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  • Same memory space being allocated again & again

    - by shadyabhi
    In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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  • Saving information in the IO System

    - by djTeller
    Hi Kernel Gurus, I need to write a kernel module that simulate a "multicaster" Using the /proc file system. Basically it need to support the following scenarios: 1) allow one write access to the /proc file and many read accesses to the /proc file. 2) The module should have a buffer of the contents last successful write. Each write should be matched by a read from all reader. Consider scenario 2, a writer wrote something and there are two readers (A and B), A read the content of the buffer, and then A tried to read again, in this case it should go into a wait_queue and wait for the next message, it should not get the same buffer again. I need to keep a map of all the pid's that already read the current buffer, and in case they try to read again and the buffer was not changed, they should be blocked until there is a new buffer. I'm trying to figure it there is a way i can save that info without a map. I heard there are some redundant fields inside the I/O system the I can use to flag a process if it already read the current buffer. Can someone give me a tip where should i look for that field ? how can i save info on the current process without keeping a "map" of pid's and buffers ? Thanks!

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  • Problem Making C++ script

    - by Abs
    Hello all, I am not sure if I can post this sort of question (apologies in advance) but I am trying to build something from this blog post. # mkdir wkthumb # cat > wkthumb.cpp # qmake -project # qmake && make # ./wkthumb I have no experience with this, but I download all the files needed in the directory wkthumb using git. I have gone inside this directory and tried to execute cat > wkthumb.cpp - this just hangs for me. In addition, I thought cat was supposed to be used like this: cat file1.txt file2.txt > file3.txt? The above is blank with the first arguments? I am using Fedora Core 10.

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  • If I start learning C on Ubuntu will it give me an edge when I start learning Objective-C later this

    - by Anonymous
    I know Ruby right now, however I want to learn a new language. I am running Ubuntu 10.04 right now but I am going to get a Mac later this summer. Anyways I want something more for GUI development. I was wondering if I should learn C on Ubuntu right now, and then learn Objective-C when I get an iMac? Will learning C give me an edge? Or should I just learn Python on Ubuntu and then learn Objective-C when I get a new computer? Please give me your opinions! Thanks!

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  • How to list library dependencies of a non-native binary?

    - by lvella
    When developing for native platform, I can use ldd to list all the shared libraries (.so files) a binary executable I build will try to load upon start-up. But when cross-compiling, I don't know how to get the same information. The ldd is not a normal binutils utility, like strip or ar, that can be built alongside gcc for cross compiling, but instead, it is a cryptic shell script that apparently can only run on native platform. So, using the cross-target binutils tools, is there any way to get a list of the dynamically linked dependency for of a foreign binary?

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  • Using wget via Python

    - by CoreIs
    How would I download files (video) with Python using wget and save them locally? There will be a bunch of files, so how do I know that one file is downloaded so as to automatically start downloding another one? Thanks.

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  • Is pthread_spin_trylock safe inside of sigsegv handler of multithreaded application?

    - by TWMouton
    I am trying to implement a handler that on SIGSEGV will collect some information such as process-id, thread-id and a backtrace and write this information to a file/pipe/socket. The problem lies in that there is the (probably pretty high) possibility that if one thread experienced a SIGSEGV that the others will shortly follow. If two threads happen to make it to the bit of code where they're writing their report out at the same time then they'll interleave their writing (to the same file). I know that I should only be using async-signal-safe functions as detailed in signal(7) I also have seen at least two cases here and video linked in top answer here where others have used pthread_spin_trylock to get around this problem. Is this a safe way to prevent the above problem?

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  • PyQt4.QtCore doesn't contain many of its classes and attributes

    - by toc777
    Hi everyone, I have built PyQt4 from source and everything went smoothly until I tried to use some of the classes and attributes located in QtCore. For some reason QtCore is missing a lot of functionality and data that should be there. For example from PyQt4.QtCore import QT_VERSION_STR is an import error. There were no errors or warnings given when building the packages and I have also tried with the PyQt packages from yum but I have the same problem. Has anyone else encountered this problem before? Thanks.

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  • Why doesn't "cd" work in a bash shell script?

    - by askgelal
    I'm trying to write a small script to change the current directory to my project directory: #!/bin/bash cd /home/askgelal/projects/java I saved this file as proj, changed the chmod, copied it to /usr/bin. When I call it by: proj, it does nothing. What am I doing wrong?

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  • Will Sytem.currentTimeMillis always return a value >= previous calls?

    - by 1984isnotamanual
    http://java.sun.com/j2se/1.4.2/docs/api/java/lang/System.html#currentTimeMillis() says: Returns the current time in milliseconds. Note that while the unit of time of the return value is a millisecond, the granularity of the value depends on the underlying operating system and may be larger. For example, many operating systems measure time in units of tens of milliseconds. It is not clear to me if I am guaranteed that this code will always print ever increasing (or the same) numbers. while (1) { System.out.println(System.currentTimeMillis() ); }

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  • Format a timestamp into text

    - by user1257114
    I want to get the Modify date of a file and then format it into a human readable date. I am running a C program that gets information on when a particular file was last modified. My C Code contains a sytem cmd which contains a number of egreps, awks, seds separated by pipes. Using sed or awk or something similar, how can I convert 06 to June (This can be any month so an array or something is required) What I am trying to achieve is to end up with a string similar to: My C code contains: char string1[100] = ""; #define MAXCHAR 100 FILE *fp; char str[MAXCHAR], str2[MAXCHAR]; char* filename = "newfile"; /* stat: run 'stat' on the dtlName file to display status information. egrep: search for the pattern 'Modify' and print the lines containing it. awk: Get columns 2 & 3 sed: replace the . with a space, leaving 3 columns of output awk: only print cols 1 & 2 to newfile sed: replace '-' with ' ' in newfile awk: format output in newfile */ sprintf(string1, "/bin/stat %s \ | egrep Modify \ | /bin/awk '{print $2, $3}' \ | /bin/sed 's/\\./ /g' \ | /bin/awk '{print $1, $2}' \ | /bin/sed 's/-/ /g' \ | /bin/awk '{print $3,$2\", \"$1,\"at\",$4}' > newfile" , dtlName); system(string1); fp = fopen(filename, "r"); while (fgets(str, MAXCHAR, fp) != NULL) sprintf(str2,"%s", str); /* Write information to file */ DisplayReportFile (report); ReportEntry (report,L"Source file: %s, Created: %s\n\n",dtlName,str2);

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  • Is there a list of programs for yum

    - by scriptingalias
    Basically I would like to know if there's is an actual web page that can be searched for the programs available under yum. I have yumex and I've tried using it but its super slow to search (sometimes it takes 5 minutes) and I would like some webpage or other method of doing a search. thanks,

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  • What is the problem with this code? How to solve it? (fork)

    - by sb2367
    What is the problem with this code? How to solve it? Parent processes goto in if or child process? first code produce zombie process or second code or both or non ? #include <signal.h> #include <sys/wait.h> main() { for (;;) { if (!fork()) { exit(0); } sleep(1); } } what about this code : #include <signal.h> #include <sys/wait.h> main() { for (;;) { if (fork()) { exit(0); } sleep(1); } }

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  • Why doesn't the Ubuntu Installer see all of my hard drives

    - by atodd
    I'm trying to setup a dual boot system with Windows Vista 64 (already installed) and Ubuntu 10.10. I added a new drive which is identical to the one Vista is installed on. When I boot into the LiveCD I can see and mount the second drive and edit it in Gparted. However, when I use the installer it will only bring up the drive that already has Vista installed. I've tried everything I know. I'm not sure if its a BIOS setting or something else I've missed.

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  • Methods of sending web-generated config files to servers and restarting services.

    - by JPG
    Hi, We're writing a web-based tool to configure our services provided by multiple servers. This includes interfaces configuration, dhcp configs etc. etc. Having configs in database and views that generate proper output, how to send it/make it available for servers? I'm thinking about sending it through scp and invoking reload command to services through ssh. I'm also thinking about using Func to do all the job, as this is Python tool and will seemingly integrate with python-based (django) config tool. Any other proposals?

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  • Low-overhead way to access the memory space of a traced process?

    - by vovick
    Hello all. I'm looking for an efficient way to access(for both read and write operations) the memory space of my ptraced child process. The size of blocks being accessed may vary from several bytes up to several megabytes in size, so using the ptrace call with PTRACE_PEEKDATA and PTRACE_POKEDATA which read only one word at a time and switch context every time they're called seems like a pointless waste of resources. The only one alternative solution I could find, though, was the /proc/<pid>/mem file, but it has long since been made read only. Is there any other (relatively simple) way to do that job? The ideal solution would be to somehow share the address space of my child process with its parent and then use the simple memcpy call to copy data I need in both directions, but I have no clues how to do it and where to begin. Any ideas?

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  • Creating a Custom Ubuntu Daemon

    - by Chris S
    What's the "correct" way to create a custom daemon in Ubuntu, that will start at boot time and be controllable by Ubuntu's standard daemon start/stop commands? Can I just copy and paste one of the scripts in /etc/init.d or do I need to "register" the daemon somewhere else?

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  • When is a program limited by the memory bandwidth?

    - by hanno
    I want to know if a program that I am using and which requires a lot of memory is limited by the memory bandwidth. When do you expect this to happen? Did it ever happen to you in a real life scenario? I found several articles discussing this issue, including http://www.cs.virginia.edu/~mccalpin/papers/bandwidth/node12.html http://www.cs.virginia.edu/~mccalpin/papers/bandwidth/node13.html http://ispass.org/ucas5/session2_3_ibm.pdf The first link is a bit old, but suggests that you need to perform less than about 1-40 floating point operations per floating point variable in order to see this effect (correct me if I'm wrong). How can I measure the memory bandwidth that a given program is using and how do I measure the (peak) bandwidth that my system can offer? I don't want to discuss any complicated cache issues here. I'm only interested in the communication between the CPU and the memory.

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  • Using directory traversal attack to execute commands

    - by gAMBOOKa
    Is there a way to execute commands using directory traversal attacks? For instance, I access a server's etc/passwd file like this http://server.com/..%01/..%01/..%01//etc/passwd Is there a way to run a command instead? Like... http://server.com/..%01/..%01/..%01//ls ..... and get an output? EDIT: To be clear here, I've found the vuln in our company's server. I'm looking to raise the risk level (or bonus points for me) by proving that it may give an attacker complete access to the system

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  • Pthread - setting scheduler parameters

    - by Andna
    I wanted to use read-writer locks from pthread library in a way, that writers have priority over readers. I read in my man pages that If the Thread Execution Scheduling option is supported, and the threads involved in the lock are executing with the scheduling policies SCHED_FIFO or SCHED_RR, the calling thread shall not acquire the lock if a writer holds the lock or if writers of higher or equal priority are blocked on the lock; otherwise, the calling thread shall acquire the lock. so I wrote small function that sets up thread scheduling options. void thread_set_up(int _thread) { struct sched_param *_param=malloc(sizeof (struct sched_param)); int *c=malloc(sizeof(int)); *c=sched_get_priority_min(SCHED_FIFO)+1; _param->__sched_priority=*c; long *a=malloc(sizeof(long)); *a=syscall(SYS_gettid); int *b=malloc(sizeof(int)); *b=SCHED_FIFO; if (pthread_setschedparam(*a,*b,_param) == -1) { //depending on which thread calls this functions, few thing can happen if (_thread == MAIN_THREAD) client_cleanup(); else if (_thread==ACCEPT_THREAD) { pthread_kill(params.main_thread_id,SIGINT); pthread_exit(NULL); } } } sorry for those a,b,c but I tried to malloc everything, still I get SIGSEGV on the call to pthread_setschedparam, I am wondering why?

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