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  • what the java command's -jar option really does

    - by JBoy
    Does the -jar option of the java command also compile the sources before running the main method? I believe so but i would like to have a better understanding of the internal process, from the man page you can clearly see a small workflow sequence: -jar Execute a program encapsulated in a JAR file. The first argument is the name of a JAR file instead of a startup class name. In order for this option to work, the manifest of the JAR file must contain a line of the form Main-Class: classname. Here, classname identifies the class having the public static void main(String[] args) method that serves as your application's starting point. See the Jar tool reference page and the Jar trail of the Java Tutorial @ But it does not mention that it compiles the sources.

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  • Repeating characters in VIM insert mode

    - by Cthutu
    Is there a way of repeating a character while in Vim's insert mode? For example, say I would like to insert 80 dashes, in something like emacs I would type: Ctrl+U 8 0 - The only way I know how to do it in VIM is to exit normal mode for the repeat argument, then go back into insert mode to type the dash, then exit to insert the actual dashes, AND then go back into insert mode to carry on typing. The sequence is a really long: <ESC> 8 0 a - <ESC> a It would be nice not to switch in and out of modes. Thanks

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  • Swap byte 2 and 4 from integer

    - by czar x
    I had this interview question - Swap byte 2 and byte4 within an integer sequence. Integer is a 4byte wide i.e. 32 bits My approach was to use char *pointer and a temp char to swap the bytes. For clarity i have broken the steps otherwise an character array can be considered. unsigned char *b2, *b4, tmpc; int n = 0xABCD; b2 = &n; b2++; b4 = &n; b4 +=3; ///swap the values; tmpc = *b2; *b2 = *b4; *b4 = tmpc; Any other methods?

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  • Codeignitor Global Array Declaration

    - by Ajith
    I have a sequence of number like follows 1 - 25, 2 - 60, 3 - 80, 4 - 100 and so on which means that if input is 1 output will be 25 and so on...I need to store it in global array.I would like to use it in multiple pages also.In codeigniter where i can declare a global array and store all these? I am trying like as follows in constants.php $CONFIDENCEVALUE = array(); $CONFIDENCEVALUE[] = array('1'=>25,'2'=>'60','3'=>80,'4'=>100); If it is correct how can access these array value in required pages.Help me please.I am not an expert with codeignitor.Thanks

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  • How to save an order (permutation) in an sql db

    - by Bendlas
    I have a tree structure in an sql table like so: CREATE TABLE containers ( container_id serial NOT NULL PRIMARY KEY, parent integer REFERENCES containers (container_id)) Now i want to define an ordering between nodes with the same parent. I Have thought of adding a node_index column, to ORDER BY, but that seem suboptimal, since that involves modifying the index of a lot of nodes when modifying the stucture. That could include adding, removing, reordering or moving nodes from some subtree to another. Is there a sql datatype for an ordered sequence, or an efficient way to emulate one? Doesn't need to be fully standard sql, I just need a solution for mssql and hopefully postgresql EDIT To make it clear, the ordering is arbitrary. Actually, the user will be able to drag'n'drop tree nodes in the GUI

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  • Would vector of vectors be contiguous?

    - by user1150989
    I need to allocate a vector of rows where row contains a vector of rows. I know that a vector would be contiguous. I wanted to know whether a vector of vectors would also be contiguous. Example code is given below vector<long> firstRow; firstRow.push_back(0); firstRow.push_back(1); vector<long> secondRow; secondRow.push_back(0); secondRow.push_back(1); vector< vector < long> > data; data.push_back(firstRow); data.push_back(secondRow); Would the sequence in memory be 0 1 0 1?

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  • SQL Full Outer Join

    - by Torment March
    I have a table named 'Logs' with the following values : CheckDate CheckType CheckTime ------------------------------------------- 2011-11-25 IN 14:40:00 2011-11-25 OUT 14:45:00 2011-11-25 IN 14:50:00 2011-11-25 OUT 14:55:00 2011-11-25 IN 15:00:00 2011-11-25 OUT 15:05:00 2011-11-25 IN 15:15:00 2011-11-25 OUT 15:20:00 2011-11-25 IN 15:25:00 2011-11-25 OUT 15:30:00 2011-11-25 OUT 15:40:00 2011-11-25 IN 15:45:00 I want to use the previous table to produce a result of: CheckDate CheckIn CheckOut ----------------------------------------- 2011-11-25 14:40:00 14:45:00 2011-11-25 14:50:00 14:55:00 2011-11-25 15:00:00 15:05:00 2011-11-25 15:15:00 15:20:00 2011-11-25 15:25:00 15:30:00 2011-11-25 NULL 15:40:00 2011-11-25 15:45:00 NULL So far I have come up with this result set : CheckDate CheckIn CheckOut ----------------------------------------- 2011-11-25 14:40:00 14:45:00 2011-11-25 14:50:00 14:55:00 2011-11-25 15:00:00 15:05:00 2011-11-25 15:15:00 15:20:00 2011-11-25 15:25:00 15:30:00 2011-11-25 15:45:00 NULL The problem is I cannot generate the log without CheckIns : CheckDate CheckIn CheckOut ----------------------------------------- 2011-11-25 NULL 15:40:00 The sequence of CheckIn - CheckOut pairing and order is in increasing time value.

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  • How to Get the Method/Function Call Trace for a Specific Run?

    - by JackWM
    Given a Java or JavaScript program, after its execution, print out a sequence of calls. The calls are in invocation order. E.g. main() { A(); } A() { B(); C(); } Then the call trace should be: main -> A() -> B() -> C() Is there any tool that can profile and output this kind of information? It seems this is common a need for debugging or performance tuning. I noticed that some profilers can do this, but I prefer a simpler/easy-to-use one. Thanks!

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  • Splitting Nucleotide Sequences in JS with Regexp

    - by TEmerson
    I'm trying to split up a nucleotide sequence into amino acid strings using a regular expression. I have to start a new string at each occurrence of the string "ATG", but I don't want to actually stop the first match at the "ATG". Valid input is any ordering of a string of As, Cs, Gs, and Ts. For example, given the input string: ATGAACATAGGACATGAGGAGTCA I should get two strings: ATGAACATAGGACATGAGGAGTCA (the whole thing) and ATGAGGAGTCA (the first match of "ATG" onward). A string that contains "ATG" n times should result in n results. I thought the expression /(?:[ACGT]*)(ATG)[ACGT]*/g would work, but it doesn't. If this can't be done with a regexp it's easy enough to just write out the code for, but I always prefer an elegant solution if one is available.

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  • How to encode(represent) an ornament?

    - by Daniyar
    I would like to find a numeric representation of kazakh national ornaments for generating new ones. The ornaments essentially consist of combinations of relatively basic ornaments. Usually the ornaments are symmetrical. Here are few examples of basic elements: (The images are a bit distorted) And this is an example of a more complex ornament: How could I encode an ornament's representation in as few numbers as possible? So that I could write a program that would generate an ornament, given some sequence of numbers Any ideas are appreciated. As I write this, I have thought that generating images of snowlfakes may be somewhat relevant, although it's possibly just a fractal.

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  • Multiple Concurrent Changes Using SVN, GIT, and CVS

    - by KlaxSmashing
    At work, we are using SVN, CVS, and GIT because there any many projects that were started at various times. Anyway, a common sequence that occurs is as follows: Working on task A, making changes to project Has new task B, some bug or functionality needs to be done on project, independent of task A but may affect same set of files Check in task B Check in task A Unfortunately, what I do at this time is two maintain 2 working copies of each project. So I can always work on task B from a clean copy. As you can imagine, this is wasteful and also, does not scale well (task C, D, E, etc.) For each of these versioning systems, are there commands that can help me do the following: "Save" task A, reverting working copy to current repository Work on task B, check in changes "Restore" task A changes back to working copy

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  • How to transfer large file (File size > Heap Size) over the network?

    - by neo
    How to transfer large file (File size Heap/RAM Size) over the network ? Lets say I have file (size 10GB) I want to transfer it machine a (RAM 512mb) to machine b (RAM 512mb). Want achieve this using java code. First, is it possible ? Any recommendation on framework. If possible, can we speed this up using threading ? Important criteria: file's data sequence needs to be maintained during transfer. Any example will be great help.

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  • How to change the text int JLabel under the while or for loop?

    - by guilgamos
    I want to create a simple clock by using java. The code is very simply that i will give an example shown below for(int i=0;i<=60;i++) jLabel11.setText( Integer.toString(i) ); The problem is while I'm running my program the result didn't show the update in sequence. I mean it show only 60 digit immediately. It didn't show the change from 1 to 2 to 3 ... something like this. How can i fix this problem. Thank you in advance.

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  • Error occurs while using SPADE method in R

    - by Yuwon Lee
    I'm currently mining sequence patterns using SPADE algorithm in R. SPADE is included in "arulesSequence" package of R. I'm running R on my CentOS 6.3 64bit. For an exercise, I've tried an example presented in http://en.wikibooks.org/wiki/Data_Mining_Algorithms_In_R/Sequence_Mining/SPADE When I tried to do "cspade(x, parameter = list(support = 0.4), control = list(verbose = TRUE))" R says: parameter specification: support : 0.4 maxsize : 10 maxlen : 10 algorithmic control: bfstype : FALSE verbose : TRUE summary : FALSE preprocessing ... 1 partition(s), 0 MB [0.096s] mining transactions ... 0 MB [0.066s] reading sequences ...Error in asMethod(object) : 's' is not an integer vector When I try to run SPADE on my Window 7 32bit, it runs well without any error. Does anybody know why such errors occur?

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  • for (Object object : list) [java] construction

    - by EugeneP
    My question, is, whether the sequence of elements picked from a list will always be the same, is this construction behaviour is deterministic for java "List"s - descendants of java.util.List 2) question, if I use for(Object o: list) construction and inside the loop's body increment a variable, will it be the index of list's elements? So, how it goes through list's elements, from 0 to size()-1 or chaotically? List.get(i) will always return this element? 3) question ( I suppose for the 2-nd question the answer will be negative, so:) for (int i=0; i < list.size(); i++) { } is the best way if I need to save the index of an element and later get it back from a list by its id?

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  • Creating a file path in C#

    - by Jason
    So I'm trying to create a path in C#. I use Environment.Machinename and store it a variable serverName. Then I create another string variable and have some other path extension in there. Here is my code so far: string serverName = Environment.MachineName; string folderName = "\\AlarmLogger"; No matter what I do I can't seem to obtain only one backslash prior to AlarmLogger. Any ideas how I can specify a path in C#? Edit: I'm wondering if my code doesn't seem to want to paste correctly. Anyways when i paste it I only see one backslash but my code has two. Because of the escape character sequence. But something like string test = @"\" + serverName + folderName doesn't seem to want to work for me.

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  • dynamic memory allocation [closed]

    - by gcc
    i wanna write a program that creates (allocating memory) and manipulates (adding elements and increasing memory etc.) integer arrays dynamically according to given input sequences. input sequence which starts with the maximum number of arrays, includes integers to be put into arrays and some one letter characters which are commands to carry out some tasks (activating next array, deleting an array etc). also, i wanna create *c_arrays which is the address of the array whose elements are the actual capacities (How many integer slots are already allocated for an array?) of arrays how should i organize(set up) the algorithm?

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  • Faster way of initializing arrays in Delphi

    - by Max
    I'm trying to squeeze every bit of performance in my Delphi application and now I came to a procedure which works with dynamic arrays. The slowest line in it is SetLength(Result, Len); which is used to initialize the dynamic array. When I look at the code for the SetLength procedure I see that it is far from optimal. The call sequence is as follows: _DynArraySetLength - DynArraySetLength DynArraySetLength gets the array length (which is zero for initialization) and then uses ReallocMem which is also unnecessary for initilization. I was doing SetLength to initialize dynamic array all the time. Maybe I'm missing something? Is there a faster way to do this?

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  • Clojure: find repetition

    - by demi
    Let we have a list of integers: 1, 2, 5, 13, 6, 5, 7 and I want to find the first number has a duplicate before it and return a vector of two indices, In my sample, it's 5 at [2, 5]. What I did so far is loop, but can I do it more elegant, short way? (defn get-cycle [xs] (loop [[x & xs_rest] xs, indices {}, i 0] (if (nil? x) [0 i] ; Sequence is over before we found a duplicate. (if-let [x_index (indices x)] [x_index i] (recur xs_rest (assoc indices x i) (inc i)))))) No need to return number itself, because I can get it by index and, second, it may be not always there.

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  • How to apply Seq map function?

    - by netmatrix01
    Hello All, I been recently playing with F# . I was wondering instead of using a for loop to generate a sequence to element which are multiplied with every other element in the list how can I use a Seq map function or something similar to generate something like below. So for e.g. I have a list [1..10] I would like to apply a fun which generates a result something like [(1*1); (1*2);(1*3); (1*4); (1*5)......(2*1);(2*2);(2*3).....(3*1);(3*2)...] How can i achieve this ?. Many thanks for all you help.

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  • sequencing function calls in javascript - are callbacks the only way?

    - by tim
    I read through various threads like this one for example. But it really escapes me how to accomplish the following: I have 4 functions, and want them happen one after another in sequence. Notice they are in incorrect order, to get my point across. I want the result that will output "1, 2, 3, 4' function firstFunction(){ // some very time consuming asynchronous code... console.log('1'); } function thirdFunction(){ // definitely dont wanna do this until secondFunction is finished console.log('3'); } function secondFunction(){ // waits for firstFunction to be completed console.log('2'); } function fourthFunction(){ // last function, not executed until the other 3 are done. console.log('4'); } I tried to figure out callbacks but am getting lost :( Isn't there some simple way to do this? Like looping through an array...

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  • ORACLE RIGHTNOW DYNAMIC AGENT DESKTOP CLOUD SERVICE - Putting the Dynamite into Dynamic Agent Desktop

    - by Andreea Vaduva
    Untitled Document There’s a mountain of evidence to prove that a great contact centre experience results in happy, profitable and loyal customers. The very best Contact Centres are those with high first contact resolution, customer satisfaction and agent productivity. But how many companies really believe they are the best? And how many believe that they can be? We know that with the right tools, companies can aspire to greatness – and achieve it. Core to this is ensuring their agents have the best tools that give them the right information at the right time, so they can focus on the customer and provide a personalised, professional and efficient service. Today there are multiple channels through which customers can communicate with you; phone, web, chat, social to name a few but regardless of how they communicate, customers expect a seamless, quality experience. Most contact centre agents need to switch between lots of different systems to locate the right information. This hampers their productivity, frustrates both the agent and the customer and increases call handling times. With this in mind, Oracle RightNow has designed and refined a suite of add-ins to optimize the Agent Desktop. Each is designed to simplify and adapt the agent experience for any given situation and unify the customer experience across your media channels. Let’s take a brief look at some of the most useful tools available and see how they make a difference. Contextual Workspaces: The screen where agents do their job. Agents don’t want to be slowed down by busy screens, scrolling through endless tabs or links to find what they’re looking for. They want quick, accurate and easy. Contextual Workspaces are fully configurable and through workspace rules apply if, then, else logic to display only the information the agent needs for the issue at hand . Assigned at the Profile level, different levels of agent, from a novice to the most experienced, get a screen that is relevant to their role and responsibilities and ensures their job is done quickly and efficiently the first time round. Agent Scripting: Sometimes, agents need to deliver difficult or sensitive messages while maximising the opportunity to cross-sell and up-sell. After all, contact centres are now increasingly viewed as revenue generators. Containing sophisticated branching logic, scripting helps agents to capture the right level of information and guides the agent step by step, ensuring no mistakes, inconsistencies or missed opportunities. Guided Assistance: This is typically used to solve common troubleshooting issues, displaying a series of question and answer sets in a decision-tree structure. This means agents avoid having to bookmark favourites or rely on written notes. Agents find particular value in these guides - to quickly craft chat and email responses. What’s more, by publishing guides in answers on support pages customers, can resolve issues themselves, without needing to contact your agents. And b ecause it can also accelerate agent ramp-up time, it ensures that even novice agents can solve customer problems like an expert. Desktop Workflow: Take a step back and look at the full customer interaction of your agents. It probably spans multiple systems and multiple tasks. With Desktop Workflows you control the design workflows that span the full customer interaction from start to finish. As sequences of decisions and actions, workflows are unique in that they can create or modify different records and provide automation behind the scenes. This means your agents can save time and provide better quality of service by having the tools they need and the relevant information as required. And doing this boosts satisfaction among your customers, your agents and you – so win, win, win! I have highlighted above some of the tools which can be used to optimise the desktop; however, this is by no means an exhaustive list. In approaching your design, it’s important to understand why and how your customers contact you in the first place. Once you have this list of “whys” and “hows”, you can design effective policies and procedures to handle each category of problem, and then implement the right agent desktop user interface to support them. This will avoid duplication and wasted effort. Five Top Tips to take away: Start by working out “why” and “how” customers are contacting you. Implement a clean and relevant agent desktop to support your agents. If your workspaces are getting complicated consider using Desktop Workflow to streamline the interaction. Enhance your Knowledgebase with Guides. Agents can access them proactively and can be published on your web pages for customers to help themselves. Script any complex, critical or sensitive interactions to ensure consistency and accuracy. Desktop optimization is an ongoing process so continue to monitor and incorporate feedback from your agents and your customers to keep your Contact Centre successful.   Want to learn more? Having attending the 3-day Oracle RightNow Customer Service Administration class your next step is to attend the Oracle RightNow Customer Portal Design and 2-day Dynamic Agent Desktop Administration class. Here you’ll learn not only how to leverage the Agent Desktop tools but also how to optimise your self-service pages to enhance your customers’ web experience.   Useful resources: Review the Best Practice Guide Review the tune-up guide   About the Author: Angela Chandler joined Oracle University as a Senior Instructor through the RightNow Customer Experience Acquisition. Her other areas of expertise include Business Intelligence and Knowledge Management.  She currently delivers the following Oracle RightNow courses in the classroom and as a Live Virtual Class: RightNow Customer Service Administration (3 days) RightNow Customer Portal Design and Dynamic Agent Desktop Administration (2 days) RightNow Analytics (2 days) Rightnow Chat Cloud Service Administration (2 days)

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  • Top ten things that don't make sense in The Walking Dead

    - by iamjames
    For those of you that don't know, The Walking Dead is a popular American TV show on AMC about a group of people trying to survive in a zombie-filled world.Here's the top ten eleven things that don't make sense on the show (and have never been explained) 1)  They never visit stores.  No Walmarts, Kmarts, Targets, shopping malls, pawn shops, gas stations, etc.  You'd think that would be the first place you'd visit for supplies, but they never have.  Not once.  There was a tiny corner store they visited in a small town, and while many products were already gone they did find several useful items.  2)  They never raid houses.  Why not?  One would imagine that they would want to search houses for useful items, but they don't.3)  They don't use 2 way radios.  Modern 2-way radios have a 36-mile range.  That's probably best possible range, but even if the range is only 10% of that, 3.6 miles, that's still more than enough for most situations, for the occasional "hey zombies attacking can you give me a hand?" or "there's zombies walking by stay inside until they leave" or "remember to pick up milk at the store love mom".  And yes they would need batteries or recharging, but they have been using gas-powered generators on the show and I'm sure a car charger would work.4)  They use gas-guzzling vehicles.  Every vehicle they have is from the 80s or 90s except for the new Kia SUV there for product placement.  Why?  They should all be driving new small SUVs or hybrids.  Visit a dealership and steal more fuel-efficient vehicles, because while the Walmart's might be empty from people raiding them for supplies, I'm sure most people weren't thinking "Gee, I should go car shopping" when the infection hit5)  They drive a motorcycle.  Seriously?  Let's find the least protective vehicle and drive that.  And while motorcycles get reasonable gas mileage, 5 people in a SUV gets better gas mileage per person than 5 people all driving motorcycles so it doesn't make economical sense either.6)  They drive loud vehicles.  The motorcycle used is commonly referred to as a chopper and is about as loud as a motorcycle can get.  The zombies are attracted to loud noise, so wouldn't it make more sense to drive vehicles that makes less sound?  Because as soon as you stop the bike and get off you're surrounded by zombies that heard you coming.  And it's not just the bike, the ~1980s Chevy SUV in the show is also very loud.7)  They never run out of food.  Seems like that would be a almost daily struggle, keeping enough food available for about a dozen people, yet I've never seen them visit a grocery store or local convenience store to stock up.8)  They don't carry swords, machetes, clubs, etc.  Let's face it, biting is not a very effective means of attack.  It's good for animals because they have fangs and little else, but humans have been finding better ways of killing each other since forever.  So why doesn't everyone on the show carry a sword or machete or at least a baseball bat?  Anything is better than wasting valuable bullets all the time.  Sure, dozen zombies approaching?  Shoot them.  One zombie approaching?  Save the bullet, cut off it's head.  9)  They do not wear protective clothing.  Human teeth are not exactly the sharpest teeth in the animal kingdom.  The leather shoes your dog ripped to shreds within minutes would probably take you days to bite through.  So why do they walk around half-naked?  Yes I know it's hot in Atlanta, but you'd think they'd at least have some tough leather coats or something for protection.  Maybe put a few small vent holes in the fabric if it's really hot.  Or better:  make your own chainmail.  Chainmail was used for thousands of years for protection from swords and is still used by scuba divers for protection from sharks.  If swords and sharks can't puncture it, human teeth don't stand a chance.  10)  They don't build barricades or dig trenches around properties.  In Season 2 they stayed at a farm in the middle of no where.  While being far away from people is a great way to stay far away from zombies, it would still make sense to build some sort of defenses.  Hordes of zombies would knock down almost any fence, but what about a trench or moat?  Maybe something not too wide so it can be jumped over easily but a zombie would fall into because I haven't seen too many jumping zombies on the show.  11)  They don't live in a mall or tall office building.  A mall would be perfect.  They have large security gates designed to keep even hundreds of people from breaking in and offer lots of supplies and food.  They're usually hundreds of thousands of square feet and fully enclosed, one could probably live their entire life happily in a mall.  Tall office building with on-site cafeteria would be another good choice.  They also usually offer good security and office furniture could be pushed out of the windows to crush approaching zombies, and the cafeteria is usually stocked to provide food for hundreds or thousands of office workers so food wouldn't be a problem for a long time. So there you have it, eleven things that don't make sense in The Walking Dead.  Have any of your own you'd like to add or were one of these things covered in the show?  Let me know in the comments.

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  • Computer Networks UNISA - Chap 14 &ndash; Insuring Integrity &amp; Availability

    - by MarkPearl
    After reading this section you should be able to Identify the characteristics of a network that keep data safe from loss or damage Protect an enterprise-wide network from viruses Explain network and system level fault tolerance techniques Discuss issues related to network backup and recovery strategies Describe the components of a useful disaster recovery plan and the options for disaster contingencies What are integrity and availability? Integrity – the soundness of a networks programs, data, services, devices, and connections Availability – How consistently and reliably a file or system can be accessed by authorized personnel A number of phenomena can compromise both integrity and availability including… security breaches natural disasters malicious intruders power flaws human error users etc Although you cannot predict every type of vulnerability, you can take measures to guard against the most damaging events. The following are some guidelines… Allow only network administrators to create or modify NOS and application system users. Monitor the network for unauthorized access or changes Record authorized system changes in a change management system’ Install redundant components Perform regular health checks on the network Check system performance, error logs, and the system log book regularly Keep backups Implement and enforce security and disaster recovery policies These are just some of the basics… Malware Malware refers to any program or piece of code designed to intrude upon or harm a system or its resources. Types of Malware… Boot sector viruses Macro viruses File infector viruses Worms Trojan Horse Network Viruses Bots Malware characteristics Some common characteristics of Malware include… Encryption Stealth Polymorphism Time dependence Malware Protection There are various tools available to protect you from malware called anti-malware software. These monitor your system for indications that a program is performing potential malware operations. A number of techniques are used to detect malware including… Signature Scanning Integrity Checking Monitoring unexpected file changes or virus like behaviours It is important to decide where anti-malware tools will be installed and find a balance between performance and protection. There are several general purpose malware policies that can be implemented to protect your network including… Every compute in an organization should be equipped with malware detection and cleaning software that regularly runs Users should not be allowed to alter or disable the anti-malware software Users should know what to do in case the anti-malware program detects a malware virus Users should be prohibited from installing any unauthorized software on their systems System wide alerts should be issued to network users notifying them if a serious malware virus has been detected. Fault Tolerance Besides guarding against malware, another key factor in maintaining the availability and integrity of data is fault tolerance. Fault tolerance is the ability for a system to continue performing despite an unexpected hardware or software malfunction. Fault tolerance can be realized in varying degrees, the optimal level of fault tolerance for a system depends on how critical its services and files are to productivity. Generally the more fault tolerant the system, the more expensive it is. The following describe some of the areas that need to be considered for fault tolerance. Environment (Temperature and humidity) Power Topology and Connectivity Servers Storage Power Typical power flaws include Surges – a brief increase in voltage due to lightening strikes, solar flares or some idiot at City Power Noise – Fluctuation in voltage levels caused by other devices on the network or electromagnetic interference Brownout – A sag in voltage for just a moment Blackout – A complete power loss The are various alternate power sources to consider including UPS’s and Generators. UPS’s are found in two categories… Standby UPS – provides continuous power when mains goes down (brief period of switching over) Online UPS – is online all the time and the device receives power from the UPS all the time (the UPS is charged continuously) Servers There are various techniques for fault tolerance with servers. Server mirroring is an option where one device or component duplicates the activities of another. It is generally an expensive process. Clustering is a fault tolerance technique that links multiple servers together to appear as a single server. They share processing and storage responsibilities and if one unit in the cluster goes down, another unit can be brought in to replace it. Storage There are various techniques available including the following… RAID Arrays NAS (Storage (Network Attached Storage) SANs (Storage Area Networks) Data Backup A backup is a copy of data or program files created for archiving or safekeeping. Many different options for backups exist with various media including… These vary in cost and speed. Optical Media Tape Backup External Disk Drives Network Backups Backup Strategy After selecting the appropriate tool for performing your servers backup, devise a backup strategy to guide you through performing reliable backups that provide maximum data protection. Questions that should be answered include… What data must be backed up At what time of day or night will the backups occur How will you verify the accuracy of the backups Where and for how long will backup media be stored Who will take responsibility for ensuring that backups occurred How long will you save backups Where will backup and recovery documentation be stored Different backup methods provide varying levels of certainty and corresponding labour cost. There are also different ways to determine which files should be backed up including… Full backup – all data on all servers is copied to storage media Incremental backup – Only data that has changed since the last full or incremental backup is copied to a storage medium Differential backup – Only data that has changed since the last backup is coped to a storage medium Disaster Recovery Disaster recovery is the process of restoring your critical functionality and data after an enterprise wide outage has occurred. A disaster recovery plan is for extreme scenarios (i.e. fire, line fault, etc). A cold site is a place were the computers, devices, and connectivity necessary to rebuild a network exist but they are not appropriately configured. A warm site is a place where the computers, devices, and connectivity necessary to rebuild a network exists with some appropriately configured devices. A hot site is a place where the computers, devices, and connectivity necessary to rebuild a network exists and all are appropriately configured.

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  • Why do apache2 upgrades remove and not re-install libapache2-mod-php5?

    - by nutznboltz
    We repeatedly see that when an apache2 update arrives and is installed it causes the libapache2-mod-php5 package to be removed and does not subsequently re-install it automatically. We must subsequently re-install the libapache2-mod-php5 manually in order to restore functionality to our web server. Please see the following github gist, it is a contiguous section of our server's dpkg.log showing the November 14, 2011 update to apache2: https://gist.github.com/1368361 it includes 2011-11-14 11:22:18 remove libapache2-mod-php5 5.3.2-1ubuntu4.10 5.3.2-1ubuntu4.10 Is this a known issue? Do other people see this too? I could not find any launchpad bug reports about it. Platform details: $ lsb_release -ds Ubuntu 10.04.3 LTS $ uname -srvm Linux 2.6.38-12-virtual #51~lucid1-Ubuntu SMP Thu Sep 29 20:27:50 UTC 2011 x86_64 $ dpkg -l | awk '/ii.*apache/ {print $2 " " $3 }' apache2 2.2.14-5ubuntu8.7 apache2-mpm-prefork 2.2.14-5ubuntu8.7 apache2-utils 2.2.14-5ubuntu8.7 apache2.2-bin 2.2.14-5ubuntu8.7 apache2.2-common 2.2.14-5ubuntu8.7 libapache2-mod-authnz-external 3.2.4-2+squeeze1build0.10.04.1 libapache2-mod-php5 5.3.2-1ubuntu4.10 Thanks At a high-level the update process looks like: package package_name do action :upgrade case node[:platform] when 'centos', 'redhat', 'scientific' options '--disableplugin=fastestmirror' when 'ubuntu' options '-o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold"' end end But at a lower level def install_package(name, version) run_command_with_systems_locale( :command = "apt-get -q -y#{expand_options(@new_resource.options)} install #{name}=#{version}", :environment = { "DEBIAN_FRONTEND" = "noninteractive" } ) end def upgrade_package(name, version) install_package(name, version) end So Chef is using "install" to do "update". This sort of moves the question around to "how does apt-get safe-upgrade" remember to re-install libapache-mod-php5? The exact sequence of packages that triggered this was: apache2 apache2-mpm-prefork apache2-mpm-worker apache2-utils apache2.2-bin apache2.2-common But the code is attempting to run checks to make sure the packages in that list are installed already before attempting to "upgrade" them. case node[:platform] when 'debian', 'centos', 'fedora', 'redhat', 'scientific', 'ubuntu' # first primitive way is to define the updates in the recipe # data bags will be used later %w/ apache2 apache2-mpm-prefork apache2-mpm-worker apache2-utils apache2.2-bin apache2.2-common /.each{ |package_name| Chef::Log.debug("is #{package_name} among local packages available for changes?") next unless node[:packages][:changes].keys.include?(package_name) Chef::Log.debug("is #{package_name} available for upgrade?") next unless node[:packages][:changes][package_name][:action] == 'upgrade' package package_name do action :upgrade case node[:platform] when 'centos', 'redhat', 'scientific' options '--disableplugin=fastestmirror' when 'ubuntu' options '-o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold"' end end tag('upgraded') } # after upgrading everything, run yum cache updater if tagged?('upgraded') # Remove old orphaned dependencies and kernel images and kernel headers etc. # Remove cached deb files. case node[:platform] when 'ubuntu' execute 'apt-get -y autoremove' execute 'apt-get clean' # Re-check what updates are available soon. when 'centos', 'fedora', 'redhat', 'scientific' node[:packages][:last_time_we_looked_at_yum] = 0 end untag('upgraded') end end But it's clear that it fails since the dpkg.log has 2011-11-14 11:22:25 install apache2-mpm-worker 2.2.14-5ubuntu8.7 on a system which does not currently have apache2-mpm-worker. I will have to discuss this with the author, thanks again.

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