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  • What Logs / Process Stats to monitor on a Ubuntu FTP server?

    - by Adam Salkin
    I am administering a server with Ubuntu Server which is running pureFTP. So far all is well, but I would like to know what I should be monitoring so that I can spot any potential stability and security issues. I'm not looking for sophisticated software, more an idea of what logs and process statistics are most useful for checking on the health of the system. I'm thinking that I can look at various parameters output from the "ps" command and compare to see if I have things like memory leaks. But I would like to know what experienced admins do. Also, how do I do a disk check so that when I reboot, I don't get a message saying something like "disk not checked for x days, forcing check" which delays the reboot? I assume there is command that I can run as a cron job late at night. How often should it be run? What things should I be looking at to spot intrusion attempts? The only shell access is SSH on a non-standard port through UFW firewall, and I regularly do a grep on auth.log for "Fail" or "Invalid". Is there anything else I should look at? I was logging the firewall (UFW) but I have very few open ports (FTP and SSH on a non standard port) so looking at lists of IP's that have been blocked did not seem useful. Many thanks

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  • Are email addresses mandatory for Windows 8 login names?

    - by Cedric Martin
    I've got a computer running Windows 8 and in the user accounts I can see four accounts (they're in french, here's a rough translation): [email protected] / administrator Veronique YYY / [email protected] ASP.NET Machine Account / local account guest account / the guest account is desactivated I've got several questions but they're all related to email addresses and login names / accounts. Are email addresses mandatory for Windows 8 login names? Can you mix live and non-live user accounts on a Windows 8 system? Is it possible to have a live Windows 8 user account which is not using a @live.xx email address? Is it possible to have a non-live Windows 8 user account which is using a @live.xx email address? If the gmail.com email address of the admin is not a live Windows 8 account, does this mean I can create a "fake" email and use that as the email of a new Windows 8 account? Basically I don't understand very well why there are email addresses displayed on the login screen and why there are both @live.xx and @gmail.com email addresses on the same system and answer to the questions I asked above may help me understand a bit better what is going on (I'm coming from a Linux / OS X background. I literally haven't used Windows in more than a decade).

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  • strange raid5 issue:

    - by 8steve8
    ok so ive had a 4x2TB(samsung HD204UI w/firmware patch) raid5 array working normally for about a month. It was in a h57 gigabyte motherboard using the intel raid with windows 7 x64. Today I got an intel h67 motherboard, so I upgraded the intel raid drivers to 10.1.0.1008 from 9.6.0.1014, and I'm not sure if i checked after a reboot, but it caused no problems. I swapped in the new dh67 motherboard, and my array status was "failed". 2 of the 4 drives listed themselves as members, while the other two drives listed themselves as non-members. I tried going back to the old h57 mobo, and downgrading the raid drivers, but the issue remains. It's not port dependent, 2 of the drives always come up as non-members regardless of what port or motherboard they are plugged into. the screenshot should show that the SNs match, which begs the question why the software doesn't realize the drive is a member of the array: http://img837.imageshack.us/img837/6145/both.png I'd like to know if anyone has experienced anything similar, and what should i do, can i force the drive to be recognized as a member (without wiping data)?

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  • Windows Server 2008 R2 creating a multi-year client certificate using the IIS certsrv page while deploying SSTP VPN

    - by Warren P
    I am trying to follow instructions on Technet about deploying a Standard (non-enterprise) SSTP based VPN) that were originally written for Server 2008, but I am using Server 2008 R2, I have gotten as far as the part where it asks you to create a request a Server Authentication certificate. I have deployed IIS, and Active Directory Certificate Services, and chose "Standalone" and "Standard" (non-enterprise) Certificate Authority because I don't have an OID and don't think I should have to get one for a simple deployment of SSTP. The resulting certificates made by the Certification Authority "Issue" command, only have a 1 year period of validity, I want a multi-year certificate. At no point in this process is there any way to input this information unless it's through the Attributes text input area on the Advance Certificate Request page, which appears to be generated using an old ActiveX control, which means I can only do this using the workarounds in the article that I linked at the top, and only using Internet Explorer. Update:: It may be that this question is pointless since self-signed keys do not appear to work, when I try them, using Windows 8 as the VPN client. The problem is that the keys that are self-created by the technique shown here do not have any Certificate Revocation Server URLs and so you get an error "The revocation function was unable to check revocation", and the VPN connection fails.

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  • Remotely port forward/launch process or a client-less remote desktop app?

    - by DC177E
    I have an XP box running Logmein at a remote location behind a linksys router, which was running well for a whole of four days, until we had a power failure. Our ISP gave us a new IP, the machine restarted, and logmein did not autorun (or, at least, it did not automatically sign in), and our service (which may or may not be a Minecraft server with non-backed-up save files) also did not run upon startup. Logmein does not register the new IP (it still displays the old one). I have a DDNS updater service, so I do know the new dynamic address. I have tried using the built in XP remote desktop service, but, as with almost all non-cloud-based remote desktop services, it requires a port forward. Thus, I would appreciate it if anyone has any ideas as to: A: Any way of accessing our router remotely to forward the remote desktop port. I've seen the Remote Management option (forwarding the setup page to port 8080), but I do not have it enabled. I've tried UPnP, but again, the setup page for our router is not forwarded. B: Any way of remotely launching a process that does not require port forwarding (or uses ports 255XX, 18XXX, or 9000.), such as a remote console service built into XP. I realize this is a near impossibility. C: A Way to remotely start logmein, and sign in, which is likely a definite impossibility. Sorry if this is too specific for Stackexchange, or if I've put it into the wrong section (is SuperUser the correct place for this?). Ideas would, again be much appreciated, as shot-in-the-dark-like this may be.

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  • XSL 2.0 unparsed text and formatting

    - by Maha
    I want the unparsed text to be formatted for bold characters or increase font-size based on the tag the example here is for replace the searched word with bold characters Example: test <b> how to <b> when bold <b> when there is more <b> than one place to bold Can you please advice what is wrong here? <xsl:variable name="tcline" select="unparsed-text('generic_tc.txt','UTF-8')"/> <xsl:analyze-string select="$tcline" regex="\'<b>'(.*?)\'<b>'"> <xsl:matching-substring> <xsl:value-of select="replace($tcline,'\"<b>"(.*?)\"<b>"','<em>$1\/em/g;')"/> </xsl:matching-substring> <xsl:non-matching-substring> <xsl:value-of select="."/> </xsl:non-matching-substring> </xsl:analyze-string>

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  • strange raid5 issue: [closed]

    - by 8steve8
    ok so ive had a 4x2TB(samsung HD204UI w/firmware patch) raid5 array working normally for about a month. It was in a h57 gigabyte motherboard using the intel raid with windows 7 x64. Today I got an intel h67 motherboard, so I upgraded the intel raid drivers to 10.1.0.1008 from 9.6.0.1014, and I'm not sure if i checked after a reboot, but it caused no problems. I swapped in the new dh67 motherboard, and my array status was "failed". 2 of the 4 drives listed themselves as members, while the other two drives listed themselves as non-members. I tried going back to the old h57 mobo, and downgrading the raid drivers, but the issue remains. It's not port dependent, 2 of the drives always come up as non-members regardless of what port or motherboard they are plugged into. the screenshot should show that the SNs match, which begs the question why the software doesn't realize the drive is a member of the array: http://img837.imageshack.us/img837/6145/both.png I'd like to know if anyone has experienced anything similar, and what should i do, can i force the drive to be recognized as a member (without wiping data)?

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  • Two cisco gigabit switches refuse to link to each other. Any idea why?

    - by Prody
    I have 3 Linksys SR2024 switches which are basically non-managed 24 port Gbit + 2 miniGBIC. I now had to add another switch to the network, and my provider didn't have the SR2024 switch anymore, so I got the Cisco SLM2024 which was a bit more expensive. It's pretty much the same thing but with management (that I don't need). So I've connected the SLM2024 to a SR2024 via Cat6 cable, and for some strange reason, I get no link. If I connect any machine with a Gbit NIC to both switches, it links with 1Gbit autonegotiated. If I connect the SLM2024 to a non-Gbit switch (I have a cheap 4port ASUS switch), it will link just fine on 100Mbit full duplex. Since the SLM2024 has management, I've tried to see if something is misconfigured on it's side, but it's not, it advertises 1Gbit and lower. (hence the machines connecting succesfully at 1Gbit). Since the SR2024 that I'm trying to connect it to also connects successfully with another SR2024 and other Gbit machines, it means that it advertises Gbit too. But for some reason when I link the SR2024 to the SLM2024 I get no link. Please note that I've properly tested the wire. Does anyone have any idea what's wrong?

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  • Different font SIZES in a Text Editor, based on Script(Alphabet) type (ie. per Unicode Code-Block)

    - by fred.bear
    Some non-Latin-based scripts(alphabets) have more detail in their glyphs than do the Latin-based-script equivalents, and typically need a larger font to give the same degree of legibility (resolution-wise). Sometimes, both script types need to be present in the same file. Notepad++ allows different font SIZES (and colour, etc) courtesy of syntax-highlighting. This allows me to display larger-fonted non-Latin-based script in a // BIG-FONT comment. Although this has been quite handy for me in some situations, it is quite limited. A Word Processor can handle this scenario, but I'm not interested in that. I want a nice simple(?) plain(?) Text Editor to do it... on a per script-type basis... eg. mixing Latin-1 and Devanagari (and Mandarin, and ... Such a thing may not exits, but Notepad++ has shown that a simple(?) plain(?) Text Editor is capable of it. Does anyone know of such a Text Editor? ...Q. Why not a Word Processor? ...A. Because GCC and Python don't like that format! but UTF-8 is fine.

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  • Debugging methods for Windows XP hangups

    - by Cooper
    I experience occasional 'freezes' on my desktop machine (Windows XP SP3). I've tried the normal debugging methods I know (watching Process Explorer, running ProcMon (hard to get a good trace because the hangups are so intermittent). Are there any additional system debugging methods that might be useful in discovering what would cause these hang ups? While this question is more about debugging methods than the actual issue itself (which is probably more of a superuser question), the symptoms of the hangup are: All windows become non-responding. Can be brought the foreground, but do not repaint. Taskbar/explorer windows are non-responsive Ctrl+Alt+Del, Ctrl+Shift+Esc, Win+L, do not do anything (though the actions are queued up, and when the system unhangs, they are performed) Oddly enough, usually I can still scroll through the current page I have open in Google Chrome, but I cannot change tabs. Hangup can happen when I have tons of apps open, but also when I only have Outlook, Chrome, and MS Communicator (plus all the corporate spyware). Usually the hang lasts between 30sec and 3 minutes or so. After which I can continue working as usual.

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  • Combine multiple network interfaces to connect to a dedicated server

    - by Dženis Macanovic
    this is an underpaid employee writing, who's apparently responsible for all the IT stuff in a very small (non-IT) company. Today said company got a bunch of PCs/workstations, a switch, a computer that's supposed to be used as a router, two DSL connections (each 16 MBit/s downstream and 1 MBit/s upstream) and a dedicated server which is hosted and managed professionally by a larger local company with some decent connection speed (1 GBit/s both directions if I'm not mistaken). This is what I've set up (note I'm not making use of the second DSL connection at all)... ETH0 ETH1 [ SWITCH ]---[LINUX DEBIAN ROUTER]---[DSL MODEM 1]---[INTERNET] | | | PC1 | | PC2 | ... ... when my boss asked me, if it was somehow possible to get 32 MBit/s downstream and 2 MBit/s upstream. At that time I replied "no" without thinking too much about it. Now I've just had the following idea... ETH1 ETH0 ETH0 ,---[DSL MODEM 1 (NON-STATIC IP)]---, ,---, ETH0 [ SWITCH ]---[LINUX DEBIAN ROUTER] [INTERNET] [LINUX DEBIAN SERVER]---[INTERNET] | | | '---[ DSL MODEM 2 (STATIC IP) ]---' '---' PC1 | | ETH2 ETH0 PC2 | ... ... but I have absolutely no clue how to implement that. Would that even be possible? What would the masquerading rules look like on the router? What about the server? I didn't find anything on the internet, mainly because I couldn't come up with any good keywords to search for to begin with. English obviously isn't my first language. Thanks in advance for your time!

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  • What Logs / Process Stats to monitor on a Ubuntu FTP server?

    - by Adam Salkin
    I am administering a server with Ubuntu Server which is running pureFTP. So far all is well, but I would like to know what I should be monitoring so that I can spot any potential stability and security issues. I'm not looking for sophisticated software, more an idea of what logs and process statistics are most useful for checking on the health of the system. I'm thinking that I can look at various parameters output from the "ps" command and compare to see if I have things like memory leaks. But I would like to know what experienced admins do. Also, how do I do a disk check so that when I reboot, I don't get a message saying something like "disk not checked for x days, forcing check" which delays the reboot? I assume there is command that I can run as a cron job late at night. How often should it be run? What things should I be looking at to spot intrusion attempts? The only shell access is SSH on a non-standard port through UFW firewall, and I regularly do a grep on auth.log for "Fail" or "Invalid". Is there anything else I should look at? I was logging the firewall (UFW) but I have very few open ports (FTP and SSH on a non standard port) so looking at lists of IP's that have been blocked did not seem useful. Many thanks

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  • Prepping a conference

    - by Laurent Bugnion
    I have had the chance to talk at many conferences these past few years, and came up with a way to prepare them which works really well for me. Most importantly, it would make it quite easy to overcome an emergency (for example if my laptop would suddenly lose data). The whole code as well as the slides and other documents are in the cloud. I also use source control for my demos, so that I always have the latest and the greatest, but also a history of changes I made to my demos. Finally I have a system of code snippets which works great, and I often had very positive remarks from the audience regarding that. Putting everything in the cloud The one thing I used to be the most scared of was a sudden crash of my laptop, and being unable to restore in time for a conference. Most conferences ask speakers to send slides a few days (or weeks…) in advance, but let's face it, we all have last minute changes to our talks and I always come in the conference with updated slides that I pass to the management team. The answer to that dilemma used to be working off memory sticks, and that worked not bad. However last year I started putting all the documents relating to a conference in a DropBox folder, and that works great too. Obviously DropBox works only if you have connectivity, so if I for instance update slides while on an international flight, I cannot save to the cloud. The obvious answer to that is to backup everything on a memory stick… but I have to admit, I have been trusting my luck and working off my laptop HD and then synching everything to the cloud after landing. Of course on some US national flights you get WiFi on board, so in that case it is even simpler :) Usually after the conference is done, I remove the files from DropBox and copy them to their "final destination". They are backed up from there to BackBlaze, the great online backup service I am using routinely (I currently have about 90GB of data in BackBlaze). Outlining the presentations I like to have a written outline of my presentations written somewhere. I keep it simple, just write the various sections of the presentation with timing. I guess it is a remnant of the time when I was a private pilot, and using checklists for flight preparation. For example: Demo about designability 15' (0:37) Switch to Blend Open MainPage.xaml Create a DataTemplate ... Here I can immediately see during the presentation if I am taking too much time for my demo (0:37 is where I need to be when I am done with this section of the presentation, and 15' is the time that this particular section takes). I keep these sections reasonable, I don't detail every step of the preparation. Typically I have one such section for every 10-15 minutes of my talks. Yes, I am timing my presentations. I keep adjusting these numbers when I rehearse, and this really helps to feel more confident during the presentations. This is especially important for presentations that are long, like my MIX11 demo which clocked at 57 minutes (I had a lot of stuff to show…). Such presentations are risky, because if anything goes wrong, you will have to cut stuff, so the answer to that is: Rehearse, rehearse and when you're done rehearsing, rehearse a little more. I also have a "Preparation" section where I outline what I need to do before a presentation. For instance: Preparation Reboot in VHD Make sure MSN and Twitter are not running. Open VS10 and load demo Open Blend and load demo Run the WP7 emulator ... I typically start preparing my laptop an hour before the talk, starting everything I need to start and then putting my laptop to sleep. Saving and printing the outline, Timing Printing is a real problem because it is really hard to find a printer at most conference venues, and also quite hard in hotels. To solve that, I simply write everything in OneNote (synched to the cloud, now you start to know what I like ;) and then I print it to a PDF (I use CutePDFWriter) that I save to my Kindle. During the presentation, I read the outline off the Kindle (I mostly just need a quick check to see how I am timing). For timing during the presentation, I use the free tool ChronoGPS on my Windows Phone 7, but of course any phone these days has a clock/chrono application. In some conferences, they even have timers that the presenters can see, but they tend to count down and I prefer to count up… so I just use my own :) Source control for demos For demos, I create a separate folder and use Mercurial as source control. Mercurial has the huge advantage (over SVN or TFS) to work offline too, so I can commit while on a plane, and all the history is saved. Then when I have connectivity I push everything to the cloud (I am using the fantastic Trunksapp.com for my private repositories). Here too the obvious downside is the risk of losing my last changes if my laptop crashes before I can push to the cloud, and here too the obvious answer would be to work from a memory stick… though I have to admit I didn't do that lately (except when I was writing Silverlight 4 Unleashed, where I was really paranoid…) And code snippets? I am one of these presenters who hates to type in front of an audience. I can type really fast (writing two books has this advantage, it really teaches you to touch type and be fast at it) but in the context of an audience, on a stage where it is often damn cold (an issue I had a lot in past conferences, air conditioning can freeze your fingers and make it really hard to type), it doesn't work as well. I don't know for you, but I really dislike seeing a presentation where the speaker uses the backspace key more often than others ;) To solve that, I like to have my code ready in snippets, and drag them to the screen. Then I can spend time explaining each code snippet, while highlighting portions of the code (always highlight what you talk about, the audience often doesn't even see the cursor and doesn't know where you are on the screen!) Over the years I have used various solutions for code snippets, and now I have one which works really well… if you take a few precautions! I use the Visual Studio Toolbox. Preparing the code snippets You can store code snippets in the Toolbox for anything, XAML, C# etc. I arrange the snippets in the order in which I need them, which is a great way to remember what comes next in the presentation. I also separate them by topic, to make it easier to find them, for example when I switch to the slides and then back to the code. Remember that no matter how experienced you are, you will feel more nervous on stage than while you are preparing, so any way to make it easier for you is going to be beneficial to the audience. To store a code snippet, I do the following: Open the final demo that you want to show to the audience in Visual Studio. In your code, select a snippet of code that you want to explain in particular. Make sure that the Visual Studio Toolbox is open (menu View, Toolbox or Ctrl-Alt-X). Drag the selected snippet from the code window to the toolbox. (if needed) drag the snippet to the correct location (for example between two other code snippets so that you can access it as you speak through the demo). Right click on the snippet and select Rename Item from the context menu. Select a meaningful name. For me I use the following conventions: If it is a method, I use the method's name. If it is not a whole method, I use a descriptive name. If it is the content of a method (i.e. the body only, without the method's signature), I use "-> MethodName". This reminds me during the presentation that this is only the body, and that I need to insert that into an existing signature. This is the case, for instance, when I use Visual Studio to automatically generate the members of an interface’s implementation; then I only need to insert my snippet inside the generated method body. Saving the snippets This is the most important!! It happened to me a few times that VS10 lost its settings. When that happens, the snippets are lost too! Yeah that really sucks, especially (as it happened once) when this is the case about an hour before a talk… Stress and sweat follows, not good conditions to start a talk in front of an audience believe me. Thankfully, saving snippets is really easy with the following steps: Select the menu Tools, Import and Export Settings. Select Export selected environment settings and press Next. Uncheck All Settings. Then expand General Settings and select Toolbox (only!). Press Next. Select your source control folder and save under a meaningful name (for instance Snippets.vssettings). Commit to source control and push to the cloud. By the way, this also has the advantage of applying source control to the snippets file (which is an XML file), so you get history for free on that file! Reimporting the snippets If VS loses its settings and you need to reimport the snippets, this can be done super easily and very fast. Make sure that the Toolbox is empty. When you import snippets, they are merged with existing ones, they do not replace the content of the Toolbox. Unless merging is really what you want, make sure that your Toolbox is clean before you import, it is really easier. Select the menu Tools, Import and Export Settings. Select Import selected environment settings and press Next. Select No, just import new settings and press Next. Press Browse and select the Snippets.vssettings file. Press Finish. Et voila, all your snippets appear again in the Toolbox. Whew, the worst was averted and you can start your demo without sweating! (I had to do that once literally 5 minutes before the start of a demo, while my laptop was already hooked to the projector, and it went just fine). What about special tools? When using special tools (for example beta versions of tools you have an early access to), or a special configuration of your laptop, things can get tricky because you cannot really be sure that you will get a laptop with the same tools and the same configuration at the conference. To solve that, I use the following precautions: I make my demos from a Virtual Hard Disk. The great John Papa made a very easy-to-follow web page where he explains how to create a VHD and install Win7 to it. This gives you the full power of your laptop (as fast as booting from the metal). For me, I have a basic configuration that I saved on a USB harddrive (Win7 plus drivers, basic settings for desktop, folder options, taskbar etc) and Visual Studio 2010 SP1 on it. When preparing, I start by copying this "basis VHD" to my laptop. I install additional tools and configurations. I save the VHD back to the USB harddrive in a different folder. This would allow me to reinstall my demo environment quite fast, for example in case of harddrive failure. Replace the harddrive, copy the VHD to it, configure the BCD and you can start. Unfortunately this only works if the laptop itself still works. In the worst case of total failure, my security is to back all the installers up: The installers I use are synched on all my laptops and backed up to BackBlaze. If the worst happens and my laptop is absolutely broken, I can download the installer from BackBlaze and install on another laptop. This of course takes some time, and if that happens 5 minutes before a presentation, well… I don't have an answer to that, except of course crossing my fingers. Still, all that gives me additional security. Conclusion Remember folks, talking to an audience, large or small, will make you nervous. Just ask Scott Hanselman :) The goal here is to create the best possible conditions for you, and to create an environment where everything is saved and easy to restore, where everything is well known and provides you with additional confidence. The cooler you feel before the presentation (and during ;)), the better your presentation will be. Here too, the goal is to provide the best user experience you can have, which in turn will make it more enjoyable for your audience! Happy presenting :) Laurent   Laurent Bugnion (GalaSoft) Subscribe | Twitter | Facebook | Flickr | LinkedIn

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  • .NET Code Evolution

    - by Alois Kraus
    Originally posted on: http://geekswithblogs.net/akraus1/archive/2013/07/24/153504.aspxAt my day job I do look at a lot of code written by other people. Most of the code is quite good and some is even a masterpiece. And there is also code which makes you think WTF… oh it was written by me. Hm not so bad after all. There are many excuses reasons for bad code. Most often it is time pressure followed by not enough ambition (who cares) or insufficient training. Normally I do care about code quality quite a lot which makes me a (perceived) slow worker who does write many tests and refines the code quite a lot because of the design deficiencies. Most of the deficiencies I do find by putting my design under stress while checking for invariants. It does also help a lot to step into the code with a debugger (sometimes also Windbg). I do this much more often when my tests are red. That way I do get a much better understanding what my code really does and not what I think it should be doing. This time I do want to show you how code can evolve over the years with different .NET Framework versions. Once there was  time where .NET 1.1 was new and many C++ programmers did switch over to get rid of not initialized pointers and memory leaks. There were also nice new data structures available such as the Hashtable which is fast lookup table with O(1) time complexity. All was good and much code was written since then. At 2005 a new version of the .NET Framework did arrive which did bring many new things like generics and new data structures. The “old” fashioned way of Hashtable were coming to an end and everyone used the new Dictionary<xx,xx> type instead which was type safe and faster because the object to type conversion (aka boxing) was no longer necessary. I think 95% of all Hashtables and dictionaries use string as key. Often it is convenient to ignore casing to make it easy to look up values which the user did enter. An often followed route is to convert the string to upper case before putting it into the Hashtable. Hashtable Table = new Hashtable(); void Add(string key, string value) { Table.Add(key.ToUpper(), value); } This is valid and working code but it has problems. First we can pass to the Hashtable a custom IEqualityComparer to do the string matching case insensitive. Second we can switch over to the now also old Dictionary type to become a little faster and we can keep the the original keys (not upper cased) in the dictionary. Dictionary<string, string> DictTable = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase); void AddDict(string key, string value) { DictTable.Add(key, value); } Many people do not user the other ctors of Dictionary because they do shy away from the overhead of writing their own comparer. They do not know that .NET has for strings already predefined comparers at hand which you can directly use. Today in the many core area we do use threads all over the place. Sometimes things break in subtle ways but most of the time it is sufficient to place a lock around the offender. Threading has become so mainstream that it may sound weird that in the year 2000 some guy got a huge incentive for the idea to reduce the time to process calibration data from 12 hours to 6 hours by using two threads on a dual core machine. Threading does make it easy to become faster at the expense of correctness. Correct and scalable multithreading can be arbitrarily hard to achieve depending on the problem you are trying to solve. Lets suppose we want to process millions of items with two threads and count the processed items processed by all threads. A typical beginners code might look like this: int Counter; void IJustLearnedToUseThreads() { var t1 = new Thread(ThreadWorkMethod); t1.Start(); var t2 = new Thread(ThreadWorkMethod); t2.Start(); t1.Join(); t2.Join(); if (Counter != 2 * Increments) throw new Exception("Hmm " + Counter + " != " + 2 * Increments); } const int Increments = 10 * 1000 * 1000; void ThreadWorkMethod() { for (int i = 0; i < Increments; i++) { Counter++; } } It does throw an exception with the message e.g. “Hmm 10.222.287 != 20.000.000” and does never finish. The code does fail because the assumption that Counter++ is an atomic operation is wrong. The ++ operator is just a shortcut for Counter = Counter + 1 This does involve reading the counter from a memory location into the CPU, incrementing value on the CPU and writing the new value back to the memory location. When we do look at the generated assembly code we will see only inc dword ptr [ecx+10h] which is only one instruction. Yes it is one instruction but it is not atomic. All modern CPUs have several layers of caches (L1,L2,L3) which try to hide the fact how slow actual main memory accesses are. Since cache is just another word for redundant copy it can happen that one CPU does read a value from main memory into the cache, modifies it and write it back to the main memory. The problem is that at least the L1 cache is not shared between CPUs so it can happen that one CPU does make changes to values which did change in meantime in the main memory. From the exception you can see we did increment the value 20 million times but half of the changes were lost because we did overwrite the already changed value from the other thread. This is a very common case and people do learn to protect their  data with proper locking.   void Intermediate() { var time = Stopwatch.StartNew(); Action acc = ThreadWorkMethod_Intermediate; var ar1 = acc.BeginInvoke(null, null); var ar2 = acc.BeginInvoke(null, null); ar1.AsyncWaitHandle.WaitOne(); ar2.AsyncWaitHandle.WaitOne(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Intermediate did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Intermediate() { for (int i = 0; i < Increments; i++) { lock (this) { Counter++; } } } This is better and does use the .NET Threadpool to get rid of manual thread management. It does give the expected result but it can result in deadlocks because you do lock on this. This is in general a bad idea since it can lead to deadlocks when other threads use your class instance as lock object. It is therefore recommended to create a private object as lock object to ensure that nobody else can lock your lock object. When you read more about threading you will read about lock free algorithms. They are nice and can improve performance quite a lot but you need to pay close attention to the CLR memory model. It does make quite weak guarantees in general but it can still work because your CPU architecture does give you more invariants than the CLR memory model. For a simple counter there is an easy lock free alternative present with the Interlocked class in .NET. As a general rule you should not try to write lock free algos since most likely you will fail to get it right on all CPU architectures. void Experienced() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); t1.Wait(); t2.Wait(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Experienced did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Experienced() { for (int i = 0; i < Increments; i++) { Interlocked.Increment(ref Counter); } } Since time does move forward we do not use threads explicitly anymore but the much nicer Task abstraction which was introduced with .NET 4 at 2010. It is educational to look at the generated assembly code. The Interlocked.Increment method must be called which does wondrous things right? Lets see: lock inc dword ptr [eax] The first thing to note that there is no method call at all. Why? Because the JIT compiler does know very well about CPU intrinsic functions. Atomic operations which do lock the memory bus to prevent other processors to read stale values are such things. Second: This is the same increment call prefixed with a lock instruction. The only reason for the existence of the Interlocked class is that the JIT compiler can compile it to the matching CPU intrinsic functions which can not only increment by one but can also do an add, exchange and a combined compare and exchange operation. But be warned that the correct usage of its methods can be tricky. If you try to be clever and look a the generated IL code and try to reason about its efficiency you will fail. Only the generated machine code counts. Is this the best code we can write? Perhaps. It is nice and clean. But can we make it any faster? Lets see how good we are doing currently. Level Time in s IJustLearnedToUseThreads Flawed Code Intermediate 1,5 (lock) Experienced 0,3 (Interlocked.Increment) Master 0,1 (1,0 for int[2]) That lock free thing is really a nice thing. But if you read more about CPU cache, cache coherency, false sharing you can do even better. int[] Counters = new int[12]; // Cache line size is 64 bytes on my machine with an 8 way associative cache try for yourself e.g. 64 on more modern CPUs void Master() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Master, 0); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Master, Counters.Length - 1); t1.Wait(); t2.Wait(); Counter = Counters[0] + Counters[Counters.Length - 1]; if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Master did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Master(object number) { int index = (int) number; for (int i = 0; i < Increments; i++) { Counters[index]++; } } The key insight here is to use for each core its own value. But if you simply use simply an integer array of two items, one for each core and add the items at the end you will be much slower than the lock free version (factor 3). Each CPU core has its own cache line size which is something in the range of 16-256 bytes. When you do access a value from one location the CPU does not only fetch one value from main memory but a complete cache line (e.g. 16 bytes). This means that you do not pay for the next 15 bytes when you access them. This can lead to dramatic performance improvements and non obvious code which is faster although it does have many more memory reads than another algorithm. So what have we done here? We have started with correct code but it was lacking knowledge how to use the .NET Base Class Libraries optimally. Then we did try to get fancy and used threads for the first time and failed. Our next try was better but it still had non obvious issues (lock object exposed to the outside). Knowledge has increased further and we have found a lock free version of our counter which is a nice and clean way which is a perfectly valid solution. The last example is only here to show you how you can get most out of threading by paying close attention to your used data structures and CPU cache coherency. Although we are working in a virtual execution environment in a high level language with automatic memory management it does pay off to know the details down to the assembly level. Only if you continue to learn and to dig deeper you can come up with solutions no one else was even considering. I have studied particle physics which does help at the digging deeper part. Have you ever tried to solve Quantum Chromodynamics equations? Compared to that the rest must be easy ;-). Although I am no longer working in the Science field I take pride in discovering non obvious things. This can be a very hard to find bug or a new way to restructure data to make something 10 times faster. Now I need to get some sleep ….

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  • Error in IE8 Win7: this tab has been recovered

    - by Sohail
    Hello everybody, I get this error every time I open IE8 in Win7, and a popup appear which says: this tab has been recovered and it close open the tab that I can't even surf a page (any page) with IE8, and after a while it crashes and close the program with no such an obvious error, I tried these methods to solve the problem but it doesn't work: 1.Reset Internet Explorer settings 2.Run IE without Add-ons 3.Scanned system for viruses with Eset Smart sercurity 4, there was no viruses. I would appreciate any suggestion, thanks.

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  • How to set resolution on mplayer with libcaca?

    - by AndrejaKo
    I'm using mplayer and libcaca on Gentoo. My framebuffer (uvesafb) is running at 1920x1200 (I don't know how many characters that is) and mplayer has problems filling up the screen, so video and audio lose synchronization. I'm looking for ways to improve performance. The most obvious solution would be to decrease resolution of mplayer, so I'm looking for ways to do that. Any other performance tips would be appriciated.

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  • Best way to connect a desktop computer to a 3g network

    - by dbyrne
    A friend of mine is moving to a building with no Internet connectivity. Ethernet and wifi are out of the question. What is the best way for him to get his desktop connected? The most obvious solution is for him to get an unlimited 3G data plan. What is the best way for him to set this up? I am assuming he should get something like Verizon's MiFi 3G access point, but does this have an ethernet jack?

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  • RDP access to DirectAccess Server via DirectAccess

    - by crgnz
    I have just setup a Win2008R2 DirectAccess server (and also a Win2008R2 Active Directory server). From the Internet I can Remote Desktop login to the AD server, but I cannot RDP into the DirectAccess server. I can PING both servers and get an IPv6 response. (I can RDP to the DirectAccess server from the internal company network) DirectAccess is configured to allow full intranet access. I think I've hit a mental block, the answer will probably be obvious, but I just can't see it.

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  • How to copy text from Console2?

    - by GJ
    I just started using Console2 as an alternative to cmd.exe I can't figure out how to copy text from the console to the clipboard -- dragging over it with the mouse won't mark anything, and there is no option in the right-click menu to "mark" as in cmd.exe It must be terribly obvious but I guess I'm overlooking it... :(

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  • Windows 7 NNTP Server

    - by int0x90
    I am doing some development that requires some interaction with an NNTP server, however I don't want to develop against a live server for obvious reasons and am trying to get a local NNTP server setup for testing, but for the life of me I can't find any guides on setting one up in (preferably) Windows 7. Can anyone shed some light? I've found that in IIS 6 you were able to setup an NNTP server, but I unfortunately do not have a 2003 VM at my disposal, I'm stuck with either XP or Windows 7. Thanks

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  • Possible to track Outlook tasks on Windows Mobile

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    I'm trying to view/add/edit MS Outlook 2007 tasks on a work PDA running Windows Mobile 6 Professional (sync'ed with MS Exchange 2007). 1) is this possible? From a quick Google search I can't find anything... However I may be missing something obvious. 2) if not, any ideas about work-arounds? Thanks

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  • Implication of variable context switching time

    - by Rob
    Hi, I know that constant switching time of the Linux scheduler was a big achievement. I was just asking myself the question what would be the implication of a non-constant switching time. The only obvious reason I can think of is real-time systems where we have to meet deadlines. There it is obviously no ideal if the switching time is "random". Are there any other good reasons that favour constant switching times? Many thanks, Rob

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  • How can I download Maven artifacts in chef?

    - by recampbell
    I want to do something like this in a chef recipe: maven_artifact "/opt/foo/my.jar" do source "com.foo:my:0.1:jar" end But I can't find a cookbook which provides this. I've written something which basically does this but it doesn't handle snapshots, which requires parsing maven-metadata.xml. Before I plunge into this, I wanted to be sure I wasn't missing something obvious since this seems like a basic usecase.

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