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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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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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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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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Mar 15, 2010
I have a problem when using awk:
e.g: awk '{processing text}' File1 > File2
But when I'm processing the File1, I want to print out some messages to the screen (not the File2). How can I do that?
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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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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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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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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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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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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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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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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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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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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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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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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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Mar 16, 2011
I have written a script and included the command
Code:
set -x
to see what happening when i run the script
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Jan 15, 2011
So I have a DAC/Headphone Amplifier which plugs in through USB. Through the system settings I'm able to set it as the preferred audio output option. This makes all the windows manager sounds come through the headphones, but all the applications still come through the laptop speakers; i guess they are completely independent of the system settings. I have to set each application's output preferences separately, and some software (like Firefox) doesn't have any output preferences. So is there a way toirect the audio output of all applications to all come through the USB DAC
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Dec 1, 2010
I have seen a post where someone was explaining the virtuality of stdout and stderr and that it can be redirected with e.g. 2>file.txt but this apparently is not working for me!
I have a CUPS filter with fprintf(stderr,...)
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Jul 3, 2009
I have this expect process:
Code:
spawn -noecho telnet my.host.com
expect {
[code]...
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Jun 1, 2009
I use tcl-expect script to ssh to the server. How can I eliminate the first 2 lines if using system(./script.sh) to execute it, as the default output will be shown on shell and the first 2 lines are included.
Essentially I just want to have the "ps" result, not the login process. code...
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Sep 19, 2011
This seems so simple when doing it from command line but I'm not able to accomplish it inside a script. I am trying to put output of following command into a text file:
CMD= mysql -uroot -psecret -e 'SHOW SLAVE STATUS G;'
FIL=~/replication-`date +%F`.txt
MAILTEXT=~/mailtext.txt
touch $FIL
$CMD > $FIL
Where FIL is a variable that contains path of the file to which to output command. I am running this command in a shell script from where I want to email contents of $FIL as attachment using mutt. But I am always getting 0 byte file. Also if I examine in directory the file is of 0 byte length.
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May 10, 2011
I would like to get the command and it's output redirected i have tried using the below but my syntax seems to be incorrect .
<<EOF
$(ls)
EOF
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May 3, 2011
When I run 'sendmail -bv', it sends the mail delivery status report as a mail to the root. Is there a way I can redirect this to the console instead of sending as a mail. requirement is to programatically find the mail host of the recipient for which I thought of using this 'sendmail -bv' command. Is there any other better way to find mail host of the recipient
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Jul 30, 2011
Today I tried to use padevchooser on Natty to send my laptop audio to my home media machine (which has the good speakers) using the "default server" option. Turns out padevchooser doesn't work on Unity and the threads I have seen say it is deprecated for other gui tools,
So what is the easy gui way to switch from my local pulse server to another one on my LAN, without using padevchooser, or switching off Unity? Or is this a regression?
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May 22, 2010
I've got a C program that I've added some 'printf' statements to monitor a couple of variables. When I run this program manually or from a script, the output is displayed on screen. However, I need to change various variables in the 'test.c' file, run 'make clean' and 'make' a few hundred thousand times. I'm using a script to read the variables in and then using sed to do in-place edits of the file. Unfortunately, with this amount of iteration, it is getting rather tired!
Anyway, I've created a script that is working as long I respond to prompts. I've tried the following to no avail: Code: /path/to/script > /tmp/output /path/to/script > /tmp/output 2>&1 /path/to/script | tee (no output even after adding the -a option) In my C program, I have the following 'printf' statement: Code: printf ("variable1: $s variable2: $s",var1,var2); What am I missing? I've worked with redirection before and it's always worked out fine, but this one plain stumps!
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Dec 28, 2010
When inserting/removing a usb device to a board based on linux system, an output is given:
Code:
# mmc1: card 0001 removed
mmc1: new SD card at address 0001
[code]...
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Nov 8, 2010
I am going through a multi-step process to produce output files, which involves 25,000 greps at one stage. While I do achieve the desired result I am wondering whether the process could be improved (sped up and/or decluttered).input 1set of dated files called ids<yyyy><mm> containing numeric id's, one per line, 280,000 lines in total:
Code:
123456
999996
[code]....
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Oct 9, 2010
I'm not sure about the following behavior so thought I would put it out to see if there is an error I need to resolve, or simply a process that I need explained.I'm also not sure if this is an Ubuntu issue, a Linux issue, or other... but here goes.I ran my "make build" in two different ways; one with just "make build" and one with "make build > output" (so I could review the full script).With just "make build" the process finished and returned to the command prompt.
With "make build > output", after the process had finished (script in output document identical to what was in the terminal with "make build") a new set of data was displayed in the terminal (see below).With the other examples of using "make build > output" the times it would parse something back to the terminal window was when there was an error. As I fixed the errors these breaks back to the terminal window would stop. So I'm wondering if this indicates a new error, but because the "make build" now completes successfully (at least it appears to), I'm wondering if this data in the terminal window is just a behavior related to redirecting the output script using the ">" process and something to do with returning to the terminal once a process completes
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