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• How do I throttle my site's API users?

  - by scotts

  The legitimate users of my site occasionally hammer the server with API requests that cause undesirable results. I want to institute a limit of no more than say one API call every 5 seconds or n calls per minute (haven't figured out the exact limit yet). I could obviously log every API call in a DB and do the calculation on every request to see if they're over the limit, but all this extra overhead on EVERY request would be defeating the purpose. What are other less resource-intensive methods I could use to institute a limit? I'm using PHP/Apache/Linux, for what it's worth.

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• mmap() for large file I/O?

  - by Boatzart

  I'm creating a utility in C++ to be run on Linux which can convert videos to a proprietary format. The video frames are very large (up to 16 megapixels), and we need to be able to seek directly to exact frame numbers, so our file format uses libz to compress each frame individually, and append the compressed data onto a file. Once all frames are finished being written, a journal which includes meta data for each frame (including their file offsets and sizes) is written to the end of the file. I'm currently using ifstream and ofstream to do the file i/o, but I am looking to optimize as much as possible. I've heard that mmap() can increase performance in a lot of cases, and I'm wondering if mine is one of them. Our files will be in the tens to hundreds of gigabytes, and although writing will always be done sequentially, random access reads should be done in constant time. Any thoughts as to whether I should investigate this further, and if so does anyone have any tips for things to look out for? Thanks!

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• kill -9 and production application

  - by valodzka

  Which problem can cause kill -9 in production application (in linux to be exact)? I have application which do some periodical work, stopping these takes long time, and I don't care if some jobs will be aborted - work can be finished by new processes. So can I use kill -9 just to stop it immediately or this can cause serious OS problems? For example, Unicorn, uses it as normal working procedure: When your application goes awry, a BOFH can just "kill -9" the runaway worker process without worrying about tearing all clients down, just one. But this article claims: The -9 (or KILL) argument to kill(1) should never be used on Unix systems

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• Creating PDF Invoices - Are there any templating solutions?

  - by smashedmercury

  Our company is looking to integrate invoices into a new system we are developing. We require some a solution to create a layout of the invoice and then convert to pdf. We have considered just laying out the invoice in html/css then converting to pdf. We have also considered using SVG-PDf conversion. Both of these solutions integrate well into our existing templating language used for our web application. Historically we have been a Microsoft based business and used Crystal Reports for such a task but we are looking an open source Linux solution for this project. Does any one have any suggestions of an approach or technology we could use for such a task?

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• Help with Python structure in *nixes.

  - by user198553

  I came from a Windows background whern it comes to development environments. I'm used to run .exe's from everything I need to run and just forget. I usually code in php, javascript, css, html and python. Now, I have to use Linux at my work, in a non changeable Ubuntu 8.04, with permissions to upgrade my system using company's repositories only. I need to install Python 2.4.3 to start coding in an old legacy system. I had Python 2.5. I downloaded Python 2.4.3 tarballs, ran ./configure make and such. Everything worked out, but now the "default" installation is my system is Python2.4 instead of of Python2.5. I want help from you to change it back, and if possible, some material to read about symlinks, multiple Python installations, virtualenvs and such: everything I need to know before installing/upgrading Python modules. I installed for example the ElementTree package and don't even know in which Python installation it was installed. Thanks in advance!

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• How can I have MySQL write outfiles as a different user?

  - by David Locke

  I'm working with a MySQL query that writes into an outfile. I run this query once every day or two and so I want to be able to remove the outfile without having to resort to su or sudo. The only way I can think of making that happen is to have the outfile written as owned by someone other than the mysql user. Is this possible? Edit: I am not redirecting output to a file, I am using the INTO OUTFILE part of a select query to output to a file. If it helps: mysql --version mysql Ver 14.12 Distrib 5.0.32, for pc-linux-gnu (x86_64) using readline 5.2

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• Need help in understanding the mapping of user-space send, sendto, sendmsg to kernel-space sendmsg

  - by bala1486

  Hello, I am trying to implement my own transport layer protocol in Linux for an experiment. I am going to use socket interface and add my protocol using sock_register. For the proto_ops i can see that the parameters for the sendmsg and recvmsg are (struct kiocb *iocb, struct socket *sock, struct msghdr *msg, size_t len, int flags). But there are three types of user api's send, sendto, sendmsg. Of these three only sendmsg contains a parameter for msghdr. I find that the other two api's are incompatible with the parameters supplied by the kernel to my kernel-space sendmsg function. So what happens when we use send and sendto user-space api's? Hope i am clear.. Thanks, Bala

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• How to file split at a line number

  - by superspace

  I want to split a 400k line long log file from a particular line number. For this question, lets make this an arbitrary number 300k. Is there a linux function that allows me to do this? I know split lets me split the file in equal parts either by size or line numbers but that's not what I want. I want to the first 300k in one file and the last 100k in the second file. Any help would be appreciated. Thanks!

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• Can a client determine whether the server has accept()'d a unix socket?

  - by Havoc P

  I'm dealing with a buggy server that will sometimes fail to accept() connections (but leaves its listening socket open). This is on Linux with unix domain sockets. Currently the only way to detect this is that after sending a bunch of data, the buffer fills up and blocks, and the server isn't sending any replies. This long-after-the-fact failure mode is hard to distinguish from other bugs - the server could be unresponsive for other reasons. Especially for unix domain sockets it seems the kernel should know whether accept() has occurred; is there any way to find this out? Can the client block until accept() happens somehow, or at least check whether it has? This is just for debugging purposes so it can be a little ugly.

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• Postgres pg_dump dumps database in a different order every time

  - by behrk2

  Hello, I am writing a PHP script (which also uses linux bash commands) which will run through test cases by doing the following: I am using a PostgreSQL database (8.4.2)... 1.) Create a DB 2.) Modify the DB 3.) Store a database dump of the DB (pg_dump) 4.) Do regression testing by doing steps 1.) and 2.), and then take another database dump and compare it (diff) with the original database dump from step number 3.) However, I am finding that pg_dump will not always dump the database in the same way. It will dump things in a different order every time. Therefore, when I do a diff on the two database dumps, the comparison will result in the two files being different, when they are actually the same, just in a different order. Is there a different way I can go about doing the pg_dump? Thanks!

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• Measuring daemon CPU utilization over a portion of it's wall clock run time

  - by WhirlWind

  I am dealing with a network-related daemon: it takes data in, processes it, and spits it out. I would like to increase the performance of this daemon by profiling it and reducing it's CPU utilization. I can do this easily on Linux with gprof. However, I would also like to use something like "time" to measure it's total CPU utilization over a period of time. If possible, I would like to time it over a period that is less than its total run time: thus, I would like to start the daemon, wait awhile, generate CPU statistics, stop generating them, then stop the daemon at some later time. The "time" command would work well for me, but it seems to require that I start and stop the daemon as a child of time. Is there a way to measure CPU utilization for only a portion of the daemon's wall clock time?

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• What interprocess locking calls should I monitor?

  - by Matt Joiner

  I'm monitoring a process with strace/ltrace in the hope to find and intercept a call that checks, and potentially activates some kind of globally shared lock. While I've dealt with and read about several forms of interprocess locking on Linux before, I'm drawing a blank on what to calls to look for. Currently my only suspect is futex() which comes up very early on in the process' execution. Update0 There is some confusion about what I'm after. I'm monitoring an existing process for calls to persistent interprocess memory or equivalent. I'd like to know what system and library calls to look for. I have no intention call these myself, so naturally futex() will come up, I'm sure many libraries will implement their locking calls in terms of this, etc. Update1 I'd like a list of function names or a link to documentation, that I should monitor at the ltrace and strace levels (and specifying which). Any other good advice about how to track and locate the global lock in mind would be great.

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• Editing Subversion post-commit script to enable automated Hudson builds

  - by Wachgellen

  Hey guys, I'm not so good with Linux, but I need to modify the post-commit file of my Subversion repository to get Hudson to build automatically on commits. This page here tells me to do this: REPOS="$1" REV="$2" UUID=`svnlook uuid $REPOS` /usr/bin/wget \ --header "Content-Type:text/plain;charset=UTF-8" \ --post-data "`svnlook changed --revision $REV $REPOS`" \ --output-document "-" \ http://server/hudson/subversion/${UUID}/notifyCommit?rev=$REV The part that I don't know is the address URL given at the bottom of that code snippet. I know the address of my Hudson server, but the /subversion part has me baffled, because on my system that doesn't refer to anything. My Subversion repository belongs somewhere else on the server, not inside Hudson. Can anyone tell me what I'm supposed to put as the URL (an example would help greatly)?

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• Avoid copying of data between user and kernel space and vice-versa

  - by bala1486

  Hello, I am developing a active messaging protocol for parallel computation that replaces TCP/IP. My goal is to decrease the latency of a packet. Since the environment is a LAN, i can replace TCP/IP with simpler protocol to reduce the packet latency. I am not writing any device driver and i am just trying to replace the TCP/IP stack with something simpler. Now I wanted to avoid copying of a packet's data from user space to kernel space and vice-versa. I heard of the mmap(). Is it the best way to do this? If yes, it will be nice if you can give links to some examples. I am a linux newbie and i really appreciate your help.. Thank you... Thanks, Bala

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• Illegal token on right side of ::

  - by Adam Haile

  I have the following template declaration: template <typename T> void IterTable(int& rIdx, std::vector<double>& rVarVector, const std::vector<T>& aTable, const T aValue, T aLowerBound = -(std::numeric_limits<T>::max()), //illegal token on right side of '::' shows here bool aLeftOpen = true) const; Which throws the illegal token error as noted, on the line with "-(std::numeric_limits::max())". I got this code from some old linux source that I'm trying to compile on Windows. Any idea what the issue is?

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• How to use NetBeans to debug C++ libraries not compiled with NetBeans?

  - by Paul Gotzel

  Hello, I am using NetBeans 6.8 on Redhat Linux. Does anyone know how to configure NetBeans to debug (step into) libraries not compiled with NetBeans? In my particular case, I'm trying to debug the VTK library which is built using cmake with the Debug flag set. I've written a C++ application that uses the shared libraries from VTK. Any ideas? I'd tried the obvious things like adding the source locations to the project. Note that with gdb I can debug the application and set breakpoints anywhere in VTK. Any help would be appreciated. Thanks, Paul

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• Netlink user-space and kernel-space communication

  - by sasayins

  Hi, I am learning programming in embedded systems using Linux as my main platform. And I want to create a Device Event Management Service. This service is a user-space application/daemon that will detect if a connected hardware module triggered an event. But my problem is I don't know where should I start. I read about Netlink implementation for userspace-kernelspace communication and it seems its a good idea but not sure if it is the best solution. But I read that the UDEV device manager uses Netlink to wait a "uevent" from the kernel space but it is not clear for me how to do that. I read about polling sysfs but it seems it is not a good idea to poll filesystem. What do you think the implementation that should I use in my service? Should I use netlink(hard/no clue how to) or just polling the sysfs(not sure if it works)? Thanks

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• making a gui editor

  - by Manny

  Hello, For my school project, I would like to build a gui that someone else can use to create a gui. Upon some research I saw lot of gui builders but didn't see anything along the lines of what I am looking for. But then I did find a tutorial using C# on here I rather create this gui editor for linux environment. Any suggestions to where I should start? what tools I can use? Any links to any tutorials? Any help/direction would be greatly appreciated.

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• Is there any Opensource Browser for touchscreen device ?

  - by Wallah

  I need internet browser on my device which has 4.3 Inch screen with 480x272 resolution, I am using embedded Qt 4.6.2 on embedded linux. Micro-controller has ARM9 with 450 Mhz. Requirements for browser are - Touch Screen Support, Panning ( No Scroll bars) - Single touch Zooming ( No Multi Touch Available). - Fit to screen width support ( No Horizontal Scrolling). - Acid 3 Standard Compliable. - Page loading should be like, display all visible text first and then load and show Images Gradually. Is there any browser which is near to this requirements.

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• gcc, UTF-8 and limits.h

  - by bobby

  My OS is Debian, my default locale is UTF-8 and my compiler is gcc. By default CHAR_BIT in limits.h is 8 which is ok for ASCII because in ASCII 1 char = 8 bits. But since I am using UTF-8, chars can be up to 32 bits which contradicts the CHAR_BIT default value of 8. If I modify CHAR_BIT to 32 in limits.h to better suit UTF-8, what do I have to do in order for this new value to come into effect ? I guess I have to recompile gcc ? Do I have to recompile the linux kernel ? What about the default installed Debian packages, will they work ?

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• How to know start and kill processes within Java code (or C or Python) on *nix

  - by recipriversexclusion

  I need to write a process controller module on Linux that handles tasks, which are each made up of multiple executables. The input to the controller is an XML file that contains the path to each executable and list of command line parameters to be passed to each. I need to implement the following functionality: Start each executable as an independent Be able to kill any of the created processes independent of the others In order to do (2), I think I need to capture the pid when I create a process, to issue a system kill command. I tried to get access to pid in Java but saw no easy way to do it. All my other logic (putting info about the tasks in DB, etc) is done in Java so I'd like to stick with that, but if there are solutions you can suggest in C, C++, or Python I'd appreciate those, too.

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• How to recive more than 65000 bytes in C++ socket using recv()

  - by Mr.Cool

  I am developing a client server application (TCP) in Linux using C++. I want to send more than 65,000 bytes at the same time. In TCP, the maximum packet size is 65,635 bytes only. How can I send the entire bytes without loss? Following is my code at server side. //Receive the message from client socket if((iByteCount = recv(GetSocketId(), buffer, MAXRECV, MSG_WAITALL)) > 0) { printf("\n Received bytes %d\n", iByteCount); SetReceivedMessage(buffer); return LS_RESULT_OK; } If I use MSG_WAITALL it takes a long time to receive the bytes so how can I set the flag to receive more than 10 lakhs bytes at time.

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• Compatibility of x-www-browser

  - by rohit.arondekar

  I want to open html files from a shell script. I know that Ubuntu has a command x-www-browser that will open the default browser on the system. I also found via some Googling that the command is part of the debian system. I was wondering if the command is available on non debian based distros. If it isn't is there a standard way of opening an html file in the default browser on a linux OS via command line? Note that I'm using Bash.

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• C++ option/long option implementation

  - by K Hein

  I am working on a parser for meta programming language using C++ on Linux platform. Right now, I need to implement option/long option for the parser to provide some additional features. Basically, if the user pass in some additional option, the parser needs to store statistics while parsing the text files. I can think of two ways to implement it. One way is to user global to store options entered by users. Another way is to create a singleton class to store options. So I would like to know if there is any other way to implement it. What is the best/most recommended way of implementing it? Thanks in advance. Regards, K.Hein

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• Using sys/socket.h functions on windows

  - by BSchlinker

  Hello, I'm attempting to utilize the socket.h functions within Windows. Essentially, I'm currently looking at the sample code at http://beej.us/guide/bgnet/output/html/multipage/clientserver.html#datagram. I understand that socket.h is a Unix function -- is there anyway I can easily emulate that environment while compiling this sample code? Does a different IDE / compiler change anything? Otherwise, I imagine that I need to utilize a virtualized Linux environment, which may be best anyways as the code will most likely be running in a UNIX environment. Thanks.

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