Programming :: How To Use Globals When Using Fork

Sep 16, 2010

As part of my ongoing project I need to put together a messaging server of sorts. So far I have coded a server which accepts multiple connections, which then runs a function that will perform a task, see below.On this sever I have a global structure which is populated using the data found in a read() buffer. However with each fork() that runs the below function each process is handed a blank structure. How could I go about allowing each fork() child process access the same structure?

My code should hopefully show what I am trying to do?
Code: void listen_for_client(int sock)


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Programming :: Can't Run Second Child In C (Fork)

Apr 10, 2011

Now,I created one parent and two children. I must create some value as random in child1 and child1 has to send these values to child2.Child2 must read them.. now,I cant create some random values and i can send them.But child2 doesnt work. I have two functions. One them is writing, another one is reading. Child2 uses reading function,but it doesnt work (child2 cant call it, because writing function in endless loop) What i must do? I used wait,usleep... No way.. I attached my file and also there is code..

PHP Code: #include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <signal.h>
#include <stdarg.h>
#include <sys/types.h>

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Programming :: Fork/exec Versus Posix_spawn

Sep 30, 2010

Just coming over from Windows here... where I've been using "CreateProcess" which returns a value depending on whether the process was created successfully or not.

Now I'm trying to create a process on linux and I've been learning about fork/exec, and I've been struggling with the fact that there seems to be no easy way to know (within the original parent process) if exec succeeded or not. (without forcing the parent process to hang around polling it or something).

Anyway, I've now just discovered the posix_spawn function, and it seems exactly what I need. However I'm finding the documentation a little hard to understand. In particular, I can't find actual confirmation that it will definitely return an error if creating the process fails (like CreateProcess does on windows). So can anyone confirm that for me?

The text on the documentation states: "If posix_spawn() or posix_spawnp() fail for any of the reasons that would cause fork() or one of the exec family of functions to fail, an error value shall be returned as described by fork() and exec"

This makes me think it uses exec/fork under the hood, and so I wonder if it can be trusted..?

And also, most of the examples on the internet for creating processes use fork/exec, so I wonder if there is some catch with posix_spawn I haven't read about... (since it seems a much simpler way of doing things)

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Programming :: Passing Usb_dev_handle After Fork Exec?

Aug 19, 2010

I have been struggling with this for about a week now. I'm working with QuickUSB to send video streams to and from a device. I get the fastest results by fork()ing and exec()ing new processes everytime I run a pipeline, which works great when reading from files, but now i have to transition it so that i am reading/writing data over a QuickUSB bus. I have it working for each individual process, but i can't run multiple processes because it won't let me open the device. After looking through QuickUSB's API a little closer, i found that the QHANDLE type that they use to describe the usb device is actually just a usb_dev_handle *. From what i have found, this is an incomplete structure, so i am having trouble with opening it in the main process and passing it to each new process to write to it. I already have semaphores set up to prevent multiple processes using it at the same time. I just CANT find out how to utilize the same usb device between two process that are forked and exec. i also must do the exec() because otherwise my gtk and gstreamer fails for trying to share resources.

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Programming :: Creating Multiple Processes Using Fork

Oct 23, 2010

As an assignment i was doing a program to create two process using fork and pass messages between them using message queue.Did it worked well until my friend tried to copy it using scp.suddenly all hell broke loose as processes without ran syncronisation ie. in tech terms the process just wont wait wen a message queue is keeps on executing randomly.but after a reboot .. everything worked fine. until again i tried to do scp on my system on purpose. and again the program just went mad.

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Programming :: Why Fork Is Executing The Program Twice From Start

May 25, 2011

I am learning about OS and I wrote this simple forking program... Here's the code..

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>


How can it print the first statement, that is BEFORE the fork() statement twice?

I am running Natty 11.04 btw..

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Programming :: Understanding Pid() And Fork() Programming?

Mar 28, 2011

I have been doing programming since the last 5 years. however, i have used to cut and paste the template without knowing in depth since i am chasing the time to finish a certain project. The title above seems easy if we read the manual, its just that im kinda confuse just for a second. Hope you guys can help me to give a better understanding for me so that i can upgrade my knowledge.Well, during my normal practice cut and paste, i try to understand this code below :-

Code: pid_t pid;
if (pid < 0) {perror("Erro spawning process : "); exit(EXIT_FAILURE);}


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Programming :: Fork()ing Multi Child Process In C - Stuck

May 12, 2011

i got basic knowledge about creating a single child from a parent using fork(). But when it comes into creating multiple children, i am simply stuck. I am trying to create two processes from a parent and it would wait for both two processes to finish. my attempt is as below


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Programming :: Python's Thread & Fork Support Is Compared To Perl?

Mar 24, 2011

I'm wondering how python's thread & fork support is compared to perl? Which one is best option among Perl and Python

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Programming :: Fork() Copies The Address Space Of The Calling Process?

May 13, 2010

I know that fork() copies the address space of the calling process. Say, however, i have a linked list allocated. Will the list be copied over to the child process's space? If so, i would have to free them in the child process as well as the parent process, correct? Or will the variables be copied but not be pointing to any valid address? Or would it just kind of not do anything?example:

struct ll_ex {
struct ll_ex * next;


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Programming :: Fork() - Variable Values Between Child And Parent Process?

Feb 24, 2010


int main()
int pi;
int i=10;


Q 1. The value of the variable pid returned by the fork() function will be greater than 0 in the parent process and equal to zero in the child process? but during forking, there values are exactly copied so what's went wrong here?

Q 2. "changes to the variable in one process is not reflected in the other process" why it is so? >> Even if we have variable i declared as a pointer or a global it wont make a difference.


int main()
int i, pid;
printf("before fork i is %d


Q. Through this program it is clear that both process is using the data from the same location, so where's the original value is residing when the child process is in execution.?

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Programming :: Redirecting Stdin / Stdout And Stderr For Program Run As Fork()/execl()?

Nov 24, 2010

I'm trying to write a program that will fork a series of FTP sessions. For each session, there should be separate input and output files associated with stdin and stdout/stderr.
I keep reading how I should be able to do that with dup2() in the child process before the execl(), but it's not working for me. Could someone please explain what I've done wrong? The program also has a 30-second sniper alarm for testing and killing of FTPs that go dormant for too long.

The code: (ftpmon.c)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


The output:

$ ftpmon
Connected to (
220 (vsFTPd 2.0.1)
ftp> waitpid(): Interrupted system call

Why am I getting the ftp> prompt? If the dup2() works, shouldn't it be taking input from my script and not my terminal? In stead, it does nothing, and winds up getting killed after 30 seconds. The log file is created, but it's empty after the run.

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Programming :: Re-mapping Stdio For A Fork'd/exec'd Executable Doesn't Seem To Behave

Jan 27, 2011

I have a monitoring program ( GIT link to sourceforge ) which I'm trying to use to track when a child exits/dies/whatever. I'm calling fork(), then close for 0,1,2, and then opening /dev/null, monitored.stdout, and monitored.stderr as a replacement. I'm not sure if I've done something incorrect (perhaps I should use dup2 for explicit assignment?) but it appears that printf() messages are just being blackholed. I've tried setting the line buffering as a last ditch effort. On a different system, using code similar to the spawn_monitor() function, this appears to work fine, which makes me think I'm relying on some implementation specific detail.

Relevant function, for those who don't click links:


26 int spawn_monitored(char *argv[])
27 {
28 int exit = 0;
29 pid_t child;
30 const struct rlimit inf = {


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Programming :: Fork: Not Enough Memory While Executing "spawn Bash"

Apr 9, 2010

I have a TCL framewrok for my test cases automation. This is been working for last 1 year. But yesterday it exited with exception when a function was called. The exception was given as fork: not enough memory while executing "spawn bash"(procedure "runtrigger" line 36) invoked from within "runtrigger $fnAfter $sid_l $mapver" ("trigger" arm line 6) invoked from within

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Programming :: Creates A Child Process With Fork And, When The Child Ends, Receives The SIGCHLD Signal And Wait For Its Termination?

May 23, 2011

I have a doubt about signals in C programming. I have done this little program to explain it. It creates a child process with fork and, when the child ends, receives the SIGCHLD signal and wait for its termination.Ok, quite easy, BUT when I execute this code the SIGCHLD signal is received twice, first as an error (returns -1) and the second one to finish the child process.I don't understand the meaning of the first received signal. Why is it generated? Is the code wrong? (if you add the SIGINT and press Ctrl+C during the execution it also receives two signals instead of one)

Code: #include <stdio.h>
#include <unistd.h>
#include <string.h>


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Programming :: Under Which Circumstances A Child Process Creates Another Child Process Using Fork

Dec 7, 2009

Consider the following code:


int main()
int i=0;
pid_t pid;


I get the following output:

Parent: chid_pid=4356 i=0 parent's pid=4355
This is child 4356 i=0
This is child 4357 i=1


I can observe instead of two children(as I expect) processes there are three. This is because child process 4356 creates its own child. Why all the messages of the type "This is child X i=Y" are concentrated one under another? How exactly fork works? Is affected by the fact that I have a dual-core processor?

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General :: How To Use Fork In My Programme

Aug 31, 2009

1) Write a C program using the fork() system call that that generates the Fibonacci sequence in the child process. The number of the sequence will be provided in the command line. For example, if 5 is provided, the first five numbers in the Fibonacci sequence will be output by the child process. Because the parent and child processes have their own copies of the data, it will be necessary for the child to output the sequence. Have the parent invoke the wait() call to wait for the child process to complete before exiting the program. Perform necessary error checking to ensure that a non-negative number is passed on the command line.

2) Repeat the preceding exercise, this time using the CreateProcess () in the Win32 API. In this instance, you will need to specify a separate program to be invoked from CreateProcess(). It is this separate program that will run as a child process outputting the Fibonacci sequence. Perform necessary error checking to ensure that a non-negative number is passed on the command line.i have done with Fibonacci sequence .but i dont know how to include tht fork() function and win32 api .any one can help to finish?

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General :: Fork Process Will Not Exit - Ksh

Aug 19, 2010

I've a script that forks to another script.

The problem is that the child will not return to main process.

Main script ""


The child process ""


when running it from the terminal "sh -x ./"


My goal is via cron connect to ~100 remote winXP computers and download a single file. There fore I like to fork the process.

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General :: Regarding Fork() Multiple Process?

Aug 2, 2011

trying to fork multiple child but the program does not go as i want...

My code :


#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>


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Fedora :: What Is The Cdrecord Original Fork Status

Feb 10, 2010

I realize the information found here is potentially biased, but it made me curious where Fedora stands. Now that even Debian has agreed to distribute the original fork of Cdrtools, is Fedora considering that option? Several other distros are distributing the original fork now, and it's where active development is ongoing.

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General :: Fork() Always Return 0 Even In The Parent Process?

Mar 18, 2011

my code is very simple:

int pid, status;
printf("parent process id=%d, to call fork


but everytime I can only get two fork return pid=0. In parent process, the pid returned by fork() should be >0 and equal to the child process id.

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General :: Fork: Resources Temporarily Unavalbale?

Apr 30, 2010

I am continuously getting fork: resources temporarily unavailable even when I am typing ls command.

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General :: Using Fork() To Create A Binary Tree?

Sep 26, 2010

I am working on a project where I need to use the C language to generate a tree of processes. I understand how fork() works but I cant seem to get fork() to create two children from one parent and then have the two children create two more children.

Right now what i am seeing is a chain...where the parent creates one child...and that child creates another ONE child..etc.

Here is what I have so far:

for (i=0; i<n;i++){
if (childpid = fork()) break;
if (childpid == -1){
perror ("


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CentOS 5 :: Fork - Resource Temporarily Unavailable

Sep 11, 2009

I installed a while ago two CentOS 5.3 servers. One of them was running Samba and another OpenLDAP. I configured Samba to act as a PDC on the network and everything was working fine. I was already on policies configuration and desktop migrations.

The following problems are Samba server problem, LDAP server is on hold until I figure out the first problem.

Software conf:

Hardware conf:

One day, both servers began crashing, and after a while, it showed the following during the boot on Samba:

After that, ALL CentOS installations had this problem after yum update, epel installation and some smb.conf modifications:

I figured out it might be EPEL (i did installed yum-priorities and tryied updating the base sistem BEFORE epel installations), so I installed the system without EPEL yum repository. After some good and relieving 15 min working, the system crashed AGAIN after yum base update and showed the following on boot time:

And it stops right there.

Maybe some wrong kernel update? the first time it crashed in one way, with running updated system (After the first update, no manual update was done). The sequel problems were all after Kernel update and EPEL. The last one was just after Kernel update. I'll try one last time with NO updates, but i can't run the system like that.

I can't do anything that might one day crash, it's a 6000-7000 user gov environment, but i don't want to install another distro, so if I don't figure it out, they will order me to.

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General :: Single Process Firefox (Disable Fork)

Aug 31, 2010

I would like to run versions of Mozilla Firefox 3.6.5+ as a single process, just as it was in versions 3.6.3 and prior. The reason is that, on Linux, I am running within proxychains - which doesn't bind to forked processes. Because the plugins in versions 3.6.5+ run in a forked process I can't use proxychains to redirect Flash streams. Is there a setting in modern versions of Firefox that allow me to run plugins in the main process?

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Ubuntu :: Resource Fork Intentionally Left Blank

Dec 1, 2010

I just found out that there are some weird files on my harddisk: they have a filename that starts with "._", have a size of 4096 bytes, and contain a string that sais "This resource fork intentionally left blank".Does anyone know what put them there?

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General :: Stat File For Permissions - Fork() Or Execve()?

May 6, 2011

When a application is ran from the shell:fork() is calledexecve() is calledI know the shell stats the file to make sure the required permissions are allowed in the child shell. But I can not find this in the man fork. Nor can I find this in man execve. Which one of these processes/calls stats the binary to be ran?

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General :: Fork Behavior While Copying File Descriptors

Jun 17, 2010

I am quite confused about the following description on fork. Could you please explain it ?The child process shall have its own copy of the parent's file descriptors. Each of the child's file descriptors shall refer to the same open file description with the corresponding file descriptor of the parent.For example, I am opening a socket and then fork. Now, does the child have a separate socket or is shares it with the parent. Does I have any impact on using it in child?

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Server :: Error - Unable To Fork: Cannot Allocate Memory

Feb 6, 2011

While Apache is off, then everything is OK, but if I start apache server after some time I get messages "Unable to fork: Cannot allocate memory" when trying to do some commands with ssh(dir,rm,top and so on).

P.S. There is free RAM when I get that message.

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Slackware :: Annuncing Utopia A Fork (only 64bits) With KDE And Gnome?

Jun 28, 2010

Annuncing Utopia a fork (only 64bits) with KDE and Gnome?

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