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• Measuring execution time of a call to system() in C++

  - by jm1234567890

  I have found some code on measuring execution time here http://www.dreamincode.net/forums/index.php?showtopic=24685 However, it does not seem to work for calls to system(). I imagine this is because the execution jumps out of the current process. clock_t begin=clock(); system(something); clock_t end=clock(); cout<<"Execution time: "<<diffclock(end,begin)<<" s."<<endl; Then double diffclock(clock_t clock1,clock_t clock2) { double diffticks=clock1-clock2; double diffms=(diffticks)/(CLOCKS_PER_SEC); return diffms; } However this always returns 0 seconds... Is there another method that will work? Also, this is in Linux. Thanks!

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• send() always interrupted by EPIPE

  - by Manuel Abeledo

  I've this weird behaviour in a multithreaded server programmed in C under GNU/Linux. While it's sending data, eventually will be interrupted by SIGPIPE. I managed to ignore signals in send() and treat errno after each action because of it. So, it has two individual sending methods, one that sends a large amount of data at once (or at least tries to), and another that sends a nearly similar amount and slices it in little chunks. Finally, I tried with this to keep it sending data. do { total_bytes_sent += send(client_sd, output_buf + total_bytes_sent, output_buf_len - total_bytes_sent, MSG_NOSIGNAL); } while ((total_bytes_sent < output_buf_len) && (errno != EPIPE)); This ugly piece of code does its work in certain situations, but not always. I'm pretty sure it's not a hardware or ISP problem, as this server is running in six european servers, four in Germany and two in France. Any ideas? Thanks in advance.

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• PhpMyAdmin; Should I disable root login?

  - by Camran

  I have this setup in Phpmyadmin: USER HOST PASSW PRIVILEGES GRANT debian-sys-maint localhost Yes ALL PRIVILEGES YES phpmyadmin localhost Yes USAGE NO root 127.0.0.1 Yes ALL PRIVILEGES YES root localhost Yes ALL PRIVILEGES YES root my_hostname Yes ALL PRIVILEGES YES username localhost Yes ALL PRIVILEGES YES Where "username" is my username and "my_hostname" is my hostname. I am currently only logging in as the last one (username, localhost). Also, I have php which also uses the last ones login details. Should I disable the other ones? And, what other security measures should I take? BTW: My server is Linux and I have root access. Thanks

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• Where to place web server root?

  - by nefo_x

  Hello everybody, I've just made an upgrade and now partly thinking on web-server directory structure for local workstation for web-development on linux platform. Running multiple hosts and different projects required. Where is it better to put all the server's docroots? /var/www? /srv? /www? I plan to make it as separate partition - could it be good for backups? :) I'm looking forward to your thoughts on this.

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• Scaling a ruby script by launching multiple processes instead of using threads.

  - by Zombies

  I want to increase the throughput of a script which does net I/O (a scraper). Instead of making it multithreaded in ruby (I use the default 1.9.1 interpreter), I want to launch multiple processes. So, is there a system for doing this to where I can track when one finishes to re-launch it again so that I have X number running at any time. ALso some will run with different command args. I was thinking of writing a bash script but it sounds like a potentially bad idea if there already exists a method for doing something like this on linux.

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• Self-modify the classpath within a Scala script?

  - by Alex R

  I'm trying to replace a bunch of Linux shell scripts with Scala scripts. One of the remaining challenges is how to scan an entire directory of JARs and place them into the classpath. Currently this is done in the shell script prior to invoking the scala JVM. I'd like to eliminate the shell script completely. Is there an elegant scala idiom for this? I have found this other question but in Java it seems hardly worthwhile to mess with it: http://stackoverflow.com/questions/252893/how-do-you-change-the-classpath-within-java

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• How to call a function from a shared library?

  - by Frank

  What is the easiest and safest way to call a function from a shared library / dll? I am mostly interested in doing this on linux, but it would be better if there were a platform-independent way. Could someone provide example code to show how to make the following work, where the user has compiled his own version of foo into a shared library? // function prototype, implementation loaded at runtime: std::string foo(const std::string); int main(int argc, char** argv) { LoadLibrary(argv[1]); // loads library implementing foo std::cout << "Result: " << foo("test"); return 0; } BTW, I know how to compile the shared lib (foo.so), I just need to know an easy way to load it at runtime.

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• Locale C++ shared library in /usr/local/lib

  - by Dave

  I'm venturing into the world of C++ and Linux, and am having problems linking against a shared library. I have a library, libicuuc.so.44.1, installed in /usr/local/lib. There is also a link in the same directory, libicuuc.so.44 pointing to that library. My /etc/ld.so.conf reads: include /etc/ld.so.conf.d/*.conf I have a file, /etc/ld.so.conf.d/libc.conf, that contains: # libc default configuration /usr/local/lib However, when I compile my program (that includes LIBS += -licuuc), I get the following error at runtime: error while loading shared libraries: libicuuc.so.44: cannot open shared object file: No such file or directory I am using Qt Creator on Ubuntu 10.04. Any help is greatly appreciated!

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• Will an IO blocked process show 100% CPU utilization in 'top' output?

  - by Alex Stoddard

  I have an analysis that can be parallelized over a different number of processes. It is expected that things will be both IO and CPU intensive (very high throughput short-read DNA alignment if anyone is curious.) The system running this is a 48 core linux server. The question is how to determine the optimum number of processes such that total throughput is maximized. At some point the processes will presumably become IO bound such that adding more processes will be of no benefit and possibly detrimental. Can I tell from standard system monitoring tools when that point has been reached? Would the output of top (or maybe a different tool) enable me to distinguish between a IO bound and CPU bound process? I am suspicious that a process blocked on IO might still show 100% CPU utilization.

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• how to google a symbol keyword like "$?"

  - by ZhengZhiren

  i saw a trick in a book: in a linux shell, we can use &? to get the return value of a command. For example,we run a command,if it exit normally, the return value is 0. And then we type $?,we will get 0 in the screen. i want to google this kind of usage, so i have to type these two symbol $? in the search blank.But the search engine just return nothing to me... i have looked at the google help page, but still can't find a solution. so my question is: how can i search with this kind of keyword. or if you can give me some advise of the usage of $? or sort of thing, that will be also appreciated.

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• Copy one column over another in a delimited file

  - by user275455

  For instance, I needed to remove column 25 and replace it with a copy of column 22 in a simple csv file with no embedded delimiters. The best I could come up with was the awkward looking: awk -F, '{ for(x=1;x<25;x++){printf("%s,", $x)};printf("%s,",$22);for(x=26;x<59;x++){printf ("%s,", $x)};print $59}' I would expect something like cut -d, -f1-24,23,26-59 to work but cut doesn't seem to want to print the same column two times... Is there a more elegant way to do it using anything typicaly available in a linux shell environment?

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• user buffer after doing 'write' to file opened with O_DIRECT

  - by user1868481

  I'm using the O_DIRECT flag to write to the disk directly from the user buffer. But as far as I understand, Linux doesn't guarantee that after this call, the data is written. It just writes directly from the user buffer to the physical device using DMA or anything else... Therefore, I don't understand if I can write to the user buffer after the call to 'write' function. I'm sure that example code will help to understand my question: char *user_buff = malloc(...); /* assume it is aligned as needed */ fd = open(..., O_DIRECT); write(fd, ...) memset(user_buff, 0, ...) Is the last line (memset) legal? Is writing to the user buffer valid that is maybe used by DMA to transfer data to the device?

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• I have some basic questions setting up a PHP daemon

  - by mike

  I will be writing my first daemon in php and I have a couple really basic questions that I need help with. 1) What packages need to be installed on my linux server and Does anything in PHP need to be enabled? So far I have gotten this - http://pear.php.net/package/System_Daemon/download 2) Where on server do I save my daemon files? 3) I have a number of files that need to be included within the daemon that contain classes and functions for gathering emails and attachments through IMAP. All of these files are currently in my web public directory, how do I include these files within my daemon? I think that is everything I need to get started. Thanks so much!

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• PHP find if file data is an image

  - by Christian Sciberras

  Imagine I have some file data in a variable $data. I need to determine whether it is an image or not. No need for details such as corrupt images etc. Firs thought would be getting the file mime type by looking at the magic number and then see whether "image" is in the mime type. No such luck, even if I have a "file extension to mime type" script, I don't have a reliable way to get mime from magic number. My next option was to have a reasonable list of image file magic numbers and consult them. However, it relatively difficult to find such magic numbers (gif for instance has different magic numbers, some of which could pretty rare - if memory serves me right). A better idea would be some linux program which can do this kind of thing. Any ideas? I'm running RHEL and PHP 5.3. I've got root access - ie able to install stuff if needed. - Chris.

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• JBoss 4.0.5 startup takes 15 minutes deploying a single war file

  - by dkblinux98

  This instance of JBoss deploys several war files. The rest of the JBoss startup takes about 5 minutes or less. But when it gets to one particular war file, startup just hangs with no further output to the jboss log. It waits there for about 15 minutes and then suddenly the war starts deploying. The rest of the JBoss startup is then fine. What I want to know is what steps do you recommend I take to diagnose the cause of this condition? It is not possible to upgrade this site to a newer version of JBoss nor java (currently 1.5.0.7). It is running on 32-bit CentOS 5.3 Linux on 3 xen-based virtual servers in a load balanced configuration. The code is common to all three servers via an nfs share. This same issue was seen, however, when the 3 servers were physical and the code was local to each server. The servers are each 2 cpu, 4GB RAM servers.

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• Fonts in a multi-platform environment

  - by Stephen Burke

  What is the best way to deal with fonts in a multi-platform distributed system? If I want to use a common font across all systems to show to the user, what's the best way to do this. From the little I've been reading each platform looks to have fonts that are of the same family (ie serif, sans-serif) but with different names. CSS looks to have the functionality baked in where it will make the best selection it can of font on the users machine. Is there similar functionality either in system libraries or external libraries for Windows & Linux. I'm using C++ mainly? Can someone point me in the right direction for documentation as well? Thanks

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• "tail -f" alternate which doesn't scroll the terminal window

  - by Jagtesh Chadha

  I want to check a file at continuous intervals for contents which keep changing. "tail -f" doesn't suffice as the file doesn't grow in size. I could use a simple while loop in bash to the same effect: while [ 1 ]; do cat /proc/acpi/battery/BAT1/state ; sleep 10; done It works, although it has the unwanted effect of scrolling my terminal window. So now I'm wondering, is there a linux/shell command that would display the output of this file without scrolling the terminal?

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• How do they read clusters/cylinders/sectors from the disk?

  - by claws

  Hello, I needed to recover the partition table I deleted accidentally. I used an application named TestDisk. Its simply mind blowing. I reads each cylinder from the disk. I've seen similar such applications which work with MBR & partitioning. I'm curious. How do they read clusters/cylinders/sectors from the disk? Is it again OS dependent? If so whats the way to for Linux & for windows?

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• Php security question

  - by Camran

  I have a linux server, and I am about to upload a classifieds website to it. The website is php based. That means php code adds/removes classifieds, with the help of the users offcourse. The php-code then adds/removes a classified to a database index called Solr (like MySql). Problem is that anybody can currently access the database, but I only want the website to access the database (solr). Solr is on port 8983 as standard btw. My Q is, if I add a rule in my firewall (iptables), to only allow connections coming from the servers IP to the Solr port nr, would this solve my issue? Thanks

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• How to limit memory of a OS X program? ulimit -v neither -m are working

  - by hectorpal

  My programs run out of memory like half of the time I run them. Under Linux I can set a hard limit to the available memory using ulimit -v mem-in-kbytes. Actually, I use ulimit -S -v mem-in-kbytes, so I get a proper memory allocation problem in the program and I can abort. But... ulimit is not working in OSX 10.6. I've tried with -s and -m options, and they are not working. In 2008 there was some discussion about the same issue in MacRumors, but nobody proposed a good alternative. The should be a way a program can learn it's spending too much memory, or setting a limit through the OS.

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• poll(2) doesn't empty the event queue

  - by sasayins

  Hi, Im using linux as my programming platform. I am using poll(2) to know if my device is triggering an event. The first call of poll is ok, it blocks and wait for the event to happen. But in the second poll function call, it will return but it capture the event. Below are my code ret = poll( fds, 1, 2000); //2 secs timeout if( fds[0].revents & POLLIN && ret > 0) { printf("event occur\n"); } It seems the queue/buffer is not empty, im just assuming. What do you think is the problem? Thanks.

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• How to edit files on the users file system from my web server?

  - by Abs

  Hello all, I am really looking for implementation advice as I have entered a new realm that I am not familiar with. At the simplest level, I would like to find a way that I can read/write to a users machine from my web server. For this to work, I think I will have to install some sort of "plugin" on the users machine which can receive (or poll?) the server for instructions. The above is the line of thought that I currently have, maybe using JAVA to do this. This needs to work on Linux, Mac and Windows OS. I am really looking for advice on the above, is it a good idea? Is there a better way of doing this? Is there something out there already that I can build on top of? I really appreciate all input and advice as this is something I have not done before. Thanks all

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• Count function calls by name or signature. Gcc, C++

  - by MajesticRa

  I have some c++ written package. Linux, gcc. I can modify compilation process (change Makefile, flags, etc.), but can not change C++ source code. One runs the package with different parameters, it does a job and exits. How to count: 1) Number of calls of function with specific name? 2) Number of calls of functions with specific signature? 3) Number of calls of functions where one of the parameters is of specific type i.e. std::string (type is specified by signature)? 4) and extra Number of calls of functions of STL objects, i.e. std::string copy constructor? (I mean count a number of calls during the run. ) I thought to do it with GDB, but I found it very tough to do (1) and have not found how to do (2)-(4) at all. All acceptable answers I will write here for humanity.

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• PHP Inotify Non-blocking way

  - by demic0de

  I am reading a file in linux which is a log file that keeps on updating weather the file has changed and output it to the webpage. i do it using php inotify but my problem is that it is blocking. How can i make php inotify non-blocking so i can do other stuff while it is monitoring the text file?. <?php $fd = inotify_init(); $watch_descriptor = inotify_add_watch($fd, '/tmp/temp.txt', IN_MODIFY); touch('/tmp/temp.txt'); $events = inotify_read($fd); $contents = file_get_contents('/tmp/temp.txt'); echo $contents; inotify_rm_watch($fd, $watch_descriptor); fclose($fd) ?> Or can i do this in java?..Thanks.

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• Understanding behaviour of read() and write()

  - by neo730

  hi i am a student and just start learning low level c programming.i tried to understand read() and write() methods with this program. #include <unistd.h> #include <stdlib.h> main() { char *st; st=calloc(sizeof(char),2);//allocate memory for 2 char read(0,st,2); write(1,st,2); } i was expecting that it would give segmentation fault when i would try to input more than 2 input characters.but when i execute program and enter " asdf " after giving " as " as output it executes "df" command. i want to know why it doesn't give segmentation fault when we assign more than 2 char to a string of size 2.and why is it executing rest(after 2 char)of input as command instead of giving it as output only? also reading man page of read() i found read() should give EFAULT error,but it doesn't. I am using linux.

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