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  • What does it mean to pass a &variable to a function? E.g., string& insert ( size_t pos1, const strin

    - by Bob Montgomery
    I understand passing a pointer, and returning a pointer: char * strcat ( char * destination, const char * source ); You're passing a variable that contains the address to a char; returning the same. But what does it mean to pass something using the reference operator? Or to return it? string& insert ( size_t pos1, const string& str ); I mean, I understand what actually happens, I just don't understand the notation. Why isn't the notation this instead: string * insert ( size_t pos1, const string * str ); //made up I presume it has something to do with passing/returning the instance of a class, but what? Is this syntax valid; if not why not and if so what does it mean? char & strcat ( char & destination, const char & source ); //made up (all of the function declarations, except the last made-up two, are from http://www.cplusplus.com )

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  • How to store and remove dynamically and automatic variable of generic data type in custum list data

    - by Vineel Kumar Reddy
    Hi I have created a List data structure implementation for generic data type with each node declared as following. struct Node { void *data; .... .... } So each node in my list will have pointer to the actual data(generic could be anything) item that should be stored in the list. I have following signature for adding a node to the list AddNode(struct List *list, void* eledata); the problem is when i want to remove a node i want to free even the data block pointed by *data pointer inside the node structure that is going to be freed. at first freeing of datablock seems to be straight forward free(data) // forget about the syntax..... But if data is pointing to a block created by malloc then the above call is fine....and we can free that block using free function int *x = (int*) malloc(sizeof(int)); *x = 10; AddNode(list,(void*)x); // x can be freed as it was created using malloc what if a node is created as following int x = 10; AddNode(list,(void*)&x); // x cannot be freed as it was not created using malloc Here we cannot call free on variable x!!!! How do i know or implement the functionality for both dynamically allocated variables and static ones....that are passed to my list.... Thanks in advance...

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  • Do variable references (alias) incure runtime costs in c++?

    - by cheshirekow
    Maybe this is a compiler specific thing. If so, how about for gcc (g++)? If you use a variable reference/alias like this: int x = 5; int& y = x; y += 10; Does it actually require more cycles than if we didn't use the reference. int x = 5; x += 10; In other words, does the machine code change, or does the "alias" happen only at the compiler level? This may seem like a dumb question, but I am curious. Especially in the case where maybe it would be convenient to temporarily rename some member variables just so that the math code is a little easier to read. Sure, we're not exactly talking about a bottleneck here... but it's something that I'm doing and so I'm just wondering if there is any 'actual' difference... or if it's only cosmetic.

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  • Why is my element variable always null in this foreach loop?

    - by ZeroDivide
    Here is the code: public IEnumerable<UserSummary> getUserSummaryList() { var db = new entityContext(); List<UserSummary> model = new List<UserSummary>(); List<aspnet_Users> users = (from user in db.aspnet_Users select user).ToList<aspnet_Users>(); foreach (aspnet_Users u in users) //u is always null while users is a list that contains 4 objects { model.Add(new UserSummary() { UserName = u.UserName, Email = u.aspnet_Membership.Email, Role = Roles.GetRolesForUser(u.UserName).First(), AdCompany = u.AD_COMPANIES.ad_company_name != null ? u.AD_COMPANIES.ad_company_name : "Not an Advertiser", EmployeeName = u.EMPLOYEE.emp_name != null ? u.EMPLOYEE.emp_name : "Not an Employee" }); } return model; } For some reason the u variable in the foreach loop is always null. I've stepped through the code and the users collection is always populated. The table entity for db.aspnet_Users is the users table that comes with asp.net membership services. I've only added a couple associations to it. edit : image of debugger

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  • Is there a better way to keep track of session variable creation/access throughout different pages?

    - by Brandon
    Here's what I am working on. At my website I have multiple processes with each one containing multiple steps. Now in one of the processes, there is an error checking routine executed before proceeding to the next step of that process. A session var is set indicating the error status and it will either redirect back to the referrer or display the next page's contents. Now this kind of functionality, I believe, is common throughout web development. The issue that is occurring is that session vars are left around and are not being cleaned up properly. At times this introduces undesired behavior. My website is growing and I find that I am requiring more and more session vars to keep track of different system and error states. So I was thinking about creating a kind of "session variable keeper" to keep track of session var usage. The idea is fairly simple. It will have the notion of a context (e.g. registration process) and allow access to a predefined set of session vars within that context. In addition, the var and context will be paired with an action to proceed to some form of event handling. So if you haven't noticed I'm new to web development. Any thoughts or comments on the idea that I am proposing would be greatly appreciated. The back-end is written in PHP/MySQL.

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  • Best way to carry & modify a variable through various instances and functions?

    - by bobsoap
    I'm looking for the "best practice" way to achieve a message / notification system. I'm using an OOP-based approach for the script and would like to do something along the lines of this: if(!$something) $messages->add('Something doesn\'t exist!'); The add() method in the messages class looks somewhat like this: class messages { public function add($new) { $messages = $THIS_IS_WHAT_IM_LOOKING_FOR; //array $messages[] = $new; $THIS_IS_WHAT_IM_LOOKING_FOR = $messages; } } In the end, there is a method in which reads out $messages and returns every message as nicely formatted HTML. So the questions is - what type of variable should I be using for $THIS_IS_WHAT_IM_LOOKING_FOR? I don't want to make this use the database. Querying the db every time just for some messages that occur at runtime and disappear after 5 seconds just seems like overkill. Using global constants for this is apparently worst practice, since constants are not meant to be variables that change over time. I don't even know if it would work. I don't want to always pass in and return the existing $messages array through the method every time I want to add a new message. I even tried using a session var for this, but that is obviously not suited for this purpose at all (it will always be 1 pageload too late). Any suggestions? Thanks!

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  • Mulitple variable containing "for loop" is not working in my code...

    - by OM The Eternity
    Below is the code I am working with and the last for loop i am iterating is not working... I think i am doing something wrong using multiple variable in a for loop,also I m aware of the fact that it can be done. $updaterbk = "SELECT j1. * FROM jos_audittrail j1 LEFT OUTER JOIN jos_audittrail j2 ON ( j1.trackid != j2.trackid AND j1.field != j2.field AND j1.changedone < j2.changedone ) WHERE j1.operation = 'UPDATE' AND j2.id IS NULL "; $selectupdrbk = mysql_query($updaterbk); while($row1 = mysql_fetch_array($selectupdrbk)) { $updrbk[] = $row1; } foreach($updrbk as $upfield) { if(!in_array($upfield['field'],$exist)) { $exist[] = $upfield['field']; $existval[] = $upfield['oldvalue']; //echo $updqueryrbk = "UPDATE `".$upfield['table_name']."` SET "; } } print_r($existval); for($i=0;$j=0;$i<count($exist);$j<count($existval);$i++;$j++) { $updqueryrbk.= $exist[$i]['field']."=".$existval[$j]['oldvalue'].","; $updqueryrbk.="="; $updqueryrbk.= $existval[$j]['oldvalue']; $updqueryrbk.=","; }

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  • I have a question about variable release in global class.

    - by Beomseok
    + (void)findAndCopyOfDatabaseIfNeeded{ NSArray *path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [path objectAtIndex:0]; NSFileManager *fileManager = [NSFileManager defaultManager]; NSString *databasePath = [documentsDirectory stringByAppendingPathComponent:@"DB"]; BOOL success = [fileManager fileExistsAtPath:databasePath]; if(!success){ NSString *resourcePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"DB"]; [fileManager copyItemAtPath:resourcePath toPath:databasePath error:NULL]; } NSString *tracePath = [documentsDirectory stringByAppendingPathComponent:@"Trace"]; BOOL traceDir = [fileManager fileExistsAtPath:tracePath]; if(!traceDir){ NSString *resourcePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Trace"]; [fileManager copyItemAtPath:resourcePath toPath:tracePath error:NULL]; } NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init]; [dateFormatter setDateFormat:@"yyyy"]; NSDate *today = [[NSDate alloc]init]; NSString *resultYear = [dateFormatter stringFromDate:today]; NSString *traceYearPath = [tracePath stringByAppendingPathComponent:resultYear]; BOOL yearDir = [fileManager fileExistsAtPath:tracePath]; if (!yearDir) { [fileManager createDirectoryAtPath:traceYearPath attributes:nil]; } //[resultYear release]; ? //[today release]; ? //[dateFormatter release]; ? } I'm using global class like this [ + (void)findAndCopyOfDatabaseIfNeeded ]. hm,, I don't know NSArray, NSString and NSFileManager are released. Variable release or Not release ? please advice for me.

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  • Using a variable derived from a drop-down list as the column name in a select statement ... Access DB

    - by user1459698
    I'm working with the world's worst DB that was already here so don't blame me for that. So, here's what I have so far ... module = txtModule.value presstype = txtPressType.value SQL_query = "SELECT * FROM tbl_spareparts WHERE '"& module &"' <> '""' AND '"& module &"' = '"& presstype &"' AND Manufacturer = '"& txtsrch.value &"' ORDER BY SAP_Part_No" Set rsData = conn.Execute(SQL_query) This brings up the following SQL statement: SELECT * FROM tbl_spareparts WHERE 'Banyan_Module' <> '"' AND 'Banyan_Module' = 'PB' AND Manufacturer = 'Tester' ORDER BY SAP_Part_No Is there any way I can use the module variable as a column name - obviously the ''s around the column name are causing an error. This is really bothering me. BTW, I'm writing this in VBScript inside a .HTA application page as it has to run locally on tech PCs. Thanks. R.

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  • Debug.Assert-s use the same error message. Should I promote it to a static variable?

    - by Hamish Grubijan
    I love Asserts and code readability but not code duplication, and in several places I use a Debug.Assert which checks for the same condition like so: Debug.Assert(kosherBaconList.SelectedIndex != -1, "An error message along the lines - you should not ever be able to click on edit button without selecting a kosher bacon first."); This is in response to an actual bug, although the actual list does not contain kosher bacon. Anyhow, I can think of two approaches: private static readonly mustSelectKosherBaconBeforeEditAssertMessage = "An error message along the lines - you should not ever be able to " + "click on edit button without selecting a something first."; ... Debug.Assert( kosherBaconList.SelectedIndex != -1, mustSelectKosherBaconBeforeEditAssertMessage) or: if (kosherBaconList.SelectedIndex == -1) { AssertMustSelectKosherBaconBeforeEdit(); } ... [Conditional("DEBUG")] private void AssertMustSelectKosherBaconBeforeEdit() { // Compiler will optimize away this variable. string errorMessage = "An error message along the lines - you should not ever be able to " + "click on edit button without selecting a something first."; Debug.Assert(false, errorMessage); } or is there a third way which sucks less than either one above? Please share. General helpful relevant tips are also welcome.

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  • Can a T-SQL variable represent an entire row?

    - by elbillaf
    I'm coding for MS SQL Server 10. I have two databases that contain dozens of tables. Each table in one database contains a table with the same name in the other database. Tables with the same name have identical format (fields and data types). The contents of the two tables are similar but not identical. I need to update one based on changes made to the other, but only under certain circumstances. I think I want to use a cursor for this, but I can't find a good example to go by. So far, the MSDN examples are reading one field at a time into a variable. I do need to be able to read /modify two fields which are identical in each table, but I gotta believe there's something less tedious than declaring variables for every field of every table. I would like to be able to FETCH an entire row, check a couple of fields and then make a decision of whether I want to write the entire row to the other table after changing two fields - but do I have to declare variables for EVERY field I want to fetch / write? There's no way to just FETCH an entire row and write an entire row?

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  • Javascript int variable from ASP.NET MVC Model data?

    - by Anders Svensson
    I need to get model data into a javascript variable and use it as an int to compare values. But I can only figure out how to get the model data as strings, otherwise the compiler complains. So how can I get the max and taskBudgetHours as int variables in the Javascript? <script type="text/javascript"> $(document).ready(function () { $("#taskForm").submit(function (e) { var taskBudgetHours = $('#BudgetHours').val(); var max = '<%: Model.Project.RemainingBudgetHours %>'; var test = 'test'; alert(taskBudgetHours); alert(max); if (taskBudgetHours <= max) { //This doesn't work, seems to treat it as strings... return true; } else { //Prevent the submit event and remain on the screen e.preventDefault(); alert('There are only ' + max + ' hours left of the project hours.'); return false; } }); return; }); </script>

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  • Mongodb, linq driver. How to construct Contains with variable or statements

    - by Syska
    I'm using the LINQ Driver for C#, works great. Sorting a lot of properties but heres a problem I can't solve, its probebly simple. var identifierList = new []{"10", "20", "30"}; var newList = list.Where(x => identifierList.Contains(x.Identifier)); This is NOT supported ... So I could do something like: var newList = list.Where(x => x.Identifier == "10" || x.Identifier == "20" || x.Identifier == "30"); But since the list is variable ... how do I construct the above? Or are there even better alternatives? The list is of type IQueryable<MyCustomClass> For information ... this is used as a filter of alot of properties. In SQL I could have a parent - child relationship. But as I can't as the parent for the main ID I need to take all the ID's out and then construct it like this. Hopes this makes sense. If needed I will explain more.

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  • C++: Static variable inside a constructor, are there any drawbacks or side effects?

    - by doc
    What I want to do: run some prerequisite code whenever instance of the class is going to be used inside a program. This code will check for requiremts etc. and should be run only once. I found that this can be achieved using another object as static variable inside a constructor. Here's an example for a better picture: class Prerequisites { public: Prerequisites() { std::cout << "checking requirements of C, "; std::cout << "registering C in dictionary, etc." << std::endl; } }; class C { public: C() { static Prerequisites prerequisites; std::cout << "normal initialization of C object" << std::endl; } }; What bothers me is that I haven't seen similar use of static variables so far. Are there any drawbacks or side-effects or am I missing something? Or maybe there is a better solution? Any suggestions are welcome.

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  • How to use a variable in a function expression which is injected in a page?

    - by anonymous
    I'm trying to inject a function into a webpage via Chrome extension content script by: function inject(code) { var actualCode = '(' + code + ')();'; var script = document.createElement('script'); script.textContent = actualCode; (document.head||document.documentElement).appendChild(script); script.parentNode.removeChild(script); } var myObj = person; // myObj/person is passed in from elsewhere var fn = function() { alert(myObj.name); }; inject(fn); // myObj undefined My issue is, since fn is a function expression, I can't pass in myObj.personName. So my question is, how can I construct a function expression that includes a variable? Do I do some sort of string concatenation instead? I also tried to pass the object to the function, as follows: function inject(code, myObj) { var actualCode = '(' + code + ')(' + myObj +');'; ... But this did not work, and caused a "Uncaught SyntaxError: Unexpected identifier" error. Related: Building a Chrome Extension - Inject code in a page using a Content script

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  • MATLAB: What is an appropriate Data Structure for a Matrix with Random Variable Entries?

    - by user568249
    I'm currently working in an area that is related to simulation and trying to design a data structure that can include random variables within matrices. To motivate this let me say I have the following matrix: [a b; c d] I want to find a data structure that will allow for a, b, c, d to either be real numbers or random variables. As an example, let's say that a = 1, b = -1, c = 2 but let d be a normally distributed random variable with mean 0 and SD 1. The data structure that I have in mind will give no value to d. However, I also want to be able to design a function that can take in the structure, simulate an uniform(0,1), obtain a value for d using an inverse CDF and then spit out an actual matrix. I have several ideas to do this (all related to the MATLAB icdf function) but would like to know how more experienced programmers would do this. In this application, it's important that the structure is as "lean" as possible since I will be working with very very large matrices and memory will be an issue.

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  • (iphone) How to access CGRect member variable inside c++ class?

    - by Eugene
    i have a c++ class with CGrect variable and i'm getting segfault when trying to access it. class Parent { //with some virtual functions/dtors }; class Child { public: void SetRect(CGRect rect) { mRect = rect; } CGRect GetRect() { return mRect; } int GetIndex() { return mIndex; } private: CGRect mRect; int mIndex; }; i'm doing CGRect rect = childPtr->GetRect(); from object c code and it segfaults. I printed *childPtr just before the call and rect looks fine with intended data value. int index = childPtr->GetIndex(); from same object c code(*.mm), works fine though. Any idea why I'm getting segfaults? Thank you edit - It's got something to do with virtual functions. (gdb) p singlePuzzlePiece-GetRect() Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00000001 0x00000001 in ?? () Cannot access memory at address 0x1 The program being debugged was signaled while in a function called from GDB. GDB remains in the frame where the signal was received. To change this behavior use "set unwindonsignal on" Evaluation of the expression containing the function (at 0x1) will be abandoned. (gdb) Somehow, the function is not properly compiled?

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  • Why does Java think my object is a variable?

    - by user2896898
    Ok so I'm trying to make a simple pong game. I have a paddle that follows the mouse and a ball that bounces around. I wrote a method collidesWith(Sprite s) inside of my Sprite class that checks if the ball collides with the paddle (this works and isn't the problem). I have two objects extending my sprite class, a ball and a paddle object. So inside of my ball class I'm trying to check if it collides with the paddle. So I've tried if(this.collidesWith(paddle) == true){ System.out.println("They touched"); } I've also tried ball.collidesWith(paddle) and other combinations but it always says the same thing about the paddle (and the ball when I use ball.collidesWith) "Cannot find symbol. Symbol: variable paddle(or ball). Location: class Ball" So if I'm reading this right, it thinks that the paddle (and ball) are variables and it's complaining because it can't find them. How can I make it understand I am passing in objects, not variables? For extra information, an earlier assignment had me make two boxes and for them to change colors when they were colliding. In that assignment I used very similar code to above with if(boxOne.collidesWith(boxTwo) == true){ System.out.println("yes"); } And in this code it worked just fine. The program knew that boxOne and boxTwo were child classes of my Sprite class. Anyone know why they wouldn't work the same?

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  • KVM/Libvirt bridged/routed networking not working on newer guest kernels

    - by SharkWipf
    I have a dedicated server running Debian 6, with Libvirt (0.9.11.3) and Qemu-KVM (qemu-kvm-1.0+dfsg-11, Debian). I am having a problem getting bridged/routed networking to work in KVM guests with newer kernels (2.6.38). NATted networking works fine though. Older kernels work perfectly fine as well. The host kernel is at version 3.2.0-2-amd64, the problem was also there on an older host kernel. The contents of the host's /etc/network/interfaces (ip removed): # Loopback device: auto lo iface lo inet loopback # bridge auto br0 iface br0 inet static address 176.9.xx.xx broadcast 176.9.xx.xx netmask 255.255.255.224 gateway 176.9.xx.xx pointopoint 176.9.xx.xx bridge_ports eth0 bridge_stp off bridge_maxwait 0 bridge_fd 0 up route add -host 176.9.xx.xx dev br0 # VM IP post-up mii-tool -F 100baseTx-FD br0 # default route to access subnet up route add -net 176.9.xx.xx netmask 255.255.255.224 gw 176.9.xx.xx br0 The output of ifconfig -a on the host: br0 Link encap:Ethernet HWaddr 54:04:a6:8a:66:13 inet addr:176.9.xx.xx Bcast:176.9.xx.xx Mask:255.255.255.224 inet6 addr: fe80::5604:a6ff:fe8a:6613/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:20216729 errors:0 dropped:0 overruns:0 frame:0 TX packets:19962220 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:14144528601 (13.1 GiB) TX bytes:7990702656 (7.4 GiB) eth0 Link encap:Ethernet HWaddr 54:04:a6:8a:66:13 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:26991788 errors:0 dropped:12066 overruns:0 frame:0 TX packets:19737261 errors:270082 dropped:0 overruns:0 carrier:270082 collisions:1686317 txqueuelen:1000 RX bytes:15459970915 (14.3 GiB) TX bytes:6661808415 (6.2 GiB) Interrupt:17 Memory:fe500000-fe520000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:6240133 errors:0 dropped:0 overruns:0 frame:0 TX packets:6240133 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:6081956230 (5.6 GiB) TX bytes:6081956230 (5.6 GiB) virbr0 Link encap:Ethernet HWaddr 52:54:00:79:e4:5a inet addr:192.168.100.1 Bcast:192.168.100.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:225016 errors:0 dropped:0 overruns:0 frame:0 TX packets:412958 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:16284276 (15.5 MiB) TX bytes:687827984 (655.9 MiB) virbr0-nic Link encap:Ethernet HWaddr 52:54:00:79:e4:5a BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:500 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) vnet0 Link encap:Ethernet HWaddr fe:54:00:93:4e:68 inet6 addr: fe80::fc54:ff:fe93:4e68/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:607670 errors:0 dropped:0 overruns:0 frame:0 TX packets:5932089 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:500 RX bytes:83574773 (79.7 MiB) TX bytes:1092482370 (1.0 GiB) vnet1 Link encap:Ethernet HWaddr fe:54:00:ed:6a:43 inet6 addr: fe80::fc54:ff:feed:6a43/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:922132 errors:0 dropped:0 overruns:0 frame:0 TX packets:6342375 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:500 RX bytes:251091242 (239.4 MiB) TX bytes:1629079567 (1.5 GiB) vnet2 Link encap:Ethernet HWaddr fe:54:00:0d:cb:3d inet6 addr: fe80::fc54:ff:fe0d:cb3d/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:9461 errors:0 dropped:0 overruns:0 frame:0 TX packets:665189 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:500 RX bytes:4990275 (4.7 MiB) TX bytes:49229647 (46.9 MiB) vnet3 Link encap:Ethernet HWaddr fe:54:cd:83:eb:aa inet6 addr: fe80::fc54:cdff:fe83:ebaa/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1649 errors:0 dropped:0 overruns:0 frame:0 TX packets:12177 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:500 RX bytes:77233 (75.4 KiB) TX bytes:2127934 (2.0 MiB) The guest's /etc/network/interfaces, in this case running Ubuntu 12.04 (ip removed): # This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). # The loopback network interface auto lo iface lo inet loopback auto eth0 iface eth0 inet static address 176.9.xx.xx netmask 255.255.255.248 gateway 176.9.xx.xx # Host IP pointopoint 176.9.xx.xx # Host IP dns-nameservers 8.8.8.8 8.8.4.4 The output of ifconfig -a on the guest: eth0 Link encap:Ethernet HWaddr 52:54:cd:83:eb:aa inet addr:176.9.xx.xx Bcast:0.0.0.0 Mask:255.255.255.255 inet6 addr: fe80::5054:cdff:fe83:ebaa/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:14190 errors:0 dropped:0 overruns:0 frame:0 TX packets:1768 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:2614642 (2.6 MB) TX bytes:82700 (82.7 KB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:954 errors:0 dropped:0 overruns:0 frame:0 TX packets:954 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:176679 (176.6 KB) TX bytes:176679 (176.6 KB) Output of ping -c4 on the guest: PING google.nl (173.194.35.151) 56(84) bytes of data. 64 bytes from muc03s01-in-f23.1e100.net (173.194.35.151): icmp_req=1 ttl=55 time=14.7 ms From static.174.82.xx.xx.clients.your-server.de (176.9.xx.xx): icmp_seq=2 Redirect Host(New nexthop: static.161.82.9.176.clients.your-server.de (176.9.82.161)) 64 bytes from muc03s01-in-f23.1e100.net (173.194.35.151): icmp_req=2 ttl=55 time=15.1 ms From static.198.170.9.176.clients.your-server.de (176.9.170.198) icmp_seq=3 Destination Host Unreachable From static.198.170.9.176.clients.your-server.de (176.9.170.198) icmp_seq=4 Destination Host Unreachable --- google.nl ping statistics --- 4 packets transmitted, 2 received, +2 errors, 50% packet loss, time 3002ms rtt min/avg/max/mdev = 14.797/14.983/15.170/0.223 ms, pipe 2 The static.174.82.xx.xx.clients.your-server.de (176.9.xx.xx) is the host's IP. I have encountered this problem with every guest OS I've tried, that being Fedora, Ubuntu (server/desktop) and Debian with an upgraded kernel. I've also tried compiling the guest kernel myself, to no avail. I have no problem with recompiling a kernel, though the host cannot afford any downtime. Any ideas on this problem are very welcome. EDIT: I can ping the host from inside the guest.

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  • Why would ssh fail to expand %h variable in .ssh/config?

    - by Zoran
    Why would ssh fail to expand %h from .ssh/config? This used to work and still works except on a RHEL box. Looking for what the origin of this could be. Is there a setting somewhere that tells ssh to not expand %h? I have something like this in my .ssh/config: Host *.foo HostName %h.mydomain.com On the RHEL box where this doesn't work, I get this: $ ssh -vvvv bar.foo OpenSSH_5.3p1, OpenSSL 1.0.0-fips 29 Mar 2010 debug1: Reading configuration data /home/zsimic/.ssh/config debug1: Applying options for *.foo debug1: Applying options for *.foo debug1: Applying options for * debug1: Reading configuration data /etc/ssh/ssh_config debug1: Applying options for * debug2: ssh_connect: needpriv 0 ssh: Could not resolve hostname %h.mydomain.com: Name or service not known

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  • Virtual Machine with Bridged Adapter to Centos not accepting ssh from host machine [migrated]

    - by javadba
    I have a bridged connection on VirtualBox from os/x 10.8.5 host to Centos 5.8 client. But I suspect this is more of a general issue than specific to the host and precise version of linux. Shown below are the networking info from the VirtualBox and from within the guest sshd is running on port 22: [root@oracle-linux ~]# ps -ef | grep sshd | grep -v grep root 3103 1 0 20:22 ? 00:00:00 /usr/sbin/sshd root 14994 3103 0 21:23 ? 00:00:00 sshd: root@pts/1 Port 22 listening: [root@oracle-linux ~]# netstat -an | grep 22 | grep tcp | grep LIST tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:2207 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:2208 0.0.0.0:* LISTEN tcp 0 0 :::22 :::* LISTEN Here are ip addresses, still on the guest os: [root@oracle-linux ~]# ip addr 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000 link/ether 08:00:27:b9:e5:79 brd ff:ff:ff:ff:ff:ff inet 10.0.15.100/24 brd 10.0.15.255 scope global eth0 inet6 fe80::a00:27ff:feb9:e579/64 scope link valid_lft forever preferred_lft forever 3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000 link/ether 08:00:27:b4:86:8a brd ff:ff:ff:ff:ff:ff inet 10.0.3.15/24 brd 10.0.3.255 scope global eth1 inet6 fe80::a00:27ff:feb4:868a/64 scope link valid_lft forever preferred_lft forever [root@oracle-linux ~]# I can ssh to the guest from the guest: root@oracle-linux ~]# ssh 10.0.3.15 The authenticity of host '10.0.3.15 (10.0.3.15)' can't be established. RSA key fingerprint is ef:08:19:72:95:4d:e5:28:af:f3:6f:54:07:84:ba:04. Are you sure you want to continue connecting (yes/no)? yes Warning: Permanently added '10.0.3.15' (RSA) to the list of known hosts. [email protected]'s password: Last login: Mon Oct 21 21:24:12 2013 from 10.0.15.100 But can NOT ssh from the host to the guest: 18:27:04/shared:11 $ssh [email protected] ssh: connect to host 10.0.15.100 port 22: Operation timed out lost connection Here is bridged connection infO; BTW I looked into other answers, and one of them mentioned doing service iptables stop That did not help. Adapter 2 is a NAT, shown below In case NAT is causing any issues, i shut it down and restarted networking. [root@oracle-linux ~]# /etc/init.d/network restart Shutting down interface eth0: [ OK ] Shutting down interface eth1: Still No joy.. 18:27:04/shared:11 $ssh [email protected] ssh: connect to host 10.0.15.100 port 22: Operation timed out lost connection

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  • How well will ntpd work when the latency is highly variable?

    - by JP Anderson
    I have an application where we are using some non-standard networking equipment (cannot be changed) that goes into a dormant state between traffic bursts. The network latency is very high for the first packet since it's essentially waking the system, waiting for it to reconnect, and then making the first round-trip. Subsequent messages (provided they are within the next minute or so) are much faster, but still highly-latent. A typical set of pings will look like 2500ms, 900ms, 880ms, 885ms, 900ms, 890ms, etc. Given that NTP uses several round trips before computing the offset, how well can I expect ntpd to work over this kind of link? Will the initially slow first round trip be ignored based on the much different (and faster) following messages to/from the ntp server? Thanks and Regards.

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  • RTNETLINK answers: Invalid argument

    - by LinuxPenseur
    When my system boots up it shows the following message. Bringing up loopback interface: [ OK ] Bringing up interface eth0: RTNETLINK answers: Invalid argument [ OK ] Bringing up interface eth1: RTNETLINK answers: Invalid argument [ OK ] Bringing up interface eth2: RTNETLINK answers: Invalid argument [ OK ] Bringing up interface eth3: RTNETLINK answers: Invalid argument [ OK ] Why is this happening. Normally it does not give the message RTNETLINK answers: Invalid argument I did ifconfig and the output is eth0 Link encap:Ethernet HWaddr 00:00:50:6D:56:B4 inet addr:120.0.10.137 Bcast:120.0.255.255 Mask:255.255.255.0 inet6 addr: fe80::200:50ff:fe6d:56b4/64 Scope:Link UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:3 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 b) TX bytes:214 (214.0 b) Base address:0xa000 eth1 Link encap:Ethernet HWaddr 00:00:50:6D:56:B5 inet addr:121.0.10.137 Bcast:121.0.255.255 Mask:255.255.255.0 inet6 addr: fe80::200:50ff:fe6d:56b5/64 Scope:Link UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:3 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 b) TX bytes:214 (214.0 b) Base address:0xc000 eth2 Link encap:Ethernet HWaddr 00:00:50:6D:56:B6 inet addr:128.0.10.137 Bcast:128.0.255.255 Mask:255.255.255.0 inet6 addr: fe80::200:50ff:fe6d:56b6/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:14 errors:0 dropped:0 overruns:0 frame:0 TX packets:4 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:1006 (1006.0 b) TX bytes:396 (396.0 b) Interrupt:16 eth3 Link encap:Ethernet HWaddr 00:00:50:6D:56:B7 inet addr:123.0.10.137 Bcast:123.0.255.255 Mask:255.255.255.0 inet6 addr: fe80::200:50ff:fe6d:56b7/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:10 errors:0 dropped:0 overruns:0 frame:0 TX packets:4 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:728 (728.0 b) TX bytes:396 (396.0 b) Interrupt:17 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:14 errors:0 dropped:0 overruns:0 frame:0 TX packets:14 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:980 (980.0 b) TX bytes:980 (980.0 b) What could be the reason for the message and how to change this to normal? Thanks

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  • Virtual Machine with Bridged Adapter to Centos not accepting ssh from host machine

    - by javadba
    I have a bridged connection on VirtualBox from os/x 10.8.5 host to Centos 5.8 client. But I suspect this is more of a general issue than specific to the host and precise version of linux. Shown below are the networking info from the VirtualBox and from within the guest sshd is running on port 22: [root@oracle-linux ~]# ps -ef | grep sshd | grep -v grep root 3103 1 0 20:22 ? 00:00:00 /usr/sbin/sshd root 14994 3103 0 21:23 ? 00:00:00 sshd: root@pts/1 Port 22 listening: [root@oracle-linux ~]# netstat -an | grep 22 | grep tcp | grep LIST tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:2207 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:2208 0.0.0.0:* LISTEN tcp 0 0 :::22 :::* LISTEN Here are ip addresses, still on the guest os: [root@oracle-linux ~]# ip addr 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000 link/ether 08:00:27:b9:e5:79 brd ff:ff:ff:ff:ff:ff inet 10.0.15.100/24 brd 10.0.15.255 scope global eth0 inet6 fe80::a00:27ff:feb9:e579/64 scope link valid_lft forever preferred_lft forever 3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000 link/ether 08:00:27:b4:86:8a brd ff:ff:ff:ff:ff:ff inet 10.0.3.15/24 brd 10.0.3.255 scope global eth1 inet6 fe80::a00:27ff:feb4:868a/64 scope link valid_lft forever preferred_lft forever [root@oracle-linux ~]# I can ssh to the guest from the guest: root@oracle-linux ~]# ssh 10.0.3.15 The authenticity of host '10.0.3.15 (10.0.3.15)' can't be established. RSA key fingerprint is ef:08:19:72:95:4d:e5:28:af:f3:6f:54:07:84:ba:04. Are you sure you want to continue connecting (yes/no)? yes Warning: Permanently added '10.0.3.15' (RSA) to the list of known hosts. [email protected]'s password: Last login: Mon Oct 21 21:24:12 2013 from 10.0.15.100 But can NOT ssh from the host to the guest: 18:27:04/shared:11 $ssh [email protected] ssh: connect to host 10.0.15.100 port 22: Operation timed out lost connection Here is bridged connection infO; BTW I looked into other answers, and one of them mentioned doing service iptables stop That did not help. Adapter 2 is a NAT, shown below In case NAT is causing any issues, i shut it down and restarted networking. [root@oracle-linux ~]# /etc/init.d/network restart Shutting down interface eth0: [ OK ] Shutting down interface eth1: Still No joy.. 18:27:04/shared:11 $ssh [email protected] ssh: connect to host 10.0.15.100 port 22: Operation timed out lost connection

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  • Pinging an external server through OpenVPN tunnel doesn’t work

    - by qdii
    I have an OpenVPN server and a client, and I want to use this tunnel to access not only 10.0.8.0/24 but the whole internet. So far, pinging the server from the client through the tun0 interface works, and vice versa. However, pinging www.google.com from the client through tun0 doesn’t work (all packets are lost). I figured that I should configure the server so that any packet coming from tun0 in destination of the internet be forwarded, so I came up with this iptables config line: interface_connecting_to_the_internet='eth0' interface_openvpn='tun0' internet_ip_address=`ifconfig "$interface_connecting_to_the_internet" | sed -n s'/.*inet \([0-9.]*\).*/\1/p'` iptables -t nat -A POSTROUTING -o "${interface_connecting_to_the_internet}" -j SNAT --to-source "${internet_ip_address}" echo '1' > /proc/sys/net/ipv4/ip_forward Yet, this doesn’t work, the packets are still lost and I am wondering what could possibly be wrong with my setup. Some details: ip route gives on the server: default via 176.31.127.254 dev eth0 metric 3 10.8.0.0/24 via 10.8.0.2 dev tun0 10.8.0.2 dev tun0 proto kernel scope link src 10.8.0.1 127.0.0.0/8 via 127.0.0.1 dev lo 176.31.127.0/24 dev eth0 proto kernel scope link src 176.31.127.109 ip route gives on the client: default via 192.168.1.1 dev wlan0 proto static 10.8.0.1 via 10.8.0.5 dev tun0 10.8.0.5 dev tun0 proto kernel scope link src 10.8.0.6 127.0.0.0/8 via 127.0.0.1 dev lo scope link 192.168.1.0/24 dev wlan0 proto kernel scope link src 192.168.1.109 client uses wifi adapter wlan0 and TUN adapter tun0. server uses ethernet adapter eth0 and TUN adapter tun0. the VPN spans on 10.0.8.0/24 both client and linux are using Linux 3.6.1.

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