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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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  • How do I write a bash script to replace words in files and then rename files?

    - by Jason
    Hi All, I have a folder structure, as shown below: I need to create a bash script that does 4 things: It searches all the files in the generic directory and finds the string 'generic' and makes it into 'something' As above, but changes "GENERIC" to "SOMETHING" As above, but changes "Generic" to "Something" Renames any filename that has "generic" in it with "something" Right now I am doing this process manually by using the search and replace in net beans. I dont know much about bash scripting, but i'm sure this can be done. I'm thinking of something that I would run and it would take "Something" as the input. Where would I start? what functions should I use? overall guidance would be great. thanks. I am using Ubuntu 10.5 desktop edition.

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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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  • Getting rails to execute root level file edits on system files without compromising security.

    - by voxobscuro
    I'm writing a Rails 3 application that needs to be able to trigger modifications to unix system config files. I'd like to insulate the file modifications from the consumer side by running them in a background process. I've considered writing out a temp file in rails and then copying the file with a bash script but that doesn't really insulate the system. I've also considered pulling from the database manually with a cron based script and updating the configs. But what I would really like is a component that can hook into the rails environment, read out what is needed from the database, and update the config files. This process needs to be run as root because the config files mostly live in /etc/whatever. Any suggestions? Thanks!

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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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  • Personalize Diff Command in Ubuntu

    - by acidboy
    I have two files, both with a lot of data, what I need is compare the first word of each file (each file always starts with a number, and each number could have many digits). The files are identical when these numbers are the same. Example: I have 3 files: a.txt, b.txt and c.txt a.txt content is "1 a b c 3 5 6 hjkj" b.txt content is "1 c f a 1234 h" c.txt content is "2 a b c 3 5 6 hjkj" diff a.txt b.txt should return "files are identical" diff a.txt c.txt should return "files are different" How can I compare them using the diff command?

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  • Secure way to run other people code (sandbox) on my server?

    - by amikazmi
    I want to make a web service that run other people code locally... Naturally, I want to limit their code access to certain "sandbox" directory, and that they wont be able to connect to other parts of my server (DB, main webserver, etc) Whats the best way to do it? Run VMware/Virtualbox: (+) I guess it's as secure as it gets.. even if someone manage to "hack".. they only hack the guest machine (+) can limit the cpu & memory the process uses (+) easy to setup.. just create the VM (-) harder to "connect" the sandbox directory from the host to the guest (-) wasting extra memory and cpu for managing the VM Run underprivileged user: (+) doesnt waste extra resources (+) sandbox directory is just a plain directory (?) cant limit cpu and memory? (?) dont know if it's secure enough... Any other way? Server running Fedora Core 8, the "other" codes written in Java & C++

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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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  • Servlet container; What is it and do I need it in my case?

    - by Camran
    I have just ordered a VPS from my provider. I have some Q however... My website uses Solr, which requires the following according to their website: "Solr requires Java 1.5 and an Application server (such as Tomcat) which supports the Servlet 2.4 standard" I also need php 5, MySql, and the usual javascript etc... The OS is Ubuntu 9.10 1- So what do I need to install then? 2- What is a servlet container? 3- The solr I have downloaded came with Jetty. Is Jetty a Servlet container? Thanks

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  • Make Tar + gzip ignore directory paths

    - by norm
    Anybody know if it is possible that when making a tar + gzip through 'tar c ...' command if the relative paths will be ignored upon expanding. e.g. tar cvf test.tgz foo ../../files/bar and then expanding the test.tgz with: tar xvf test.tgz gives a dir containing: foo files/bar i want the dir to contain the files foo bar is this possible?

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  • Very simple mod_rewrite questions

    - by Camran
    1- Does mod_rewrite means that if I make this url: domain.com/ad.php?id=8498292 INTO domain.com/8498292 that all links on my website will have to be changed to the later above? example the link: domain.com/ad.php?id=8498292 wont work now, unless I replace it with domain.com/8498292 ? Or will the server know that they are the same still? 2- Will the rewritten link appear rewritten in the browsers adress bars also, so if I enter domain.com/ad.php?id=8498292 it will actually appear as domain.com/8498292 in the adress bar itself? 3- Will images and all other related links and material on the page whose link is rewritten remain intact? ie will pictures and links still work FROM that page which are relative? Thanks

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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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  • find string from the file in somewhere

    - by lightmanhk
    I want to find a string from some file in subdirectory. Like we are in bundle/. and in bundle/ there are multiple subdirectories and multiple txt files I want to do something like find . -type f -exec grep "\<F8\>" {} \; want to get the file where it contain string < F8 this command does work, find the string, but never return filename I hope anyone can give me a better solution to this, like display filename along with the line containing that string

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  • Same memory space being allocated again & again while using malloc()

    - 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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  • Strange mod_rewrite problem; Website works partially

    - by Camran
    I have Ubuntu 9.10 Server... I need to get mod_rewrite working... the mod_rewrite module IS LOADED. On my server, the httpd.conf is empty, instead everything (almost) is in a file called apache2.conf. Anyways, I have also read I have to change the AllowOverride None to AllowOverride All in some file... My httpd.conf is empty as you know, but I have a folder called sites-enabled which contains a 000-default file. This is where I have set: AllowOverride All Now my goal as I stated in the last Q is to turn this link: http://mydomain.com/ad.php?ad_id=Bmw_nice_M3_497379462 into this: http://mydomain.com/Bmw_nice_M3_497379462 So as I got an answer in the last Q i inserted this into the htaccess file: Options +FollowSymLinks Options +Indexes RewriteEngine On RewriteCond %{REQUEST_URI} !^/ad\.php RewriteRule ^(.*)$ ad.php?ad_id=$1 [L] Now, this works (no fully) when entering the url manually in the adress bar, but my website isn't working now for some reason. It is like the website is locked down or something, and unless I change AllowOverride to None it will act like that. Any ideas why? Also another note, the links inside the rewritten url doesn't work properly (images are not shown, while some are shown)...

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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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  • 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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  • What scripts should not be ported from bash to python?

    - by Jack
    I decided to rewrite all our Bash scripts in Python (there are not so many of them) as my first Python project. The reason for it is that although being quite fluent in Bash I feel it's somewhat archaic language and since our system is in the first stages of its developments I think switching to Python now will be the right thing to do. Are there scripts that should always be written in Bash? For example, we have an init.d daemon script - is it OK to use Python for it? We run CentOS. Thanks.

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