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  • Fork bomb protection not working : Amount of processes not limited

    - by d_inevitable
    I just came to realize that my system is not limiting the amount of processes per user properly thus not preventing a user from dring a fork-bomb and crashing the entire system: user@thebe:~$ cat /etc/security/limits.conf | grep user user hard nproc 512 user@thebe:~$ ulimit -u 1024 user@thebe:~$ :(){ :|:& };: [1] 2559 user@thebe:~$ ht-bash: fork: Cannot allocate memory -bash: fork: Cannot allocate memory -bash: fork: Cannot allocate memory -bash: fork: Cannot allocate memory -bash: fork: Cannot allocate memory -bash: fork: Cannot allocate memory -bash: fork: Cannot allocate memory -bash: fork: Cannot allocate memory ... Connection to thebe closed by remote host. Is this a bug or why is it ignoring the limit in limits.conf and why is not applying the limit that ulimit -n claims it to be? PS: I really don't think the memory limit is hit before the process limit. This machine has 8GB ram and it was using only 4% of it at the time when I dropped the fork bomb.

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  • fork() within a fork()

    - by codingfreak
    Hi Is there any way to differentiate the child processes created by different fork() functions within a program. global variable i; SIGCHLD handler function() { i--; } handle() { fork() --> FORK2 } main() { while(1) { if(i<5) { i++; if( (fpid=fork())==0) --> FORK1 handle() else (fpid>0) ..... } } } Is there any way I can differentiate between child processes created by FORK1 and FORK2 ?? because I am trying to decrement the value of global variable 'i' in SIGCHLD handler function and it should be decremented only for the processes created by FORK1 .. I tried to use an array and save the process id [this code is placed in fpid0 part] of the child processes created by FORK1 and then decrement the value of 'i' only if the process id of dead child is within the array ... But this didn't work out as sometimes child processes dead so fastly that updating the array is not done perfectly and everything messed up. So is there any better solution for this problem ??

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  • How does fork() return for child process

    - by EpsilonVector
    I know that fork() returns differently for the son and father processes, but I'm unable to find information on how this happens. How does the son process receive the return value 0 from fork? And what is the difference in regards to the call stack? As I understand it, for the father it goes something like this: father process--invokes fork--system_call--calls fork--fork executes--returns to--system_call--returns to--father process. What happens in the son side?

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  • How does fork() return for son process

    - by EpsilonVector
    I know htat fork() returns differently for the son and father processes, but I'm unable to find information on how this happens. How does the son process receives the return value 0 from fork? And what is the difference in regards to the call stack? As I understand it, for the father it goes something like this: father process--invokes fork--system_call--calls fork--fork executes--returns to--system_call--returns to--father process. What happens in the son side?

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  • double fork using vfork

    - by Oren S
    HI I am writing a part of a server which should dispatch some other child processes. Because I want to wait on some of the processes, and dispatch others without waiting for completion, I use double fork for the second kind of processes (thus avoiding the zombie processes). Problem is, my server holds a lot of memory, so forking takes a long time (even the copy-on-write fork used in Linux which copies only the paging tables) I want to replace the fork() with vfork(), and it's easy for the second fork (as it only calls execve() in the child), but I couldn't find any way I can replace the first one. Does anyone know how I can do that? Thanks! The server is a linux (RH5U4), written in C++.

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  • Behavior of a pipe after a fork()

    - by Steve Melvin
    When reading about pipes in Advanced Programming in the UNIX Environment, I noticed that after a fork that the parent can close() the read end of a pipe and it doesn't close the read end for the child. When a process forks, does its file descriptors get retained? What I mean by this is that before the fork the pipe read file descriptor had a retain count of 1, and after the fork 2. When the parent closed its read side the fd went to 1 and is kept open for the child. Is this essentially what is happening? Does this behavior also occur for regular file descriptors?

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  • What's the proper way to fork() in FastCGI ?

    - by eugene y
    I have an app running under Catalyst+FastCGI. And I want it to fork() to do some work in background. I used this code for plain CGI long ago: defined(my $pid = fork) or die "Can't fork: $!"; if ($pid) { # print response exit 0; } die "Can't start a new session: $!" if setsid == -1; close STDIN or die $!; close STDOUT or die $!; close STDERR or die $!; # do some work in background I tried some variations on this under FastCGI but with no success. How should forking be done under FastCGI?

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  • Help with output generated by this C code using fork()

    - by Seephor
    I am trying to figure out the output for a block of C code using fork() and I am having some problems understanding why it comes out the way it does. I understand that when using fork() it starts another instance of the program in parallel and that the child instance will return 0. Could someone explain step by step the output to the block of code below? Thank you. main() { int status, i; for (i=0; i<2; ++i){ printf("At the top of pass %d\n", i); if (fork() == 0){ printf("this is a child, i=%d\n", i); } else { wait(&status); printf("This is a parent, i=%d\n", i); } } }

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  • fork() in perl on windows

    - by Darioush
    I'm using fork() on PERL in windows (activeperl) for a basic socket server, but apparently there are problems (it won't accept connections after a few times), is there any workaround? while($client = $bind->accept()) { $client->autoflush(); if(fork()){ $client->close(); } else { $bind->close(); new_client($client); exit(); } } is the portion of the relevant code.

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  • Fork in Perl not working inside a while loop reading from file

    - by Sag
    Hi, I'm running a while loop reading each line in a file, and then fork processes with the data of the line to a child. After N lines I want to wait for the child processes to end and continue with the next N lines, etc. It looks something like this: while ($w=<INP>) { # ignore file header if ($w=~m/^\D/) { next;} # get data from line chomp $w; @ws = split(/\s/,$w); $m = int($ws[0]); $d = int($ws[1]); $h = int($ws[2]); # only for some days in the year if (($m==3)and($d==15) or ($m==4)and($d==21) or ($m==7)and($d==18)) { die "could not fork" unless defined (my $pid = fork); unless ($pid) { some instructions here using $m, $d, $h ... } push @qpid,$pid; # when all processors are busy, wait for child processes if ($#qpid==($procs-1)) { for my $pid (@qpid) { waitpid $pid, 0; } reset 'q'; } } } close INP; This is not working. After the first round of processes I get some PID equal to 0, the @qpid array gets mixed up, and the file starts to get read at (apparently) random places, jumping back and forth. The end result is that most lines in the file get read two or three times. Any ideas? Thanks a lot in advance, S.

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  • c - fork() and wait()

    - by Joe
    Hi there, I need to use the fork() and wait() functions to complete an assignment. We are modelling non-deterministic behaviour and need the program to fork() if there is more than one possible transition. In order to try and work out how fork and wait work, I have just made a simple program. I think I understand now how the calls work and would be fine if the program only branched once because the parent process could use the exit status from the single child process to determine whether the child process reached the accept state or not. As you can see from the code that follows though, I want to be able to handle situations where there must be more than one child processes. My problem is that you seem to only be able to set the status using an _exit function once. So, as in my example the exit status that the parent process tests for shows that the first child process issued 0 as it's exit status, but has no information on the second child process. I tried simply not _exit()-ing on a reject, but then that child process would carry on, and in effect there would seem to be two parent processes. Sorry for the waffle, but I would be grateful if someone could tell me how my parent process could obtain the status information on more than one child process, or I would be happy for the parent process to only notice accept status's from the child processes, but in that case I would successfully need to exit from the child processes which have a reject status. My test code is as follows: #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <errno.h> #include <sys/wait.h> int main(void) { pid_t child_pid, wpid, pid; int status = 0; int i; int a[3] = {1, 2, 1}; for(i = 1; i < 3; i++) { printf("i = %d\n", i); pid = getpid(); printf("pid after i = %d\n", pid); if((child_pid = fork()) == 0) { printf("In child process\n"); pid = getpid(); printf("pid in child process is %d\n", pid); /* Is a child process */ if(a[i] < 2) { printf("Should be accept\n"); _exit(1); } else { printf("Should be reject\n"); _exit(0); } } } if(child_pid > 0) { /* Is the parent process */ pid = getpid(); printf("parent_pid = %d\n", pid); wpid = wait(&status); if(wpid != -1) { printf("Child's exit status was %d\n", status); if(status > 0) { printf("Accept\n"); } else { printf("Complete parent process\n"); if(a[0] < 2) { printf("Accept\n"); } else { printf("Reject\n"); } } } } return 0; } Many thanks Joe

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  • Weird behavior of fork() and execvp() in C

    - by ron
    After some remarks from my previous post , I made the following modifications : int main() { char errorStr[BUFF3]; while (1) { int i , errorFile; char *line = malloc(BUFFER); char *origLine = line; fgets(line, 128, stdin); // get a line from stdin // get complete diagnostics on the given string lineData info = runDiagnostics(line); char command[20]; sscanf(line, "%20s ", command); line = strchr(line, ' '); // here I remove the command from the line , the command is stored in "commmand" above printf("The Command is: %s\n", command); int currentCount = 0; // number of elements in the line int *argumentsCount = &currentCount; // pointer to that // get the elements separated char** arguments = separateLineGetElements(line,argumentsCount); printf("\nOutput after separating the given line from the user\n"); for (i = 0; i < *argumentsCount; i++) { printf("Argument %i is: %s\n", i, arguments[i]); } // here we call a method that would execute the commands pid_t pid ; if (-1 == (pid = fork())) { sprintf(errorStr,"fork: %s\n",strerror(errno)); write(errorFile,errorStr,strlen(errorStr + 1)); perror("fork"); exit(1); } else if (pid == 0) // fork was successful { printf("\nIn son process\n"); // if (execvp(arguments[0],arguments) < 0) // for the moment I ignore this line if (execvp(command,arguments) < 0) // execute the command { perror("execvp"); printf("ERROR: execvp failed\n"); exit(1); } } else // parent { int status = 0; pid = wait(&status); printf("Process %d returned with status %d.", pid, status); } // print each element of the line for (i = 0; i < *argumentsCount; i++) { printf("Argument %i is: %s\n", i, arguments[i]); } // free all the elements from the memory for (i = 0; i < *argumentsCount; i++) { free(arguments[i]); } free(arguments); free(origLine); } return 0; } When I enter in the Console : ls out.txt I get : The Command is: ls execvp: No such file or directory In son process ERROR: execvp failed Process 4047 returned with status 256.Argument 0 is: > Argument 1 is: out.txt So I guess that the son process is active , but from some reason the execvp fails . Why ? Regards REMARK : The ls command is just an example . I need to make this works with any given command . EDIT 1 : User input : ls > qq.out Program output : The Command is: ls Output after separating the given line from the user Argument 0 is: > Argument 1 is: qq.out In son process >: cannot access qq.out: No such file or directory Process 4885 returned with status 512.Argument 0 is: > Argument 1 is: qq.out

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  • About fork system call and global variables

    - by lurks
    I have this program in C++ that forks two new processes: #include <pthread.h> #include <iostream> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h> #include <cstdlib> using namespace std; int shared; void func(){ extern int shared; for (int i=0; i<10;i++) shared++; cout<<"Process "<<getpid()<<", shared " <<shared<<", &shared " <<&shared<<endl; } int main(){ extern int shared; pid_t p1,p2; int status; shared=0; if ((p1=fork())==0) {func();exit(0);}; if ((p2=fork())==0) {func();exit(0);}; for(int i=0;i<10;i++) shared++; waitpid(p1,&status,0); waitpid(p2,&status,0);; cout<<"shared variable is: "<<shared<<endl; cout<<"Process "<<getpid()<<", shared " <<shared<<", &shared " <<&shared<<endl; } The two forked processes make an increment on the shared variables and the parent process does the same. As the variable belongs to the data segment of each process, the final value is 10 because the increment is independent. However, the memory address of the shared variables is the same, you can try compiling and watching the output of the program. How can that be explained ? I cannot understand that, I thought I knew how the fork() works, but this seems very odd.. I need an explanation on why the address is the same, although they are separate variables.

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  • printf anomaly after "fork()"

    - by pechenie
    OS: Linux, Language: pure C I'm moving forward in learning C progpramming in general, and C programming under UNIX in a special case :D So, I detected a strange (as for me) behaviour of the printf() function after using a fork() call. Let's take a look at simple test program: #include <stdio.h> #include <system.h> int main() { int pid; printf( "Hello, my pid is %d", getpid() ); pid = fork(); if( pid == 0 ) { printf( "\nI was forked! :D" ); sleep( 3 ); } else { waitpid( pid, NULL, 0 ); printf( "\n%d was forked!", pid ); } return 0; } In this case the output looks like: Hello, my pid is 1111 I was forked! :DHello, my pid is 1111 2222 was forked! Why the second "Hello" string occured in the child's output? Yes, it is exactly what the parent printed on it's start, with the parent's pid. But! If we place '\n' character in the end of each string we got the expected output: #include <stdio.h> #include <system.h> int main() { int pid; printf( "Hello, my pid is %d\n", getpid() ); // SIC!! pid = fork(); if( pid == 0 ) { printf( "I was forked! :D" ); //removed the '\n', no matter sleep( 3 ); } else { waitpid( pid, NULL, 0 ); printf( "\n%d was forked!", pid ); } return 0; } And the output looks like: Hello, my pid is 1111 I was forked! :D 2222 was forked! Why does it happen? Is it ... ummm ... correct behaviour? Or it's a kind of the 'bug'?

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  • fork within Cocoa application

    - by liuliu
    My problem is not the best scenario for fork(). However, this is the best func I can get. I am working on a Firefox plugin on Mac OSX. To make it robust, I need to create a new process to run my plugin. The problem is, when I forked a new process, much like this: if (fork() == 0) exit(other_main()); However, since the state is not cleaned, I cannot properly initialized my new process (call NSApplicationLoad etc.). Any ideas? BTW, I certainly don't want create a new binary and exec it.

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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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  • Profile Picture Thumbnails, Following Projects, and Fork Collaboration

    [Do you tweet? Follow us on Twitter @matthawley and @adacole_msft] We deployed a new version of the CodePlex website last week. Profile Picture Thumbnails We have added a way to select a thumbnail from your profile picture, which will start appearing next to usernames across the site.  Managing your thumbnail is simple. From your profile page, choose Edit your profile.  On the left side, you’ll find an intuitive widget for choosing a profile picture, uploading it, and editing your thumbnail image. If you previously uploaded a profile picture, we’ve used that to generate a starter thumbnail. We welcome your suggestions and ideas for areas where seeing user thumbnails would be useful or interesting. Following Projects Based on some feedback we’ve received recently, we have taken several steps to help you discover and follow interesting and popular projects on CodePlex: The homepage now surfaces the top Projects Users are Following from the previous 7 days. When you visit any project homepage, you can see at a glance how many people follow the project. When you visit the People tab for any project, you will see both the project contributors and the 25 most recent project followers. Fork Collaboration We now support enabling collaborators on a fork based on a large number of user requests.  From the Source Code management page for your fork, you will now see the following on the right side: To add a collaborator, type in a username and click Add. All fork collaborators will have the ability to push to the fork and send/cancel pull requests.  To remove a collaborator, hover over user, and click on the X that appears: The CodePlex team values your feedback, and is frequently monitoring Twitter, our Discussions and Issue Tracker for new features or problems. If you’ve not visited the Issue Tracker recently, please take a few moments to log an idea or vote for the features you would most like to see implemented on CodePlex.

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  • Best way to fork SVN project with Git

    - by Jeremy Thomerson
    I have forked an SVN project using Git because I needed to add features that they didn't want. But at the same time, I wanted to be able to continue pulling in features or fixes that they added to the upstream version down into my fork (where they don't conflict). So, I have my Git project with the following branches: master - the branch I actually build and deploy from feature_* - feature branches where I work or have worked on new things, which I then merge to master when complete vendor-svn - my local-only git-svn branch that allows me to "git svn rebase" from their svn repo vendor - my local branch that i merge vendor-svn into. then i push this (vendor) branch to the public git repo (github) So, my flow is something like this: git checkout vendor-svn git svn rebase git checkout vendor git merge vendor-svn git push origin vendor Now, the question comes here: I need to review each commit that they made (preferably individually since at this point I'm about twenty commits behind them) before merging them into master. I know that I could run git checkout master; git merge vendor, but this would pull in all changes and commit them, without me being able to see if they conflict with what I need. So, what's the best way to do this? Git seems like a great tool for handling forks of projects since you can pull and push from multiple repos - I'm just not experienced with it enough to know the best way of doing this. Here's the original SVN project I'm talking about: https://appkonference.svn.sourceforge.net/svnroot/appkonference My fork is at github.com/jthomerson/AsteriskAudioKonf (sorry - I couldn't make it a link since I'm a new user here)

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  • Problem with fork exec kill when redirecting output in perl

    - by Edu
    I created a script in perl to run programs with a timeout. If the program being executed takes longer then the timeout than the script kills this program and returns the message "TIMEOUT". The script worked quite well until I decided to redirect the output of the executed program. When the stdout and stderr are being redirected, the program executed by the script is not being killed because it has a pid different than the one I got from fork. It seems perl executes a shell that executes my program in the case of redirection. I would like to have the output redirection but still be able to kill the program in the case of a timeout. Any ideas on how I could do that? A simplified code of my script is: #!/usr/bin/perl use strict; use warnings; use POSIX ":sys_wait_h"; my $timeout = 5; my $cmd = "very_long_program 1>&2 > out.txt"; my $pid = fork(); if( $pid == 0 ) { exec($cmd) or print STDERR "Couldn't exec '$cmd': $!"; exit(2); } my $time = 0; my $kid = waitpid($pid, WNOHANG); while ( $kid == 0 ) { sleep(1); $time ++; $kid = waitpid($pid, WNOHANG); print "Waited $time sec, result $kid\n"; if ($timeout > 0 && $time > $timeout) { print "TIMEOUT!\n"; #Kill process kill 9, $pid; exit(3); } } if ( $kid == -1) { print "Process did not exist\n"; exit(4); } print "Process exited with return code $?\n"; exit($?); Thanks for any help.

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  • confusing fork system call

    - by benjamin button
    Hi, i was just checking the behaviour of fork system call and i found it very confusing. i saw in a website that Unix will make an exact copy of the parent's address space and give it to the child. Therefore, the parent and child processes have separate address spaces #include <stdio.h> #include <sys/types.h> int main(void) { pid_t pid; char y='Y'; char *ptr; ptr=&y; pid = fork(); if (pid == 0) { y='Z'; printf(" *** Child process ***\n"); printf(" Address is %p\n",ptr); printf(" char value is %c\n",y); sleep(5); } else { sleep(5); printf("\n ***parent process ***\n",&y); printf(" Address is %p\n",ptr); printf(" char value is %c\n",y); } } the output of the above program is : *** Child process *** Address is 69002894 char value is Z ***parent process *** Address is 69002894 char value is Y so from the above mentioned statement it seems that child and parent have separet address spaces.this is the reason why char value is printed separately and why am i seeing the address of the variable as same in both child and parent processes.? Please help me understand this!

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  • Avoiding a fork()/SIGCHLD race condition

    - by larry
    Please consider the following fork()/SIGCHLD pseudo-code. // main program excerpt for (;;) { if ( is_time_to_make_babies ) { pid = fork(); if (pid == -1) { /* fail */ } else if (pid == 0) { /* child stuff */ print "child started" exit } else { /* parent stuff */ print "parent forked new child ", pid children.add(pid); } } } // SIGCHLD handler sigchld_handler(signo) { while ( (pid = wait(status, WNOHANG)) > 0 ) { print "parent caught SIGCHLD from ", pid children.remove(pid); } } In the above example there's a race-condition. It's possible for "/* child stuff */" to finish before "/* parent stuff */" starts which can result in a child's pid being added to the list of children after it's exited, and never being removed. When the time comes for the app to close down, the parent will wait endlessly for the already-finished child to finish. One solution I can think of to counter this is to have two lists: started_children and finished_children. I'd add to started_children in the same place I'm adding to children now. But in the signal handler, instead of removing from children I'd add to finished_children. When the app closes down, the parent can simply wait until the difference between started_children and finished_children is zero. Another possible solution I can think of is using shared-memory, e.g. share the parent's list of children and let the children .add and .remove themselves? But I don't know too much about this. EDIT: Another possible solution, which was the first thing that came to mind, is to simply add a sleep(1) at the start of /* child stuff */ but that smells funny to me, which is why I left it out. I'm also not even sure it's a 100% fix. So, how would you correct this race-condition? And if there's a well-established recommended pattern for this, please let me know! Thanks.

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  • problem with fork()

    - by john
    I'm writing a shell which forks, with the parent reading the input and the child process parsing and executing it with execvp. pseudocode of main method: do{ pid = fork(); print pid; if (p<0) { error; exit; } if (p>0) { wait for child to finish; read input; } else { call function to parse input; exit; } }while condition return; what happens is that i never seem to enter the child process (pid printed is always positive, i never enter the else). however, if i don't call the parse function and just have else exit, i do correctly enter parent and child alternatingly. full code: int main(int argc, char *argv[]){ char input[500]; pid_t p; int firstrun = 1; do{ p = fork(); printf("PID: %d", p); if (p < 0) {printf("Error forking"); exit(-1);} if (p > 0){ wait(NULL); firstrun = 0; printf("\n> "); bzero(input, 500); fflush(stdout); read(0, input, 499); input[strlen(input)-1] = '\0'; } else exit(0); else { if (parse(input) != 0 && firstrun != 1) { printf("Error parsing"); exit(-1); } exit(0); } }while(strcmp(input, "exit") != 0); return 0; }

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  • Why "Fork me on github"?

    - by NoBugs
    I understand how Github works, but one thing I've been confused about is, why almost every OSS project lately has a "Fork me on Github" link on their homepage. For example, http://jqtjs.com/, http://www.daviddurman.com/flexi-color-picker/, and others. Why is this so common? Is it that they want/need code validation, checking for security/performance improvements that they may not know how to do? Is it meant to show that this is a collaborative project - you're welcome to add improvements? Do they work for Github, or want to promote their service? Oddly enough, I don't think I've seen a "Fork project on Bitbucket" logo recently. My first reaction to that logo was that the project probably needs to be modified (forked) in order to integrate it with anything useful - or that they are encouraging fragmented codebase, encouraging everyone to make their own fork of the project. But I don't think that is the intent.

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