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  • Write magic bytes to the stack to monitor its usage

    - by tkarls
    I have a problem on an embedded device that I think might be related to a stack overflow. In order to test this I was planning to fill the stack with magic bytes and then periodically check if the stack has overflowed by examining how much of my magic bytes that are left intact. But I can't get the routine for marking the stack to work. The application keeps crashing instantly. This is what I have done just at the entry point of the program. //fill most of stack with magic bytes int stackvar = 0; int stackAddr = int(&stackvar); int stackAddrEnd = stackAddr - 25000; BYTE* stackEnd = (BYTE*) stackAddrEnd; for(int i = 0; i < 25000; ++i) { *(stackEnd + i) = 0xFA; } Please note that the allocated stack is larger than 25k. So I'm counting on some stack space to already be used at this point. Also note that the stack grows from higher to lower addresses that's why I'm trying to fill from the bottom and up. But as I said, this will crash. I must be missing something here.

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  • Command not write in buffer with Expect

    - by Romuald
    Hello, I try to backup a Linkproof device with expect script and i have some trouble. It's my first script in expect and i have reach my limits ;) #!/usr/bin/expect spawn ssh @IPADDRESS expect "username:" # Send the username, and then wait for a password prompt. send "@username\r" expect "password:" # Send the password, and then wait for a shell prompt. send "@password\r" expect "#" # Send the prebuilt command, and then wait for another shell prompt. send "system config immediate\r" #Send space to pass the pause expect -re "^ *--More--\[^\n\r]*" send "" expect -re "^ *--More--\[^\n\r]*" send "" expect -re "^ *--More--\[^\n\r]*" send "" # Capture the results of the command into a variable. This can be displayed, or written to disk. sleep 10 expect -re .* set results $expect_out(buffer) # Copy buffer in a file set config [open linkproof.txt w] puts $config $results close $config # Exit the session. expect "#" send "logout\r" expect eof The content of the output file: The authenticity of host '@IP (XXX.XXX.XXX.XXX)' can't be established. RSA key fingerprint is XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX. Are you sure you want to continue connecting (yes/no)? @username Please type 'yes' or 'no': @password Please type 'yes' or 'no': system config immediate Please type 'yes' or 'no': Like you can see, the result of the command is not in the file. Could you, please, help me to understantd why ? Thanks for your help. Romuald

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  • using in-line asm to write a for loop with 2 comparisons

    - by aCuria
    I want to convert the for loop in the following code into assembly but i am not sure how to start. An explanation of how to do it and why it works would be appreciated. I am using VS2010, C++, writing for the x86. The code is as follows: for (n = 0; norm2 < 4.0 && n < N; ++n) { __asm{ ///a*a - b*b + x fld a // a fmul st(0), st(0) // aa fld b // b aa fmul st(0), st(0) // bb aa fsub // (aa-bb) // st(0) - st(1) fld x // x (aa-bb) fadd // (aa-bb+x) /// 2.0*a*b + y; fld d // d (aa-bb+x) fld a // d a (aa-bb+x) fmul // ad (aa-bb+x) fld b // b ad (aa-bb+x) fmul // abd (aa-bb+x) fld y // y adb (aa-bb+x) fadd // b:(adb+y) a:(aa-bb+x) fld st(0) //b b:(adb+y) a:(aa-bb+x) fmul st(0), st(0) // bb b:(adb+y) a:(aa-bb+x) fld st(2) // a bb b:(adb+y) a:(aa-bb+x) fmul st(0), st(0) // aa bb b:(adb+y) a:(aa-bb+x) fadd // aa+bb b:(adb+y) a:(aa-bb+x) fstp norm2 // store aa+bb to norm2, st(0) is popped. fstp b fstp a } }

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  • Why would this Lua optimization hack help?

    - by Ian Boyd
    i'm looking over a document that describes various techniques to improve performance of Lua script code, and i'm shocked that such tricks would be required. (Although i'm quoting Lua, i've seen similar hacks in Javascript). Why would this optimization be required: For instance, the code for i = 1, 1000000 do local x = math.sin(i) end runs 30% slower than this one: local sin = math.sin for i = 1, 1000000 do local x = sin(i) end They're re-declaring sin function locally. Why would this be helpful? It's the job of the compiler to do that anyway. Why is the programmer having to do the compiler's job? i've seen similar things in Javascript; and so obviously there must be a very good reason why the interpreting compiler isn't doing its job. What is it? i see it repeatedly in the Lua environment i'm fiddling in; people redeclaring variables as local: local strfind = strfind local strlen = strlen local gsub = gsub local pairs = pairs local ipairs = ipairs local type = type local tinsert = tinsert local tremove = tremove local unpack = unpack local max = max local min = min local floor = floor local ceil = ceil local loadstring = loadstring local tostring = tostring local setmetatable = setmetatable local getmetatable = getmetatable local format = format local sin = math.sin What is going on here that people have to do the work of the compiler? Is the compiler confused by how to find format? Why is this an issue that a programmer has to deal with? Why would this not have been taken care of in 1993? i also seem to have hit a logical paradox: Optimizatin should not be done without profiling Lua has no ability to be profiled Lua should not be optimized

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  • Why 'The' is used? [closed]

    - by akula
    I'm looking for a clear answer for this English grammar question: Why do we write: The UCI Road World Championships 2012 (when the year mentioned) The Republic of India (when there is only one nation) but NOT The India? The Monaco Grand Prix (only one place which holds GP with that name) Lake Baikal in South of the Russia (why not Lake Baikal in the Russia?) I know the answer: The grammar usage is Definite Article but I'm looking for a clear explanation to this question. Thank you

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  • Why does hardware get slower with time?

    - by Alexey Kulikov
    Why does hardware get slower with time? I have been a PC owner since 1990 and every computer I have had in my life became really, really slow after 3-4 years (even with a full system-reinstall). It is the case with Windows PCs. It is also the case with Apple Hardware. Why is this happening? Can this be avoided?

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  • Why does Kerberos need Ticket Granting Server?

    - by Narsil
    It's probably something fundamental but I can't find a certain statement. Why can't KDC authenticate then provide the service ticket directly. Is it about security or performance or some other thing? Since users don't log in each time they request a service and assumably they will keep logged in for a long time, AS doesn't seem so busy. Why do they have to be seperated?

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  • Why would you use IPv6 internally?

    - by KCotreau
    Of course, I realize the need to go to IPv6 out on the open Internet since we are running out of addresses, but I really don't understand why there is any need to use it on an internal network. I have done zero with IPv6, so I also wonder: Won't modern firewalls do NAT between internal IPv4 addresses, and external IPv6 addresses? I was just wondering since I have seen so many people struggling with IPv6 questions here, and wonder why bother?

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  • Why specifying keyboard layout?

    - by amyassin
    Most operating systems (if not all) asks about the keyboard layout during installation. Why do they need to know the layout? I mean, when pressing key, does the keyboard send a specific signal indicating what it represents (if so, why needing to specify the layout?) or it sends a signal indicating its position (the second raw, third key) and then the OS detects what key is that from the layout specified?

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  • not able to write log file to specified path(Microsoft Enterprise Library Logging)

    - by prince23
    hi, i am trying to implement the logging Configuration using Microsoft Enterprise Library Logging class Program { static void Main(string[] args) { LogEntry entry = new LogEntry() { Message = "Hello Ent. Lib. Logging" }; Logger.Write(entry); } } here the entry conyain she details. but these details are not written in the file i web config i have the settings done like this. <?xml version="1.0" encoding="utf-8"?> <configuration> <configSections> <section name="loggingConfiguration" type="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.LoggingSettings, Microsoft.Practices.EnterpriseLibrary.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" /> <section name="exceptionHandling" type="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Configuration.ExceptionHandlingSettings, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" /> <section name="dataConfiguration" type="Microsoft.Practices.EnterpriseLibrary.Data.Configuration.DatabaseSettings, Microsoft.Practices.EnterpriseLibrary.Data, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" /> </configSections> <loggingConfiguration name="Logging Application Block" tracingEnabled="true" defaultCategory="General" logWarningsWhenNoCategoriesMatch="true"> <listeners> <add fileName="C:\Inetpub\wwwroot\trace.log" header="----------------------------------------" footer="----------------------------------------" formatter="" listenerDataType="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.FlatFileTraceListenerData, Microsoft.Practices.EnterpriseLibrary.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" traceOutputOptions="None" filter="All" type="Microsoft.Practices.EnterpriseLibrary.Logging.TraceListeners.FlatFileTraceListener, Microsoft.Practices.EnterpriseLibrary.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" name="FlatFile TraceListener" /> <add source="Enterprise Library Logging" formatter="Text Formatter" log="Application" machineName="" listenerDataType="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.FormattedEventLogTraceListenerData, Microsoft.Practices.EnterpriseLibrary.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" traceOutputOptions="None" filter="All" type="Microsoft.Practices.EnterpriseLibrary.Logging.TraceListeners.FormattedEventLogTraceListener, Microsoft.Practices.EnterpriseLibrary.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" name="Formatted EventLog TraceListener" /> </listeners> <formatters> <add template="Timestamp: {timestamp}&#xD;&#xA;Message: {message}&#xD;&#xA;Category: {category}&#xD;&#xA;Priority: {priority}&#xD;&#xA;EventId: {eventid}&#xD;&#xA;Severity: {severity}&#xD;&#xA;Title:{title}&#xD;&#xA;Machine: {machine}&#xD;&#xA;Application Domain: {appDomain}&#xD;&#xA;Process Id: {processId}&#xD;&#xA;Process Name: {processName}&#xD;&#xA;Win32 Thread Id: {win32ThreadId}&#xD;&#xA;Thread Name: {threadName}&#xD;&#xA;Extended Properties: {dictionary({key} - {value}&#xD;&#xA;)}" type="Microsoft.Practices.EnterpriseLibrary.Logging.Formatters.TextFormatter, Microsoft.Practices.EnterpriseLibrary.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" name="Text Formatter" /> </formatters> <categorySources> <add switchValue="All" name="General"> <listeners> <add name="Formatted EventLog TraceListener" /> </listeners> </add> </categorySources> <specialSources> <allEvents switchValue="All" name="All Events" /> <notProcessed switchValue="All" name="Unprocessed Category" /> <errors switchValue="All" name="Logging Errors &amp; Warnings"> <listeners> <add name="Formatted EventLog TraceListener" /> </listeners> </errors> </specialSources> </loggingConfiguration> <exceptionHandling> <exceptionPolicies> <add name="Exception Policy"> <exceptionTypes> <add type="System.Exception, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" postHandlingAction="NotifyRethrow" name="Exception" /> </exceptionTypes> </add> </exceptionPolicies> </exceptionHandling> </configuration> i am trying by best to solve this from past 2 days. if any one knw what is the issue here. why my log file is not written in the specified path. and even the details of log are not written in the file path fileName="C:\Inetpub\wwwroot\trace.log"

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  • Trying to write a std::iterator : Compilation error

    - by Naveen
    I am trying to write an std::iterator for the CArray<Type,ArgType> MFC class. This is what I have done till now: template <class Type, class ArgType> class CArrayIterator : public std::iterator<std::random_access_iterator_tag, ArgType> { public: CArrayIterator(CArray<Type,ArgType>& array_in, int index_in = 0) : m_pArray(&array_in), m_index(index_in) { } void operator++() { ++m_index; } void operator++(int) { ++m_index; } void operator--() { --m_index; } void operator--(int) { --m_index; } void operator+=(int n) { m_index += n; } void operator-=(int n) { m_index -= n; } typename ArgType operator*() const{ return m_pArray->GetAt(m_index); } typename ArgType operator->() const { return m_pArray->GetAt(m_index); } bool operator==(const CArrayIterator& other) const { return m_pArray == other.m_pArray && m_index == other.m_index; } bool operator!=(const CArrayIterator& other) const { return ! (operator==(other)); } private: CArray<Type,ArgType>* m_pArray; int m_index; }; I also provided two helper functions to create the iterators like this: template<class Type, class ArgType> CArrayIterator<Type,ArgType> make_begin(CArray<Type,ArgType>& array_in) { return CArrayIterator<Type,ArgType>(array_in, 0); } template<class Type, class ArgType> CArrayIterator<Type,ArgType> make_end(CArray<Type,ArgType>& array_in) { return CArrayIterator<Type,ArgType>(array_in, array_in.GetSize()); } To test the code, I wrote a simple class A and tried to use it like this: class A { public: A(int n): m_i(n) { } int get() const { return m_i; } private: int m_i; }; struct Test { void operator()(A* p) { std::cout<<p->get()<<"\n"; } }; int main(int argc, char **argv) { CArray<A*, A*> b; b.Add(new A(10)); b.Add(new A(20)); std::for_each(make_begin(b), make_end(b), Test()); return 0; } But when I compile this code, I get the following error: Error 4 error C2784: 'bool std::operator <(const std::_Tree<_Traits &,const std::_Tree<_Traits &)' : could not deduce template argument for 'const std::_Tree<_Traits &' from 'CArrayIterator' C:\Program Files\Microsoft Visual Studio 9.0\VC\include\xutility 1564 Vs8Console Can anybody throw some light on what I am doing wrong and how it can be corrected? I am using VC9 compiler if it matters.

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  • Write to file depending on minSdkVersion - android

    - by Simon Rosenqvist
    Hi, I have written a filewriter for my android application. It is to function on a Galaxy Tab, so my minSdkVersion has to be at least 4, so it will fill the screen. I originally started out with SdkVersion = 2 and at that point my filewriter worked perfectly. Changing the SdkVersion to 4 introduced the problem. My filewriter doesn't work anymore! The application runs fine, but a file doesn't get created. My .java file looks like this: public class HelloAndroid extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); TextView tv = new TextView(this); tv.setText("Hello, Android"); setContentView(R.layout.main); //definerer en knap kaldet button1 og sætter en listener på denne. Button button1 = (Button)findViewById(R.id.btnClickMe); button1.setOnClickListener(btnListener); //definerer en knap kaldet button2 og sætter en listener på denne. Button button2 = (Button)findViewById(R.id.btnClickMe2); button2.setOnClickListener(btnListener2); } //en variabel af typen 'long' deklæres og kaldes tid1. public long time1; private OnClickListener btnListener = new OnClickListener() { public void onClick(View v) { //Når der klikkes på button1 gemmes et tal i variablen tid1. time1 = System.currentTimeMillis(); } }; //en variabel af typen 'long' deklæres og kaldes tid2. public long time2; // en variabel af typen 'string' deklæres og kaldes tid: public String string1 = "time:"; private OnClickListener btnListener2 = new OnClickListener() { public void onClick(View v) { //Når der klikkes på button2 gemmes et tal i variablen tid2. time2 = System.currentTimeMillis(); // Herefter oprettes en fil kaldet "file.txt". try{ File file = new File(Environment.getExternalStorageDirectory(), "file.txt"); file.createNewFile(); BufferedWriter writer = new BufferedWriter(new FileWriter(file,true)); //string1 og tid2-tid1 skrives til filen. tid2-tid1 giver den tid der går fra der er trykket på den ene knap til den anden i millisekunder. writer.write(string1 + "\t" + (time2-time1)); writer.newLine(); writer.flush(); writer.close(); } catch (IOException e) { e.printStackTrace(); } } }; } And my manifest.xml looks like this: <?xml version="1.0" encoding="utf-8"?> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".HelloAndroid" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> Why does my filewriter not work with minSdkVersion 2? Do i have to make a new filewriter? or what to do? Sorry for the messy code, i'm quite new to programming :)

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  • File Segmentation when trying to write in a file

    - by user1286390
    I am trying in C language to use the method of bisection to find the roots of some equation, however when I try to write every step of this process in a file I get the problem "Segmentation fault". This might be an idiot fault that I did, however I have been trying to solve this for a long time. I am compiling using gcc and that is the code: #include <stdio.h> #include <stdlib.h> #include <math.h> #define R 1.0 #define h 1.0 double function(double a); void attractor(double *a1, double *a2, double *epsilon); void attractor(double *a1, double *a2, double *epsilon) { FILE* bisection; double a2_copia, a3, fa1, fa2; bisection = fopen("bisection-part1.txt", "w"); fa1 = function(*a1); fa2 = function(*a2); if(function(*a1) - function(*a2) > 0.0) *epsilon = function(*a1) - function(*a2); else *epsilon = function(*a2) - function(*a1); fprintf(bisection, "a1 a2 fa1 fa2 epsilon\n"); a2_copia = 0.0; if(function(*a1) * function(*a2) < 0.0 && *epsilon >= 0.00001) { a3 = *a2 - (*a2 - *a1); a2_copia = *a2; *a2 = a3; if(function(*a1) - function(*a2) > 0.0) *epsilon = function(*a1) - function(*a2); else *epsilon = function(*a2) - function(*a1); if(function(*a1) * function(*a2) < 0.0 && *epsilon >= 0.00001) { fprintf(bisection, "%.4f %.4f %.4f %.4f %.4f\n", *a1, *a2, function(*a1), function(*a1), *epsilon); attractor(a1, a2, epsilon); } else { *a2 = a2_copia; *a1 = a3; if(function(*a1) - function(*a2) > 0) *epsilon = function(*a1) - function(*a2); else *epsilon = function(*a2) - function(*a1); if(function(*a1) * function(*a2) < 0.0 && *epsilon >= 0.00001) { fprintf(bisection, "%.4f %.4f %.4f %.4f %.4f\n", *a1, *a2, function(*a1), function(*a1), *epsilon); attractor(a1, a2, epsilon); } } } fa1 = function(*a1); fa2 = function(*a2); if(function(*a1) - function(*a2) > 0.0) *epsilon = function(*a1) - function(*a2); else *epsilon = function(*a2) - function(*a1); fprintf(bisection, "%.4f %.4f %.4f %.4f %.4f\n", a1, a2, fa1, fa2, epsilon); } double function(double a) { double fa; fa = (a * cosh(h / (2 * a))) - R; return fa; } int main() { double a1, a2, fa1, fa2, epsilon; a1 = 0.1; a2 = 0.5; fa1 = function(a1); fa2 = function(a2); if(fa1 - fa2 > 0.0) epsilon = fa1 - fa2; else epsilon = fa2 - fa1; if(epsilon >= 0.00001) { fa1 = function(a1); fa2 = function(a2); attractor(&a1, &a2, &epsilon); fa1 = function(a1); fa2 = function(a2); if(fa1 - fa2 > 0.0) epsilon = fa1 - fa2; else epsilon = fa2 - fa1; } if(epsilon < 0.0001) printf("Vanish at %f", a2); else printf("ERROR"); return 0; } Thanks anyway and sorry if this question is not suitable.

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  • DELL Inspiron 9400 SD Card Reader not working on 10.11 ubuntu

    - by Mario Martz
    Im new in linux, just installed Ubuntu 11.10 in a Dell Inspiron 9400, everything works fine with the exception of the SD card reader, everytime I insert a card the computer doesnt do anything, its like the SD card reader is not there. I did a $lspci and it shows the next drivers 03:01.0 FireWire (IEEE 1394): Ricoh Co Ltd R5C832 IEEE 1394 Controller 03:01.1 SD Host controller: Ricoh Co Ltd R5C822 SD/SDIO/MMC/MS/MSPro Host Adapter (rev 19) 03:01.2 System peripheral: Ricoh Co Ltd R5C592 Memory Stick Bus Host Adapter (rev 0a) 03:01.3 System peripheral: Ricoh Co Ltd xD-Picture Card Controller (rev 05) Everytime I insert a memory card, dmesg shows the next d status 0x600b00 [ 2687.227351] end_request: I/O error, dev mmcblk0, sector 64 [ 2687.229436] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.229440] end_request: I/O error, dev mmcblk0, sector 65 [ 2687.230512] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.230515] end_request: I/O error, dev mmcblk0, sector 66 [ 2687.231588] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.231592] end_request: I/O error, dev mmcblk0, sector 67 [ 2687.232674] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.232678] end_request: I/O error, dev mmcblk0, sector 68 [ 2687.234763] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.234766] end_request: I/O error, dev mmcblk0, sector 69 [ 2687.236864] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.236868] end_request: I/O error, dev mmcblk0, sector 70 [ 2687.238942] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.238946] end_request: I/O error, dev mmcblk0, sector 71 [ 2687.238949] Buffer I/O error on device mmcblk0, logical block 8 [ 2687.241028] mmcblk0: retrying using single block read [ 2687.243104] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.243108] end_request: I/O error, dev mmcblk0, sector 64 [ 2687.245212] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.245215] end_request: I/O error, dev mmcblk0, sector 65 [ 2687.247298] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.247302] end_request: I/O error, dev mmcblk0, sector 66 [ 2687.248389] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.248393] end_request: I/O error, dev mmcblk0, sector 67 [ 2687.250476] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.250480] end_request: I/O error, dev mmcblk0, sector 68 [ 2687.252617] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 [ 2687.252621] end_request: I/O error, dev mmcblk0, sector 69 [ 2687.254737] mmcblk0: error -110 sending read/write command, response 0x0, card status 0x600b00 and more of the same but with different sector number Im using Kernel 3.0.0-12-generic By the way, when I was installing it and ubuntu asks about installation (If I want to install it along with windows or delete something or change the partitions of the HDD) if I go to the window to change the partition of the disc, linux detects the SD Card (if there's one inserted course). Any help with this it would be appreciated -sorry for my english Thank you

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  • Why is domU faster than dom0 on IO?

    - by Paco
    I have installed debian 7 on a physical machine. This is the configuration of the machine: 3 hard drives using RAID 5 Strip element size: 1M Read policy: Adaptive read ahead Write policy: Write Through /boot 200 MB ext2 / 15 GB ext3 SWAP 10GB LVM rest (~500GB) emphasized text I installed postgresql, created a big database (over 1GB). I have an SQL request that takes a lot of time to run (a SELECT statement, so it only reads data from the database). This request takes approximately 5.5 seconds to run. Then, I installed XEN, created a domU, with another debian distro. On this OS, I also installed postgresql, with the same database. The same SQL request takes only 2.5 seconds to run. I checked the kernel on both dom0 and domU. uname-a returns "Linux debian 3.2.0-4-amd64 #1 SMP Debian 3.2.41-2+deb7u2 x86_64 GNU/Linux" on both systems. I checked the kernel parameters, which are approximately the same. For those that are relevant, I changed their values to make them match on both systems using sysctl. I saw no changes (the requests still take the same amount of time). After this, I checked the file systems. I used ext3 on domU. Still no changes. I installed hdparm, and ran hdparm -Tt on both systems, on all my partitions on both systems, and I get similar results. Now, I am stuck, I don't know what is different, and what could be the cause of such a big difference. Additional Info: Debian runs on a Dell server PowerEdge 2950 postgresql: 9.1.9 (both dom0 and domU) xen-linux-system: 3.2.0 xen-hypervisor: 4.1 Thanks EDIT: As Krzysztof Ksiezyk suggested, it might be due to some file caching system. I ran the dd command to test both the read and write speed. Here is domU: root@test1:~# dd if=/dev/zero of=/root/dd count=5MB bs=1MB ^C2020+0 records in 2020+0 records out 2020000000 bytes (2.0 GB) copied, 18.8289 s, 107 MB/s root@test1:~# dd if=/root/dd of=/dev/null count=5MB bs=1MB 2020+0 records in 2020+0 records out 2020000000 bytes (2.0 GB) copied, 15.0549 s, 134 MB/s And here is dom0: root@debian:~# dd if=/dev/zero of=/root/dd count=5MB bs=1MB ^C1693+0 records in 1693+0 records out 1693000000 bytes (1.7 GB) copied, 8.87281 s, 191 MB/s root@debian:~# dd if=/root/dd of=/dev/null count=5MB bs=1MB 1693+0 records in 1693+0 records out 1693000000 bytes (1.7 GB) copied, 0.501509 s, 3.4 GB/s What can be the cause of this caching system? And how can we "fix" it? Can we apply it to dom0? EDIT 2: I switched my virtual disk type. To do so I followed this article. I did a dd if=/dev/vg0/test1-disk of=/mnt/test1-disk.img bs=16M Then in /etc/xen/test1.cfg, I changed the disk parameter to use file: instead of phy: it should have removed the file caching, but I still get the same numbers (domU being much faster for Postgres)

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  • Why did MAC-Adress Cloning Fix My Router?

    - by FranticPedantic
    I have a Belkin router, and about a year ago, I suddenly lost my internet connectivity from Comcast. The internet worked fine when I plugged it right into my laptop, so I just ignored it. When I moved to another apartmnet I eventually took the dive and called tech support. The tech told me to clone my MAC address which completely fixed the issue. Now I know what a MAC address is and I've read what MAC cloning is. What has bothered me since is that I don't see how this fixed the issue. As I have understood MAC address cloning, it has the router pretend it has the same MAC address as my computer. Here is why I don't understand why this fixes my issue: I have used several different computers with this router. Cloning the MAC address fixed it for ALL of my computers. The laptop I first used with my ISP was not the one that I eventually had connected when I cloned the address. Furthermore, I didn't have any problems for quite some time after I stopped using the first computer. It wasn't like the internet suddenly stopped working when I changed which laptop I was using Now it occurred to me that maybe there was some sort of expiration? Except... Which MAC address did it clone? It was just an option in the router administration page. Did it just pick whichever computer was connected to it? If my ISP still wanted the MAC of my first computer, how did some other computer's fix it? As mentioned earlier, why did this problem seemingly stem from nowhere? Anyway, I don't have any current problems so this is more just out of general curiosity. If anybody can explain it, it would be appreciated!

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  • Why are folders disappearing in Windows XP?

    - by XenoFoxx
    I am researching a problem for a friend, and unfortunatly do not have direct access to his computer. I've tried to gather as much information as possible and I have researched it on various websites. I've not found anyone having the same problem my friend is having. So here goes: He has a media server in his home running Microsoft Windows XP. It has 3 drives, 1 for the OS and 2 for mass storage. Not long ago he went to access one of the mass storage media drives and it was empty, except for a single folder. His first assumption was that his roommate had deleted everything on the drive (excluding the remaining folder). He then checked the properties of the drive and it was still saying that the hard drive was nearly full. I told him to check the recycling bin, thinking that whoever deleted them didn't clear them from recycling and that they were still taking up space on the drive. My friend said the recycling bin was empty. So we have a drive that the Windows file management system says is empty (again except for the remaining folder), but the properties of the drive say it's mostly full. Now it gets weirder My friend tried to create a new folder on this drive and it auto-named itself "New Folder(1)" which means that it recognizes there is already a "New Folder" in that directory. He tried to rename it to a name that he KNEW was there previsouly, and Windows wouldn't allow it because it was a duplicate folder name. SO now it seems the folders are there, but not displaying in Windows Explorer. Both of us have no idea why this is occuring, why the folders vanished, why the one remaining folder didn't vanish, or how to make them visable again. Anyone else ever experience this? I can get more details if needed.

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  • Why are my socks proxies slow

    - by vps_newcomer
    I have a linux vps, and i have tried a few socks proxy setups to test their performance: All tests were using speedtest.net The standard ssh tunnel proxy 0.8mbit/s download and 0.1-0.2mbit/s upload speeds dante-server proxy 1.3mbit/s download and 0.4-0.5mbit/s upload I am wondering why are these speeds so slow? Is anything shaping them? Is it just the nature of socks proxies? I know that the ssh tunnel has to do encryption and what not so that is why its slow, but i was surprised to see that the second setup was also quite slow. On the VPS i have received download speeds of 25MB/s per second (thats about 200mbit/s and upload speed of atleast 5MB/s (haven't got a good enough pipe to test anything faster). The other option i was going to try is to setup OpenVPN and see how that goes, however i need to find a good tutorial as it's fairly complicated to setup. So why is it so slow? How can i test to see where the bottleneck is? How can i make it faster :D

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