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• Should I convert overly-long UTF-8 strings to their shortest normal form?

  - by Grant McLean

  I've just been reworking my Encoding::FixLatin Perl module to handle overly-long UTF-8 byte sequences and convert them to the shortest normal form. My question is quite simply "is this a bad idea"? A number of sources (including this RFC) suggest that any over-long UTF-8 should be treated as an error and rejected. They caution against "naive implementations" and leave me with the impression that these things are inherently unsafe. Since the whole purpose of my module is to clean up messy data files with mixed encodings and convert them to nice clean utf8, this seems like just one more thing I can clean up so the application layer doesn't have to deal with it. My code does not concern itself with any semantic meaning the resulting characters might have, it simply converts them into a normalised form. Am I missing something. Is there a hidden danger I haven't considered?

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• concurrent doubly-linked list (1 writer, n-readers)

  - by Arne

  Hi guys, I am back in the field of programming for my Diploma-thesis now and stumbled over the following issue: I need to implement a thread-safe doubly-linked list for one thread writing the list at any position (delete, insert, mutate node data) and one to many threads traversing and reading the list. I am well aware that mutexes can be used to serialize access to the list, still I presume that a naive lock around any write operation will be less than optimal. I am wondering whether there are better variants. (I am well aware that 'optimal' has not much of a practical meaning as long as no exact measure/profiling are available but this is an academic thesis after all..) I am very gratefull for code-samples as well as references to academic granted these have at least a tiny bit of practical relevance. Thanks at lot

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• I want to make my own Malloc

  - by Unknown

  I want to make my own malloc/free so I can make a precise copying allocator. Any gurus have any tips and suggestions? I have a few questions for now: Should I just malloc large chunks of memory, and then distribute from that so I don't have to call the system calls? How are copying collectors usually done? I would imagine that this part is a bit complicated to do efficiently. My naive implementation would just malloc a block the size of the remaining objects which would require 2x the space.

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• How do I build (get/download) time.h library?

  - by coffeenet

  I am trying to build a project on Linux via Makefile. I keep getting cannot find <sys/time.h> error. I asked around, and I was told that my project doesn't have access to library folders. Therefore, I am trying to solve this problem by using the time library locally inside my project's folder. I am very new to Linux. So, please forgive my question if it sounds naive. I found this, but I don't know what files I need, and how to build the library. http://sourceware.org/git/?p=glibc.git;a=tree;f=time;h=c950c5d4dd90541e8f3c7e1649fcde4aead989bb;hb=master Where can I find the time.h library/package? How do I build the library?

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• MySQL: How to separate a name field in one table into firstname / lastname in two separate tables?

  - by Eileen

  I have a drupal database where the node table is full of profiles. The field node.title is "Firstname Lastname". I want to separate the names so that node.title = "Firstname", and over in another table entirely, content_type_profile.field_lastname_value = "Lastname". The entries in the two tables can be joined on the field nid. I'd love to run a SQL command to do this, and I am fine with taking the naive approach that the first word is the first name, and everything else in the field is last name -- it will mean a few manual corrections down the line, but that's much better than doing it all by hand in the first place. (I read this question and surely the answer lies in there but I am not that SQL-savvy and am not sure how to make it work for my database.) Thanks!

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• Any good idioms for error handling in straight C programs?

  - by Will Hartung

  Getting back in to some C work. Many of my functions look like this: int err = do_something(arg1, arg2, arg3, &result); With the intent the result gets populated by the function, and the return value is the status of the call. The darkside is you get something naive like this: int err = func1(...); if (!err) { err = func2(...); if (!err) { err = func3(...); } } return err; I could macro it I suppose: #define ERR(x) if (!err) { err = (x) } int err = 0; ERR(func1(...)); ERR(func2(...)); ERR(func3(...)); return err; But that only works if I'm chaining function calls, vs doing other work. Obviously Java, C#, C++ have exceptions that work very well for these kinds of things. I'm just curious what other folks do and how other folks do error handling in their C programs nowadays.

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• Concatenation awk outputs

  - by Rookie_22

  I'm using regex to parse NMAP output. I want the ip addresses which are up with the corresponding ports open. Now I've a very naive method of doing that: awk '/^Scanning .....................ports]/ {print substr ($2,1,15);}' results.txt awk '/^[0-9][0-9]/ {print substr($1,1,4);}' results.txt | awk -f awkcode.awk where awkcode.awk contains the code to extract numbers out of the substring. The first line prints all the ips that are up and 2nd gives me the ports. My problem is that I want them mapped to each other. Is there any way to do that? Even sed script would do.

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• Standard way of allowing general XML data

  - by Greg Jackson

  I'm writing a data gathering and reporting application that takes XML files as input, which will then be read, processed, and stored in a strongly-typed database. For example, an XML file for a "Job" might look like this: <Data type="Job"> <ID>12345</ID> <JobName>MyJob</JobName> <StartDate>04/07/2012 10:45:00 AM</StartDate> <Files> <File name="a.jpeg" path="images\" /> <File name="b.mp3" path="music\mp3\" /> </Files> </Data> I'd like to use a schema to have a standard format for these input files (depending on what type of data is being used, for example "Job", "User", "View"), but I'd also like to not fail validation if there is extra data provided. For example, perhaps a Job has additional properties such as "IsAutomated", "Requester", "EndDate", and so on. I don't particularly care about these extra properties. If they are included in the XML, I'll simply ignore them when I'm processing the XML file, and I'd like validation to do the same, without having to include in the schema every single possible property that a customer might provide me with. Is there a standard way of providing such a schema, or of allowing such a general XML file that can still be validated without resorting to something as naïve (and potentially difficult to deal with) as the below? <Data type="Job"> <Data name="ID">12345</Data> . . . <Data name="Files"> <Data name="File"> <Data name="Filename">a.jpeg</Data> <Data name="path">images</Data> . . . </Data> </Data>

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• Economic modelling - Resources for valuing goods

  - by Rushyo

  tl;dr: What economic/computer science books would you suggest for learning about economic valuation of goods and simulations thereof? I'm looking to create an economic model for a game based on goods created procedurally. Every natural resource and produced good would be procedurally generated, with certain goods being assigned certain uses. Fakesium might be used for the production of Weapon A and produced from Fakesium factories which use Dilithium and Widgets as reagents, where Widgets are also the product of Foo and Bar The problem is not creating the resources and their various production utlities - but getting the game's AI empires and merchants to correctly value the goods according to their scarcity, utility and production costs. I need to create a simulation of goods which allows the various game factions to assign a common value denominator (credits) to each resource, depending on how much its worth to that empire. I see the simulation being something like: "I have a high requirement for Weapon A. Since I don't have much of Fakesium, which is needed for Weapon A - I must have a high demand for Fakesium. If I can acquire Fakesium, devalue it. If not, increase its value - and also increase demand for Dilithium and Widgets too." This is very naive - because it may be much much cheaper for the empire to simply purchase Dilithium and Widgets directly rather than purchasing Fakesium, for example. Another example is two resources might allow the creation of Weapon A (Fakesium and Lieron), so we'd need to consider that. I've been scratching my head over the problem and it keeps growing. By the time the player joins the world, I'd expect enough iterations of this process to have occurred that prices would have largely normalised - and would then only trigger rarely to compensate for major changes (eg. if the player blows up the world's only Foo mine!) Could anyone suggest resources (books, largely) which outline this style of modelling, preferably in the context of simulations? Since this problem would never occur outside fantasy worlds, I figured this is probably the most likely place to find people who have encountered similar problems and I'm sure there's people who know of good places for Games Developers to start looking at less specific economic theory too. Additionally, does anyone know of any developers with blogs whose games or research applications perform similar modelling?

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• Finding the lowest average Hamming distance when the order of the strings matter

  - by user1049697

  I have a sequence of binary strings that I want to find a match for among a set of longer sequences of binary strings. A match means that the compared sequence gives the lowest average Hamming distance when all elements in the shorter sequence have been matched against a sequence in one of the longer sets. Let me try to explain with an example. I have a set of video frames that have been hashed using a perceptual hashing algorithm so that the video frames that look the same has roughly the same hash. I want to match a short video clip against a set of longer videos, to see if the clip is contained in one of these. This means that I need to find out where the sequence of the hashed frames in the short video has the lowest average Hamming distance when compared with the long videos. The short video is the sub strings Sub1, Sub2 and Sub3, and I want to match them against the hashes of the long videos in Src. The clue here is that the strings need to match in the specific order that they are given in, e.g. that Sub1 always has to match the element before Sub2, and Sub2 always has to match the element before Sub3. In this example it would map thusly: Sub1-Src3, Sub2-Src4 and Sub3-Src5. So the question is this: is there an algorithm for finding the lowest average Hamming distance when the order of the elements compared matter? The naïve approach to compare the substring sequence to every source string won't cut it of course, so I need something that preferably can match a (much) shorter sub string to a set of million of elements. I have looked at MVP-trees, BK-trees and similar, but everything seems to only take into account one binary string and not a sequence of them. Sub1: 100111011111011101 Sub2: 110111000010010100 Sub3: 111111010110101101 Src1: 001011010001010110 Src2: 010111101000111001 Src3: 101111001110011101 Src4: 010111100011010101 Src5: 001111010110111101 Src6: 101011111111010101 I have added a calculation of the examples below. (The Hamming distances aren't correct, but it doesn't matter) **Run 1.** dist(Sub1, Src1) = 8 dist(Sub2, Src2) = 10 dist(Sub3, Src3) = 12 average = 10 **Run 2.** dist(Sub1, Src2) = 10 dist(Sub2, Src3) = 12 dist(Sub3, Src4) = 10 average = 11 **Run 3.** dist(Sub1, Src3) = 7 dist(Sub2, Src4) = 6 dist(Sub3, Src5) = 10 average = 8 **Run 4.** dist(Sub1, Src3) = 10 dist(Sub2, Src4) = 4 dist(Sub3, Src5) = 2 average = 5 So the winner here is sequence 4 with an average distance of 5.

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• What type of interview questions should you ask for "legacy" programmers?

  - by Marcus Swope

  We have recently been receiving lots of applicants for our open developer positions from people who I like to refer to as "legacy" programmers. I don't like the term "old" because it seems a little prejudiced (especially to HR!) and it doesn't accurately reflect what I mean. We are a company that does primarily .NET development using TDD in an Agile environment, we use Git as a source control system, we make heavy use of OSS tools and projects and we contribute to them as well, we have a strong bias towards adhering to strong Object-Oriented principles, SOLID, etc, etc, etc... Now, the normal list of questions that we ask doesn't really seem to apply to applicants that are fresh out of school, nor does it seem to apply to these "legacy" programmers. Here is how I (loosely) define a "legacy" programmer. Spent a significant amount of their career working almost exclusively with Assembly/Machine Languages. Primary accomplishments include work done with TANDEM systems. Has extensive experience with technologies like FoxPro and ColdFusion It's not that we somehow think that what we do is "better" than what they do, on the contrary, we respect these types of applicants and we are scared that we may be missing a good candidate. It is just very difficult to get a good read on someone who is essentially speaking a different language than you. To someone like this, it seems a little strange to ask a question like: What is the difference between an abstract class and an interface? Because, I would think that they would almost never know the answer or even what I'm talking about. However, I don't want to eliminate someone who could be a very good candidate in their own right and could be able to eventually learn the stuff that we do. But, I also don't want to just ask a bunch of behavioral questions, because I want to know about their technical background as well. Am I being too naive? Should "legacy" programmers like this already know about things like TDD, source control strategies, and best practices for object-oriented programming? If not, what questions should we ask to get a good representation about whether or not they are still able to learn them and be able to keep up in our fast-paced environment? EDIT: I'm not concerned with whether or not applicants that meet these criteria are in general capable or incapable, as I have already stated that I believe that they can be 100% capable. I am more interested in figuring out how to evaluate their talents, as I am having a hard time figuring out how to determine if they are an A+ "legacy" programmer or if they are a D- "legacy" programmer. I've worked with both.

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• ray collision with rectangle and floating point accuracy

  - by phq

  I'm trying to solve a problem with a ray bouncing on a box. Actually it is a sphere but for simplicity the box dimensions are expanded by the sphere radius when doing the collision test making the sphere a single ray. It is done by projecting the ray onto all faces of the box and pick the one that is closest. However because I'm using floating point variables I fear that the projected point onto the surface might be interpreted as being below in the next iteration, also I will later allow the sphere to move which might make that scenario more likely. Also the bounce coefficient might be as low as zero, making the sphere continue along the surface. So my naive solution is to project not only forwards but backwards to catch those cases. That is where I got into problems shown in the figure: In the first iteration the first black arrow is calculated and we end up at a point on the surface of the box. In the second iteration the "back projection" hits the other surface making the second black arrow bounce on the wrong surface. If there are several boxes close to each other this has further consequences making the sphere fall through them all. So my main question is how to handle possible floating point accuracy when placing the sphere on the box surface so it does not fall through. In writing this question I got the idea to have a threshold to only accept back projections a certain amount much smaller than the box but larger than the possible accuracy limitation, this would only cause the "false" back projection when the sphere hit the box on an edge which would appear naturally. To clarify my original approach, the arrows shown in the image is not only the path the sphere travels but is also representing a single time step in the simulation. In reality the time step is much smaller about 0.05 of the box size. The path traveled is projected onto possible sides to avoid traveling past a thinner object at higher speeds. In normal situations the floating point accuracy is not an issue but there are two situations where I have the concern. When the new position at the end of the time step is located very close to the surface, very unlikely though. When using a bounce factor of 0, here it happens every time the sphere hit a box. To add some loss of accuracy, the motivation for my concern, is that the sphere and box are in different coordinate systems and thus the sphere location is transformed for every test. This last one is why I'm not willing to stand on luck that one floating point value lying on top of the box always will be interpreted the same. I did not know voronoi regions by name, but looking at it I'm not sure how it would be used in a projection scenario that I'm using here.

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• MS in Computer Science after BE in electronics

  - by Abhinav

  I am doing my 3rd year Bachelors in Electronics and Electrical Communication but from the first year I have been interested in Computer Science. But at that time it was just my hobby. But in second year when I joined robotics my love for computer science rose. I with my team came in top three in 2 National Competition (Technical fests of different IITs) where we used Image Processing, Hardware interfacing etc. But then I realised that Computer Science is not just about coding. I took many lectures from online free schools like Udacity, Coursera in subjects related to Artificial Intelligence, Building a Search Engine, Design and Analysis of Algorithm, Programming a Robotic Car, Programming Languages, Machine Learning, Software Engineering as a Service, WebApps Engineering, Compilers, Applied Crypotography etc. I also did some courses in Core and Advanced Java in my second year from training institute. I will also be taking course in Statistics, Databases, Discrete Mathematics from 25th June. Now I realized how vast is the field of Computer Science and how efficient you become on deciding algorithms and classifying problems into different subfields which have been thoroughly researched so you don't always do brute force thing or naive programming. Now this field has become kind of passion for me. Adding to the fact I am also doing my 6 months internship in software field in Texas Instruments where I am working on Automation and Algorithms. I also have some 5-6 good college level projects in Softwares and Robotics. I also like Electronics but only some fields like Operating System(this subject was there in Electronics also), Micro Processor, Digital, Computer Architecture, DSPs etc. I really want to pursue MS in some field of Computer Science. I am giving GRE in October/November. Till now I have good CG of around 9.4/10 and my 1 year in college is still left. Do I have any chance that some good University in US will consider me for MS in field related to computer science or Robotics. Also Can you suggest somethings that I can do during this 1 year to increase my chances for MS or should I apply for EECS(Electrical Engineering and Computer Science) and then I can shift more towards Computer Science as my major option. My main aim is to do Phd after Ms in CS if I am able to do that somehow. I know that I have to put much extra effort to understand things in MS than CS undergraduates but I will do that with my full dedication, also when I communicate with my college CS students or during my internship period I didn't feel that I am missing very much stuff that they know and was very comfortable during my internship with software employees.

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• How to export 3D models that consist of several parts (eg. turret on a tank)?

  - by Will

  What are the standard alternatives for the mechanics of attaching turrets and such to 3D models for use in-game? I don't mean the logic, but rather the graphics aspects. My naive approach is to extend the MD2-like format that I'm using (blender-exported using a script) to include a new set of properties for a mesh that: is anchored in another 'parent' mesh. The anchor is a point and normal in the parent mesh and a point and normal in the child mesh; these will always be colinear, giving the child rotation but not translation relative to the parent point. has a normal that is aligned with a 'target'. Classically this target is the enemy that is being engaged, but it might be some other vector e.g. 'the wind' (for sails and flags (and smoke, which is a particle system but the same principle applies)) or 'upwards' (e.g. so bodies of riders bend properly when riding a horse up an incline etc). that the anchor and target alignments have maximum and minimum and a speed coeff. there is game logic for multiple turrets and on a model and deciding which engages which enemy. 'primary' and 'secondary' or 'target0' ... 'targetN' or some such annotation will be there. So to illustrate, a classic tank would be made from three meshes; a main body mesh, a turret mesh that is anchored to the top of the main body so it can spin only horizontally and a barrel mesh that is anchored to the front of the turret and can only move vertically within some bounds. And there might be a forth flag mesh on top of the turret that is aligned with 'wind' where wind is a function the engine solves that merges environment's wind angle with angle the vehicle is travelling in an velocity, or something fancy. This gives each mesh one degree of freedom relative to its parent. Things with multiple degrees of freedom can be modelled by zero-vertex connecting meshes perhaps? This is where I think the approach I outlined begins to feel inelegant, yet perhaps its still a workable system? This is why I want to know how it is done in professional games ;) Are there better approaches? Are there formats that already include this information? Is this routine?

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• Using HBase or Cassandra for a token server

  - by crippy

  I've been trying to figure out how to use HBase/Cassandra for a token system we're re-implementing. I can probably squeeze quite a lot more from MySQL, but it just seems it has come to clinging on to the wrong tool for the task just because we know it well. Eventually will hit a wall (like happened to us in other areas). Naturally I started looking into possible NoSQL solutions. The prominent ones (at least in terms of buzz) are HBase and Cassandra. The story is more or less like this: A user can send a gift other users. Each gift has a list of recipients or is public in which case limited by number or expiration date For each gift sent we generate some token that uniquely identifies that gift. For each gift we track the list of potential recipients and their current status relating to that gift (accepted, declinded etc). A user can request to see all his currently pending gifts A can request a list of users he has sent a gift to today (used to limit number of gifts sent) Required the ability to "dump" or "ignore" expired gifts (x day old gifts are considered expired) There are some other requirements but I believe the above covers the essentials. How would I go and model that using HBase or Cassandra? Well, the wall was performance. A few 10s of millions of records per day over 2 tables kept for 2 weeks (wish I could have kept it for more but there was no way). The response times kept getting slower and slower until eventually we had to start cutting down number of days we kept data. Caching helps here but it's not an ideal solution since a big part of the ops are updates. Also, as I hinted in my original post. We use MySQL extensively. We know exactly what it can and can't do both in naive implementations followed by native partitioning and finally by horizontally sharding our dataset on the application level to reside on multiple DB nodes. It can be done, but that's not really what I'm trying to get from this. I asked a very specific question about designing a solution using a NoSQL solution since it's very hard to find examples for designs out there. Brainlag, not trying to come off as rude. I actually appreciate it a lot that you are the only one who even bothered to respond. but I see it over and over again. People ask questions and others assume they have no idea what they're talking about and give an irrelevant answer. Ignore RDBMS please. The question is about nosql.

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• What economic books would you suggest for learning about economic valuation of goods and simulations thereof?

  - by Rushyo

  I'm looking to create an economic model for a game based on goods created procedurally. Every natural resource and produced good would be procedurally generated, with certain goods being assigned certain uses. Fakesium might be used for the production of Weapon A and produced from Fakesium factories which use Dilithium and Widgets as reagents, where Widgets are also the product of Foo and Bar The problem is not creating the resources and their various production utlities - but getting the game's AI empires and merchants to (Addendum: somewhat) correctly value the goods according to their scarcity, utility and production costs. I need to create a simulation of goods which allows the various game factions to assign a common value denominator (credits) to each resource, depending on how much its worth to that empire. I see the simulation being something like: "I have a high requirement for Weapon A. Since I don't have much of Fakesium, which is needed for Weapon A - I must have a high demand for Fakesium. If I can acquire Fakesium, devalue it. If not, increase its value - and also increase demand for Dilithium and Widgets too." This is very naive - because it may be much much cheaper for the empire to simply purchase Dilithium and Widgets directly rather than purchasing Fakesium, for example. Another example is two resources might allow the creation of Weapon A (Fakesium and Lieron), so we'd need to consider that. I've been scratching my head over the problem and it keeps growing. By the time the player joins the world, I'd expect enough iterations of this process to have occurred that prices would have largely normalised - and would then only trigger rarely to compensate for major changes (eg. if the player blows up the world's only Foo mine!) Could anyone suggest resources (books, largely) which outline this style of modelling, preferably in the context of simulations? Since this problem would never occur outside fantasy worlds, I figured this is probably the most likely place to find people who have encountered similar problems and I'm sure there's people who know of good places for Games Developers to start looking at less specific economic theory too. Additionally, does anyone know of any developers with blogs whose games or research applications perform similar modelling? EDIT: I think I should underline that I'm not looking for optimal solutions. I'm looking to make the actors impulsive - making rudimentary decisions based on fuzzy inputs about what they care about or don't. I'm aiming to understand the problem area better not derive answers. All the textbooks I've found seem to be about real-world economics or how to solve complex theoretical problems, neither of which are terribly relevant to the actor's decision making.

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• How quickly to leave contract-to-hire gig where you don't want to be hired? [closed]

  - by nono

  So you move to a big new city with tons of software development opportunity, having taken a six month contract-to-hire job. The company treats you really well and has a good team and work environment. However, the recruiter assured you when offering the gig that it would be a good position in which you can advance your learning from more senior developers (a primary concern of yours) but you're starting to realize that a job recruiter isn't going to understand that the team in question isn't very up on modern software practices (you start to sympathize with this guy and read his post over and over again: http://stackoverflow.com/questions/1586166/career-killer-nhibernate-oop-design-patterns-domain-driven-design-test-driv) and that much of the company's software is very old and very very poorly architected, and the company (like so many others) seems to be only concerned with continually extending the software without investing in any structural improvements. You're absolutely dismayed at how long it takes your team (including) to fulfill simple feature requests (maybe 500-1000% longer than with better designed software that you've worked on in the past), but no one else there seems to think anything of it. You find that the work and the company's business are intensely uninteresting to you, but due to the convoluted design of their various software systems, fulfilling the work will require as much mental engagement as any other development position. You feel a bit naive about not having asked the right questions during your interview process, and for not having anticipated that your team at your former podunk company might possibly be light-years ahead of any team in Big Shiny City, but you know you don't want to stay at this place, and (were it not for your personal, after-hours studying and personal programming efforts) fear that you might actually give a worse interview after completing your 6 months than you did when you started at the place. You read about how hard of a time local companies are having filling their positions with qualified software development candidates. You read all sorts of fabulous sounding job postings online and feel like you're really missing out. In spite of the comfortable environment you feel like you would willingly accept a somewhat more demanding or aggressive lifestyle to feel like you are learning and progressing and producing something meaningful. My questions are: how quickly do you leave and how do you go about giving a polite reason for departing? The contract is written to allow them to "can" you and to allow you to leave with 2 weeks notice. Do you ethically owe the 6 months? Upon taking the position, the company told you they were not interested in candidates who were intending to only stay for 6 months and then leave (you were not intending to bail after 6 months, at that time), so perhaps they might be fine if you split now, knowing that you don't want to stick around for the full time hire?

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• How to get lookahead symbol when constructing LR(1) NFA for parser?

  - by greenoldman

  I am reading an explanation (awesome "Parsing Techniques" by D.Grune and C.J.H.Jacobs; p.292 in the 2nd edition) about how to construct an LR(1) parser, and I am at the stage of building the initial NFA. What I don't understand is how to get/compute a lookahead symbol. Here is the example from the book, the grammar: S -> E E -> E - T E -> T T -> ( E ) T -> n n is terminal. The "weird" transitions for me are is the sequence: 1) S -> . E eof 2) E -> . E - T eof 3) E -> . E - T - 4) E -> E . - T - 5) E -> E - . T - (Note: In the above table, the state numbers are in front and the lookahead symbol is at the end.) What puzzles me is that transition from (4) to (5) means reading - token, right? So how is it that - is still a lookahead symbol and even more important why is it that eof is no longer a lookahead symbol? After all in an input such as n - n eof there is only one - symbol. My naive thinking tells me (5) should be written as: 5) E -> E - . T - eof And another thing -- n is terminal. Why it is not used at all as a lookahead symbol? I mean -- we expect to see - or (, it is ok, but lack of n means we are sure it won't appear in input? Update: after more reading I am only more confused ;-) I.e. what is really a lookahead? Because I see such state as (p.292, 2nd column, 2nd row): E -> E . - T eof Lookahead says eof but the incoming input says -. Isn't it a contradiction? And it is not only in this book.

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• Ideal Bacula appliance?

  - by Ricket

  I'm an intern at a small company and we (the IT department of two) manage <100 client computers and a handful of servers. Currently we're using a company's appliance to handle backup; it does a small backup every night and a full backup every weekend, and a guy comes on Wednesday to take an offsite backup drive (and gives back last week's drive to swap with it). Lately this system, mainly the appliance, has been having problems, so we are looking for an alternative. I'm researching other companies but also looking into what we might expect from trying to do this ourselves. There will undoubtedly be a large learning curve, but hey, that's what serverfault is for, right? :) So anyway I was looking at Bacula. Feature list sounds great, documentation is plentiful, but it's only software. So my question is, what is the ideal backup server to run the Bacula server software on? And not only the server but other related appliances. Our current backup appliance uses only hard drives, not tape drives. It has several plugged into it at one time, in hotswap bays on the front of the machine. I couldn't help but notice though, it's hardly more than Windows XP with hard drive bays, a PCI eSATA card (which connects to another appliance extension piece with 2 more bays), and their software. Since the company will take back their appliance if/when we cancel with them, where can I go to configure a server with these kinds of things? Maybe I'm being naive, I'm sure Dell (and any other computer company) sells them in the small business section of their website, but I wanted to make sure that there's not some other more recommended place that other companies are getting their hardware from, and that I don't need anything special for Bacula.

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• Recovery of Windows DFS partion with shadow copy versioned files when overwritten with older modifie

  - by patjbs

  I've noticed the following "bug" on a DFS volume with shadow copies: Pretend you have the following folders/files under shadow copy versioning, going back two weeks. MyDirectory+ MyFile - Modified Date 8/1/2009 The current date: 8/30/2009 You have another version of MyFile stored elsewhere, with a modified date of 7/1/2009. Copy your other version of MyFile into MyDirectory, overwriting the newest version. I expected that you could roll back to the version that was there when it last imaged, say on the prior day and recover your 8/1 version. Not the case. Now, when you go to look at previous versions for the past two weeks, the versioning of that file will be entirely lost, and you'll be stuck with your older 7/1 version. Suckage. Questions: (1) Is this intentional, and if so, what's the rationale? I assume that DFS picks up on the versioning based on the current file, and that's what's wiping out prior versions, but it seems like a fairly stupid/naive way of handling versioning to me. (2) Is there a way to backtrack out of this, without resorting to restoration from other backup mediums? Thanks!

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• mdadm+zfs vs mdadm+lvm

  - by Alex

  This may be a naive question since I'm new to this and I cannot find any results about mdadm+zfs, but after some testing it seems it might work: The use case is a server with RAID6 for some data that is backed-up somewhat infrequently. I think I'm well served by any of ZFS or RAID6. Platform is Linux. Performance is secondary. So the two setups I am considering are: A RAID6 array plus regular LVM and ext4 A RAID6 array plus ZFS (without redundancy). Is this second option that I don't see discussed at all. Why ZFS+RAID6? It's mainly because the inability of ZFS to grow a raidz2 with new disks. You can replace disks with larger ones, I know, but not add another disk. You can accomplish 2-disk redundancy and ZFS disk growth using mdadm as the redundancy layer. Besides that main point (otherwise I could go directly to raidz2 without RAID under it), these are the pros-cons that I see for each option: ZFS has snapshots without preallocated space. LVM requires preallocation (might be no longer true). ZFS has checksumming (very interested in this) and compression (nice bonus). LVM has online filesystem growth (ZFS can do it offline with export/mdadm --grow/import). LVM has encryption (ZFS-on-Linux has not). This is the only major con of this combo I see. I guess I could go RAID6+LVM+ZFS... seems too heavy, or not? So, to close with a proper question: 1) Is there anything that inherently discourages or precludes RAID6+ZFS? Anyone has experience with a setup like this? 2) Are there possibilities for checksumming and compression that would make ZFS unnecessary (maintaining the possibility of filesystem growth)? Because the RAID6+LVM combo seems the sanctioned, tested way.

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• New virtualization project and old SAN

  - by Chris

  Hi, We'll start shortly a partial virtualization of our infrastructure and consolidate a dozen servers into virtuals instances. We'll also add some client application virtualization into the mix for good measure. Two HP DL 380 with the new xeons 56xx and 96 GB of memory each running xenserver + xenapp will then take charge of most of our IT needs. So far, so good. One element that is missing from the picture is the storage part. We need some sort of shared storage to enable live motion and other HA features. We have an IBM DS 4300 SAN that we can use for that. But since it's in production since 2005, I'm not sure about such a critical role for a 5yr old part. So my question is: What is the reliability of this kind of equipment after 5 yr ? Can it last 10 yr with no or few problems ? Since our budjet is tight, not buying another SAN will be a big plus. This lead me to another question: FC disks cost an arm and a leg from IBM. When I type the replacement # in google (for example IBM 300GB 15K 4GBPS FC HDD 42D0410), I can find it at a fraction of the price at various sites. So am I stupid to buy from IBM or naive to trust 3rd party reseller ?? Thanks, Chris

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• how do i write an init script for django-supervisor

  - by amateur

  pardon me as this is my first time attempting to write a init script for centos 5. I am using django + supervisor to manage my celery workers, scheduler. Now, this is my naive simple attempt /etc/init.d/supervisor #!/bin/sh # # /etc/rc.d/init.d/supervisord # # Supervisor is a client/server system that # allows its users to monitor and control a # number of processes on UNIX-like operating # systems. # # chkconfig: - 64 36 # description: Supervisor Server # processname: supervisord # Source init functions /home/foo/virtualenv/property_env/bin/python /home/foo/bar/manage.py supervisor --daemonize inside my supervisor.conf: [program:celerybeat] command=/home/property/virtualenv/property_env/bin/python manage.py celerybeat --loglevel=INFO --logfile=/home/property/property_buyer/logfiles/celerybeat.log [program:celeryd] command=/home/foo/virtualenv/property_env/bin/python manage.py celeryd --loglevel=DEBUG --logfile=/home/foo/bar/logfiles/celeryd.log --concurrency=1 -E [program:celerycam] command=/home/foo/virtualenv/property_env/bin/python manage.py celerycam I couldn't get it to work. 2013-08-06 00:21:03,108 INFO exited: celerybeat (exit status 2; not expected) 2013-08-06 00:21:06,114 INFO spawned: 'celeryd' with pid 11772 2013-08-06 00:21:06,116 INFO spawned: 'celerycam' with pid 11773 2013-08-06 00:21:06,119 INFO spawned: 'celerybeat' with pid 11774 2013-08-06 00:21:06,146 INFO exited: celerycam (exit status 2; not expected) 2013-08-06 00:21:06,147 INFO gave up: celerycam entered FATAL state, too many start retries too quickly 2013-08-06 00:21:06,147 INFO exited: celeryd (exit status 2; not expected) 2013-08-06 00:21:06,152 INFO gave up: celeryd entered FATAL state, too many start retries too quickly 2013-08-06 00:21:06,152 INFO exited: celerybeat (exit status 2; not expected) 2013-08-06 00:21:07,153 INFO gave up: celerybeat entered FATAL state, too many start retries too quickly I believe it is the init script, but please help me understand what is wrong.

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• What are the disadvantages of domain email forwarding?

  - by naivedeveloper

  I have a domain, example.com. My domain registrar gives me two options concerning email. Set up forwarding email addresses (e.g., [email protected] forwarded to [email protected]. Set up Google Apps for email management Thus far, I have gone with option 1. I have a generic GMail email, [email protected], and I subsequently set up various email addresses on my registrar to forward to this gmail address: [email protected] -> [email protected] [email protected] -> [email protected] [email protected] -> [email protected] Through the GMail account, I have the option to alias these addresses when sending email. For example, from [email protected], I can "send email as" [email protected]. That way from the vantage point of the receiver of the email, the email came from [email protected] as opposed to [email protected]. My question is: Are there any disadvantages of this approach? Are these emails more susceptible to being picked up by spam filters vs using the Google Apps approach? Is there any hidden indication that the email is being aliased? When viewing the email headers, it shows the email was sent from [email protected] and not [email protected] or "forwarded from [email protected]" or anything like that. Am I naive in assuming that my cheap approach to email is masked by aliasing my outgoing emails? I have chosen approach number 1 simply because of the ease of setup. With that said, are there any advantages of going with approach 2 (the Google Apps approach)? Thanks for suggestions and advice.

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• Updating PHP on Linux - "No Packages marked for Update"?

  - by Aristotle

  I'm very new to server-administration, but I was thinking the task of updating PHP to 5.2+ should be relatively simple. Online I found that the following was allegedly sufficient to do this: yum update php But when I run this, the following is output: [root@ip-XXX-XXX-XXX-XXX /]# php -v PHP 5.1.6 (cli) (built: Jan 13 2010 17:13:05) Copyright (c) 1997-2006 The PHP Group Zend Engine v2.1.0, Copyright (c) 1998-2006 Zend Technologies [root@ip-XXX-XXX-XXX-XXX /]# yum update php Loaded plugins: fastestmirror Determining fastest mirrors * addons: p3plmirror02.prod.phx3.secureserver.net * base: p3plmirror02.prod.phx3.secureserver.net * extras: p3plmirror02.prod.phx3.secureserver.net * turbopanel-base: p3plmirror02.prod.phx3.secureserver.net * turbopanel-centos5: p3plmirror02.prod.phx3.secureserver.net * update: p3plmirror02.prod.phx3.secureserver.net addons | 951 B 00:00 addons/primary | 201 B 00:00 base | 2.1 kB 00:00 base/primary_db | 1.6 MB 00:00 extras | 1.1 kB 00:00 extras/primary | 107 kB 00:00 extras 325/325 turbopanel-base | 951 B 00:00 turbopanel-base/primary | 72 kB 00:00 turbopanel-base 494/494 turbopanel-centos5 | 951 B 00:00 turbopanel-centos5/primary | 2.1 kB 00:00 turbopanel-centos5 8/8 update | 1.9 kB 00:00 update/primary_db | 463 kB 00:00 Setting up Update Process No Packages marked for Update [root@ip-XXX-XXX-XXX-XXX /]# php -v PHP 5.1.6 (cli) (built: Jan 13 2010 17:13:05) Copyright (c) 1997-2006 The PHP Group Zend Engine v2.1.0, Copyright (c) 1998-2006 Zend Technolog [root@ip-XXX-XXX-XXX-XXX /]# No Packages marked for Update [root@ip-XXX-XXX-XXX-XXX /]# php -v bash: No: command not found [root@ip-XXX-XXX-XXX-XXX /]# [root@ip-XXX-XXX-XXX-XXX /]# php -v bash: [root@ip-XXX-XXX-XXX-XXX: command not found [root@ip-XXX-XXX-XXX-XXX /]# PHP 5.1.6 (cli) (built: Jan 13 2010 17:13:05) bash: syntax error near unexpected token `(' [root@ip-XXX-XXX-XXX-XXX /]# Copyright (c) 1997-2006 The PHP Group bash: syntax error near unexpected token `c' [root@ip-XXX-XXX-XXX-XXX /]# Zend Engine v2.1.0, Copyright (c) 1998-2006 Zend Technologies bash: syntax error near unexpected token `(' [root@ip-XXX-XXX-XXX-XXX /]# My PHP version is 5.1.6 before, and after running the command. Am I being too naive here with this update process? Is there a more verbose route that is necessary for me to take?

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