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• Why would you use the ternary operator without assigning a value for the "true" condition?

  - by RickNotFred

  In the Android open-source qemu code I ran across this line of code: machine->max_cpus = machine->max_cpus ?: 1; /* Default to UP */ It this just a confusing way of saying: if (machine->max_cpus) { ; //do nothing } else { machine->max_cpus = 1; } If so, wouldn't it be clearer as: if (machine->max_cpus == 0) machine->max_cpus = 1; Interestingly, this compiles and works fine with gcc, but doesn't compile on http://www.comeaucomputing.com/tryitout/ .

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• Javascript === vs == : Does it matter which "equal" operator I use?

  - by bcasp

  I'm using JSLint to go through some horrific JavaScript at work and it's returning a huge number of suggestions to replace == with === when doing things like comparing 'idSele_UNVEHtype.value.length == 0' inside of an if statement. I'm basically wondering if there is a performance benefit to replacing == with ===. Any performance improvement would probably be welcomed as there are hundreds (if not thousands) of these comparison operators being used throughout the file. I tried searching for relevant information to this question, but trying to search for something like '=== vs ==' doesn't seem to work so well with search engines...

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• Does this collection operator method also work on the iPhone?

  - by dontWatchMyProfile

  NSNumber *salaryOverhead = [anEmployee valueForKeyPath:@"[email protected]"];

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• Is it bad practice to make an iterator that is aware of its own end

  - by aaronman

  For some background of why I am asking this question here is an example. In python the method chain chains an arbitrary number of ranges together and makes them into one without making copies. Here is a link in case you don't understand it. I decided I would implement chain in c++ using variadic templates. As far as I can tell the only way to make an iterator for chain that will successfully go to the next container is for each iterator to to know about the end of the container (I thought of a sort of hack in where when != is called against the end it will know to go to the next container, but the first way seemed easier and safer and more versatile). My question is if there is anything inherently wrong with an iterator knowing about its own end, my code is in c++ but this can be language agnostic since many languages have iterators. #ifndef CHAIN_HPP #define CHAIN_HPP #include "iterator_range.hpp" namespace iter { template <typename ... Containers> struct chain_iter; template <typename Container> struct chain_iter<Container> { private: using Iterator = decltype(((Container*)nullptr)->begin()); Iterator begin; const Iterator end;//never really used but kept it for consistency public: chain_iter(Container & container, bool is_end=false) : begin(container.begin()),end(container.end()) { if(is_end) begin = container.end(); } chain_iter & operator++() { ++begin; return *this; } auto operator*()->decltype(*begin) { return *begin; } bool operator!=(const chain_iter & rhs) const{ return this->begin != rhs.begin; } }; template <typename Container, typename ... Containers> struct chain_iter<Container,Containers...> { private: using Iterator = decltype(((Container*)nullptr)->begin()); Iterator begin; const Iterator end; bool end_reached = false; chain_iter<Containers...> next_iter; public: chain_iter(Container & container, Containers& ... rest, bool is_end=false) : begin(container.begin()), end(container.end()), next_iter(rest...,is_end) { if(is_end) begin = container.end(); } chain_iter & operator++() { if (begin == end) { ++next_iter; } else { ++begin; } return *this; } auto operator*()->decltype(*begin) { if (begin == end) { return *next_iter; } else { return *begin; } } bool operator !=(const chain_iter & rhs) const { if (begin == end) { return this->next_iter != rhs.next_iter; } else return this->begin != rhs.begin; } }; template <typename ... Containers> iterator_range<chain_iter<Containers...>> chain(Containers& ... containers) { auto begin = chain_iter<Containers...>(containers...); auto end = chain_iter<Containers...>(containers...,true); return iterator_range<chain_iter<Containers...>>(begin,end); } } #endif //CHAIN_HPP

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• Objective-C scanf spaces issue

  - by Rob

  I am learning objective-C and for the life of me can't figure out why this is happening. When the user inputs when the code is: scanf("%c %lf", &operator, &number); For some reason it messes with this code: doQuit = 0; [deskCalc setAccumulator: 0]; while (doQuit == 0) { NSLog(@"Please input an operation and then a number:"); scanf("%c %lf", &operator, &number); switch (operator) { case '+': [deskCalc add: number]; NSLog (@"%lf", [deskCalc accumulator]); break; case '-': [deskCalc subtract: number]; NSLog (@"%lf", [deskCalc accumulator]); break; case '*': case 'x': [deskCalc multiply: number]; NSLog (@"%lf", [deskCalc accumulator]); break; case '/': if (number == 0) NSLog(@"You can't divide by zero."); else [deskCalc divide: number]; NSLog (@"%lf", [deskCalc accumulator]); break; case 'S': [deskCalc setAccumulator: number]; NSLog (@"%lf", [deskCalc accumulator]); break; case 'E': doQuit = 1; break; default: NSLog(@"You did not enter a valid operator."); break; } } When the user inputs for example "E 10" it will exit the loop but it will also print "You did not enter a valid operator." When I change the code to: scanf(" %c %lf", &operator, &number); It all of a sudden doesn't print this last line. What is it about the space before %c that fixes this?

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• Why we can't we overload "=" using friend function?

  - by ashish-sangwan

  Why it is not allowed to overload "=" using friend function? I have written a small program but it is giving error. class comp { int real; int imaginary; public: comp(){real=0; imaginary=0;} void show(){cout << "Real="<<real<<" Imaginary="<<imaginary<<endl;} void set(int i,int j){real=i;imaginary=j;} friend comp operator=(comp &op1,const comp &op2); }; comp operator=(comp &op1,const comp &op2) { op1.imaginary=op2.imaginary; op1.real=op2.real; return op1; } int main() { comp a,b; a.set(10,20); b=a; b.show(); return 0; } The compilation gives the following error :- [root@dogmatix stackoverflow]# g++ prog4.cpp prog4.cpp:11: error: ‘comp operator=(comp&, const comp&)’ must be a nonstatic member function prog4.cpp:14: error: ‘comp operator=(comp&, const comp&)’ must be a nonstatic member function prog4.cpp: In function ‘int main()’: prog4.cpp:25: error: ambiguous overload for ‘operator=’ in ‘b = a’ prog4.cpp:4: note: candidates are: comp& comp::operator=(const comp&) prog4.cpp:14: note: comp operator=(comp&, const comp&)

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• C++ overloading comparative operators for a MyString class

  - by Taylor Gang

  bool operator == (const MyString& left, const MyString& right) { if(left.value == right.value) return true; else return false; } bool operator != (const MyString& left, const MyString& right) { if(left == right) return false; else return true; } bool operator < (const MyString& left, const MyString& right) { if(strcmp(left.value, right.value) == -1) return true; else return false; } bool operator > (const MyString& left, const MyString& right) { if(strcmp(left.value, right.value) == 1) return true; else return false; } bool operator <= (const MyString& left, const MyString& right) { if(strcmp(left.value, right.value) == -1 || strcmp(left.value, right.value) == 0) return true; else return false; } bool operator >= (const MyString& left, const MyString& right) { if(strcmp(left.value, right.value) == 1 || strcmp(left.value, right.value) == 0) return true; else return false; } So these are my implemented comparison operators for my MyString class, they fail the test program that my professor gave me and could use some direction. Thanks in advance for any and all help I receive.

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• C++ unrestricted union workaround

  - by Chris

  #include <stdio.h> struct B { int x,y; }; struct A : public B { // This whines about "copy assignment operator not allowed in union" //A& operator =(const A& a) { printf("A=A should do the exact same thing as A=B\n"); } A& operator =(const B& b) { printf("A = B\n"); } }; union U { A a; B b; }; int main(int argc, const char* argv[]) { U u1, u2; u1.a = u2.b; // You can do this and it calls the operator = u1.a = (B)u2.a; // This works too u1.a = u2.a; // This calls the default assignment operator >:@ } Is there any workaround to be able to do that last line u1.a = u2.a with the exact same syntax, but have it call the operator = (don't care if it's =(B&) or =(A&)) instead of just copying data? Or are unrestricted unions (not supported even in Visual Studio 2010) the only option?

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• OWB 11gR2 &ndash; Degenerate Dimensions

  - by David Allan

  Ever wondered how to build degenerate dimensions in OWB and get the benefits of slowly changing dimensions and cube loading? Now its possible through some changes in 11gR2 to make the dimension and cube loading much more flexible. This will let you get the benefits of OWB's surrogate key handling and slowly changing dimension reference when loading the fact table and need degenerate dimensions (see Ralph Kimball's degenerate dimensions design tip). Here we will see how to use the cube operator to load slowly changing, regular and degenerate dimensions. The cube and cube operator can now work with dimensions which have no surrogate key as well as dimensions with surrogates, so you can get the benefit of the cube loading and incorporate the degenerate dimension loading. What you need to do is create a dimension in OWB that is purely used for ETL metadata; the dimension itself is never deployed (its table is, but has not data) it has no surrogate keys has a single level with a business attribute the degenerate dimension data and a dummy attribute, say description just to pass the OWB validation. When this degenerate dimension is added into a cube, you will need to configure the fact table created and set the 'Deployable' flag to FALSE for the foreign key generated to the degenerate dimension table. The degenerate dimension reference will then be in the cube operator and used when matching. Create the degenerate dimension using the regular wizard. Delete the Surrogate ID attribute, this is not needed. Define a level name for the dimension member (any name). After the wizard has completed, in the editor delete the hierarchy STANDARD that was automatically generated, there is only a single level, no need for a hierarchy and this shouldn't really be created. Deploy the implementing table DD_ORDERNUMBER_TAB, this needs to be deployed but with no data (the mapping here will do a left outer join of the source data with the empty degenerate dimension table). Now, go ahead and build your cube, use the regular TIMES dimension for example and your degenerate dimension DD_ORDERNUMBER, can add in SCD dimensions etc. Configure the fact table created and set Deployable to false, so the foreign key does not get generated. Can now use the cube in a mapping and load data into the fact table via the cube operator, this will look after surrogate lookups and slowly changing dimension references.   If you generate the SQL you will see the ON clause for matching includes the columns representing the degenerate dimension columns. Here we have seen how this use case for loading fact tables using degenerate dimensions becomes a whole lot simpler using OWB 11gR2. I'm sure there are other use cases where using this mix of dimensions with surrogate and regular identifiers is useful, Fact tables partitioned by date columns is another classic example that this will greatly help and make the cube operator much more useful. Good to hear any comments.

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• Separating physics and game logic from UI code

  - by futlib

  I'm working on a simple block-based puzzle game. The game play consists pretty much of moving blocks around in the game area, so it's a trivial physics simulation. My implementation, however, is in my opinion far from ideal and I'm wondering if you can give me any pointers on how to do it better. I've split the code up into two areas: Game logic and UI, as I did with a lot of puzzle games: The game logic is responsible for the general rules of the game (e.g. the formal rule system in chess) The UI displays the game area and pieces (e.g. chess board and pieces) and is responsible for animations (e.g. animated movement of chess pieces) The game logic represents the game state as a logical grid, where each unit is one cell's width/height on the grid. So for a grid of width 6, you can move a block of width 2 four times until it collides with the boundary. The UI takes this grid, and draws it by converting logical sizes into pixel sizes (that is, multiplies it by a constant). However, since the game has hardly any game logic, my game logic layer [1] doesn't have much to do except collision detection. Here's how it works: Player starts to drag a piece UI asks game logic for the legal movement area of that piece and lets the player drag it within that area Player lets go of a piece UI snaps the piece to the grid (so that it is at a valid logical position) UI tells game logic the new logical position (via mutator methods, which I'd rather avoid) I'm not quite happy with that: I'm writing unit tests for my game logic layer, but not the UI, and it turned out all the tricky code is in the UI: Stopping the piece from colliding with others or the boundary and snapping it to the grid. I don't like the fact that the UI tells the game logic about the new state, I would rather have it call a movePieceLeft() method or something like that, as in my other games, but I didn't get far with that approach, because the game logic knows nothing about the dragging and snapping that's possible in the UI. I think the best thing to do would be to get rid of my game logic layer and implement a physics layer instead. I've got a few questions regarding that: Is such a physics layer common, or is it more typical to have the game logic layer do this? Would the snapping to grid and piece dragging code belong to the UI or the physics layer? Would such a physics layer typically work with pixel sizes or with some kind of logical unit, like my game logic layer? I've seen event-based collision detection in a game's code base once, that is, the player would just drag the piece, the UI would render that obediently and notify the physics system, and the physics system would call a onCollision() method on the piece once a collision is detected. What is more common? This approach or asking for the legal movement area first? [1] layer is probably not the right word for what I mean, but subsystem sounds overblown and class is misguiding, because each layer can consist of several classes.

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• Patterns for Handling Changing Property Sets in C++

  - by Bhargav Bhat

  I have a bunch "Property Sets" (which are simple structs containing POD members). I'd like to modify these property sets (eg: add a new member) at run time so that the definition of the property sets can be externalized and the code itself can be re-used with multiple versions/types of property sets with minimal/no changes. For example, a property set could look like this: struct PropSetA { bool activeFlag; int processingCount; /* snip few other such fields*/ }; But instead of setting its definition in stone at compile time, I'd like to create it dynamically at run time. Something like: class PropSet propSetA; propSetA("activeFlag",true); //overloading the function call operator propSetA("processingCount",0); And the code dependent on the property sets (possibly in some other library) will use the data like so: bool actvFlag = propSet["activeFlag"]; if(actvFlag == true) { //Do Stuff } The current implementation behind all of this is as follows: class PropValue { public: // Variant like class for holding multiple data-types // overloaded Conversion operator. Eg: operator bool() { return (baseType == BOOLEAN) ? this->ToBoolean() : false; } // And a method to create PropValues various base datatypes static FromBool(bool baseValue); }; class PropSet { public: // overloaded[] operator for adding properties void operator()(std::string propName, bool propVal) { propMap.insert(std::make_pair(propName, PropVal::FromBool(propVal))); } protected: // the property map std::map<std::string, PropValue> propMap; }; This problem at hand is similar to this question on SO and the current approach (described above) is based on this answer. But as noted over at SO this is more of a hack than a proper solution. The fundamental issues that I have with this approach are as follows: Extending this for supporting new types will require significant code change. At the bare minimum overloaded operators need to be extended to support the new type. Supporting complex properties (eg: struct containing struct) is tricky. Supporting a reference mechanism (needed for an optimization of not duplicating identical property sets) is tricky. This also applies to supporting pointers and multi-dimensional arrays in general. Are there any known patterns for dealing with this scenario? Essentially, I'm looking for the equivalent of the visitor pattern, but for extending class properties rather than methods. Edit: Modified problem statement for clarity and added some more code from current implementation.

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• C++11 Tidbits: Decltype (Part 2, trailing return type)

  - by Paolo Carlini

  Following on from last tidbit showing how the decltype operator essentially queries the type of an expression, the second part of this overview discusses how decltype can be syntactically combined with auto (itself the subject of the March 2010 tidbit). This combination can be used to specify trailing return types, also known informally as "late specified return types". Leaving aside the technical jargon, a simple example from section 8.3.5 of the C++11 standard usefully introduces this month's topic. Let's consider a template function like: template <class T, class U> ??? foo(T t, U u) { return t + u; } The question is: what should replace the question marks? The problem is that we are dealing with a template, thus we don't know at the outset the types of T and U. Even if they were restricted to be arithmetic builtin types, non-trivial rules in C++ relate the type of the sum to the types of T and U. In the past - in the GNU C++ runtime library too - programmers used to address these situations by way of rather ugly tricks involving __typeof__ which now, with decltype, could be rewritten as: template <class T, class U> decltype((*(T*)0) + (*(U*)0)) foo(T t, U u) { return t + u; } Of course the latter is guaranteed to work only for builtin arithmetic types, eg, '0' must make sense. In short: it's a hack. On the other hand, in C++11 you can use auto: template <class T, class U> auto foo(T t, U u) -> decltype(t + u) { return t + u; } This is much better. It's generic and a construct fully supported by the language. Finally, let's see a real-life example directly taken from the C++11 runtime library as implemented in GCC: template<typename _IteratorL, typename _IteratorR> inline auto operator-(const reverse_iterator<_IteratorL>& __x, const reverse_iterator<_IteratorR>& __y) -> decltype(__y.base() - __x.base()) { return __y.base() - __x.base(); } By now it should appear be completely straightforward. The availability of trailing return types in C++11 allowed fixing a real bug in the C++98 implementation of this operator (and many similar ones). In GCC, C++98 mode, this operator is: template<typename _IteratorL, typename _IteratorR> inline typename reverse_iterator<_IteratorL>::difference_type operator-(const reverse_iterator<_IteratorL>& __x, const reverse_iterator<_IteratorR>& __y) { return __y.base() - __x.base(); } This was guaranteed to work well with heterogeneous reverse_iterator types only if difference_type was the same for both types.

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• WHERE x = @x OR @x IS NULL

  - by steveh99999

  Every SQL DBA and developer should read the blog of MVP Erland Sommarskog – but particularly  his article on dynamic search conditions in T-SQL. I’ve linked above to his SQL 2005 article but his 2008 version is also a must-read. I seem to regularly come across uses of the SQL in the title above… Erland’s article explains in detail why this is inefficient, but I came across a nice example recently… A stored procedure contained the following code :- WHERE @Name is null or [Name] like @Name as a nonclustered index exists on the Name column, you might assume this would be handled efficiently by SQL Server. However, I got the following output from SET STATISTICS IO Table 'xxxxx'. Scan count 15, logical reads 47760, physical reads 9, read-ahead reads 13872, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Note the high number of logical reads… After a bit of investigation, we found that @Name could never actually be set to NULL in this particular example. ie the @x IS NULL was spurious… So, we changed the call to WHERE  [Name] like @Name Now, how much more efficient is this code ? Table 'xxxxx'. Scan count 3, logical reads 24, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0 A nice easy win in this case…… a full index scan has been replaced by a significantly more efficient index seek. I managed to recreate the same behaviour on Adventureworks – here’s a quick query to demonstrate :- USE adventureworks SET STATISTICS IO ON DECLARE @id INT = 51721 SELECT * FROM Sales.SalesOrderDetail WHERE @id IS NULL OR salesorderid = @id SELECT * FROM Sales.SalesOrderDetail WHERE salesorderid = @id Take a look at the STATISTICS IO output and compare the actual query plans used to prove the impact of  WHERE @id IS NULL. And just to follow some of Erland’s advice – here’s how you could get similar performance if it was possible that @id could actually sometimes contain NULL. DECLARE @sql NVARCHAR(4000), @parameterlist NVARCHAR(4000) DECLARE @id INT = 51721 – or change to NULL to prove query is functionally correct SET @sql = 'SELECT * FROM Sales.SalesOrderDetail WHERE 1 = 1' IF @id IS NOT NULL SET @sql = @sql + ' AND salesorderid = @id' IF @id IS NULL SET @sql = @sql + ' AND salesorderid IS NULL' SET @parameterlist = '@id INT' EXEC sp_executesql @sql, @parameterlist,@id Sometimes I think we focus too much on hardware and SQL Server configuration – when really the answer is focus on writing efficient SQL.

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• extern(al) problem

  - by Knowing me knowing you

  Why can't I compile this code? //main #include "stdafx.h" #include "X.h" #include "Y.h" //#include "def.h" extern X operator*(X, Y);//HERE ARE DECLARED EXTERNAL *(X,Y) AND f(X) extern int f(X); /*GLOBALS*/ X x = 1; Y y = x; int i = 2; int _tmain(int argc, _TCHAR* argv[]) { i + 10; y + 10; y + 10 * y; //x + (y + i); x * x + i; f(7); //f(y); //y + y; //106 + y; return 0; } //X struct X { int i; X(int value):i(value) { } X operator+(int value) { return X(i + value); } operator int() { return i; } }; //Y struct Y { int i; Y(X x):i(x.i) { } Y operator+(X x) { return Y(i + x.i); } }; //def.h int f(X x); X operator*(X x, Y y); //def.cpp #include "stdafx.h" #include "def.h" #include "X.h" #include "Y.h" int f(X x) { return x; } X operator*(X x, Y y) { return x * y; } I'm getting err msg: Error 2 error LNK2019: unresolved external symbol "int __cdecl f(struct X)" Error 3 error LNK2019: unresolved external symbol "struct X __cdecl operator*(struct X,struct Y)" Another interesting thing is that if I place the implementation in def.h file it does compiles without errs. But then what about def.cpp? Why I'm not getting err msg that function f(X) is already defined? Here shouldn't apply ODR rule. Second concern I'm having is that if in def.cpp I change the return type of f from int to double intelliSense underlines this as an error but program still compiles? Why?

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• Undefined Behavior and Sequence Points Reloaded

  - by Nawaz

  Consider this topic a sequel of the following topic: Previous Installment Undefined Behavior and Sequence Points Let's revisit this funny and convoluted expression (the italicized phrases are taken from the above topic *smile* ): i += ++i; We say this invokes undefined-behavior. I presume that when say this, we implicitly assume that type of i is one of built-in types. So my question is: what if the type of i is a user-defined type? Say it's type is Index which is defined later in this post (see below). Would it still invoke undefined-behavior? If yes, why? Is it not equivalent to writing i.operator+=(i.operator ++()); or even syntactically simpler i.add(i.inc());? Or, do they too invoke undefined-behavior? If no, why not? After all, the object i gets modified twice between consecutive sequence points. Please recall the rule of thumb : an expression can modify an object's value only once between consecutive "sequence points. And if i += ++i is an expression, then it must invoke undefined-behavior. If so, then it's equivalents i.operator+=(i.operator ++()); and i.add(i.inc()); must also invoke undefined-behavior which seems to be untrue! (as far as I understand) Or, i += ++i is not an expression to begin with? If so, then what is it and what is the definition of expression? If it's an expression, and at the same time, it's behavior is also well-defined, then it implies that number of sequence points associated with an expression somehow depends on the type of operands involved in the expression. Am I correct (even partly)? By the way, how about this expression? a[++i] = i; //taken from the previous topic. but here type of `i` is Index. class Index { int state; public: Index(int s) : state(s) {} Index& operator++() { state++; return *this; } Index& operator+=(const Index & index) { state+= index.state; return *this; } operator int() { return state; } Index & add(const Index & index) { state += index.state; return *this; } Index & inc() { state++; return *this; } };

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• Package upgrade on Ubuntu raid server and grub setup issue

  - by RecNes

  I have remote Ubuntu 10.10 server running on raid system. I did package upgrade yesterday night for security reasons. During the upgrade, grub installation screen appeared and asked me which partition I wanted to install grub. Options are sda,sdb,md1 and md2. I decide to install them on both sda and sdb partitions. I wondering, was I make true decision? If machine get reboot is it can be boot up safely? You can find fdisk output and fstab mount points below: Fstab: proc /proc proc defaults 0 0 none /dev/pts devpts gid=5,mode=620 0 0 /dev/md0 none swap sw 0 0 /dev/md1 /boot ext3 defaults 0 0 /dev/md2 / ext3 defaults 0 0 Fdisk: Disk /dev/sda: 750.2 GB, 750156374016 bytes 255 heads, 63 sectors/track, 91201 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: 0x00029bb5 Device Boot Start End Blocks Id System /dev/sda1 1 262 2102562 fd Linux raid autodetect /dev/sda2 263 295 265072+ fd Linux raid autodetect /dev/sda3 296 91201 730202445 fd Linux raid autodetect Disk /dev/md0: 2152 MB, 2152923136 bytes 2 heads, 4 sectors/track, 525616 cylinders Units = cylinders of 8 * 512 = 4096 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Disk /dev/md0 doesn't contain a valid partition table Disk /dev/md1: 271 MB, 271319040 bytes 2 heads, 4 sectors/track, 66240 cylinders Units = cylinders of 8 * 512 = 4096 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Disk /dev/md1 doesn't contain a valid partition table Disk /dev/md2: 747.7 GB, 747727224832 bytes 2 heads, 4 sectors/track, 182550592 cylinders Units = cylinders of 8 * 512 = 4096 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Disk /dev/md2 doesn't contain a valid partition table Disk /dev/sdb: 750.2 GB, 750156374016 bytes 255 heads, 63 sectors/track, 91201 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: 0x00088969 Device Boot Start End Blocks Id System /dev/sdb1 1 262 2102562 fd Linux raid autodetect /dev/sdb2 263 295 265072+ fd Linux raid autodetect /dev/sdb3 296 91201 730202445 fd Linux raid autodetect

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• How to use Hardware RAID in Ubuntu Server

  - by user2071938

  I have an Adaptec RAID-Controller and created an RAID-1(Mirroring) succesfully. Now I have installed Ubuntu Server 12.04.3. When I type fdisk -l I get this output: bf@fileserver:~$ sudo fdisk -l Disk /dev/sda: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x00000000 Disk /dev/sda doesn't contain a valid partition table Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x00000000 Disk /dev/sdb doesn't contain a valid partition table Disk /dev/sdc: 80.0 GB, 80026361856 bytes 255 heads, 63 sectors/track, 9729 cylinders, total 156301488 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: 0x0004c454 Device Boot Start End Blocks Id System /dev/sdc1 * 2048 499711 248832 83 Linux /dev/sdc2 501758 156301311 77899777 5 Extended /dev/sdc5 501760 156301311 77899776 8e Linux LVM Disk /dev/mapper/fileserver--vg-root: 75.6 GB, 75606523904 bytes 255 heads, 63 sectors/track, 9191 cylinders, total 147668992 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 Disk /dev/mapper/fileserver--vg-root doesn't contain a valid partition table Disk /dev/mapper/ddf1_Data: 1000.1 GB, 1000065728512 bytes 255 heads, 63 sectors/track, 121584 cylinders, total 1953253376 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x00000000 Disk /dev/mapper/ddf1_Data doesn't contain a valid partition table Disk /dev/mapper/fileserver--vg-swap_1: 4160 MB, 4160749568 bytes 255 heads, 63 sectors/track, 505 cylinders, total 8126464 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 Disk /dev/mapper/fileserver--vg-swap_1 doesn't contain a valid partition table The 80 GB HDD is for the System The 1000.2 GB HDD should be for my data. But I'm a bit confused becauser there are listed two 1000.2 GB HDDs, due the Hardware RAID shoudln't there be only one HDD vissible to the OS? (I have two 1000.2 GB HDDs in an Raid-1 Array) dmraid gives me bf@fileserver:~$ sudo dmraid -r /dev/sdb: ddf1, ".ddf1_disks", GROUP, ok, 1953253376 sectors, data@ 0 /dev/sda: ddf1, ".ddf1_disks", GROUP, ok, 1953253376 sectors, data@ 0 so It seems to be ok? But how do I partitionate this disks and which one should I mount(sdb or sda?) Hope you can help me thx Florian

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• Merging free space of hard drive to primary partition

  - by Dibya Ranjan

  I have purchased a new HDD, I tried to format making 1 primary partition, I converted the rest unallocated space to extended partition then to logical drive now I have 3 logical drives. I feel that the size allocated to the primary partition is less so I used shrink option to the 3 logical partitions in diskmgmt but each partition is resulting in one memory block of Free space. Now I want to merge these free spaces to my primary partition.

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• Recover RAID 5 data after created new array instead of re-using

  - by Brigadieren

  Folks please help - I am a newb with a major headache at hand (perfect storm situation). I have a 3 1tb hdd on my ubuntu 11.04 configured as software raid 5. The data had been copied weekly onto another separate off the computer hard drive until that completely failed and was thrown away. A few days back we had a power outage and after rebooting my box wouldn't mount the raid. In my infinite wisdom I entered mdadm --create -f... command instead of mdadm --assemble and didn't notice the travesty that I had done until after. It started the array degraded and proceeded with building and syncing it which took ~10 hours. After I was back I saw that that the array is successfully up and running but the raid is not I mean the individual drives are partitioned (partition type f8 ) but the md0 device is not. Realizing in horror what I have done I am trying to find some solutions. I just pray that --create didn't overwrite entire content of the hard driver. Could someone PLEASE help me out with this - the data that's on the drive is very important and unique ~10 years of photos, docs, etc. Is it possible that by specifying the participating hard drives in wrong order can make mdadm overwrite them? when I do mdadm --examine --scan I get something like ARRAY /dev/md/0 metadata=1.2 UUID=f1b4084a:720b5712:6d03b9e9:43afe51b name=<hostname>:0 Interestingly enough name used to be 'raid' and not the host hame with :0 appended. Here is the 'sanitized' config entries: DEVICE /dev/sdf1 /dev/sde1 /dev/sdd1 CREATE owner=root group=disk mode=0660 auto=yes HOMEHOST <system> MAILADDR root ARRAY /dev/md0 metadata=1.2 name=tanserv:0 UUID=f1b4084a:720b5712:6d03b9e9:43afe51b Here is the output from mdstat cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid5 sdd1[0] sdf1[3] sde1[1] 1953517568 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU] unused devices: <none> fdisk shows the following: fdisk -l Disk /dev/sda: 80.0 GB, 80026361856 bytes 255 heads, 63 sectors/track, 9729 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: 0x000bf62e Device Boot Start End Blocks Id System /dev/sda1 * 1 9443 75846656 83 Linux /dev/sda2 9443 9730 2301953 5 Extended /dev/sda5 9443 9730 2301952 82 Linux swap / Solaris Disk /dev/sdb: 750.2 GB, 750156374016 bytes 255 heads, 63 sectors/track, 91201 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: 0x000de8dd Device Boot Start End Blocks Id System /dev/sdb1 1 91201 732572001 8e Linux LVM Disk /dev/sdc: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 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: 0x00056a17 Device Boot Start End Blocks Id System /dev/sdc1 1 60801 488384001 8e Linux LVM Disk /dev/sdd: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 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: 0x000ca948 Device Boot Start End Blocks Id System /dev/sdd1 1 121601 976760001 fd Linux raid autodetect Disk /dev/dm-0: 1250.3 GB, 1250254913536 bytes 255 heads, 63 sectors/track, 152001 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: 0x00000000 Disk /dev/dm-0 doesn't contain a valid partition table Disk /dev/sde: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 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: 0x93a66687 Device Boot Start End Blocks Id System /dev/sde1 1 121601 976760001 fd Linux raid autodetect Disk /dev/sdf: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 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: 0xe6edc059 Device Boot Start End Blocks Id System /dev/sdf1 1 121601 976760001 fd Linux raid autodetect Disk /dev/md0: 2000.4 GB, 2000401989632 bytes 2 heads, 4 sectors/track, 488379392 cylinders Units = cylinders of 8 * 512 = 4096 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 524288 bytes / 1048576 bytes Disk identifier: 0x00000000 Disk /dev/md0 doesn't contain a valid partition table Per suggestions I did clean up the superblocks and re-created the array with --assume-clean option but with no luck at all. Is there any tool that will help me to revive at least some of the data? Can someone tell me what and how the mdadm --create does when syncs to destroy the data so I can write a tool to un-do whatever was done? After the re-creating of the raid I run fsck.ext4 /dev/md0 and here is the output root@tanserv:/etc/mdadm# fsck.ext4 /dev/md0 e2fsck 1.41.14 (22-Dec-2010) fsck.ext4: Superblock invalid, trying backup blocks... fsck.ext4: Bad magic number in super-block while trying to open /dev/md0 The superblock could not be read or does not describe a correct ext2 filesystem. If the device is valid and it really contains an ext2 filesystem (and not swap or ufs or something else), then the superblock is corrupt, and you might try running e2fsck with an alternate superblock: e2fsck -b 8193 Per Shanes' suggestion I tried root@tanserv:/home/mushegh# mkfs.ext4 -n /dev/md0 mke2fs 1.41.14 (22-Dec-2010) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=128 blocks, Stripe width=256 blocks 122101760 inodes, 488379392 blocks 24418969 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=0 14905 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, 102400000, 214990848 and run fsck.ext4 with every backup block but all returned the following: root@tanserv:/home/mushegh# fsck.ext4 -b 214990848 /dev/md0 e2fsck 1.41.14 (22-Dec-2010) fsck.ext4: Invalid argument while trying to open /dev/md0 The superblock could not be read or does not describe a correct ext2 filesystem. If the device is valid and it really contains an ext2 filesystem (and not swap or ufs or something else), then the superblock is corrupt, and you might try running e2fsck with an alternate superblock: e2fsck -b 8193 <device> Any suggestions? Regards!

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• Re-sizing disk partition linux/vm

  - by Tiffany Walker

  I VM Player running a linux guest and I was wanting to know how do I expand the disk? In the VM player I gave more disk space but I am not sure how to mount/expand/connect the new disk space to the system. My old disk space was 14GB [root@localhost ~]# df -h / Filesystem Size Used Avail Use% Mounted on /dev/mapper/VolGroup-lv_root 14G 4.5G 8.2G 36% / Then I expanded it and now I see sda2 which is the new space? [root@localhost ~]# fdisk -l Disk /dev/sda: 128.8 GB, 128849018880 bytes 255 heads, 63 sectors/track, 15665 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: 0x000cd44d Device Boot Start End Blocks Id System /dev/sda1 * 1 64 512000 83 Linux Partition 1 does not end on cylinder boundary. /dev/sda2 64 2611 20458496 8e Linux LVM Disk /dev/mapper/VolGroup-lv_root: 14.5 GB, 14537457664 bytes 255 heads, 63 sectors/track, 1767 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: 0x00000000 Disk /dev/mapper/VolGroup-lv_swap: 6408 MB, 6408896512 bytes 255 heads, 63 sectors/track, 779 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: 0x00000000 Do I need to mount the new space first? resize2fs -p /dev/mapper/VolGroup-lv_root 108849018880 resize2fs 1.41.12 (17-May-2010) The containing partition (or device) is only 3549184 (4k) blocks. You requested a new size of 1474836480 blocks. resize2fs -p /dev/mapper/VolGroup-lv_root 128849018880 resize2fs 1.41.12 (17-May-2010) resize2fs: Invalid new size: 128849018880 [root@localhost ~]# lvextend -L+90GB /dev/mapper/VolGroup-lv_root Extending logical volume lv_root to 103.54 GiB Insufficient free space: 23040 extents needed, but only 0 available [root@localhost ~]# lvextend -L90GB /dev/mapper/VolGroup-lv_root Extending logical volume lv_root to 90.00 GiB Insufficient free space: 19574 extents needed, but only 0 available EDIT: So after trying pvcreate/vgextend nothing has so far worked. I'm guessing the new disk space added from VM Player is not showing up? pvscan PV /dev/sda2 VG VolGroup lvm2 [19.51 GiB / 0 free] Total: 1 [19.51 GiB] / in use: 1 [19.51 GiB] / in no VG: 0 [0 ]

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• linux hardware raid 10 / lvm / virtual machine partition alignment and filesystem optimization

  - by Jason Ward

  I've been reading everything I can find about partition alignment and filesystem optimization (ext4 and xfs) but still don't know enough to be confident in setting up my current configuration. My remaining confusion comes from the LVM layer and if I should use raid parameters on the filesystem in guest os'es. My main questions are: When I use 'pvcreate --dataalignment' do I use the stripe-width as calculated for a filesystem on RAID (128kB for ext4 in my situation), the Stripe size of the RAID set (256kB), something else altogether, or do I not need this? When I create ext2/3/4 or xfs filesystems in guests on the Logical Volumes, should I add the settings for the underlying RAID (e.g. mkfs.ext4 -b 4096 -E stride=64,stripe-width=128)? Does anyone see any glaring errors in my set up below? I'm running some benchmarks now but haven't done enough to start comparing results. I have four drives in RAID 10 on a 3ware 9750-4i controller (more details on the settings below) giving me a 6.0TB device at /dev/sda. Here is my partition table: Model: LSI 9750-4i DISK (scsi) Disk /dev/sda: 5722024MiB Sector size (logical/physical): 512B/512B Partition Table: gpt Number Start End Size File system Name Flags 1 1.00MiB 257MiB 256MiB ext4 BOOTPART boot 2 257MiB 4353MiB 4096MiB linux-swap(v1) 3 4353MiB 266497MiB 262144MiB ext4 4 266497MiB 4460801MiB 4194304MiB Partition 1 is to be the /boot partition for my xen host. Partition 2 is swap. Partition 3 is to be the root (/) for my xen host. Partition 4 is to be (the only) physical volume to be used by LVM (for those who are counting, I left about 1.2TB unallocated for now) For my Xen guests, I usually create a Logical Volume of the needed size and present it to the guests for them to partition as needed. I know there are other ways of handling that but this method works best for my situation. Here's the hardware of interest on my CentOS 6.3 Xen Host: 4x Seagate Barracuda 3TB ST3000DM001 Drives (sector size: 512 logical/4096 physical) 3ware 9750-4i w/BBU (sector size reported: 512 logical/512 physical) All four drives make up a RAID 10 array. Stripe: 256kB Write Cache enabled Read Cache: intelligent StoreSave: Balance Thanks!

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• How can I recover XFS partitions from a formatted HD?

  - by giuprivite

  I deleted the partition table of my HD. I wanted to format another one, but by mistake, I formatted the wrong one. Then I also created some new partition on it. Now I would like, if possible, to recover my old data. The old configuration was this: A primary NTFS partition with Windows, and a secondary partition with four logical partitions: a swap and three XFS partitions (two for Ubuntu and OpenSuSE, and one with the home for both systems). This is the output I get when I run gpart in a terminal: ubuntu@ubuntu:~$ sudo gpart /dev/sdb Begin scan... Possible partition(Windows NT/W2K FS), size(39997mb), offset(0mb) Possible extended partition at offset(39997mb) Possible partition(Linux swap), size(8189mb), offset(39997mb) Possible partition(SGI XFS filesystem), size(40942mb), offset(48187mb) Possible partition(SGI XFS filesystem), size(40942mb), offset(89149mb) Possible partition(SGI XFS filesystem), size(175044mb), offset(130112mb) End scan. Checking partitions... Partition(OS/2 HPFS, NTFS, QNX or Advanced UNIX): primary Partition(Linux swap or Solaris/x86): logical Partition(Linux ext2 filesystem): logical Partition(Linux ext2 filesystem): orphaned logical Partition(Linux ext2 filesystem): orphaned logical Ok. Guessed primary partition table: Primary partition(1) type: 007(0x07)(OS/2 HPFS, NTFS, QNX or Advanced UNIX) size: 39997mb #s(81915360) s(63-81915422) chs: (0/1/1)-(1023/254/63)d (0/1/1)-(5098/254/51)r Primary partition(2) type: 015(0x0F)(Extended DOS, LBA) size: 265245mb #s(543221849) s(81915435-625137283) chs: (1023/254/63)-(1023/254/63)d (5099/0/1)-(38912/254/2)r Primary partition(3) type: 000(0x00)(unused) size: 0mb #s(0) s(0-0) chs: (0/0/0)-(0/0/0)d (0/0/0)-(0/0/0)r Primary partition(4) type: 000(0x00)(unused) size: 0mb #s(0) s(0-0) chs: (0/0/0)-(0/0/0)d (0/0/0)-(0/0/0)r Looking the first eight lines, it seems the data are still there... but I don't know how to recover them. I have a free second HD of about 500 GB (the formatted one is 320 GB) that I can use for the recovery process.

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• How can I recover XFS partitions from a formatted HD?

  - by giuprivite

  I deleted the partition table of my HD. I wanted to format another one, but by mistake, I formatted the wrong one. Then I also created some new partition on it. Now I would like, if possible, to recover my old data. The old configuration was this: A primary NTFS partition with Windows, and a secondary partition with four logical partitions: a swap and three XFS partitions (two for Ubuntu and OpenSuSE, and one with the home for both systems). This is the output I get when I run gpart in a terminal: ubuntu@ubuntu:~$ sudo gpart /dev/sdb Begin scan... Possible partition(Windows NT/W2K FS), size(39997mb), offset(0mb) Possible extended partition at offset(39997mb) Possible partition(Linux swap), size(8189mb), offset(39997mb) Possible partition(SGI XFS filesystem), size(40942mb), offset(48187mb) Possible partition(SGI XFS filesystem), size(40942mb), offset(89149mb) Possible partition(SGI XFS filesystem), size(175044mb), offset(130112mb) End scan. Checking partitions... Partition(OS/2 HPFS, NTFS, QNX or Advanced UNIX): primary Partition(Linux swap or Solaris/x86): logical Partition(Linux ext2 filesystem): logical Partition(Linux ext2 filesystem): orphaned logical Partition(Linux ext2 filesystem): orphaned logical Ok. Guessed primary partition table: Primary partition(1) type: 007(0x07)(OS/2 HPFS, NTFS, QNX or Advanced UNIX) size: 39997mb #s(81915360) s(63-81915422) chs: (0/1/1)-(1023/254/63)d (0/1/1)-(5098/254/51)r Primary partition(2) type: 015(0x0F)(Extended DOS, LBA) size: 265245mb #s(543221849) s(81915435-625137283) chs: (1023/254/63)-(1023/254/63)d (5099/0/1)-(38912/254/2)r Primary partition(3) type: 000(0x00)(unused) size: 0mb #s(0) s(0-0) chs: (0/0/0)-(0/0/0)d (0/0/0)-(0/0/0)r Primary partition(4) type: 000(0x00)(unused) size: 0mb #s(0) s(0-0) chs: (0/0/0)-(0/0/0)d (0/0/0)-(0/0/0)r Looking the first eight lines, it seems the data are still there... but I don't know how to recover them. I have a free second HD of about 500 GB (the formatted one is 320 GB) that I can use for the recovery process.

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• Deployment of broadband network

  - by sthustfo

  Hi all, My query is related to broadband network deployment. I have a DSL modem connection provided by my operator. Now the DSL modem has a built-in NAT and DHCP server, hence it allocates IP addresses to any client devices (laptops, PC, mobile) that connect to it. However, the DSL modem also gets a public IP address X that is provisioned by the operator. My question is Whether this IP address X provisioned by operator is an IP address that is directly on the public Internet? Is it likely (practical scenario) that my broadband operator will put in one more NAT+DHCP server and provide IP addresses to all the modems within his broadband network. In this case, the IP addresses allotted to the modem devices will not be directly on the public Internet. Thanks in advance.

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• solaris + EMC + power-path

  - by yael

  please advice - when I run powercf command on my Solaris machine , which changes this command do on the EMC storage , or on Solaris file system ? from maanual page: DESCRIPTION During system boot on Solaris hosts, the powercf utility configures PowerPath devices by scanning the HBAs for both single-ported and multiported storage system logical dev- ices. (A multiported logical device shows up on two or more HBAs with the same storage system subsystem/device identity. The identity comes from the serial number for the logical device.) For each storage system logical device found in the scan of the HBAs, powercf creates a corresponding emcpower device entry in the emcp.conf file, and it saves a primary path and an alternate primary path to that device.

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