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• Regular Expressions Cookbook Code Samples

  - by Jan Goyvaerts

  %COOKBOOKFRAME% One of the common criticisms against the first edition was that we didn’t have the regular expressions and code samples available for download. Since our book only has very short code snippets rather than complete programs, we (the authors) did not have these available as separate files either. But for the second edition we’re trying to do better. You can now download the code samples from the 2nd edition of Regular Expressions Cookbook. This HTML file contains all the blocks with regular expressions and source code from the book, along with the titles of the chapters, recipes, and sections that they are found in. If you have purchased the book, you can use this file to easily copy and paste the regular expressions and source code snippets. Even if you purchased the ebook, you may prefer to use this file. The regexes in the ebook are formatted with line breaks and gray dots for spaces to make them easier to read in print. The HTML file does not use such formatting, so you can copy and paste them directly. This means that some very regexes will run beyond the edge of your browser window.

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• One of the partion on a usb harddisk cannot automount

  - by holmescn

  It is a very strange problem. My usb harddisk has four partitions, one is primary, the other three are logical (contained within an extended partition). When I plug in the disk, three of the partitions are mounted automatically except one--the first logical partition in the extended partition. Initially I thought it is the problem of system (at that time I used Mint). But after I change to Ubuntu 12.04, the problem wasn't solved. I don't want to add a rule in fstab, and I want to know what happened. The disk is fine, and the partition can be accessed in Windows and mounted manually. result of dmesg | tail: [100933.557649] usb 2-1.2: new high-speed USB device number 4 using ehci_hcd [100933.651891] scsi8 : usb-storage 2-1.2:1.0 [100934.649047] scsi 8:0:0:0: Direct-Access SAMSUNG PQ: 0 ANSI: 0 [100934.650963] sd 8:0:0:0: Attached scsi generic sg2 type 0 [100934.651342] sd 8:0:0:0: [sdb] 625142448 512-byte logical blocks: (320 GB/298 GiB) [100934.651977] sd 8:0:0:0: [sdb] Write Protect is off [100934.651989] sd 8:0:0:0: [sdb] Mode Sense: 03 00 00 00 [100934.652836] sd 8:0:0:0: [sdb] No Caching mode page present [100934.652848] sd 8:0:0:0: [sdb] Assuming drive cache: write through [100934.655354] sd 8:0:0:0: [sdb] No Caching mode page present [100934.655367] sd 8:0:0:0: [sdb] Assuming drive cache: write through [100934.734652] sdb: sdb1 sdb3 < sdb5 sdb6 sdb7 > [100934.737706] sd 8:0:0:0: [sdb] No Caching mode page present [100934.737725] sd 8:0:0:0: [sdb] Assuming drive cache: write through [100934.737731] sd 8:0:0:0: [sdb] Attached SCSI disk result of parted -l: Model: SAMSUNG (scsi) Disk /dev/sdb: 320GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 32.3kB 21.5GB 21.5GB primary ntfs 3 21.5GB 320GB 299GB extended lba 5 21.5GB 129GB 107GB logical ntfs 6 129GB 236GB 107GB logical ntfs 7 236GB 320GB 83.8GB logical ntfs

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• Was API hooking done as needed for Stuxnet to work? I don't think so

  - by The Kaykay

  Caveat: I am a political science student and I have tried my level best to understand the technicalities; if I still sound naive please overlook that. In the Symantec report on Stuxnet, the authors say that once the worm infects the 32-bit Windows computer which has a WINCC setup on it, Stuxnet does many things and that it specifically hooks the function CreateFileA(). This function is the route which the worm uses to actually infect the .s7p project files that are used to program the PLCs. ie when the PLC programmer opens a file with .s7p the control transfers to the hooked function CreateFileA_hook() instead of CreateFileA(). Once Stuxnet gains the control it covertly inserts code blocks into the PLC without the programmers knowledge and hides it from his view. However, it should be noted that there is also one more function called CreateFileW() which does the same task as CreateFileA() but both work on different character sets. CreateFileA works with ASCII character set and CreateFileW works with wide characters or Unicode character set. Farsi (the language of the Iranians) is a language that needs unicode character set and not ASCII Characters. I'm assuming that the developers of any famous commercial software (for ex. WinCC) that will be sold in many countries will take 'Localization' and/or 'Internationalization' into consideration while it is being developed in order to make the product fail-safe ie. the software developers would use UNICODE while compiling their code and not just 'ASCII'. Thus, I think that CreateFileW() would have been invoked on a WINCC system in Iran instead of CreateFileA(). Do you agree? My question is: If Stuxnet has hooked only the function CreateFileA() then based on the above assumption there is a significant chance that it did not work at all? I think my doubt will get clarified if: my assumption is proved wrong, or the Symantec report is proved incorrect. Please help me clarify this doubt. Note: I had posted this question on the general stackexchange website and did not get appropriate responses that I was looking for so I'm posting it here.

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• Obstacle Avoidance steering behavior: how can an entity avoid an obstacle while other forces are acting on the entity?

  - by Prog

  I'm trying to implement the Obstacle Avoidance steering behavior in my 2D game. Currently my approach is to apply a force on the entity, in the direction of the normal of the heading, scaled by a number that gets bigger the closer we are to the obstacle. This is supposed to push the entity to the side and avoid the obstacle that blocks it's way. However, in the same time that my entity tries to avoid an obstacle, it Seeks to a point more or less behind the obstacle (which is the reason it needs to avoid the obstacle in the first place). The Seek algorithm constantly applies a force on the entity that pushes it (more or less) in the direction of the obstacle, while the Obstacle Avoidance algorithm constantly applies a force that pushes the entity away (more accurately, to the side) of the obstacle. The result is that sometimes the entity succesfully avoids the obstacle, and sometimes it collides with it, depending on the strength of the avoidance force I'm applying. How can I make sure that a force will succeed in steering the entity in some direction, while other forces are currently acting on the entity? (And while still looking natural). I can't allow entities to collide with obstacles when realistically they should be able to easily avoid them, doesn't matter what they're currently doing. Also, the Obstacle Avoidance algorithm is made exactly for the case where another force is acting on the entity. Otherwise it wouldn't be moving and there would be no need to avoid anything. So maybe I'm missing something. Thanks

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• Accessing second hard drive

  - by Jonathan

  Hi, So I recently installed Ubuntu 10.10 64-bit on my computer. I installed it on my 60gb SSD hard drive, and in the installation it never acknowledged the existence of my second hard drive. The hard drive that I keep all my files on, and which I want to make my home folder if I can, is a Western Digital Caviar Black 1TB SATA 6Gb/s 64MB cache (WD1002FAEX). I've read the following: https://help.ubuntu.com/community/Mount but honestly cannot work out how to access the hard drive from my Ubuntu installation. I did have Windows 7 64-bit prior to installing Ubuntu. I have backed up all the files on the hard drive, but if I could just access them straight off that would be super cool. Does anyone know how I can use the second hard drive? Thank you for your help EDIT: The following directories are currently in my /dev/ folder: ati/, block/, bsg/, bus/, char/, cpu/, isk/, input/, mapper/, net/, pktcdvd/, pts/, shm/, snd/, and usb/ EDIT: Result from sudo fdisk -l Disk /dev/sda: 60.0 GB, 60022480896 bytes 255 heads, 63 sectors/track, 7297 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000d2dfd Device Boot Start End Blocks Id System /dev/sda1 * 1 6994 56174592 83 Linux /dev/sda2 6994 7298 2438145 5 Extended /dev/sda5 6994 7298 2438144 82 Linux swap / Solaris

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• Will We See More Partisan Splits from the SEC?

  - by Theresa Hickman

  The SEC's lawsuit against Goldman Sachs has made recent headlines. The fact that the SEC seems to be growing more litigious by making examples out of invididuals and companies is not the topic of my blog. The most interesting thing about this case is that the 5 SEC commissioners did not vote unanimously to bring the lawsuit. The commissioners had a 3-2 partisan split. Ms. Shapiro (a registered independent) voted with the 2 Democrats. Split votes rarely happen by the SEC, especially when they are enforcing actions against firms they regulate. I wonder if we will be seeing more of these partisan split votes when it comes to other decisions, say IFRS adoption? I know both the Democrats and Republicans have stated that they support a unified accounting standard. However, will the Republicans want to push back simply because there is a Democrat in office? (Seems childish to me, but I never understood politics). I think Ms. Shapiro will most definitely want a unanimous consensus related to the IFRS topic. There is already talk that we will be seeing more SEC split votes in the future. For example, there will most likely be a split vote regarding Obama's proposed financial-regulatory overhaul. I don't see why IFRS would be exempt. I really hope it doesn't happen because the last thing we need is more road blocks on our IFRS road trip.

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• Breakout ball collision detection, bouncing against the walls

  - by Sri Harsha Chilakapati

  I'm currently trying to program a breakout game to distribute it as an example game for my own game engine. http://game-engine-for-java.googlecode.com/ But the problem here is that I can't get the bouncing condition working properly. Here's what I'm using. public void collision(GObject other){ if (other instanceof Bat || other instanceof Block){ bounce(); } else if (other instanceof Stone){ other.destroy(); bounce(); } //Breakout.HIT.play(); } And here's by bounce() method public void bounce(){ boolean left = false; boolean right = false; boolean up = false; boolean down = false; if (dx < 0) { left = true; } else if (dx > 0) { right = true; } if (dy < 0) { up = true; } else if (dy > 0) { down = true; } if (left && up) { dx = -dx; } if (left && down) { dy = -dy; } if (right && up) { dx = -dx; } if (right && down) { dy = -dy; } } The ball bounces the bat and blocks but when the block is on top of the ball, it won't bounce and moves upwards out of the game. What I'm missing? Is there anything to implement? Please help me.. Thanks

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• Hide icons encrypted file system partitions in Nautilus

  - by Eddy Pronk

  I've installed Ubuntu 10.04 from the alternate CD. It has an encrypted root and swap partition. The root partition is visible in Nautilus as 'File Syste' icon. There is another icon "216 GB Filesystem". If I click it says: Unable to mount 216 GB Filesystem. /dev/mapper/sda5_crypt is mounted. Then there is another icon "6.1 GB Swap Space". If I click it it says: Unable to mount 6.1 GB Swap Space. Not a mountable file system. How can I hide these last two icons? Partition layout: $ sudo fdisk -l /dev/sda [sudo] password for eddyp: Disk /dev/sda: 320.1 GB, 320072933376 bytes 255 heads, 63 sectors/track, 38913 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xa6e92df4 Device Boot Start End Blocks Id System /dev/sda1 1 11749 94373811 7 HPFS/NTFS /dev/sda2 11871 38914 217219073 5 Extended /dev/sda3 * 11750 11871 976896 83 Linux /dev/sda5 11871 38167 211220480 83 Linux /dev/sda6 38167 38914 5997568 83 Linux Partition table entries are not in disk order Mounted as: $ mount /dev/mapper/sda5_crypt on / type ext4 (rw,errors=remount-ro) proc on /proc type proc (rw,noexec,nosuid,nodev) none on /sys type sysfs (rw,noexec,nosuid,nodev) none on /sys/fs/fuse/connections type fusectl (rw) none on /sys/kernel/debug type debugfs (rw) none on /sys/kernel/security type securityfs (rw) none on /dev type devtmpfs (rw,mode=0755) none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620) none on /dev/shm type tmpfs (rw,nosuid,nodev) none on /var/run type tmpfs (rw,nosuid,mode=0755) none on /var/lock type tmpfs (rw,noexec,nosuid,nodev) none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755) /dev/sda3 on /boot type ext4 (rw) binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,noexec,nosuid,nodev) gvfs-fuse-daemon on /home/eddyp/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=eddyp) /dev/sda1 on /media/S3A6595D003 type fuseblk (rw,nosuid,nodev,allow_other,blksize=4096,default_permissions)

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• Long-term Freelance contract: should it have a salary-day or not?

  - by otto

  I don't like to speak about money. I just like to work. I still believe in a relationship between good work and good compensation. Hence I don't want ask my employer about my compensations, actually they are asking me. So I created a liberal contract with unspecified salary-day -- I did not want to lose my rights to my own projects and I did not pay any attention to the salary-day. Now the firm said that they would have paid me 1 month earlier if I had provided a tax -paper. I provided it before the next payment -day (unspecified). During the next month, the co-employer pretty much blocks my working -- does not allow me to access working repository and the co-employer goes to cruise when we should finalize a project so I cannot do anything. Now the project is not finalized, the co-employer has apparently provided some false statements to the boss about my doings (not getting anything for one month's work and 1 month when the co-employer pretty much wasted just my time) -- I was only allowed to debug the code of my co-employer and not to do anything. I feel that co-employer did not allow me to work by purpose so that they have an excuse not to pay any salary. The co-employer says that I cannot speak to the boss. The boss say that I need to speak directly to co-employer, not to him. I haven't said anything about the situation. I did not get things done because I was not allowed and now I am not even allowed to speak. Boss is the person who pays salaries. But both boss and co-employer have stages in the firm -- I think co-employer and boss are the same person pretty much, they created a theatre so that they get almost 2 month's work for free. Now I have multiple ideas how to avoid this kind of situations in the future: specify the salary day make sure you can speak directly to the manager and the boss, not through middle-hand other?

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• How to cover the widest range of computers when publishing?

  - by DevilWithin

  When you plan a game, or even when you already made a game, and its time to publish, you wonder how much of your audience is covered by the game technology demands. I'm directing this essentialy to casual games, as I constantly see people having old laptops and being unable to replace them. Laptops with integrated cards whose OpenGL version doesn't even support textures larger than 1024x1024. These people may be avid gamers as well, and a reasonable share of the audience to consider giving them the chance to play casual games, once they cannot play any blockbusters. As I've seen happening, a very "noticeable" example is Angry Birds. It's gameplay is merely casual (I think nobody disagrees here) and still, it uses so high resolution textures that at least OpenGL 2.0 or around is needed, which blocks away a lot of people. So, the actual question is: what is a good tradeoff for this issue? Would it be better to just sacrifice the texture resolution for everyone, but have more supported hardware? Would it be better to keep the high quality and just slice the textures into smaller ones, sacrificing the performance a little bit? What else? Any ideas about this topic are welcome for discussion.

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• How do you encode Algebraic Data Types in a C#- or Java-like language?

  - by Jörg W Mittag

  There are some problems which are easily solved by Algebraic Data Types, for example a List type can be very succinctly expressed as: data ConsList a = Empty | ConsCell a (ConsList a) consmap f Empty = Empty consmap f (ConsCell a b) = ConsCell (f a) (consmap f b) l = ConsCell 1 (ConsCell 2 (ConsCell 3 Empty)) consmap (+1) l This particular example is in Haskell, but it would be similar in other languages with native support for Algebraic Data Types. It turns out that there is an obvious mapping to OO-style subtyping: the datatype becomes an abstract base class and every data constructor becomes a concrete subclass. Here's an example in Scala: sealed abstract class ConsList[+T] { def map[U](f: T => U): ConsList[U] } object Empty extends ConsList[Nothing] { override def map[U](f: Nothing => U) = this } final class ConsCell[T](first: T, rest: ConsList[T]) extends ConsList[T] { override def map[U](f: T => U) = new ConsCell(f(first), rest.map(f)) } val l = (new ConsCell(1, new ConsCell(2, new ConsCell(3, Empty))) l.map(1+) The only thing needed beyond naive subclassing is a way to seal classes, i.e. a way to make it impossible to add subclasses to a hierarchy. How would you approach this problem in a language like C# or Java? The two stumbling blocks I found when trying to use Algebraic Data Types in C# were: I couldn't figure out what the bottom type is called in C# (i.e. I couldn't figure out what to put into class Empty : ConsList< ??? >) I couldn't figure out a way to seal ConsList so that no subclasses can be added to the hierarchy What would be the most idiomatic way to implement Algebraic Data Types in C# and/or Java? Or, if it isn't possible, what would be the idiomatic replacement?

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• Designing generic render/graphics component in C++?

  - by s73v3r

  I'm trying to learn more about Component Entity systems. So I decided to write a Tetris clone. I'm using the "style" of component-entity system where the Entity is just a bag of Components, the Components are just data, a Node is a set of Components needed to accomplish something, and a System is a set of methods that operates on a Node. All of my components inherit from a basic IComponent interface. I'm trying to figure out how to design the Render/Graphics/Drawable Components. Originally, I was going to use SFML, and everything was going to be good. However, as this is an experimental system, I got the idea of being able to change out the render library at will. I thought that since the Rendering would be fairly componentized, this should be doable. However, I'm having problems figuring out how I would design a common Interface for the different types of Render Components. Should I be using C++ Template types? It seems that having the RenderComponent somehow return it's own mesh/sprite/whatever to the RenderSystem would be the simplest, but would be difficult to generalize. However, letting the RenderComponent just hold on to data about what it would render would make it hard to re-use this component for different renderable objects (background, falling piece, field of already fallen blocks, etc). I realize this is fairly over-engineered for a regular Tetris clone, but I'm trying to learn about component entity systems and making interchangeable components. It's just that rendering seems to be the hardest to split out for me.

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• One Step-Ahead A-Star

  - by Jonathan Dickinson

  I am attempting to create a server-centric RTS (as opposed to usual parallel synchronised simulation route of most RTS games today) - however I am still leveraging the discreet N-turns-ahead paradigm discussed by one of the AOE developers on Gamasutra. I have [possibly questionably?] decided that the path finding should only ever find the next cell the entity needs to move to, and was wondering if anyone has any clever ideas on how to optimize the algorithm for this specific scenario - or any other ideas on how to keep the pathfinding as lean as possible on the server. I have investigated a few possible algorithms but could only come up with one appropriation: Tiered A-Star - Relatively large T1 tiles, work out (and cache) each cell as you enter it. Other than that: doing the full A-Star pass and caching the entire path, which might use too much memory if a large amount of units are present. I know about the existence of naive progressive pathfinding algorithms (if you hit a block, turn in the direction closer to your target etc.) but they suffer from infinite feedback loops - and very poor pathing even if visited blocks are memorised. Not an option. Many thanks.

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• Security in Robots and Automated Systems

  - by Roger Brinkley

  Alex Dropplinger posted a Freescale blog on Securing Robotics and Automated Systems where she asks the question,“How should we secure robotics and automated systems?”.My first thought on this was duh, make sure your robot is running Java. Java's built-in services for authentication, authorization, encryption/confidentiality, and the like can be leveraged and benefit robotic or autonomous implementations. Leveraging these built-in services and pluggable encryption models of Java makes adding security to an exist bot implementation much easier. But then I thought I should ask an expert on robotics so I fired the question off to Paul Perrone of Perrone Robotics. Paul's build automated vehicles and other forms of embedded devices like auto monitoring of commercial vehicles on highways.He says that most of the works that robots do now are autonomous so it isn't a problem in the short term. But long term projects like collision avoidance technology in automobiles are going to require it.Some of the work he's doing with his Java-based MAX, set of software building blocks containing a wide range of low level and higher level software modules that developers can use to build simple to complex robot and automation applications faster and cheaper, already provide some support for JAUS compliance and because their based on Java, access to standards based security APIs.But, as Paul explained to me, "the bottom line is…it depends on the criticality level of the bot, it's network connectivity, and whether or not a standards compliance is required."

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• Deleting Unused Swaps Partions

  - by Nikita Kononov

  Good evening everyone , I got a little issue with Swap Partitions. Due to some issues after installing Ubuntu first time, I reinstalled it and now I have 3 Swaps. Here is sudo fdisk -l result Disk /dev/sda: 750.2 GB, 750156374016 bytes 255 heads, 63 sectors/track, 91201 cylinders, total 1465149168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0xaa9693fe Device Boot Start End Blocks Id System /dev/sda1 2048 52430847 26214400 1c Hidden W95 FAT32 (LBA) /dev/sda2 * 52430848 540677076 244123114+ 7 HPFS/NTFS/exFAT /dev/sda3 540678142 1465147391 462234625 5 Extended Partition 3 does not start on physical sector boundary. /dev/sda5 1452750848 1465147391 6198272 82 Linux swap / Solaris /dev/sda6 1440352256 1452742655 6195200 82 Linux swap / Solaris /dev/sda7 540678144 1427951615 443636736 83 Linux /dev/sda8 1427953664 1440339967 6193152 82 Linux swap / Solaris So Swaps in /dev/sda5 and /dev/sda6 are no longer in use as far as I understand and thus I was planning to delete them, however faced a problem. What I did is download and burn Gparted Live CD and boot it up, tried to delete those partitions but I have no idea how to add 12GB unallocated memory to the existing OS partition in this case to /dev/sda7 Is there anyway I can delete 2 swaps and extend unallocated memory to /dev/sda7 partion? Thank you in advance!

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• Is there a Source Insight alternative?

  - by hansioux

  I am not a developer, but for my work I trace a lot of codes. It is actually rather difficult reading other people's code, especially for bigger projects. Source Insight is a great application that stores all the symbols in a data base, so you can see a new function being called, click on it and see how the function is written. You can see all the referrer of a object or jump to a caller. You don't need to break the train of thought and think up shell commands just to find these things every time you ran into a new variable/structure/function from some other files. I have it running on WINE, but there are little glitches that sometimes gets in the way. I know people will mention C-scope, I've tried it, but it really isn't the same. So, with so many huge open source projects out there for Ubuntu, are there native tools to help read them efficiently? EDIT: Thanks for the suggestions, but does CODE::BLOCKS or CodeLite provide abilities to see the function that the mouse clicked on without jumping to it, so I can see the caller and callee at the same time?

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• Oracle OpenWorld 2012 is Around the Corner - Discover AutoVue Activities

  - by Pam Petropoulos

  Planning to attend Oracle OpenWorld 2012?  If so, be sure to check out the various AutoVue Enterprise Visualization activities that you can take advantage of while in San Francisco. AutoVue Sessions: CON8381 - Streamline PLM Design-to-Manufacturing Processes with AutoVue Visualization   Click here for full session description. Date: Monday, October 1, 2012 Time: 10:45 a.m. – 11:45 a.m. Location: Intercontinental Hotel - Telegraph Hill Customer Speaker: Siew Yeow Loye, Global Foundries   CON8385 - Optimize Asset Performance and Reliability with AutoVue Visualization   Click here for full session description. Date:Thursday, October 4, 2012 Time: 2:15 p.m. – 3:15 p.m. Location: Palace Hotel – Gold Ballroom AutoVue Demo Pods: Demo   Demo ID: 3122   AutoVue: PLM & Enterprise Visualization Moscone West; Workstation: W-082 Demo ID: 3001  Oracle E-Business Suite Enterprise Asset Management and AutoVue Visualization Solutions Palace Hotel Level 2 HPU-008   Customers are also invited to attend the Oracle OpenWorld 2012 Supply Chain Management Customer Reception on Tuesday, October 2, 2012. This year's event is being held at ROE Lounge, located just 2 blocks from Moscone Center, and offers a casual and upbeat atmosphere so you can mix and mingle with friends and colleagues. This event sold out last year and space is again limited so Register Today. Date: Tuesday, October 2, 2012 Time: 6:00 p.m. – 8:00 p.m. Location: ROE Lounge, 651 Howard Street, San Francisco   For additional information regarding AutoVue sessions, demos, and activities be sure to review the AutoVue FocusOn Document.   Join us at Oracle OpenWorld, September 30–October 4, 2012 and discover new products, solutions, and practices to make you even more successful in your job and in your industry.

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• Cannot access the filesystems using LiveCD (LVM2,EXT2)

  - by ftkg

  I have to restore the /etc/passwd file I accidentally renamed in my Ubuntu Server, so I booted the machine using a LiveCD. Problem is, the system filesystem does not appear in Nautilus, under 'Devices'. Am I missing anything? ubuntu@ubuntu:~$ sudo fdisk -l Disk /dev/sda: 320.1 GB, 320072933376 bytes 255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000956dc Device Boot Start End Blocks Id System /dev/sda1 * 2048 499711 248832 83 Linux /dev/sda2 501758 625141759 312320001 5 Extended /dev/sda5 501760 625141759 312320000 8e Linux LVM ubuntu@ubuntu:~$ mount /cow on / type overlayfs (rw) proc on /proc type proc (rw,noexec,nosuid,nodev) sysfs on /sys type sysfs (rw,noexec,nosuid,nodev) udev on /dev type devtmpfs (rw,mode=0755) devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620) tmpfs on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755) /dev/sr0 on /cdrom type iso9660 (ro,noatime) /dev/loop0 on /rofs type squashfs (ro,noatime) none on /sys/fs/fuse/connections type fusectl (rw) none on /sys/kernel/debug type debugfs (rw) none on /sys/kernel/security type securityfs (rw) tmpfs on /tmp type tmpfs (rw,nosuid,nodev) none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880) none on /run/shm type tmpfs (rw,nosuid,nodev) gvfs-fuse-daemon on /home/ubuntu/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=ubuntu) ubuntu@ubuntu:~$ sudo blkid /dev/loop0: TYPE="squashfs" /dev/sda1: UUID="aad69790-198d-45bc-9ccd-e4cba7456914" TYPE="ext2" /dev/sda5: UUID="wbIDX7-RILL-VtFT-gX15-N1GJ-Yyfg-V8Oe5m" TYPE="LVM2_member" /dev/sr0: LABEL="Ubuntu 12.04 LTS i386" TYPE="iso9660" ubuntu@ubuntu:~$ cat /etc/fstab overlayfs / overlayfs rw 0 0 tmpfs /tmp tmpfs nosuid,nodev 0 0

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• It could be worse....

  - by Darryl Gove

  As "guest" pointed out, in my file I/O test I didn't open the file with O_SYNC, so in fact the time was spent in OS code rather than in disk I/O. It's a straightforward change to add O_SYNC to the open() call, but it's also useful to reduce the iteration count - since the cost per write is much higher: ... #define SIZE 1024 void test_write() { starttime(); int file = open("./test.dat",O_WRONLY|O_CREAT|O_SYNC,S_IWGRP|S_IWOTH|S_IWUSR); ... Running this gave the following results: Time per iteration 0.000065606310 MB/s Time per iteration 2.709711563906 MB/s Time per iteration 0.178590114758 MB/s Yup, disk I/O is way slower than the original I/O calls. However, it's not a very fair comparison since disks get written in large blocks of data and we're deliberately sending a single byte. A fairer result would be to look at the I/O operations per second; which is about 65 - pretty much what I'd expect for this system. It's also interesting to examine at the profiles for the two cases. When the write() was trapping into the OS the profile indicated that all the time was being spent in system. When the data was being written to disk, the time got attributed to sleep. This gives us an indication how to interpret profiles from apps doing I/O. It's the sleep time that indicates disk activity.

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• How to Set Up a MongoDB NoSQL Cluster Using Oracle Solaris Zones

  - by Orgad Kimchi

  This article starts with a brief overview of MongoDB and follows with an example of setting up a MongoDB three nodes cluster using Oracle Solaris Zones. The following are benefits of using Oracle Solaris for a MongoDB cluster: • You can add new MongoDB hosts to the cluster in minutes instead of hours using the zone cloning feature. Using Oracle Solaris Zones, you can easily scale out your MongoDB cluster. • In case there is a user error or software error, the Service Management Facility ensures the high availability of each cluster member and ensures that MongoDB replication failover will occur only as a last resort. • You can discover performance issues in minutes versus days by using DTrace, which provides increased operating system observability. DTrace provides a holistic performance overview of the operating system and allows deep performance analysis through cooperation with the built-in MongoDB tools. • ZFS built-in compression provides optimized disk I/O utilization for better I/O performance. In the example presented in this article, all the MongoDB cluster building blocks will be installed using the Oracle Solaris Zones, Service Management Facility, ZFS, and network virtualization technologies. Figure 1 shows the architecture:

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• Grub does not show a Windows 8 option after dual boot

  - by skytreader

  So, I've successfully dual-booted my Windows 8 machine with Ubuntu 12.04 . However, I still don't have a convenient method of choosing what OS to load at boot time. After installing Ubuntu, my computer still loads Windows 8 directly. I then added grubx64.efi to the white list of my boot loader. But after that, my machine loads Ubuntu directly without even a shadow of GRUB showing up! I used boot-repair and I got this paste.ubuntu URL: paste.ubuntu.com/1326074. After running boot-repair (and re-white listing the grubx64.efi file), GRUB now shows up but without any Windows 8 option! Lastly, I ran sudo fdisk -l and it gave me this: WARNING: GPT (GUID Partition Table) detected on '/dev/sda'! The util fdisk doesn't support GPT. Use GNU Parted. Disk /dev/sda: 750.2 GB, 750156374016 bytes 255 heads, 63 sectors/track, 91201 cylinders, total 1465149168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x6396389f Device Boot Start End Blocks Id System /dev/sda1 1 1465149167 732574583+ ee GPT Partition 1 does not start on physical sector boundary. I'm guessing my problem has something to do with the warning from fdisk above but I don't know what to do with it. How do I proceed now?

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• Why do we have to use break in switch

  - by trejder

  Who decided, and basing on what concepts, that switch construction (in many languages) has to be, like it is? Why do we have to use break in each statement? Why do we have to write something like this: switch(a) { case 1: result = 'one'; break; case 2: result = 'two'; break; default: result = 'not determined'; break; } I've noticed this construction in PHP and JS, but there are probably many other languages that uses it. If switch is an alternative of if, why we can't use the same construction for switch, as for if? I.e.: switch(a) { case 1: { result = 'one'; } case 2: { result = 'two'; } default: { result = 'not determined'; } } It is said, that break prevents execution of a blocks following current one. But, does someone really run into situation, where there was any need for execution of current block and following ones? I didn't. For me, break is always there. In every block. In every code.

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• How to access a fake raid?

  - by maaartinus

  I have a fake raid, which I wanted to access using mdadm /dev/md0 -A -c 128 -l stripe --verbose /dev/sda /dev/sdc which should be right, as far as I understand the man page. But I get the message mdadm: option -l not valid in assemble mode leaving the offending option out leads to mdadm: failed to create /dev/md0 and (despite verbose) no more information. I'm assuming that -A requires some mdadm-specific header which is obviously missing. I probably need to use "build" instead of assemble, but from the description I'm really unsure whether this is a non-destructive operation. Is it? What should I exactly do? UPDATE I see I haven't made clear, that the array already exists as a fake-raid (I can't give the details about my mainboard now). It looks like doing nothing except for interleaving blocks, so I hoped it could be easily done using mdadm, too. Maybe I'm completely wrong, but all the info I've found was concerned with booting from fake-raid, what I don't really need. I'd be happy with a read access for now.

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• What do you wish language designers paid attention to?

  - by Berin Loritsch

  The purpose of this question is not to assemble a laundry list of programming language features that you can't live without, or wish was in your main language of choice. The purpose of this question is to bring to light corners of languge design most language designers might not think about. So, instead of thinking about language feature X, think a little more philisophically. One of my biases, and perhaps it might be controversial, is that the softer side of engineering--the whys and what fors--are many times more important than the more concrete side. For example, Ruby was designed with a stated goal of improving developer happiness. While your opinions may be mixed on whether it delivered or not, the fact that was a goal means that some of the choices in language design were influenced by that philosophy. Please do not post: Syntax flame wars (I could care less whether you use whitespace [Python], keywords [Ruby], or curly braces [Java, C/C++, et. al.] to denote program blocks). That's just an implementation detail. "Any language that doesn't have feature X doesn't deserve to exist" type comments. There is at least one reason for all programming languages to exist--good or bad. Please do post: Philisophical ideas that language designers seem to miss. Technical concepts that seem to be poorly implemented more often than not. Please do provide an example of the pain it causes and if you have any ideas of how you would prefer it to function. Things you wish were in the platform's common library but seldom are. One the same token, things that usually are in a common library that you wish were not. Conceptual features such as built in test/assertion/contract/error handling support that you wish all programming languages would implement properly--and define properly. My hope is that this will be a fun and stimulating topic.

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• How to keep background requests in sequence

  - by Jason Lewis

  I'm faced with implementing interfaces for some rather archaic systems, for handling online deposits to stored value accounts (think campus card accounts for students). Here's my dilemma: stage 1 of the process involves passing the user off to a thrid-party site for the credit card transaction, like old-school PayPal. Step two involves using a proprietary protocol for communicating with a legacy system for conducting the actual deposit. Step two requires that each transaction have a unique sequence number, and that the requests' seqnums are in order. Since we're logging each transaction in Postgres, my first thought was to take a number from a sequence in the DB, guaranteeing uniqueness. But since we're dealing with web requests that might come in near-simultaneously, and since latency with the return from the off-ste payment processor is beyond our control, there's always the chance for a race condition in the order of requests passed back to the proprietary system, and if the seqnums are out of order, the request fails silently (brilliant, right?). I thought about enqueuing the requests in Redis and using Resque workers to process them (single worker, single process, so they are processed in order), but we need to be able to give the user feedback as to whether the transaction was processed successfully, so this seems less feasible to me. I've tried to make this application handle concurrency well (as much as possible for a Ruby on Rails app), but now we're in a situation where we have to interact with a system that is designed to be single process, single threaded, and sequential. If it at least gave an "out of order" error, I could just increment (or take the next value off the sequence), but it's designed to fail silently in the event of ANY error. We are handling timeouts in a way that blocks on I/O, but since the application uses multiple workers (Unicorn), that's no guarantee. Any ideas/suggestions would be appreciated.

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