Do anyone know some research papers or details or blogs or something related to these topics.

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  • Help using Horner's rule and Hash Functions in JAVA?

    - by Matt
    I am trying to use Horner's rule to convert words to integers. I understand how it works and how if the word is long, it may cause an overflow. My ultimate goal is to use the converted integer in a hash function h(x)=x mod tableSize. My book suggests, because of the overflow, you could "apply the mod operator after computing each parenthesized expression in Horner's rule." I don't exactly understand what they mean by this. Say the expression looks like this: ((14*32+15)*32+20)*32+5 Do I take the mod tableSize after each parenthesized expression and add them together? What would it look like with this hash function and this example of Horner's rule?

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  • Sum of path products in DAG

    - by Jules
    Suppose we have a DAG with edges labeled with numbers. Define the value of a path as the product of the labels. For each (source,sink)-pair I want to find the sum of the values of all the paths from source to sink. You can do this in polynomial time with dynamic programming, but there are still some choices that can be made in how you decompose the problem. In my case I have one DAG that has to be evaluated repeatedly with different labelings. My question is: for a given DAG, how can we pre-compute a good strategy for computing these values for different labelings repeatedly. It would be nice if there was an algorithm that finds an optimal way, for example a way that minimizes the number of multiplications. But perhaps this is too much to ask, I would be very happy with an algorithm that just gives a good decomposition.

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  • openSSL tutorial not fully working - Can sign but cannot restore original file

    - by djechelon
    I'm writing, and testing, a little tutorial for my groupmates involved in an openSSL homework. We have a bunch of PDF files, I'm the CA and each one should send me a signed PDF for me to be verified. I've told them to do the following (and tried to do it by myself) Request and obtain a certificate (I'll skip this part) Create a MIME message with the PDF file in it makemime -c "text/pdf" -a "Content-Disposition: attachment; filename=”Elaborato.pdf" Elaborato.pdf > Elaborato.pdf.msg Sign with openSSL openssl smime -sign -in Elaborato.pdf.msg -out Elaborato.pdf.p7m -certfile ca.pem -certfile nomegruppo.crt -inkey nomegruppo.key -signer nomegruppo.crt Verify with openssl smime -verify -in Elaborato.pdf.p7m -out Elaborato-verified.msg -CAfile ca.pem -signer nomegruppo.crt Extract attachment with munpack Elaborato-verified.msg View with Acrobat Reader The problem is that even if I get a file that (from its binary content) resembles a PDF file my current Ubuntu PDF viewer doesn't read it. The XXXElaborato.pdf extracted by munpack is a little bit smaller than the original. What's the problem with this procedure? In theory, they should send me the signed S/MIME message and I should be able to read the PDF within it. Why can't I restore the original content of the PDF file?

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  • DAS vs SAN storage for serving 2 to 4 nodes

    - by Luke404
    We currently have 4 Linux nodes with local storage, arranged in two active/passive pairs with storage mirrored using DRBD, running virtual machines (actually using Xen Hypervisor) for typical hosting workloads (mail, web, a couple VPS, etc.). We're approaching the (presumed) maximum IOPS of those servers, and we're planning to migrate to an external storage solution with two active nodes, with capacity for up to four active nodes. Since we're an all-Dell shop I've done some research and found the MD3200 / MD3200i products should be the ones we're looking for. We are pretty sure we won't be attaching more than 4 hosts on a single storage and I'm wondering if there is any clear advantage for one or the other. In theory I should be able to attach 4 SAS hosts to a single MD3200 (single links on a single controller MD3200, or dual redundant SAS links from each host to a dual-controller MD3200), or 4 iSCSI hosts to a single MD3200i (directly on its 4 GigE ports without any switch, again with dual links for the dual controller option). Both setups should let us implement live VM migration since all hosts can access all the LUNs at the same time, and also some shared filesystem like GFS2 or OCFS2. Also, both setups should allow full redundancy of the whole system (assuming dual controllers in the storage). One difference I can see is that the DAS solution is actually limited to 4 hosts while the iSCSI one should be able to grow to more hosts (adding two GigE switches to the mix). One point for the iSCSI solution is that it would allow us to start out with our current nodes and upgrade them at a later time (we can't add other SAS controllers, but they already have 4 GigE ports each). With the right (iSCSI|SAS) controllers I should be able to connect diskless nodes and boot them off the external storage which I think is a good thing (get rid of any local storage). On the other hand, I would have thought the SAS one to be cheaper but it seems like an MD3200 actually costs a little less than an MD3200i (?) (please note: I've used Dell gear in my examples since that's what we're looking for but I assume the same goes with other vendors) I would like to know if my assumptions above are correct, and if I'm missing any important difference between the two setups.

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  • Binomial test in Python

    - by Morlock
    I need to do a binomial test in Python that allows calculation for 'n' numbers of the order of 10000. I have implemented a quick binomial_test function using scipy.misc.comb, however, it is pretty much limited around n = 1000, I guess because it reaches the biggest representable number while computing factorials or the combinatorial itself. Here is my function: from scipy.misc import comb def binomial_test(n, k): """Calculate binomial probability """ p = comb(n, k) * 0.5**k * 0.5**(n-k) return p How could I use a native python (or numpy, scipy...) function in order to calculate that binomial probability? If possible, I need scipy 0.7.2 compatible code. Many thanks!

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  • In C#, can I hide/modify accessors in subclasses?

    - by Diego
    I'm not even sure what this principle is called or how to search for it, so I sincerely apologize if it has been brought up before, but the best way to do it is with an example. class Properties { public string Name { get; set; } } class MyClass { class SubProperties: Properties { public override Name { get { return GetActualName(); } set { _value = SetActualName(value); } } } public SubProperties ClassProperties; private GetActualName() { ClassProperties.Name = "name"; } private SetActualName(string s) { ClassProperties.Name = SomeOtherFunction(s); } } The idea is to have any object that instantiates MyClass have a fully accessible property ClassProperties. To that object, it would look exactly like a Properties object, but behind the scenes, MyClass is actually computing and modifying the results of the fields. This method of declaration is obviously wrong since I can't access GetActualName() and SetActualName() from within the SubProperties definition. How would I achieve something like this?

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  • Mouse receiver stopped working after pairing mouse to an unifying receiver

    - by mp19uy
    I bought this mouse, logitech m510, which came with a nano receiver (no-unifying). Yes I know, the mouse is supposed to come with a unifying receiver but I bought it knowing that it won't come on it's original package and it will come with a no-unifying receiver. When I received it, everything worked ok but, after connecting the mouse to another computer using an unifying receiver (that also worked ok, btw), then, when I tried to connect back the mouse to my computer using the no-unifying receiver, I couldn't connect it. I tried everything from removing the batteries and reinstalling the drivers to restarting the computer and trying in different computers, but I couldn't connect them. What I think it happened, is that in fact if you check the documentation of the logitech m510 it says that it works with unifying receivers only, and even more, there is the following article explaining it: http://logitech-en-amr.custhelp.com/app/answers/detail/a_id/18001/~/using-my-m510-with-a-different-usb-receiver So my theory is that the problem was connecting it to a unifying receiver, and now, isn't recognize by another receiver. The receiver (the no-unifying one) itself is recognized by windows, and if I connect the mouse using a unifying receiver, it works. I would like to know if there is any know solution for this or if I can try something else to see if I can solve this.

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  • Scripting window positioning in OS X

    - by Matt Trent
    My primary computing setup is a macbook pro with a large external monitor. I'm looking for a convenient way of moving a number of the windows of open programs from the laptop screen to the external monitor when I plug it in. I've seen a few partial scripts for accomplishing this, but nothing comprehensive. Ideally I'd like to specify the laptop screen location and external monitor location for each window and be able to toggle between them. Is anyone aware of any existing utility or Applscripts that can perform this?

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