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• Should programmers use boolean variables to "document" their code?

  - by froadie

  I'm reading McConell's Code Complete, and he discusses using boolean variables to document your code. For example, instead of: if((elementIndex < 0) || (MAX_ELEMENTS < elementIndex) || (elementIndex == lastElementIndex)){ ... } He suggests: finished = ((elementIndex < 0) || (MAX_ELEMENTS < elementIndex)); repeatedEntry = (elementIndex == lastElementIndex); if(finished || repeatedEntry){ ... } This strikes me as logical, good practice, and very self-documenting. However, I'm hesitant to start using this technique regularly as I've almost never come across it; and perhaps it would be confusing just by virtue of being rare. However, my experience is not very vast yet, so I'm interested in hearing programmers' opinion of this technique, and I'd be curious to know if anyone uses this technique regularly or has seen it often when reading code. Is this a worthwhile convention/style/technique to adopt? Will other programmers understand and appreciate it, or consider it strange?

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• std::thread and class constructor and destructor

  - by toeplitz

  When testing threads in C++11 I have created the following example: #include <iostream> #include <thread> class Foo { public: Foo(void) { std::cout << "Constructor called: " << this << std::endl; } ~Foo(void) { std::cout << "Destructor called: " << this << std::endl; } void operator()() const { std::cout << "Operatior called: " << this << std::endl; } }; void test_normal(void) { std::cout << "====> Standard example:" << std::endl; Foo f; } void test_thread(void) { std::cout << "====> Thread example:" << std::endl; Foo f; std::thread t(f); t.detach(); } int main(int argc, char **argv) { test_normal(); test_thread(); for(;;); } Which prints the following: Why is the destructor called 6 times for the thread? And why does the thread report different memory locations?

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• A loop (while/foreach) with "offset" wrapping and

  - by DarkGhostHunter

  After applying what wrapping objects using math operator, I just tought it will be over. But no. By far. <?php $faces= array( 1 => '<div class="block">happy</div>', 2 => '<div class="block">sad</div>', (sic) 21 => '<div class="block">angry</div>' ); $i = 1; foreach ($faces as $face) { echo $face; if ($i == 3) echo '<div class="block">This is and ad</div>'; if ($i % 3 == 0) { echo "<br />"; // or some other wrapping thing } $i++; } ?> In the code I have to put and ad after the second one, becoming by that the third object. And then wrap the three all in a <div class="row"> (a br after won't work out by design reasons). I thought I will going back to applying a switch, but if somebody put more elements in the array that the switch can properly wrap, the last two remaining elements are wrapped openly. Can i add the "ad" to the array in the third position? That would make things simplier, only leaving me with guessing how to wrap the first and the third, the fourth and the sixth, an so on.

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• How to structure Javascript programs in complex web applications?

  - by mixedpickles

  Hi there. I have a problem, which is not easily described. I'm writing a web application that makes heavy usage of jquery and ajax calls. Now I don't have experience in designing the architecture for javascript programms, but I realize that my program has not a good structure. I think I have to many identifiers referring to the same (at least more or less) thing. Let's have an exemplary look at an arbitrary UI widget: The eventhandlers use DOM elements as parameters. The DOM element represents a widget in the browser. A lot of times I use jQuery objects (I think they are basically a wrapper around DOM elements) to do something with the widget. Sometimes they are used transiently, sometimes they are stored in a variable for later purposes. The ajax function calls use strings identifiers for these widgets. They are processed server side. Beside that I have a widget class whose instances represents a widget. It is instantiated through the new operator. Now I have somehow four different object identifiers for the same thing, which needs to be kept in sync until the page is loaded anew. This seems not to be a good thing. Any advice?

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• set countdown correctly, as3

  - by VideoDnd

  How can I set my countdown correctly? I'm counting from 33,000.00 to zero. It works in a fashion, but the minus operator appears in the textfield. //Countdown from 33,000.00 to zero var timer:Timer = new Timer(10); var count:int = -3300000; var fcount:int = 0; timer.addEventListener(TimerEvent.TIMER, incrementCounter); timer.start(); function incrementCounter(event:TimerEvent) { count++; fcount=int(count); mytext.text = formatCount(fcount); } function formatCount(i:int):String { var fraction:int = i % 100; var whole:int = i / 100; return ("0000000" + whole).substr(-7, 7) + "." + (fraction < 10 ? "0" + fraction : fraction); } EXAMPLE I need something I can update with XML, to be an up-counter or down-counter depending on the variables. //Count up from 33,000.00 var countValue:int = 3300000; count = countValue; //Count down from 33,000.00 var countValue:int = -3300000; count = countValue;

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• when will come the new C++ standard? C++0x

  - by Oops

  Hi, when will the new C++ standard became official? C++ was standardized in 1998 and the standard is called C++98 the C++ standard was updated in 2003 and is called C++03 so the unofficial name "C++0x" lead us to the wrong conclusion that it will come within the first decade of the 20th century. Have u also mentioned that we all make the year 2000 bug again? Now we have 2010 so if you take the X as the latin sign for 10 it should come out this year. But no, also this would be wrong. The answer: The name of the language was always part of the language itself. As we all know the ++ operator means: one more But we have learned in some situations it would be better to write ++C so the other way around often is better. and what does the characters 0x mean in the C++ language? Right it's the prefix for a hexadecimal number. Now the question is easy to answer, it's meaning is: 0x++C int main(){ std::cout << "When will the new C++ standard come out? " << std::endl; int x0_ = 0x7D0, _0x = x0_, C = 0xC, Y1 = C+++_0x, Y2 = x0_+++C; std::cout << "it will be standardized between the Years: " << Y1 << " and " << Y2 << std::endl; char c; std::cin >> c; return 0; } do you agree? regards Oops

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• How to return function in document ready?

  - by FatDogMark

  I don't know if it is possible to do this, like I have 2 js files. The first Js File: var news_pos, about_pos, services_pos, clients_pos; function define_pos(){ var $top_slides=$('#top_slides'), $mid_nav=$('#mid_nav'), $news_section=$('#section-1'); var fixed_height = $top_slides.height()+$mid_nav.height(); news_pos = fixed_height-20 ; about_pos = fixed_height+$news_section.height(); services_pos = fixed_height+$news_section.height()*2; clients_pos = fixed_height+$news_section.height()*3; } $(document).ready(function(){ var section_news = $('#section-1'), section_about = $('#section-2'), section_services = $('#section-3'), section_clients = $('#section-4'); setheight(); function setheight(){ var section_height=$(window).height()+200; $section_news.height(section_height); $section_about.height(section_height); $section_services.height(section_height); $section_clients.height(section_height); define_pos(); } }); The second JS File: $(document).ready(function(){ var nav = { '$btn1':$('#btn1'), '$btn2':$('#btn2'), '$btn3':$('#btn3'), '$btn4':$('#btn4'), '$btn5':$('#btn5'), myclick : function(){ myclicked(nav.$btn1,0); myclicked(nav.$btn2,news_pos); myclicked(nav.$btn3,about_pos); myclicked(nav.$btn4,services_pos); myclicked(nav.$btn5,clients_pos); function myclicked(j,k){ j.click(function(e) { e.preventDefault(); $('html,body').animate({scrollTop: k}, 1000); }); } //Is it right to do return{'myclick':myclick}, how to call? seems not logical } } nav.myclick(); // Here will not work because it say news_pos is undefined //if I use setTimeout(nav.myclick,1000), it will works but I want to run it right the when position is caculated. }); How do I pass the nav.myclick() function to the frist js file and put it in setheight() and under define_pos()? By the way writing codes right in stackoverflow is strange,press tab not really give you any spacing.

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• Please explain this delete top 100 SQL syntax

  - by Patrick

  Basically I want to do this: delete top( 100 ) from table order by id asc but MS SQL doesn't allow order in this position The common solution seems to be this: DELETE table WHERE id IN(SELECT TOP (100) id FROM table ORDER BY id asc) But I also found this method here: delete table from (select top (100) * from table order by id asc) table which has a much better estimated execution plan (74:26). Unfortunately I don't really understand the syntax, please can some one explain it to me? Always interested in any other methods to achieve the same result as well. EDIT: I'm still not getting it I'm afraid, I want to be able to read the query as I read the first two which are practically English. The above queries to me are: delete the top 100 records from table, with the records ordered by id ascending delete the top 100 records from table where id is anyone of (this lot of ids) delete table from (this lot of records) table I can't change the third one into a logical English sentence... I guess what I'm trying to get at is how does this turn into "delete from table (this lot of records)". The 'from' seems to be in an illogical position and the second mention of 'table' is logically superfluous (to me).

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• Is this the best way to grab common elements from a Hash of arrays?

  - by Hulihan Applications

  I'm trying to get a common element from a group of arrays in Ruby. Normally, you can use the & operator to compare two arrays, which returns elements that are present or common in both arrays. This is all good, except when you're trying to get common elements from more than two arrays. However, I want to get common elements from an unknown, dynamic number of arrays, which are stored in a hash. I had to resort to using the eval() method in ruby, which executes a string as actual code. Here's the function I wrote: def get_common_elements_for_hash_of_arrays(hash) # get an array of common elements contained in a hash of arrays, for every array in the hash. # ["1","2","3"] & ["2","4","5"] & ["2","5","6"] # => ["2"] # eval("[\"1\",\"2\",\"3\"] & [\"2\",\"4\",\"5\"] & [\"2\",\"5\",\"6\"]") # => ["2"] eval_string_array = Array.new # an array to store strings of Arrays, ie: "[\"2\",\"5\",\"6\"]", which we will join with & to get all common elements hash.each do |key, array| eval_string_array << array.inspect end eval_string = eval_string_array.join(" & ") # create eval string delimited with a & so we can get common values return eval(eval_string) end example_hash = {:item_0 => ["1","2","3"], :item_1 => ["2","4","5"], :item_2 => ["2","5","6"] } puts get_common_elements_for_hash_of_arrays(example_hash) # => 2 This works and is great, but I'm wondering...eval, really? Is this the best way to do it? Are there even any other ways to accomplish this(besides a recursive function, of course). If anyone has any suggestions, I'm all ears. Otherwise, Feel free to use this code if you need to grab a common item or element from a group or hash of arrays, this code can also easily be adapted to search an array of arrays.

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• What is the best practice when using UIStoryboards?

  - by Scott Sherwood

  Having used storyboards for a while now I have found them extremely useful however, they do have some limitations or at least unnatural ways of doing things. While it seems like a single storyboard should be used for your app, when you get to even a moderately sized application this presents several problems. Working within teams is made more difficult as conflicts in Storyboards can be problematic to resolve (any tips with this would also be welcome) The storyboard itself can become quite cluttered and unmanageable. So my question is what are the best practices of use? I have considered using a hybrid approach having logical tasks being split into separate storyboards, however this results in the UX flow being split between the code and the storyboard. To me this feels like the best way to create reusable actions such as login actions etc. Also should I still consider a place for Xibs? This article has quite a good overview of many of the issues and it proposes that for scenes that only have one screen, xibs should be used in this case. Again this feels unusual to me with Apples support for instantiating unconnected scenes from a storyboard it would suggest that xibs won't have a place in the future but I could be wrong.

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• Should I Teach My Son Programming? What approaches should I take? [closed]

  - by DaveDev

  I was wondering if it's a good idea to teach object oriented programming to my son? I was never really good at math as a kid, but I think since I've started programming it's given me a greater ability to understand math by being better able to visualise relationships between abstract models. I thought it might give him a better advantage in learning & applying logical & mathematical concepts throughout his life if he was able to take advantage of the tools available to programmers. what would be the best programming fields, techniques and/or concepts? What approach should I take? what concepts should I avoid? what fields of mathematics would he find this benfits him most? He's only 2 now so it wouldn't be for another few years before I do this, (and even at that, only from a very high level point of view). I thought I'd put it to the programming community and see what you guys thought? Possible Duplicate: What are some recommended programming resources for pre-teens?

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• Is this the best way to grab Common element from a Hash of arrays?

  - by Hulihan Applications

  I'm trying to get a common element from a group of arrays in Ruby. Normally, you can use the & operator to compare two arrays, which returns elements that are present or common in both arrays. This is all good, except when you're trying to get common elements from more than two arrays. However, I want to get common elements from an unknown, dynamic number of arrays, which are stored in a hash. I had to resort to using the eval() method in ruby, which executes a string as actual code. Here's the function I wrote: def get_common_elements_for_hash_of_arrays(hash) # get an array of common elements contained in a hash of arrays, for every array in the hash. # ["1","2","3"] & ["2","4","5"] & ["2","5","6"] # => ["2"] # eval("[\"1\",\"2\",\"3\"] & [\"2\",\"4\",\"5\"] & [\"2\",\"5\",\"6\"]") # => ["2"] eval_string_array = Array.new # an array to store strings of Arrays, ie: "[\"2\",\"5\",\"6\"]", which we will join with & to get all common elements hash.each do |key, array| eval_string_array << array.inspect end eval_string = eval_string_array.join(" & ") # create eval string delimited with a & so we can get common values return eval(eval_string) end example_hash = {:item_0 => ["1","2","3"], :item_1 => ["2","4","5"], :item_2 => ["2","5","6"] } puts get_common_elements_for_hash_of_arrays(example_hash) # => 2 This works and is great, but I'm wondering...eval, really? Is this the best way to do it? Are there even any other ways to accomplish this(besides a recursive function, of course). If anyone has any suggestions, I'm all ears. Otherwise, Feel free to use this code if you need to grab a common item or element from a group or hash of arrays, this code can also easily be adapted to search an array of arrays.

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• What are advantages of using a one-to-one table relationship? (MySQL)

  - by byronh

  What are advantages of using a one-to-one table relationship as opposed to simply storing all the data in one table? I understand and make use of one-to-many, many-to-one, and many-to-many all the time, but implementing a one-to-one relationship seems like a tedious and unnecessary task, especially if you use naming conventions for relating (php) objects to database tables. I couldn't find anything on the net or on this site that could supply a good real-world example of a one-to-one relationship. At first I thought it might be logical to separate 'users', for example, into two tables, one containing public information like an 'about me' for profile pages and one containing private information such as login/password, etc. But why go through all the trouble of using unnecessary JOINS when you can just choose which fields to select from that table anyway? If I'm displaying the user's profile page, obviously I would only SELECT id,username,email,aboutme etc. and not the fields containing their private info. Anyone care to enlighten me with some real-world examples of one-to-one relationships?

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• Are Interfaces "Object"?

  - by PrashantGupta

  package inheritance; class A{ public String display(){ return "This is A!"; } } interface Workable{ public String work(); } class B extends A implements Workable{ public String work(){ return "B is working!"; } } public class TestInterfaceObject{ public static void main(String... args){ B obj=new B(); Workable w=obj; //System.out.println(w.work()); //invoking work method on Workable type reference System.out.println(w.display()); //invoking display method on Workable type reference //System.out.println(w.hashCode()); // invoking Object's hashCode method on Workable type reference } } As we know that methods which can be invoked depend upon the type of the reference variable on which we are going to invoke. Here, in the code, work() method was invoked on "w" reference (which is Workable type) so method invoking will compile successfully. Then, display() method is invoked on "w" which yields a compilation error which says display method was not found, quite obvious as Workable doesn't know about it. Then we try to invoke the Object class's method i.e. hashCode() which yields a successful compilation and execution. How is it possible? Any logical explanation?

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• Best Methods for Dynamically Creating New Objects

  - by frankV

  I'm looking for a method to dynamically create new class objects during runtime of a program. So far what I've read leads me to believe it's not easy and normally reserved for more advanced program requirements. What I've tried so far is this: // create a vector of type class vector<class_name> vect; // and use push_back (method 1) vect.push_back(*new Object); //or use for loop and [] operator (method 2) vect[i] = *new Object; neither of these throw errors from the compiler, but I'm using ifstream to read data from a file and dynamically create the objects... the file read is taking in some weird data and occasionally reading a memory address, and it's obvious to me it's due to my use/misuse of the code snippet above. The file read code is as follows: // in main ifstream fileIn fileIn.open( fileName.c_str() ); // passes to a separate function along w/ vector loadObjects (fileIn, vect); void loadObjects (ifstream& is, vector<class_name>& Object) { int data1, data2, data3; int count = 0; string line; if( is.good() ){ for (int i = 0; i < 4; i++) { is >> data1 >> data2 >> data3; if (data1 == 0) { vect.push_back(*new Object(data2, data3) ) } } } }

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• Failing to use Array.Copy() in my WPF App

  - by Steven Wilson

  I am a C++ developer and recently started working on WPF. Well I am using Array.Copy() in my app and looks like I am not able to completely get the desired result. I had done in my C++ app as follows: static const signed char version[40] = { 'A', 'U', 'D', 'I', 'E', 'N', 'C', 'E', // name 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , // reserved, firmware size 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , // board number 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , // variant, version, serial 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 // date code, reserved }; unsigned char sendBuf[256] = {}; int memloc = 0; sendBuf[memloc++] = 0; sendBuf[memloc++] = 0; // fill in the audience header memcpy(sendBuf+memloc, version, 8); // the first 8 bytes memloc += 16; // the 8 copied, plus 8 reserved bytes I did the similar operation in my WPF (C#) app as follows: Byte[] sendBuf = new Byte[256]; char[] version = { 'A', 'U', 'D', 'I', 'E', 'N', 'C', 'E', // name '0', '0', '0', '0', '0', '0', '0', '0' , // reserved, firmware size '0', '0', '0', '0', '0', '0', '0', '0' , // board number '0', '0', '0', '0', '0', '0', '0', '0' , // variant, version, serial '0', '0', '0', '0', '0', '0', '0', '0' // date code, reserved }; // fill in the address to write to -- 0 sendBuf[memloc++] = 0; sendBuf[memloc++] = 0; // fill in the audience header Array.Copy(sendBuf + memloc, version, 8); // the first 8 bytes memloc += 16; But it throws me an error at Array.Copy(sendBuf + memloc, version, 8); as Operator '+' cannot be applied to operands of type 'byte[]' and 'int'. How can achieve this???? :) please help :)

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• Lighttpd 403 Errors on HTML and PHP pages

  - by Brian

  I installed lighttpd on CentOS 5.5 64-bit. Everything seems fine and running except I cannot get past 403 errors on both HTML and PHP pages. I have used CHMOD and CHOWN, changed ownership in the config file, done everything possible and have been stuck for 2 days. Appreciate any help, and here's hoping to a stupid error on my part. Here is the log file with debug options on: 2011-02-21 11:23:13: (request.c.304) fd: 7 request-len: 408 GET /index.html HTTP/1.1 Host: 10.0.1.8 User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Connection: keep-alive Cache-Control: max-age=0 2011-02-21 11:23:13: (response.c.241) run condition 2011-02-21 11:23:13: (response.c.300) -- splitting Request-URI 2011-02-21 11:23:13: (response.c.301) Request-URI : /index.html 2011-02-21 11:23:13: (response.c.302) URI-scheme : http 2011-02-21 11:23:13: (response.c.303) URI-authority: 10.0.1.8 2011-02-21 11:23:13: (response.c.304) URI-path : /index.html 2011-02-21 11:23:13: (response.c.305) URI-query : 2011-02-21 11:23:13: (response.c.349) -- sanatising URI 2011-02-21 11:23:13: (response.c.350) URI-path : /index.html 2011-02-21 11:23:13: (response.c.470) -- before doc_root 2011-02-21 11:23:13: (response.c.471) Doc-Root : /srv/www/lighttpd 2011-02-21 11:23:13: (response.c.472) Rel-Path : /index.html 2011-02-21 11:23:13: (response.c.473) Path : 2011-02-21 11:23:13: (response.c.521) -- after doc_root 2011-02-21 11:23:13: (response.c.522) Doc-Root : /srv/www/lighttpd 2011-02-21 11:23:13: (response.c.523) Rel-Path : /index.html 2011-02-21 11:23:13: (response.c.524) Path : /srv/www/lighttpd/index.html 2011-02-21 11:23:13: (response.c.541) -- logical -> physical 2011-02-21 11:23:13: (response.c.542) Doc-Root : /srv/www/lighttpd 2011-02-21 11:23:13: (response.c.543) Rel-Path : /index.html 2011-02-21 11:23:13: (response.c.544) Path : /srv/www/lighttpd/index.html 2011-02-21 11:23:13: (response.c.561) -- handling physical path 2011-02-21 11:23:13: (response.c.562) Path : /srv/www/lighttpd/index.html 2011-02-21 11:23:13: (response.c.608) -- access denied 2011-02-21 11:23:13: (response.c.609) Path : /srv/www/lighttpd/index.html 2011-02-21 11:23:13: (response.c.128) Response-Header: HTTP/1.1 403 Forbidden Content-Type: text/html Content-Length: 345 Date: Mon, 21 Feb 2011 16:23:13 GMT Server: lighttpd/1.4.28 Here is the directory listing. I used CHOWN to set to lighttpd:lighttpd [root@localhost lighttpd]# ls -al total 40 drwxrwxrwx 2 lighttpd lighttpd 4096 Feb 21 10:48 . drwxrwxrwx 3 lighttpd lighttpd 4096 Feb 21 10:57 .. -rwxrwxrwx 1 lighttpd lighttpd 10 Feb 20 08:32 index.html -rwxrwxrwx 1 lighttpd lighttpd 20 Feb 21 10:48 index.php -rwxrwxrwx 1 lighttpd lighttpd 20 Feb 21 10:39 info.php [root@localhost lighttpd]# Requested Commands: [root@localhost lighttpd]# ls -ld / /srv /srv/www drwxr-xr-x 22 root root 4096 Feb 21 04:39 / drwxrwxrwx 3 lighttpd lighttpd 4096 Feb 20 07:38 /srv drwxrwxrwx 3 lighttpd lighttpd 4096 Feb 21 10:57 /srv/www [root@localhost lighttpd]# ps auxZ | grep lighttpd root:system_r:httpd_t lighttpd 3842 0.0 0.2 48368 896 ? S 12:24 0:00 /usr/sbin/lighttpd -f /etc/lighttpd/lighttpd.conf root:system_r:unconfined_t:SystemLow-SystemHigh root 3845 0.0 0.2 61152 764 pts/0 R+ 12:24 0:00 grep lighttpd

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• Linux HA cluster w/Xen, Heartbeat, Pacemaker. domU does not failover to secondary node

  - by Kendall

  I am having the followig problem with an OenSuSE + Heartbeat + Pacemaker + Xen HA cluster: when the node a Xen domU is running on is "dead" the Xen domU running on it is not restarted on the second node. The cluster is setup with two nodes, each running OpenSuSE-11.3, Heartbeat 3.0, and Pacemaker 1.0 in CRM mode. For storage I am using a LUN on an iSCSI SAN device; the LUN is formatted with OCFS2 and managed with LVM. The Xen domU has two logical volumes; one for root and the other for swap. I am using IPMI cards for STONITH devices, and a dedicated ethernet link for heartbeat communications. The ha.cf file is as follows: keepalive 1 deadtime 10 warntime 5 udpport 694 ucast eth1 auto_failback off node dhcp-166 node stage use_logd yes crm yes My resources look as follows: shocrm(live)configure# show node $id="5c1aa924-bba4-4f95-a367-6c9a58ac4a38" dhcp-166 node $id="cebc92eb-af24-4833-aaf0-672adf80b58e" stage primitive Xen-Util ocf:heartbeat:Xen \ meta target-role="Started" \ operations $id="Xen-Util-operations" \ op start interval="0" timeout="60" start-delay="0" \ op stop interval="0" timeout="120" \ params xmfile="/etc/xen/vm/xen-util" primitive my-stonith stonith:external/ipmi \ params hostname="dhcp-166" ipaddr="192.168.3.106" userid="ADMIN" passwd="xxx" \ op monitor interval="2m" timeout="60s" primitive my-stonith2 stonith:external/ipmi \ params hostname="stage" ipaddr="192.168.3.105" userid="ADMIN" passwd="xxx" \ op monitor interval="2m" timeout="60s" property $id="cib-bootstrap-options" \ dc-version="1.0.9-89bd754939df5150de7cd76835f98fe90851b677" \ cluster-infrastructure="Heartbeat" The Xen domU config file is as follows: name = "xen-util" bootloader = "/usr/lib/xen/boot/domUloader.py" #bootargs = "xvda1:/vmlinuz-xen,/initrd-xen" bootargs = "--entry=xvda1:/boot/vmlinuz-xen,/boot/initrd-xen" memory = 4096 disk = [ 'phy:vg_xen/xen-util-root,xvda1,w', 'phy:vg_xen/xen-util-swap,xvda2,w', ] root = "/dev/xvda1" vif = [ 'mac=00:16:3e:42:42:06' ] #vfb = [ 'type=vnc,vncunused=0,vnclisten=192.168.3.172' ] extra = "" Say domU "Xen-Util" is running on node "stage"; if "stage" goes down, "Xen-Util" does not restart on node "dhcp-166". It seems to want to try as an "xm list" will show it for a few seconds and if you "xm console xen-util" it will give a message like "copying /boot/kernel.gz from xvda1 to /var/lib/xen/tmp/kernel.a53gs for booting". However, it never gets past that, eventually gives up, and no longer appears in "xm list". Now, when node "stage" comes back online after being power cycled, it detects that "Xen-Util" isn't running, and starts it (on stage). I've tried starting "Xen-Util" on node "dhcp-166" without the cluster running, and it works fine. No problems. So, I know it works in that respect. Any ideas? Thanks!

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• Linux Software RAID recovery

  - by Zoredache

  I am seeing a discrepancy between the output of mdadm --detail and mdadm --examine, and I don't understand why. This output mdadm --detail /dev/md2 /dev/md2: Version : 0.90 Creation Time : Wed Mar 14 18:20:52 2012 Raid Level : raid10 Array Size : 3662760640 (3493.08 GiB 3750.67 GB) Used Dev Size : 1465104256 (1397.23 GiB 1500.27 GB) Raid Devices : 5 Total Devices : 5 Preferred Minor : 2 Persistence : Superblock is persistent Seems to contradict this. (the same for every disk in the array) mdadm --examine /dev/sdc2 /dev/sdc2: Magic : a92b4efc Version : 0.90.00 UUID : 1f54d708:60227dd6:163c2a05:89fa2e07 (local to host) Creation Time : Wed Mar 14 18:20:52 2012 Raid Level : raid10 Used Dev Size : 1465104320 (1397.23 GiB 1500.27 GB) Array Size : 2930208640 (2794.46 GiB 3000.53 GB) Raid Devices : 5 Total Devices : 5 Preferred Minor : 2 The array was created like this. mdadm -v --create /dev/md2 \ --level=raid10 --layout=o2 --raid-devices=5 \ --chunk=64 --metadata=0.90 \ /dev/sdg2 /dev/sdf2 /dev/sde2 /dev/sdd2 /dev/sdc2 Each of the 5 individual drives have partitions like this. Disk /dev/sdc: 1500.3 GB, 1500301910016 bytes 255 heads, 63 sectors/track, 182401 cylinders, total 2930277168 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: 0x00057754 Device Boot Start End Blocks Id System /dev/sdc1 2048 34815 16384 83 Linux /dev/sdc2 34816 2930243583 1465104384 fd Linux raid autodetect Backstory So the SATA controller failed in a box I provide some support for. The failure was a ugly and so individual drives fell out of the array a little at a time. While there are backups, we the are not really done as frequently as we really need. There is some data that I am trying to recover if I can. I got additional hardware and I was able to access the drives again. The drives appear to be fine, and I can get the array and filesystem active and mounted (using read-only mode). I am able to access some data on the filesystem and have been copying that off, but I am seeing lots of errors when I try to copy the most recent data. When I am trying to access that most recent data I am getting errors like below which makes me think that the array size discrepancy may be the problem. Mar 14 18:26:04 server kernel: [351588.196299] dm-7: rw=0, want=6619839616, limit=6442450944 Mar 14 18:26:04 server kernel: [351588.196309] attempt to access beyond end of device Mar 14 18:26:04 server kernel: [351588.196313] dm-7: rw=0, want=6619839616, limit=6442450944 Mar 14 18:26:04 server kernel: [351588.199260] attempt to access beyond end of device Mar 14 18:26:04 server kernel: [351588.199264] dm-7: rw=0, want=20647626304, limit=6442450944 Mar 14 18:26:04 server kernel: [351588.202446] attempt to access beyond end of device Mar 14 18:26:04 server kernel: [351588.202450] dm-7: rw=0, want=19973212288, limit=6442450944 Mar 14 18:26:04 server kernel: [351588.205516] attempt to access beyond end of device Mar 14 18:26:04 server kernel: [351588.205520] dm-7: rw=0, want=8009695096, limit=6442450944

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• How to reinstall Mac OS X on OS X/Linux dual-boot system?

  - by strangeronyourtrain

  My setup: I have a MacBook Pro 5,5 with a Mac OS X Snow Leopard partition and a Linux partition. I use rEFIt to boot into Linux. I didn't use Boot Camp when I originally installed Linux; instead, I manually created the partition (with either Disk Utility in OS X or Gparted on a Linux live CD--I don't recall which one) and then installed Linux on it from a live CD. The problem: My OS X partition is corrupt, and I need to reinstall Snow Leopard. Since I installed rEFIt from within OS X, I'm concerned that wiping the OS X partition will prevent me from booting into my Linux partition. How can I do this without losing access to my Linux partition? Is it possible to install Snow Leopard on the partition I reserved for it, or will it automatically overwrite the entire drive? And if I do the fresh OS X install and then install rEFIt again, will it automatically recognize my Linux partition? Thanks for any tips! Specs: MacBook Pro 5,5 (Mid-2009); Snow Leopard 10.6.7/64-bit Sabayon Linux, 2.6.36 kernel EDIT/UPDATE: Thanks, but the situation has taken a more complicated turn: I tried to reinstall Snow Leopard from the DVD, but it refused to install onto my Mac partition, claiming: "The disk cannot be used to start up your computer." Disk Utility wouldn't let me resize the partition or create a new one, and it doesn't see my Linux partition. It only displays the two partitions "Macintosh HD" and Linux Swap. I can, however, see all the partitions from Linux. This is the partition table as shown in Gparted: And the output of "fdisk -l" is: WARNING: GPT (GUID Partition Table) detected on '/dev/sda'! The util fdisk doesn't support GPT. Use GNU Parted. Disk /dev/sda: 250.1 GB, 250059350016 bytes 255 heads, 63 sectors/track, 30401 cylinders, total 488397168 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: 0x00000000 Device Boot Start End Blocks Id System /dev/sda1 1 409639 204819+ ee GPT /dev/sda2 409640 349590464 174590412+ af HFS / HFS+ /dev/sda3 483122745 488392064 2634660 82 Linux swap / Solaris /dev/sda4 * 349590465 483122744 66766140 83 Linux Partition table entries are not in disk order I wonder if this is because I originally partitioned my disk with Gparted instead of OS X's Disk Utility (at this point, I don't recall whether I used Gparted or Disk Utility). In any case, it doesn't seem safe to do any reformatting with Disk Utility now, as I'm afraid it will wipe sda2 ("Macintosh HD") as well as sda4 (my Linux partition). So... I'm hoping to find a solution that doesn't involve wiping my entire hard disk. Would it be safe/possible to use Gparted to erase sda2 ("Macintosh HD") and then use the Snow Leopard DVD to install OS X onto [I]just[/I] sda2 without touching the other partitions? Thanks for any insight!

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• kernel panic after LVM setup

  - by Manuel Sopena Ballesteros

  I broke my webserver... My setup is: VMWare ESXi environemt CPanel installed CentOS release 6.5 (Final) 4 CPUs 2G RAM 2x VM disks 100G each LVM system This was my previous storage settings (the server was working fine at this time): # df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg_test01-lv_root 95G 1.4G 88G 2% / tmpfs 939M 0 939M 0% /dev/shm /dev/sdb1 99G 188M 94G 1% /tmp /dev/sda1 485M 54M 407M 12% /boot My web developer asked me to merge /tmp and / disks so this is what I did: Delete /dev/sdb1 partition using fdisk Create a new partition as LVM on /dev/sdb1 using fdisk Create a new physical volume -- pvcreate /dev/sdb1 Extend volume group -- vgextend /dev/sdb1 vg_test01 Extend logical volume -- lvextend -l +100%FREE /dev/vg_test01/lv_root Resize filesystem -- resize2fs /dev/vg_test01/lv_root This is the new configuration: # df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg_test01-lv_root 213G 105G 97G 52% / tmpfs 939M 0 939M 0% /dev/shm /dev/sda1 485M 54M 407M 12% /boot /usr/tmpDSK 4.0G 145M 3.6G 4% /tmp Since I have the new settings my web server is throwing kernel panics quite often (around every 2 days). The message says: INFO: task <taskName>:<pid> blocked for more than 120 seconds. The list of process affected that I can see from the console are: mysqld queueprocd httpd suphp vmtoolsd loop0 auditd The only way I can fix this is reseting (cold reboot) the VM. I don't think it is a hardware issue as sar is not showing any bottleneck: Linux 2.6.32-431.3.1.el6.x86_64 (test01) 08/22/2014 _x86_64_ (4 CPU) 12:00:01 AM CPU %user %nice %system %iowait %steal %idle 12:10:01 AM all 26.86 0.01 0.98 0.57 0.00 71.57 12:20:01 AM all 1.78 0.02 1.03 0.08 0.00 97.09 12:30:01 AM all 26.34 0.02 0.85 0.05 0.00 72.74 12:40:01 AM all 27.12 0.01 1.11 1.22 0.00 70.54 12:50:01 AM all 1.59 0.02 0.94 0.13 0.00 97.32 01:00:01 AM all 26.10 0.01 0.77 0.04 0.00 73.07 01:10:01 AM all 27.51 0.01 1.16 0.14 0.00 71.18 01:20:01 AM all 1.80 0.07 1.06 0.08 0.00 96.99 01:30:01 AM all 26.19 0.01 0.78 0.05 0.00 72.96 01:40:01 AM all 26.62 0.02 0.87 0.05 0.00 72.45 01:50:02 AM all 1.35 0.01 0.87 0.02 0.00 97.75 02:00:01 AM all 26.11 0.02 0.69 0.02 0.00 73.17 02:10:01 AM all 26.73 0.02 0.89 0.14 0.00 72.21 02:20:01 AM all 1.45 0.01 0.92 0.04 0.00 97.58 02:30:01 AM all 26.59 0.01 1.06 0.03 0.00 72.31 02:40:01 AM all 26.27 0.01 0.72 0.05 0.00 72.95 02:50:01 AM all 0.86 0.01 0.50 0.09 0.00 98.53 03:00:01 AM all 25.61 0.02 0.39 0.03 0.00 73.96 03:10:01 AM all 26.30 0.08 0.66 0.14 0.00 72.82 03:20:01 AM all 0.81 0.01 0.51 0.04 0.00 98.63 03:30:02 AM all 26.15 0.02 0.53 0.07 0.00 73.24 03:40:01 AM all 26.06 0.01 0.47 0.04 0.00 73.42 03:50:01 AM all 0.96 0.02 0.51 0.03 0.00 98.48 Average: all 17.69 0.02 0.79 0.14 0.00 81.36 06:58:14 AM LINUX RESTART 07:00:01 AM CPU %user %nice %system %iowait %steal %idle 07:10:01 AM all 1.04 0.02 0.57 0.95 0.00 97.42 07:20:02 AM all 0.66 0.01 0.39 0.06 0.00 98.87 07:30:01 AM all 25.71 0.01 0.45 0.16 0.00 73.67 07:40:01 AM all 25.88 0.01 0.35 0.08 0.00 73.68 07:50:01 AM all 1.13 0.02 0.55 0.11 0.00 98.19 As you can see the server became unresponsive at 03.50 AM and I had to reset the VM at 06.58 AM to bring the website up again. I would appreciate any help/assistance to fix this issue. thank you very much

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• Best Practise: DNS and VPN (with private network IPs)

  - by ribx

  I am trying to find the best solution for my DNS problem. We are running several services in our company that you can reach only over VPN. Other services, that are reachable through the internet got the domain ... At the moment all services inside the VPN network go by .local... These have an VPN IP of the private network 192.168.252.0/24. Clients reach from Linux over OSX to Windows. I can think of 4 possibilities to implement a DNS infrastructure: Most common: an internal DNS Server, that is pushed by the VPN. But this has several drawbacks: your DNS responses are limited to the speed of the VPN Connection and your own DNS server. Because of very complex websites, this can increase the time for a page to load quite a lot. Also: we have several VPNs that are not connected to each other and all of them have their own DNS server. Several DNS servers locally. These have to be configured by hand. And you have to use some third party tool like dnsmasq. If you start a DNS request, you ask your locally running DNS server, which decides which server to ask for which domain name. One college of mine uses such a solution with this OSX (I am sorry, I don't remember the name of the application). You use your domain hoster. Most of them have APIs available to manipulate your DNS entries. So you could pull your private network informations to your domain hoster. I am not sure whether they all accept private network IPs. But I guess there will be some problems in the same way as in number 4. The one we currently use, because it's for us the most logical choice: we forward the sub domain *.local.. to our own public DNS Server. This works quite good for some public DNS Servers like Google. But most ISPs do not forward the answers. Or don't do that always. Like my ISP sends me a positive result of the a DNS request of a *.local.. domain only every 10th time I make a nslookup. (Can someone explain this?) Here the real Question: Is there another solution we were not thinking about? Or: What of these methods do you use?

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• Determining the health of a Cisco switch port?

  - by ewwhite

  I've been chasing a packet-loss and network stability issue for a handful of end-users on an internal network for the past few days... These issues surfaced recently, however, the location was struck by lightning six weeks ago. I was seeing 5-10% packet loss between a stack of four Cisco 2960's and several PC's and phones on the other side of a 77-meter run. The PC's were run inline with the phones over a trunked link. We were seeing dropped calls and interruptions in client-server applications and Microsoft Exchange connectivity. I tried the usual troubleshooting steps remotely, having a local technician do the following during breaks in user and production activity: change cables between the wall jack and device. change patch cables between the patch panel and switch port(s). try different switch ports within the 2960 stack. change end-user devices with known-good equipment (new phones, different PC's). clear switch port interface counters and monitor incrementing errors closely. (Pastebin output of sh int) Pored over the device logs and Observium RRD graphs. No link up/down issues from the switch side. change power strips on the end-user side. test cable runs from the Cisco 2960 using test cable-diagnostics tdr int Gi4/0/9 (clean)* test cable runs with a Tripp-Lite cable tester. (clean) run diagnostics on the switch stack members. (clean) In the end, it took three changes of switch ports to find a stable solution. The only logical conclusion is that a few Cisco 2960 switch ports are bad or flaky... Not dead, but not consistent in behavior either. I'm not used to seeing individual ports die in this manner. What else can I test or check to determine if these devices are bad? Is it common for single ports to have problems, rather than a contiguous bank of ports? BTW - show cable-diagnostics tdr int Gi4/0/14 is very cool... Interface Speed Local pair Pair length Remote pair Pair status --------- ----- ---------- ------------------ ----------- -------------------- Gi4/0/14 1000M Pair A 79 +/- 0 meters Pair B Normal Pair B 75 +/- 0 meters Pair A Normal Pair C 77 +/- 0 meters Pair D Normal Pair D 79 +/- 0 meters Pair C Normal

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• HP DAT72x6 autoloader

  - by ericmayo

  Hoping someone here has seen this similar issue and can offer soem advise... I have an HP DAT72x6 auto loader tape backup unit. The external kind, here is a link to an owner's manual I found of it. http://www.dectrader.com/docs/set2/emr_na-c00070400-1.pdf I purchased the unit used about 6 months ago. The unit stopped working after 3-4 back-ups, it's used one day a month to do a monthly backup of another system. Suffice it to say the unit gets very little usage. There is an amber light on the front of the unit called the OAR (Operator Attention Required). The manual states to call for service when this light comes on and stays on. I've tried a few things to resolve but none are working. I've tried power cycling, re-securing the SCSI cables at both ends. Unit was used so I didn't pay much ($500) and so I don't want to spend a lot to have it fixed; might as well buy something new one if fixing this is going to cost more than $100-$150 bucks. I'm curious to see if anyone here has been around these devices or possibly is an HP repair person that can give me some things to try to resolve. The manual states that a solid amber OAR light indicates a hardware failure. When I power cycle the unit I see one of two scenarios so far. The unit powers up, shows self test in the LCD, then LCD changes to show all possible images and the OAR light comes on. The unit powers up, LCD is completely blank, the green lights go through some sort of process of going on and off and later the amber OAR light comes on and stays on. If it's a simple misalignment issue, I may be able to fix myself but not knowing what could cause the OAR light to come on gives me no where to even start. Google around gave no help either. I hoping someone here has experience with this and can help or point me in the right direction. Also, I don't have the HP Diagnostic tools mentioned in many manuals. The unit is connected to a Linux box. The 3-4 backups I've done with it so far have had no issues. We run amanda backup. Before this incident the unit was backing up and reading tapes fine. Thanks for any help or suggestions.

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• How to correctly partition usb flash drive and which filesystem to choose considering wear leveling?

  - by random1

  Two problems. First one: how to partition the flash drive? I shouldn't need to do this, but I'm no longer sure if my partition is properly aligned since I was forced to delete and create a new partition table after gparted complained when I tried to format the drive from FAT to ext4. The naive answer would be to say "just use default and everything is going to be alright". However if you read the following links you'll know things are not that simple: https://lwn.net/Articles/428584/ and http://linux-howto-guide.blogspot.com/2009/10/increase-usb-flash-drive-write-speed.html Then there is also the issue of cylinders, heads and sectors. Currently I get this: $sfdisk -l -uM /dev/sdd Disk /dev/sdd: 30147 cylinders, 64 heads, 32 sectors/track Warning: The partition table looks like it was made for C/H/S=*/255/63 (instead of 30147/64/32). For this listing I'll assume that geometry. Units = mebibytes of 1048576 bytes, blocks of 1024 bytes, counting from 0 Device Boot Start End MiB #blocks Id System /dev/sdd1 1 30146 30146 30869504 83 Linux $fdisk -l /dev/sdd Disk /dev/sdd: 31.6 GB, 31611420672 bytes 255 heads, 63 sectors/track, 3843 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: 0x00010c28 So from my current understanding I should align partitions at 4 MiB (currently it's at 1 MiB). But I still don't know how to set the heads and sectors properly for my device. Second problem: file system. From the benchmarks I saw ext4 provides the best performance, however there is the issue of wear leveling. How can I know that my Transcend JetFlash 700's microcontroller provides for wear leveling? Or will I just be killing my drive faster? I've seen a lot of posts on the web saying don't worry the newer drives already take care of that. But I've never seen a single piece of backed evidence of that and at some point people start mixing SSD with USB flash drives technology. The safe option would be to go for ext2, however a serious of tests that I performed showed horrible performance!!! These values are from a real scenario and not some synthetic test: 42 files: 3,429,415,284 bytes copied to flash drive original fat32: 15.1 MiB/s ext4 after new partition table: 10.2 MiB/s ext2 after new partition table: 1.9 MiB/s Please read the links that I posted above before answering. I would also be interested in answers backed up with some references because a lot is said and re-said but then it lacks facts. Thank you for the help.

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