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• Performance Overhead of Perf Event Subsystem in Linux Kernel

  - by Bo Xiao

  Performance counters for Linux are a new kernel-based subsystem that provide a framework for all things performance analysis. It covers hardware level (CPU/PMU, Performance Monitoring Unit) features and software features (software counters, tracepoints) as well. Since 2.6.33, the kernel provide 'perf_event_create_kernel_counter' kernel api for developers to create kernel counter to collect system runtime information. What I concern most is the performance impact on overall system when tracepoint/ftrace is enabled. There are no docs I can find about them. I was once told that ftrace was implemented by dynamically patching code, will it slow the system dramatically?

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• Understanding top output in Linux

  - by Rayne

  Hi, I'm trying to determine the CPU usage of a program by looking at the output from Top in Linux. I understand that %us means userspace and %sy means system/kernel etc. But say I see 100%us. Does this mean that the CPU is really only doing useful work? What if a CPU is tied up waiting for resources that are not avaliable, or cache misses, would it also show up in the %us column, or any other column? Thank you.

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• Linux - File was deleted and then reappeared when folder was zipped

  - by davee9

  Hello, I am using Backtrack 4 Final, which is a Linux distro that is Ubuntu based. I had a directory that contained around 5 files. I deleted one of the files, which sent it to the trash. I then zipped the directory up (now containing 4 files), using this command: zip -r directory.zip directory/ When I then unzipped directory.zip, the file I deleted was in there again. I couldn't believe this, so I zipped up the directory again, and the file reappeared again but this time could not be opened because the operating system said it didn't exist or something. I don't remember the exact error, and I cannot make this happen again. Would anyone happen to know why a file that was deleted from a directory would reappear in that directory after it was zipped up? Thank you.

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• Preallocate memory for a program in Linux before it gets started

  - by Fyg

  Hi, folks, I have a program that repeatedly solves large systems of linear equations using cholesky decomposition. Characterising is that I sometimes need to store the complete factorisation which can exceed about 20 GB of memory. The factorisation happens inside a library that I call. Furthermore, this matrix and the resulting factorisation changes quite frequently and as such the memory requirements as well. I am not the only person to use this compute-node. Therefore, is there a way to start the program under Linux and preallocate free memory for the process? Something like: $: prealloc -m 25G ./program

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• Test for undefined references in Linux

  - by Charles

  Is there a built in linux utility that I can use to test a newly compiled shared library for external undefined references? Gcc seems to be intelligent enough to check for undefined symbols in my own binary, but if the symbol is a reference to another library gcc does not check at link time. Instead I only get the message when I try to link to my new library from another program. It seems a little silly to get undefined reference messages in a library when I am compiling a different project so I want to know if I can do a check on all references internal and external when I build the library not when I link to it. Example error: make -C UnitTests debug make[1]: Entering directory `~/projects/Foo/UnitTests` g++ [ tons of objects ] -L../libbar/bin -lbar -o UnitTests libbar.so: undefined reference to `DoSomethingFromAnotherLibrary` collect2: ld returned 1 exit status make[1]: *** [~/projects/Foo/UnitTests] Error 1

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• How send html mail using linux command line

  - by Diesel Draft

  Hi, I need send mail with html format. I have only linux comand line and command "mail". Currently have used: echo "To: [email protected]" > /var/www/report.csv echo "Subject: Subject" >> /var/www/report.csv echo "Content-Type: text/html; charset=\"us-ascii\"" >> /var/www/report.csv echo "<html>" >> /var/www/report.csv mysql -u ***** -p***** -H -e "select * from users LIMIT 20" dev >> /var/www/report.csv echo "</html>" >> /var/www/report.csv mail -s "Built notification" [email protected] < /var/www/report.csv But in my mail-agent i get only plain/text.

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• linux's fork and system resources

  - by Dmitry Bespalov

  Suppose I have following code in linux: int main() { FILE* f = fopen("file.txt", "w"); fork(); fwrite("A", 1, 1, f); fclose(f); return 0; } What I know about fork from documentation, is that it makes the copy of current process. It copies state of the memory as well, so *f should be equal in both instances. But what happens with system resources, such as a file handle? In this example I open the file with write intentions, so only one instance can write into file, right? Which of the instances will actually write into file? Who should care further about the file handle, and call fclose() ?

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• How to change FPU context in signal handler (C++/Linux)

  - by Henry Fané

  I wrote a signal handler to catch FPE errors. I need to continue execution even if this happens. I receive a ucontext_t as parameter, I can change the bad operand from 0 to another value but the FPU context is still bad and I run into an infinite loop ? Does someone already manupulate the ucontext_t structure on Linux ? I finally found a way to handle these situations by clearing the status flag of ucontext_t like this: ... const long int cFPUStatusFlag = 0x3F; aContext->uc_mcontext.fpregs->sw &= ~cFPUStatusFlag; ... 0x3F is negated to put 0 in the 6 bits of the status register of the FPU (x87). Doing this implies to check for FPE exceptions after calculation.

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• Linux, C++ audio capturing (just microphone) library

  - by TheOm3ga

  I'm developing a musical game, it's like a singstar but instead of singing, you have to play the recorder. It's called oFlute, and it's still in early development stage. In the game, I capture the microphone input, then run a simple FFT analysis and compare the results to typical recorder's frequencies, thus getting the played note. At the beginning, the audio library I was using was RtAudio, but I don't remember why I switched to PortAudio, which is what I'm currently using. The problem is that, from time to time, either it crashes randomly or stops capturing, like if there were no sound coming from the microphone. My question is, what's the best option to capture microphone input on Linux? I just need to open, read, and close a flow of bytes from the microphone. I've been reading this guide, and (un)surprisingly it says: I don't think that PortAudio is very good API for Unix-like operating systems. So, what do you recommend me?

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• Ofstream writes empty file on linux

  - by commanderz

  Hi, I have a program which writes its output using ofstream. Everything works perfectly fine on Windows when compiled with Visual Studio, but it only writes empty file on Linux when compiled with GCC. ofstream out(path_out_cstr, ofstream::out); if(out.bad()){ cout << "Could not write the file" << flush; } else{ cout << "writing"; out << "Content" << endl; if(out.fail()) cout << "writing failed"; out.flush(); out.close(); } The directory which is being writen into has 0777 privileges. Thanks for help

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• malloc hangs in Linux

  - by Rahul

  I am using Linux on a 16 G with 2 quad core CPU. There are 8 processes which are doing some work (CPU intensive/network i/o). Out of which 4 have a memory leak (These are test conditions so no problem in having leaks here). Total space is occupied by all processes is around 15.4 G only 200 MB is free in system. Things are fine for some hours. But after that malloc hangs (for a process which doesn't have a memory leak). Its stuck for for more than 4 minutes (Note CPU is not 100% but io has gone up signficantly). Now there is no problem in the hanged process. (It has not corrupted the memory). What malloc is doing? (is it tryibg to defragment or builidng up swap space).I am using SUSE 10. Any pointers?

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• How can I "interconnect" two sockets in Linux?

  - by Vi

  There are two connected sockets. How can I interconnect them? Data appeared on the one socket should be written to the other. EOF/FIN should propogate well. If one is half-closed, the other should also be half-closed. int client = get_connected_client_socket(); int proxy = get_connected_proxy_socket(); negotiate_with_proxy(proxy); iterconnect(client, proxy); // Now forgot about both client and proxy. // System should handle IO/shutdown/close. // Ideally even without any support of the user-space process. Can Linux do it? Can it be done by tricking connection tracking to change tracking status of existing connection? @related http://stackoverflow.com/questions/2673975/determine-how-much-can-i-write-into-a-filehandle-copying-data-from-one-fh-to-the

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• Scheduling jobs from a web environment on Linux

  - by Anders Feder

  Hi. I am developing an application in PHP on Linux/Apache. I want to be able to schedule PHP jobs (scripts) for execution at some specific time in the future from within the application. I know that many people will recommend cron and at, but first of all I don't need recurrence (cron) and secondly and most importantly, I need the solution to be able to scale. At was not designed with race condititions in mind, and if two users try to add a job at the same time one or both may fail. It's also important that jobs are executed at their specified time, and not just 'polled' once per minute or so. Can anyone please suggest solutions for this task? Thank you.

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• [Linux] Coding a GTK+ application without window manager?

  - by ShoX

  Hi, I want to code sth. that basically works like TiVo. Switch it on, you only see the menu or an output, so no underlying OS or anything else is directly visible to the user. So I want to use Linux as base. Can you suggest a good base distribution? Can I code a frontend without having a window-manager up and running? If yes, is that possible with java-gnome or what language/gui-framework combination would you suggest? If no, what's the minimal window manager that can handle fancy menus, etc? What does it take to create video-overlays over a HD-stream? Are there some libraries I should take a look at? Thanks

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• UTF8 issues on Linux

  - by user363808

  Hi, I have some code that fetches some data from the database, database codepage is UTF8. When I run the code on a linux box, some characters come out as question marks (?) but when I run the same code on a windows server, all characters appear correctly. When I do: $ $LANG Following is returned en_SG.UTF-8 en_SG is something that doesn't look correct, it should be en_US but the latter part of the returned string is UTF-8 which is good. Is there anything else that I can look into to fix the character corruption problem?

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• Memory allocation in Linux

  - by Goofy

  Hello! I have a multi threaded application where I allocate buffers with data, which then wait in queues to be send via sockets. All buffers are reproducible because I use only buffers of fixed size in whole program (1024, 2048, 2080 and 5248 bytes). I noticed, that my program usually use up to 10 buffers of each length type at the same moment. So far I always manually allocate new buffer and then free it (using malloc() and free ()) where it's not needed any more. I started wondering if Linux is enough smart to cache this memory for me, so next time I allocate new buffer system only quickly receive a buffer I have already used before and not perform heavy operation of allocating new memory block?

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• prevent linux thread from being interrupted by scheduler

  - by johnnycrash

  How do you tell the thread scheduler in linux to not interrupt your thread for any reason? I am programming in user mode. Does simply locking a mutex acomplish this? I want to prevent other threads in my process from being scheduled when a certain function is executing. They would block and I would be wasting cpu cycles with context switches. I want any thread executing the function to be able to finish executing without interruption even if the threads' timeslice is exceeded.

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• Recursively disabling CONFIG dependencies on linux kernel builds

  - by Corey Henderson

  When configuring a Linux kernel, I normally start with my distribution's kernel config file. I often want to turn off some entries, but they are sometimes unchangeable because other CONFIG options that depend on it are enabled. I can look up the dependencies manually, which often have dependencies of their own. It can be pretty time consuming to did through them all, especially if you're trying to turn off something like CONFIG_KALLSYMS. Is there a way to specify a CONFIG option you want gone, and have all dependencies automatically selected/disselected as nessisary for you? I looked through all the make options and in the scripts directory, and didn't see anything available for this.

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• How to check whether your code environment on Windows or on Linux or other OS

  - by justjoe

  hi, right now, i code custom wordpress theme and testing it in xampp windows XP on apache server. But as long as i concern, there's no wp build-in function to identify the code environment. Is there's any PHP build-in function to identify such thing ? for the record, what i want to code need to read a directory. in my apache (in windows), the path will be c:/xampp/htdocs where apache on linux will be \somepath\somepath\ so, is there any code solution to know what is the OS environment without i have to compare the path ? i hope it will also work on other OS with other webserver then APACHE such as IIS

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• What is linux equivalent of running a .bat file on windows from PHP using system()

  - by undefined

  I have a PHP script that runs a .bat file on my windows machine using $result = system("cmd /C nameOfBatchFile.bat"); This sets some environmental variables and is used to call Amazon EC2 API from the command line. How do I do the same from a Linux server? I have renamed my .bat file to a shell (.sh) and changed the script to use 'export' when setting env vars. I have tested by running the code from a putty terminal and it does what it should. So I know the commands in the script are good. How do I run this from PHP? I have tried running the same command as above with the new filename and I don't get any errors, or file not found etc but it doesn't appear to work. Where do I start trying to solve this?

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• Port a Rails App from Windows to Mac or Linux

  - by Ryan Max

  Hello I've been a Rails developer on Windows for quite some time now, but I recently completed my biggest project yet (it's quite extensive, took me over a year to build) but I am having trouble deploying it. The combination of it's size, complexity and a windows environment is making it needlessly complex to deploy. I am thinking about getting an old mac mini and using it just for rails development. Either that or install unix on another box. Is there any way I can port my app to this mac or linux machine, without having to start over? I can't find any resources on the internets about this.

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• Problems with system() calls in Linux

  - by Thomas

  I'm working on a init for an initramfs in C++ for Linux. This script is used to unlock the DM-Crypt w/ LUKS encrypted drive, and set the LVM drives to be available. Since I don't want to have to reimplement the functionality of cryptsetup and gpg I am using system calls to call the executables. Using a system call to call gpg works fine if I have the system fully brought up already (I already have a bash script based initramfs that works fine in bringing it up, and I use grub to edit the command line to bring it up using the old initramfs). However, in the initramfs it never even acts like it gets called. Even commands like system("echo BLAH"); fail. So, does anyone have any input?

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• Question about regex in linux commands.

  - by smwikipedia

  I ran the following command at linux bash: apt-cache search hex.*(view|edit) My intention was to find any software packages whose name/description contains the pattern 'hex.*(view|edit)'. But among the results I got this: kipi-plugins - image manipulation/handling plugins for KIPI aware programs How could this be in the results list? I didn't see any matching string in this result. Is this a bug of the apt-cache search command? Or do I mis-understand how the regex is used by this command? Many thanks.

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• How to get notified of modification in the memory in Linux

  - by Song Yuan

  In a userspace program in Linux, I get a piece of memory via allocation from the heap, then the pointer is distributed to a lot of other components running in other threads to use. I would like to get notified when the said piece of memory is modified. I can of course develop a custom userspace solution for other components to use when they try to modify the memory. The problem in my case is that these are legacy components and they can write to memory in many occasions. So I'm wondering whether there is a similar API like inotify (get notified when file is changed) or other approaches in order to get notified when a piece of memory is changed. I considered using mmap and inotify, which obviously won't work if the changes are not flushed. Any suggestions are appreciated :-)

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• Error during installation of Mesa on Linux

  - by rodnower

  Hello, I have a problem. I try to install Mesa 7.8 on CentOS 3.9 for i386 on VMVare 7.0.1 like described here: http://linux-sxs.org/multimedia/mesa.html When I perform configuration stage: ++++++++++++++++++++++++++++++++++++++++++++++++++ [root@CentOS Mesa-7.8]# ./configure --prefix=/usr --sysconfdir=/etc ++++++++++++++++++++++++++++++++++++++++++++++++++ (root is actualy root) This is what I get: ++++++++++++++++++++++++++++++++++++++++++++++++++ . . . checking pkg-config files for X11 are available... no checking for X... no configure: error: X11 development libraries needed for dri driver ++++++++++++++++++++++++++++++++++++++++++++++++++ (Three dots says that there is some output before) Put attention to error. Any idea? Thank you very much forahead.

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