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• How Exactly Is One Linux OS “Based On” Another Linux OS?

  - by Jason Fitzpatrick

  When reviewing different flavors of Linux, you’ll frequently come across phrases like “Ubuntu is based on Debian” but what exactly does that mean? Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites. The Question SuperUser reader PLPiper is trying to get a handle on how Linux variants work: I’ve been looking through quite a number of Linux distros recently to get an idea of what’s around, and one phrase that keeps coming up is that “[this OS] is based on [another OS]“. For example: Fedora is based on Red Hat Ubuntu is based on Debian Linux Mint is based on Ubuntu For someone coming from a Mac environment I understand how “OS X is based on Darwin”, however when I look at Linux Distros, I find myself asking “Aren’t they all based on Linux..?” In this context, what exactly does it mean for one Linux OS to be based on another Linux OS? So, what exactly does it mean when we talk about one version of Linux being based off another version? The Answer SuperUser contributor kostix offers a solid overview of the whole system: Linux is a kernel — a (complex) piece of software which works with the hardware and exports a certain Application Programming Interface (API), and binary conventions on how to precisely use it (Application Binary Interface, ABI) available to the “user-space” applications. Debian, RedHat and others are operating systems — complete software environments which consist of the kernel and a set of user-space programs which make the computer useful as they perform sensible tasks (sending/receiving mail, allowing you to browse the Internet, driving a robot etc). Now each such OS, while providing mostly the same software (there are not so many free mail server programs or Internet browsers or desktop environments, for example) differ in approaches to do this and also in their stated goals and release cycles. Quite typically these OSes are called “distributions”. This is, IMO, a somewhat wrong term stemming from the fact you’re technically able to build all the required software by hand and install it on a target machine, so these OSes distribute the packaged software so you either don’t need to build it (Debian, RedHat) or they facilitate such building (Gentoo). They also usually provide an installer which helps to install the OS onto a target machine. Making and supporting an OS is a very complicated task requiring a complex and intricate infrastructure (upload queues, build servers, a bug tracker, and archive servers, mailing list software etc etc etc) and staff. This obviously raises a high barrier for creating a new, from-scratch OS. For instance, Debian provides ca. 37k packages for some five hardware architectures — go figure how much work is put into supporting this stuff. Still, if someone thinks they need to create a new OS for whatever reason, it may be a good idea to use an existing foundation to build on. And this is exactly where OSes based on other OSes come into existence. For instance, Ubuntu builds upon Debian by just importing most packages from it and repackaging only a small subset of them, plus packaging their own, providing their own artwork, default settings, documentation etc. Note that there are variations to this “based on” thing. For instance, Debian fosters the creation of “pure blends” of itself: distributions which use Debian rather directly, and just add a bunch of packages and other stuff only useful for rather small groups of users such as those working in education or medicine or music industry etc. Another twist is that not all these OSes are based on Linux. For instance, Debian also provide FreeBSD and Hurd kernels. They have quite tiny user groups but anyway. Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.     

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• OS Development. Only Few Particular Questions

  - by Total Anime Immersion

  I am new to this site as a member but have consulted its answers quite a lot of times. Besides my questions regarding OS Development hasn't been answered in any forum. In OS Dev. we make a bootloader. The org point is 7C00H. Why so? Why not 0000h? What are the last two signatures in the bootloader used for? People on every forum have answered that it is important for the system to recognize it as a bootable media. But I want a specific answer. What do each of those signatures do. I have the basic concept of a kernel. Point is.. it relates to different files required in a system. It sort of binds up everything that is individually developed. Now the thing is that that I have floating ideas in my mind regarding different aspects like keyboard, mouse, etc.. how do I put them all together? Which should I start with first? If possible please provide a step by step procedure of the startups of the kernel. Suppose I have developed my language entirely in C and Assembly. Now questions is will exe files work on my system.. if it doesn't then I have to create my own files and publish them. Which is a bad idea.. next step would be for me to go for a compiler for a language which I have designed myself. Now the point is.. How do I implement the compiler into my OS? After all this my final question is that.. How do you go about multitasking and multithreading? and I don't want to use int 21h as its dos specific.. how do I go about making files, renaming them, etc. and all assembly books teach 16 but programming.. how do i go about doing 32 bit or 64 bit with the knowledge I have.. if the basics and instructions are the same.. I don't mind.. but how do i go about otherwise? Don't tell me to give up the idea because I WON'T. And don't tell me it's too complex because I have a sharp knowledge of working of a system, C, Java, Assembly, C++ and python, C#, visual basic.. and not just basics but full fledged api developments.. but I really want to go deep into the systems part.. so I want professional help.. And I have gone through many OS project files but I want help particularly from this site as there are people with knowledge depth who can guide me the right way. And please don't suggest any books above 20$ and they should be available on flipkart as amazon charges massively for shipping and I prefer free shipping from flipkart.

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• Issuing Current Time Increments in StreamInsight (A Practical Example)

  The issuing of a Current Time Increment, Cti, in StreamInsight is very definitely one of the most important concepts to learn if you want your Streams to be responsive. A full discussion of how to issue Ctis is beyond the scope of this article but a very good explanation in addition to Books Online can be found in these three articles by a member of the StreamInsight team at Microsoft, Ciprian Gerea. Time in StreamInsight Series http://blogs.msdn.com/b/streaminsight/archive/2010/07/23/time-in-streaminsight-i.aspx http://blogs.msdn.com/b/streaminsight/archive/2010/07/30/time-in-streaminsight-ii.aspx http://blogs.msdn.com/b/streaminsight/archive/2010/08/03/time-in-streaminsight-iii.aspx A lot of the problems I see with unresponsive or stuck streams on the MSDN Forums are to do with how Ctis are enqueued or in a lot of cases not enqueued. If you enqueue events and never enqueue a Cti then StreamInsight will be perfectly happy. You, on the other hand, will never see data on the output as you have not told StreamInsight to flush the stream. This article deals with a specific implementation problem I had recently whilst working on a StreamInsight project. I look at some possible options and discuss why they would not work before showing the way I solved the problem. The stream of data I was dealing with on this project was very bursty that is to say when events were flowing they came through very quickly and in large numbers (1000 events/sec), but when the stream calmed down it could be a few seconds between each event. When enqueuing events into the StreamInsight engne it is best practice to do so with a StartTime that is given to you by the system producing the event . StreamInsight processes events and it doesn't matter whether those events are being pushed into the engine by a source system or the events are being read from something like a flat file in a directory somewhere. You can apply the same logic and temporal algebra to both situations. Reading from a file is an excellent example of where the time of the event on the source itself is very important. We could be reading that file a long time after it was written. Being able to read the StartTime from the events allows us to define windows that will hold the correct sets of events. I was able to do this with my stream but this is where my problems started. Below is a very simple script to create a SQL Server table and populate it with sample data that will show exactly the problem I had. CREATE TABLE [dbo].[t] ( [c1] [int] PRIMARY KEY, [c2] [datetime] NULL ) INSERT t VALUES (1,'20100810'),(2,'20100810'),(3,'20100810') Column c2 defines the StartTime of the event on the source and as you can see the values in all 3 rows of data is the same. If we read Ciprian’s articles we know that we can define how Ctis get injected into the stream in 3 different places The Stream Definition The Input Factory The Input Adapter I personally have always been a fan of enqueing Ctis through the factory. Below is code typical of what I would use to do this On the class itself I do some inheriting public class SimpleInputFactory : ITypedInputAdapterFactory<SimpleInputConfig>, ITypedDeclareAdvanceTimeProperties<SimpleInputConfig> And then I implement the following function public AdapterAdvanceTimeSettings DeclareAdvanceTimeProperties<TPayload>(SimpleInputConfig configInfo, EventShape eventShape) { return new AdapterAdvanceTimeSettings( new AdvanceTimeGenerationSettings(configInfo.CtiFrequency, TimeSpan.FromTicks(-1)), AdvanceTimePolicy.Adjust); } The configInfo .CtiFrequency property is a value I pass through to define after how many events I want a Cti to be injected and this in turn will flush through the stream of data. I usually pass a value of 1 for this setting. The second parameter determines the CTI timestamp in terms of a delay relative to the events. -1 ticks in the past results in 1 tick in the future, i.e., ahead of the event. The problem with this method though is that if consecutive events have the same StartTime then only one of those events will be enqueued. In this example I use the following to define how I assign the StartTime of my events currEvent.StartTime = (DateTimeOffset)dt.c2; If I go ahead and run my StreamInsight process with this configuration i can see on the output adapter that two events have been removed To see this in a little more depth I can use the StreamInsight Debugger and see what happens internally. What is happening here is that the first event arrives and a Cti is injected with a time of 1 tick after the StartTime of that event (Also the EndTime of the event). The second event arrives and it has a StartTime of before the Cti and even though we specified AdvanceTimePolicy.Adjust on the factory we know that a point event can never be adjusted like this and the event is dropped. The same happens for the third event as well (The second and third events get trumped by the Cti). For a more detailed discussion of why this happens look here http://www.sqlis.com/sqlis/post/AdvanceTimePolicy-and-Point-Event-Streams-In-StreamInsight.aspx We end up with a single event being pushed into the output adapter and our result now makes sense. The next way I tried to solve this problem by changing the value of the second parameter to TimeSpan.Zero Here is how my factory code now looks public AdapterAdvanceTimeSettings DeclareAdvanceTimeProperties<TPayload>(SimpleInputConfig configInfo, EventShape eventShape) { return new AdapterAdvanceTimeSettings( new AdvanceTimeGenerationSettings(configInfo.CtiFrequency, TimeSpan.Zero), AdvanceTimePolicy.Adjust); } What I am doing here is declaring a policy that says inject a Cti together with every event and stamp it with a StartTime that is equal to the start time of the event itself (TimeSpan.Zero). This method has plus points as well as a downside. The upside is that no events will be lost by having the same StartTime as previous events. The Downside is that because the Cti is declared with the StartTime of the event itself then it does not actually flush that particular event because in the StreamInsight algebra, a Cti commits only those events that occurred strictly before them. To flush the events we need a Cti to be enqueued with a greater StartTime than the events themselves. Here is what happened when I ran this configuration As you can see all we got through was the Cti and none of the events. The debugger output shows the stamps on the Cti and the events themselves. Because the Cti issued has the same timestamp (StartTime) as the events then none of the events get flushed. I was nearly there but not quite. Because my stream was bursty it was possible that the next event would not come along for a few seconds and this was far too long for an event to be enqueued and not be flushed to the output adapter. I needed another solution. Two possible solutions crossed my mind although only one of them made sense when I explored it some more. Where multiple events have the same StartTime I could add 1 tick to the first event, two to the second, three to third etc thereby giving them unique StartTime values. Add a timer to manually inject Ctis The problem with the first implementation is that I would be giving the events a new StartTime. This would cause me the following problems If I want to define windows over the stream then some events may not be captured in the right windows and therefore any calculations on those windows I did would be wrong What would happen if we had 10,000 events with the same StartTime? I would enqueue them with StartTime + n ticks. Along comes a genuine event with a StartTime of the very first event + 1 tick. It is now too far in the past as far as my stream is concerned and it would be dropped. Not what I would want to do at all. I decided then to look at the Timer based solution I created a timer on my input adapter that elapsed every 200ms. private Timer tmr; public SimpleInputAdapter(SimpleInputConfig configInfo) { ctx = new SimpleTimeExtractDataContext(configInfo.ConnectionString); this.configInfo = configInfo; tmr = new Timer(200); tmr.Elapsed += new ElapsedEventHandler(t_Elapsed); tmr.Enabled = true; } void t_Elapsed(object sender, ElapsedEventArgs e) { ts = DateTime.Now - dtCtiIssued; if (ts.TotalMilliseconds >= 200 && TimerIssuedCti == false) { EnqueueCtiEvent(System.DateTime.Now.AddTicks(-100)); TimerIssuedCti = true; } }   In the t_Elapsed event handler I find out the difference in time between now and when the last event was processed (dtCtiIssued). I then check to see if that is greater than or equal to 200ms and if the last issuing of a Cti was done by the timer or by a genuine event (TimerIssuedCti). If I didn’t do this check then I would enqueue a Cti every time the timer elapsed which is not something I wanted. If the difference between the two times is greater than or equal to 500ms and the last event enqueued was by a real event then I issue a Cti through the timer to flush the event Queue, otherwise I do nothing. When I enqueue the Ctis into my stream in my ProduceEvents method I also set the values of dtCtiIssued and TimerIssuedCti   currEvent = CreateInsertEvent(); currEvent.StartTime = (DateTimeOffset)dt.c2; TimerIssuedCti = false; dtCtiIssued = currEvent.StartTime; If I go ahead and run this configuration I see the following in my output. As we can see the first Cti gets enqueued as before but then another is enqueued by the timer and because this has a later timestamp it flushes the enqueued events through the engine. Conclusion Hopefully this has shown how the enqueuing of Ctis can have a dramatic effect on the responsiveness of your output in StreamInsight. Understanding the temporal nature of the product is for me one of the most important things you can learn. I have attached my solution for the demos. It is all in one project and testing each variation is a simple matter of commenting and un-commenting the parts in the code we have been dealing with here.

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• Jump-start Your Mind

  - by João Angelo

  I haven’t written in a while mostly because I’ve spent my time reading what others wrote and today I’m writing purely motivated by what I just finished reading. Mindfire: Big Ideas for Curious Mind by Scott Berkun was such a pleasure to read and ended up igniting parts of my mind which I have to admit were becoming a bit numb that I felt the urge to take some time to first say thank you to the author and then recommend it to all your curious minds out there. Now, go read it… it’s time well spent.

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• How can calculus and linear algebra be useful to a system programmer?

  - by Victor

  I found a website saying that calculus and linear algebra are necessary for System Programming. System Programming, as far as I know, is about osdev, drivers, utilities and so on. I just can't figure out how calculus and linear algebra can be helpful on that. I know that calculus has several applications in science, but in this particular field of programming I just can't imagine how calculus can be so important. The information was on this site: http://www.wikihow.com/Become-a-Programmer Edit: Some answers here are explaining about algorithm complexity and optimization. When I made this question I was trying to be more specific about the area of System's Programming. Algorithm complexity and optimization can be applied to any area of programming not just System's Programming. That may be why I wasn't able to came up with such thinking at the time of the question.

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• SPARC at 25: Past, Present and Future

  - by kgee

  Join us online to celebrate a quarter-century of innovation. Watch Scott McNealy, Bill Joy, and Andy Bechtolsheim along with other significant SPARC contributors discuss the challenges and rewards of consistently redefining the limits of enterprise IT. Hear Mark Hurd and John Fowler talk about the aggressive plans for SPARC’s future. All of this was recently captured in video at the SPARC anniversary event held at the Computer History Museum in Mountain View, California. In addition to getting unique insights from the people behind 25 years of SPARC technology, you can access exclusive content and resources, read case studies and e-Books, view webcasts and infographics, and more. Be sure to take some time to rediscover why and how SPARC was developed, the considerable impact it had on the entire IT industry, and the continuing innovations coming in the future.http://www.oracle.com/go/?&Src=7618691&Act=721&pcode=WWMK12044691MPP051

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• Why is Android VM-based? [closed]

  - by adib

  By about 2004, it was clear that ARM is the clear winner for mobile CPUs, beating out MIPS, SH3, and DragonBall. PocketPC (Windows Mobile) applications was natively-compiled (at least most of them - except for .NET compact and its competitors). Likewise, Apple's iOS (named iPhone OS at the time) prefers natively-compiled applications. Then why Android chose a virtual machine based system stack? (the Dalvik VM). Wouldn't it be simpler to just compile applications down to ARM code using GCJ or something? Is the decision influenced by the J2ME-way of doing things, or was just because it's "cool"? Perhaps like most things Java, the culture that prefers multiple levels of indirection and abstractions, they just added another layer of abstraction for "just in case"?

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• How much does it cost to develop an Android application?

  - by raychenon

  Following the same iPhone question. How much can a development team charge for an Android app like the official Twitter Inc ? In general how much amount of time is devoted to build the likes of Google Goggles , Google Skymap, Gmail with server side applications included :) Now if you're a solo developer and proud to show your app. How much time have you spent so far ? What was your background GUI desktop in Java, C#, web developer, started from zero programming experience ? Disclaimer : I've developed Android apps ( 10 000 downloads) on my free time and one commercial to be published. Just to know the amount of efforts needed to catch up :)

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• Exadata - Following up on customer deployments

  - by Carlos M. Orozco -Oracle

  Over the last year or so I've been visiting customers who have had Exadata deployed and have been enjoying the benefits the platform has been providing. Benefits include greater performance, consolidating multiple databases, data compression and time to value improvements. Most often I hear my reports run faster. One hospitality company report times that used to take 3 hrs now run in 12 seconds. Another services company reported all their batch reports taking 11hrs now run in 38 mins. Also reported that their transactions post faster, and batch updates run faster. So what does that mean? For most of them it means that now they have a platform that can handle growth. Most are growing 15% organically, but I've also seen 40% growth thru acquisition. Exadata has been keeping up with the additional data demand by customers leveraging compression and the smart storage features.

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• Becoming an expert vs boredom [closed]

  - by QAH

  I am a college student, and I love to program, period. I code all kinds of things in different kinds of languages. Although I enjoy programming, I have an extremely hard time sticking to one project for a long time. I attribute this shortcoming to my high level of curiosity, exploring different technologies, languages, libraries, etc. What would be best? Should I settle down more and spend time on becoming an expert in one or two programming fields, or should I be more of a jack of all trades, trying out all kinds of new technologies, languages, programming methods, etc.? I'm guessing that somewhere in the middle would be best. I'm always amazed at how many developers are able to create one or two projects, and develop on them for years. What techniques do you guys employ to help you stay focused on a project?

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• how do you spend your day? a day from a programmer's life [closed]

  - by RBA

  First of all I'm 26 and I'm asking this question because I want to see how do you manage your time. Also I'm interested how do the programmers with a family(wife, several kids) manage their time. I'm asking this due the fact that I'm working aprox 7,5 hours at work (9 to 5), spent 1,5 hours on the way to/from workplace, and when I'm home I must cook/clean/etc and LEARN! And I have the impression that I don't have enough time to learn. Did you have a period similar in your life? To want to learn another language/improve your development/other skills? I saw here and on SO that there are a lot of peoples with +10k points, this in my mind means that they stay on blogs/forums more than 15 hours a day. If you consider this question is a good question, please vote to reopen it. best regards, Radu

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• Meaning of directories on Unix and Unix like systems

  - by Luke

  I've been using Linux for a couple of years now but I still haven't figured out what the origin or meaning of some the directory names are on Unix and Unix like systems. E.g. what does etc stand for or var? Where does the opt name come from? And while we're on the topic anyway. Can someone give a clear explanation of what directory is best used for what. I sometimes get confused where certain software is installed or what the most appropriate directory is to install software into.

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• Keeping local windows folder in sync with remote ftp folder in real time

  - by bobo

  I know it has been asked before, but I would like it to happen in real time and transparently (without the need to open a separate FTP client such as FileZilla). For example, if I edit a text file in the local folder and then save it, it should immediately detect it and push the changes to the remote folder. It can be unidirectional (changes made on the local folder has to be pushed to the remote folder but the reverse is not necessary). It should also be able to specify some excluded files/folders which do not need to be in sync. Is there such an application that you know of?

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• Bidirectional real-time sync of large file tree between two distant linux servers

  - by dlo

  By large file tree I mean about 200k files, and growing all the time. A relatively small number of files are being changed in any given hour though. By bidirectional I mean that changes may occur on either server and need to be pushed to the other, so rsync doesn't seem appropriate. By distant I mean that the servers are both in data centers, but geographically remote from each other. Currently there are only 2 servers, but that may expand over time. By real-time, it's ok for there to be a little latency between syncing, but running a cron every 1-2 minutes doesn't seem right, since a very small fraction of files may change in any given hour, let alone minute. EDIT: This is running on VPS's so I might be limited on the kinds of kernel-level stuff I can do. Also, the VPS's are not resource-rich, so I'd shy away from solutions that require lots of ram (like Gluster?). What's the best / most "accepted" approach to get this done? This seems like it would be a common need, but I haven't been able to find a generally accepted approach yet, which was surprising. (I'm seeking the safety of the masses. :) I've come across lsyncd to trigger a sync at the filesystem change level. That seems clever though not super common, and I'm a bit confused by the various lsyncd approaches. There's just using lsyncd with rsync, but it seems this could be fragile for bidirectionality since rsync doesn't have a notion of memory (eg- to know whether a deleted file on A should be deleted on B or whether it's a new file on B that should be copied to A). lipsync appears to be just a lsyncd+rsync implementation, right? Then there's using lsyncd with csync2, like this: http://www.axivo.com/community/threads/lightning-fast-synchronization-with-csync2-and-lsyncd.121/ ... I'm leaning towards this approach, but csync2 is a little quirky, though I did do a successful test of it. I'm mostly concerned that I haven't been able to find a lot of community confirmation of this method. People on here seem to like Unison a lot, but it seems that it is no longer under active development and it's not clear that it has an automatic trigger like lsyncd. I've seen Gluster mentioned, but maybe overkill for what I need? UPDATE: fyi- I ended up going with the original solution I mentioned: lsyncd+csync2. It seems to work quite well, and I like the architectural approach of having the servers be very loosely joined, so that each server can operate indefinitely on its own regardless of the link quality between them.

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• Keeping local windows folder in sync with remote ftp folder in real time

  - by bobo

  I know it has been asked before, but I would like it to happen in real time and transparently (without the need to open a separate FTP client such as FileZilla). For example, if I edit a text file in the local folder and then save it, it should immediately detect it and push the changes to the remote folder. It can be unidirectional (changes made on the local folder has to be pushed to the remote folder but the reverse is not necessary). It should also be able to specify some excluded files/folders which do not need to be in sync. Is there such an application that you know of?

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• Coding exercise for Linux Systems Admin?

  - by Prashanth Sundaram

  Hello All, I am preparing for a Systems Admin(linux) role for a big company(top 10 companies) and one of the requisite is knowledge of a language like perl, python or Ruby. I have a phone interview which involves sharing a editor with the interviewer, now what kind of coding exercise can I expect on a phone interview or a regular interview? I have used shell for most of my day-to-day tasks and occasionally Perl and python for bigger tasks. Now I don't expect them to ask Write a script that sync's AD users to LDAP? I don't think data structures, algorithms or sorting questions apply to me role? Can you give me any examples of SysAdmin related coding questions?

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• Hardware asset management systems

  - by Dave

  I need to track a bunch of specialized testing tools, They are hardware devices used for testing other equipement. Each device has a serial number and is sent out for use in testing. Occasionally they break and have to be sent to the manufacture for repair. I'm looking for an open source application (preferably a webapp) to help manage them. Right now we're using Excel and it's not scaling as we get more tools. They aren't computers so all the standard IT asset management systems don't really fit the bill. I found h-harmony, but that project seems dead?

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• Try exchange in real domain

  - by AndreaCi

  We (as a company) 'd like to try exchange server to replace our mail server. I downloaded the demo version from Microsoft website, but during the installation it wants administrator access to domain to edit the Active Directory database structure. The test will last for (at least) a month to see if it will bring real advantages to our management systems. Here is my question: Is it "dangerous"? If I uninstall the exchange server everything will be reverted to previous state? I'm kind of "scared" about the changes he may apply to our domain controllers.

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• What equipment do real ISP's use?

  - by Allanrbo

  In a dormitory of 550 residents, people often mistakenly set up DHCP servers for the whole network by plugging in their private Wi-Fi routers wrongly. Also recently, someone mistakenly configured their PC to a static IP being the same as that of the default gateway. We use cheap 3Com switches at the moment. I know that Cisco switches support DHCP snooping to solve the DHCP problem, but that still does not solve the default gateway IP takeover problem. What sort of switch equipment do real ISP's use so their customers cannot break the network for the other customers?

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• Sharing external storage between different operating systems?

  - by CT

  I just received a Lacie 1TB external usb/firewire/esata drive. I have 2 machines. A macbook running osx 10.6 and a desktop running windows 7. I would like to rip my dvd collection to iso and store on my external. Right now I use my macbook's disk utility to rip dvds to iso. However my desktop is what is connected to my hdtv. I mainly just use the desktop for media. I'd like to format the external with a 200 GB partition for time machine backups and have the rest for storage. DVD iso are often above 8GB so that sort of eliminates FAT file systems correct? Do I have any options to be able to have my mac and pc both see the drive?

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• Real time mirroring between two sql server databases

  - by Matt Thrower

  Hi, I'm a c# programmer, not a DBA and I've had the (mis)fortune to be handed a database admin task. So please bear this in mind when answering this question. What I've been asked to do is to create a real time two-way mirror between two databases with a 10 Megabit connection between them. So when either changes it updates the other. This is not a standard data mirroring/failover task where one DB is the master and the other is a backup - both are live and each needs to instantly reflect changes made to the other. In my head this sounds like a tall order, one which may even be impossible - after all in a rapidly changing environment with lots of users this is going to be massively resource intensive and create locks and queues of jobs all over the place. Is it possible? If so, can anyone either give me some basic instructions and/or point me at some places to start my reading and research? Cheers, Matt

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• multiple file systems for mysql

  - by RainDoctor

  Does mysql support multiple file systems for a single database with most of the tables being on MyISAM? Context: we have a 1.5TB mysql database, which is increasing at the rate of 200GB per month. The storage is directly attached, whose slots are almost full. I can add another DAS, and increase the file system. But resizing volume, resizing file system, etc are getting messy. Is there a concept of "tablespace, datafile" (like in oracle) in MySql world? Or how you guys manage mysql db with these kind of constraints?

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• thought on real time web analytics

  - by Linus

  we have a few web servers and am planning to create a dashboard to show the real time stats ip address,geo-location and other custom data based on database lookups. Splunk sort of fits perfectly but wondering if there are any open source alternative . i have looked at logstash and graylog2, but to my knowledge they are more of a log analysis tools. Piwik is sort of interesting except that i cannot put any javascript on the webpages. All i have access to is apache web log. Any recommendations please..

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• Resolving real IP address out of a dynamic dns address

  - by stavnir

  I recently opened a dynamic dns user (at no-ip for that matter..) for my own personal needs and especially for ssh-ing my computer whenever I need to, without knowing it's static IP. My questions are: Am I misusing the concept of dynamic dns? Are there more appropriate methods to do what I want to do? If not, how do I resolve my router's real ip address? Firefox somehow manages to do so, nslookup and other similar commands only resolve the ip of the ddns server (e.g. no-ip.org). Trying to figure this mystery with wireshark failed miserably ;)

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• What equipment do real ISP's use?

  - by Allanrbo

  In a dormitory of 550 residents, people often mistakenly set up DHCP servers for the whole network by plugging in their private Wi-Fi routers wrongly. Also recently, someone mistakenly configured their PC to a static IP being the same as that of the default gateway. We use cheap 3Com switches at the moment. I know that Cisco switches support DHCP snooping to solve the DHCP problem, but that still does not solve the default gateway IP takeover problem. What sort of switch equipment do real ISP's use so their customers cannot break the network for the other customers? What we ended up doing In case anyone are courious, we ended up doing seperate VLANs for each user. And as a matter of fact, not just the 550 users, but for 2500 users (11 dorms). Here's a page describing the setup: http://k-net.dk/technicalsetup/ (the section "Transparent firewall using VLANs"). There was no significant load on the router server as I feared in one of the comments below. Even at 800Mpbs.

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