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>

[code]....

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

Dec 7, 2009

Consider the following code:

Code:

int main()
{
int i=0;
pid_t pid;
for(i=0;i<2;i++)

[code]....

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

[code]....

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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Programming :: Why Does A Child Exit When The Parent Receives A Signal

Mar 16, 2011

I have a problem with the last point of some homework I have for an OS class. I need the program to print the pid upon execution, then for 10 seconds react to SIGUSR1, SIGUSR2 and SIGTERM. If either USR1 or USR2 is received, the 10 seconds are reset. Some of the functions I'm told to use are alarm(), pause() and signal(). The nicest way I found was to handle SIGUSR1, SIGUSR2 and SIGALRM in the parent process, with SIGALRM killing the child (with a SIGTERM). In the child a pause() (or for(; pause() would be enough for it to be alive until killed from the SIGALRM handler in the parent.

What I found is that I can't just do a wait() in the parent process, waiting for the child to be killed, since whenever the parent receives a SIGUSR1 or SIGUSR2, the right handler is called but the child exits nicely. I tried blocking/ignoring those signals in the child, since the default behaviour for SIGUSR1 and SIGUSR2 is to terminate the process, but the result is the same. The only way I could do it is using a waitpid() within a do { } while(!WIFSIGNALED(status)) since when the child gets killed with the parent's kill(), it's WIFSIGNALED, whereas when it exits after the parent handles a SIGUSR1/2, it's WIFEXITED.

P.S. What I'm doing to achieve the expected 10s window is calling alarm(10) in the parent process and again within the SIGUSR1/2 handlers. In the SIGALRM handler I kill the child and within the child I simply do a for(; pause()

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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

[Code]....

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

Feb 24, 2010

Code:

int main()
{
int pi;
int i=10;
pid=fork();

[code]....

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.

Code:

int main()
{
int i, pid;
i=10;
printf("before fork i is %d

[code]....

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 :: 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>
[Code].....

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General :: Sending Signal From Child Process To Parent Process?

Sep 8, 2010

Code:

#include <stdio.h>
#include <unistd.h>
#include <signal.h>

[code]....

Description of what the code does or what i intended to do:

1. Created a child process from parent process using 'fork()'

2. Sent a signal 'SIGALRM' from child process to parent process using 'sigqueue' function.

(The Third parameter of 'siqueue' function contains the message (message msg) which the child process wants to send to the parent process.'msg' is a stucture instance containing a) pid of child and b) string) 5. Print the 'msg' sent by child process inside the signal handler function 'sig_action_function' of the parent process I am getting some junk value when this line is executed

Code:

printf("%d
",msg->cpid);

I expected to get the pid of child process, which the child process sent to parent process through the signal.

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General :: Difference Between Child THREAD And Child PROCESS?

Jul 30, 2009

I am troubleshooting something and I got this problem.

If I do "pstree -p"

It shows,

Code:

[code]....

However, it does NOT show up in "ps -elf"

Code:

ps -elf | grep soffi
0 S whho 7734 1 0 80 0 - 36435 - 11:14 pts/2 00:00:03 /usr/lib/openoffice/program/soffice.bin -splash-pipe=5
0 S whho 7833 7759 0 80 0 - 751 - 11:21 pts/3 00:00:00 grep soffi

I was wondering if 7735, 7736, 7737, 7743 were really processes. Then I checked /proc, I could cd to /proc/7735, /proc/7736, etc, but I could not ls them out. I looked at the man page of "pstree", it says,

Code:

Child threads of a process are found under the parent process and are shown with the process name in curly braces, e.g.

icecast2---13*[{icecast2}]

So, what does all this mean? Does it mean that 7735, 7736, 7737, 7743 are just threads but not processes? If so, why could I cd to /proc/<id> but not see them in "ps -elf".

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Programming :: SetUID On Different PID Or Child Process

Aug 18, 2010

I have a root process (on linux) that forks a child and the child process then drops privileges by doing a setuid() to a normal user. After the child setuid()'s, it is of course impossible for it to gain root again by itself. But since the main process is still running as root, i was wondering if there was a simple/smart way of getting the root-master-process to elevate the child back to root (or maybe just to another non-privi uid). Is there some way to do a setuid() on another pid? or maybe something can be done through /proc/<pid>/? Killing the child is not an option (because its what it does today and im trying to find a smarter way). (The program is apache2's mpm-itk worker and the "child" is the actual apache2 process serving a page.)

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Programming :: Gdb Debugging Exec From Child Process?

Jul 14, 2011

Im using gdb for debugging my application.. I was able to debug child process(when fork comes) .. and in child process we have an exec call to .... So the problem is, when the control come to exec , the exec process is executing at a time... I could not debug the exec. process... error is stack curruption due to same frame So, is there any way to debug the exec process

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Programming :: Get Error Code From Child Process?

Mar 28, 2011

I'm writing a sort of toy shell using fork() and execv(). It runs smoothly enough untill the user enters an invalid command at which point the program hangs, so I need a way to check if the program loaded using execv returned correclty or not in the parent process and kill it if it didntI tried writing stderr to a text file to see if something whent wrong but doesnt really work out. Try running ./digenv GDM -i -Q for instance. (-Q is an invalid option for grep which the program runs at a certain point).Heres the code:

Code:
//digenv
//Carl Reg�rdh 2011-03-24

[code]....

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Programming :: How To Redirect Stdin For Child Process

Aug 18, 2010

I'm trying to write a shell script that do ftp and download file periodically, this script should be called by a daemon running in the background.

the shell script "script.sh" is as follows:

Code:
yafc ftp://test:test@192.168.1.225:21 < commands
and the "commands" files is

Code:
d Root/md5* /
quit

if I run script.sh it will work just fine. But when the daemon software calls the "script.sh", the script will send ftp login request to the ftp server, but will not even answer the username or anything.

I believe it is something about child process redirection, but I don't know how to deal with it.

This problem is not only with yafc, it is the same with any ftp client or any application like telnet and so.

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Programming :: Passing Arguments To A Child Process In C++?

Feb 7, 2010

what I am trying to do is to pass an argument to the standard input stream of a child process. I mean I create two programs .. first one invokes the other. second one contains something like

Code:

scanf("%d", &n);

now I want my first program to be able to pass a value to the second one so that it gets stored in n.

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Programming :: Redirecting The Output Of Child Process To New Xterm?

Aug 2, 2010

I am developing a application. In this I fork() 3 childs(lets say child1 , child2, child3) . The parent is now waiting for some input from keyboard.Child3 is continously getting data from child1 and child2 using pipe which it then will print using printf.Now as the parent is waiting for input from user through keyboard while child3 is continously printing the data. I want to do it in different terminals.Can you please guide me how to proceed ahead so that on one terminal , the parent waits for input fromser while on other terminal child3 prints data.

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Programming :: Parent Process Block - Status Of Child

Mar 22, 2011

I am going to create a parent process and fork a child process from it. I want to write a code in such a way that whenever my child process end it must indicate that the child process is terminated by a signal or not. This code must be written in the parent process block.

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Programming :: Disallow File Access For Child Process With Execv?

Mar 8, 2011

I need to disable file access (fopen, freopen, open etc) for application which is running under chroot jail and with restrictions (rlimit) via execv. Before that I redirected stdin/out to files within jail. I tried this:

Code:
// Redirect stdin/stdout to files
int fd = open (file_input, O_RDONLY);
if (fd < 0)
fatal_error ("input open failed!");

[Code].....

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Programming :: Splitting A Parent Process Into 2 Child And Then Merging Result?

Sep 15, 2010

What i am trying to do is i want to add numbers from 1 to 100. but that too using multiprocessing. So i made a c programme and using fork() command made two child processes. Now in one child process i am adding from 1 to 50. and in another i am adding 51 to 100. and then in the parent process adding the two results to get the final one. Now the result from the two function i am getting correctly. But after the wait() call the value returned is lost : See the programme below for reference

# include<stdio.h>
# include<unistd.h>
# include<sys/wait.h>
# include<stdlib.h>

[code].....

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General :: Killing Parent Process Without Killing Child Process (Linux C Programming)?

Mar 10, 2011

I want to kill parent process after "fork()" method. but if I kill parent process with "exit(0)" method, main() thread is terminated as well so child prosess doesn't work anymore. Is there any way to kill only parent process without affecting to child process?

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

[code]....

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General :: Error Child Pid 13810 Exit Signal Segmentation Fault (11)

May 23, 2011

I installed Centos 5, httpd 2.2.3 and php5.3.6 with yum.

We have a website which can upload JPEG file to the server via php. But when we uploaded file, it showed the error

Quote:

child pid 13810 exit signal Segmentation fault (11)

I tried to run gdb on my computer and it showed that

Quote:

0xb6d1a600 in ?? () from /usr/lib/libjpeg.so.62

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Ubuntu :: What Is Child Process - GE Cannot Open

Aug 4, 2010

what is child process - GE cannot open

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General :: Child Process That Dies And Has No Parent?

Dec 17, 2010

What happens to a child process that dies and has no parent process to wait for it and what's bad about this?

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General :: Child Process Does Not Core Dump

Jul 27, 2011

In my program, I fork() to get a child process. Because of some problem, child process terminates by a segmentation fault. Parent process is still running. I have compiled my code with -g option. I have done: ulimit -c unlimited. I am not getting core dump of the child process. How can I get the core dump of child process?

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General :: Command Line For Child Process

May 20, 2011

I have created three child process from one parent. And different child has different functions. Child 2 has got function to load file called "wc" to count file1 and and its required to get their files by command line arguments. I can get the files through command line but couldn't get the files when child 2 process start.

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Fedora :: Error Creating Child Process For This Terminal

Aug 4, 2009

Terminal will not open
Error message: There was an error creating the child process for this terminal
Got this after doing a update to testing repo; to try to fix another issue with my media player sound not working.

Solved
The_Source_HIM
Just add yourself to 'tty' group and relogin

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Ubuntu :: There Was An Error Creating The Child Process Of This Terminal

Feb 13, 2010

I get the error

Code:
there was an error creating the child process of this terminal

When I run this code:

Code:
gnome-terminal --window-with-profile=Scripts

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Ubuntu :: Error Creating Child Process R-commander - On LTS 10.4

May 8, 2010

I work with social sciences and I really need to use "R". R is a program used for statistics and it has a module called R-commander, which let things easier to deal and comes with several options as opening SPSS files (another statistical package commonly used by Windows users) and other things. THe problem is, as Rcmdr is a module for R, when I run it, it opens a terminal window and then he runs the module, which opens a friendly gui.

It worked okay and clean in Ubuntu 9.10, but for LTS 10.4 I keep getting an error, no matter I reinstall the modules or the entire program. I even installed Ubuntu again without upgrading it from karmic Koala. But there is the same error msg.

The error message says: "Error while creating a child process for this terminal". The strange part is there is no other msgs in the terminal or errorlogs. I really need to use this software for work.

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SUSE :: Kill Child Process Without Killing The Parent?

Jun 21, 2010

I am trying to kill child process without killing the parent and seem to be having issues doing so. I have tried quite a few different commands and the end result is either killing all of them including the parent or not killing them at all.

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General :: Command To Find Parent And Child Process?

Apr 21, 2011

I have a script that calls other scripts/commands which may or may not spawn other process. From my understanding, when I do a ps -ef, the highest numbered process ID is supposed to be the parent ID of all the other related child processes, is this correct? In most or all circumstances, I do a ps -ef | grep <processid> of my script and anything that spawns off that process IDs I assumed are the child processes of my script. If I want to terminate my script and all other child processes, then I kill the parent ID which is the highest numbered PID and this will subsequently kill all other child process IDs, is this correct?

Now, my question is whether there is any quick way of showing what are the child processes of a parent ID instead of what am currently doing now which is visually checking which one is the parent ID and "assuming" that the highest numbered PID is the parent ID of all the other processes. Below is a sample output of running ps -ef | grep exp | grep -v grep. I assume from the output below that the parent process/ID is PID 11322, is that correct?

Code:

oracle 11154 11153 0 21:20 ? 00:00:00 /bin/sh -c (. ~oracle/.profile; /bin/ksh /usr/local/oracle/scripts/expdp_o
oracle 11155 11154 0 21:20 ? 00:00:00 /bin/sh -c (. ~oracle/.profile; /bin/ksh /usr/local/oracle/scripts/expdp_o
oracle 11190 11155 0 21:20 ? 00:00:00 /bin/ksh /usr/local/oracle/scripts/expdp_schema.ksh dev01
oracle 11322 11190 0 21:20 ? 00:00:00 expdp

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OpenSUSE :: Failed To Execute Child Process (Permission Denied)

Jul 11, 2011

I'm trying to start a program, but I keep getting the error:

"There was an error launching the application." Details: Failed to execute child process "/home/jjo/Desktop/0ad/build/resources" (Permission denied)

I've tried changing the permissions of the file, with no luck.

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Ubuntu :: Failed To Execute Child Process Skype-wrapper?

Apr 6, 2011

Just figured this one out and thought I'd post it here in case it helped someone else. Skype just upgraded itself from 2.1 to 2.2. After upgrading it didn't start, and I got the message

"failed to execute child process skype-wrapper" First test out if skype runs from the command line, by running this in a terminal

Code: skype & If it runs, you're good to go: simply right click on the menu, locate your entry for skype and change the command to launch it from skype-wrapper to skype. The reason for this is that in the 2.1 version, skype needed a script called skype-wrapper to set some varibles before start up. Upgrading removes the script, but failed to update the menu entry.

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