If a process forks its child and communicate with the child using pipe, do closing the write end of the pipe and terminating the writing process have the same effect?
View 3 Repliesi wanted to capture the stdout and stdin of a child process within a parent so that any output of child is sent to the parent and any input taken from the parent. code is simple enough and i have followed all code guidlines on the internet (some guidlines do differ also) my select call either hangs if i do not give a tmeout and with a timeout it returns 0 descriptors to be written to or read from:
below is the simple code for parent:
int main(void)
{
int outfd[2];
int infd[2];
[code].....
why select hangs without a timeout ... why can it not detect that the pipe is write ready i.e parent can write to it ... if it does not detect tha read pipe as having data...
I am facing an issue where the process starts hanging. When I closely look at the logs I come to know that some of the child processes that are forked by the parent process are not finished.
1) Is it possible that the child processes that are not finished occupy the socket memory of the parent process and ultimately a point is reached where no socket memory is available to fork new child processes.
2) What is the standard limit of socket memory in linux?
3) What is the fate of such child processes (as I have mentioned above)?
4) How to debug such cases so that the exact problematic area is identified?
well i have just started with shell scripting...how to find all child processes of a parent process given to script as argument.
View 10 Replies View Relatedi need C code to get child pids from its parent pid in linux and in kernel mode, is there anything like getpid() or getppid() which works in kernel mode?
View 2 Replies View RelatedI am writing a perl script where forking a child and the child is waiting for some response from C++ exe. Here is the code snippet:
Code:
my $retPid = fork;
if ($retPid) {
# I am parent ...
# Install signal handler
$SIG{CHLD} = &REAPER; ...
# sleep for a week (6 hours at a time)
for ($cnt = 0; $cnt < 28 ; $cnt++) {
select(undef, undef, undef, 21600);
last if ( ! -e "/proc/$retPid" ); } ...
} else {
# I am child
($iid, $rc, %data) = $cpp_exe->getResponse(604800); # 1 week timeout ... }
If the cpp_exe takes very long time (around 30 hours) to respond then the perl script (both parent and child) is dieing. The SIG{CHLD} handler defined in parent is not getting called. It seems parent is dieing first then child is dieing (or may be both dieing at the same time). Why the script is dieing?
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.
View 6 Replies View RelatedI 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()
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.?
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].....
I work on Linux for ARM processor for cable modem. There is a tool that I have written (as the job demands) that sends/storms customized UDP packets using raw sockets. I form the packet from scratch so that we have the flexibility to play with different options. This tool is mainly for stress testing routers.
The details are here.
I actually have multiple interfaces created. Each interface will obtain IP addresses using DHCP. This is done in order to make the modem behave as virtual customer premises equipment (vcpe).
When the system comes up, I start those processes that are asked to. Every process that I start will continuously send packets. So process 0 will send packets using interface 0 and so on. Each of these processes that send packets would allow configuration (change in UDP parameters and other options at run time). Thats the reason I decide to have separate processes.
I start these processes using fork and excec from the provisioning processes of the modem.
The problem now is that each process takes up a lot of memory. Starting just 3 such processes, causes the system to crash and reboot.
I have tried the following:- 1-I have always assumed that pushing more code to the Shared Libraries will help. So when I tried moving many functions into shared library and keeping minimum code in the processes, it made no difference to my surprise.
2-I also removed all arrays and made them use the heap. However it made no difference. This maybe because the processes runs continuously and it makes no difference if it is stack or heap?
3-I suspect the process from I where I call the fork is huge and that is the reason for the processes that I make result being huge. I am not sure how else I could go about. say process A is huge -> I start process B by forking and excec. B inherits A's memory area. So now I do this -> A starts C which inturn starts B will also not help as C still inherits A?. I used vfork as an alternative which did not help either. I do wonder why.
reduce the memory used by each independent child processes.
the wrong part of the forum but basically im working on a project and getting no where what so ever and i was wondering if i could get your help. Basically i have to create two scripts do:
The parent script which is going to:
o spawn several child processes.
o keep track of the progress of the child processes.
[code]...
I'm in the process of writing a program that is a server- it will accept connections and stuff, and spawn a child process for each. However, i've run into a small problem. I do NOT want to bother with keeping track of the processes unless i need to. So, i set SA_NOCLDWAIT (#ifdef) on a SIG_IGN to the SIGCHLD handler through sigaction interface. The standard says that it the kernel will then keep track of reaping zombie processes for me (a HUGE plus). However, upon receiving a SIGINT signal, i want to stop the server from accepting new connections (done), and then wait for there to be no new connections. I was thinking of just putting a loop like so:
Code:
while((wait(NULL) != (pid_t)-1) && errno != ECHILD);
However, I'm not *sure* that this will work, especially with SIGCHLD still ignored. So how can i tell if there are still child processes? I can't find any call like int getnumchld(pid_t proc); (i wish). Plus it would be inefficient to spin on that function anyway. OTOH, i would rather *NOT* have to do the same thing in a loop with a system("ps |...>file"); read(file); etc. either. Is there a way i can portably implement this feature (I was hoping i could run it on linux and the major BSDs, at least).
TO SUM IT UP:
How can i tell if a process has no child processes if i've SIG_IGN'd SA_NOCLDWAIT'd the SIGCHLD? Is there a _reasonably_ portable way to do so? I *don't* want to manually wait for EVERY process. Maybe only those still active at the time of SIGTERM, but that requires keeping track of the number of connections and whether those have terminated...
EDIT: Does anyone know if the above code *would* work, even with SIGCHLD ignored and the kernel cleaning up zombies *for* me? I checked the manpage and it doesn't say much.
EDIT1: Note that all of the processes are in the same process group and session. SO i can find them through this as well. Perhaps even setting the uid/gid and finding all processes run by that group?
EDIT2: i have an idea if the above isn't feasible. If there is no "elegant" way to do it, i could reduce the complexity by sending a SIGUSR1 to the whole process group. Each process would then set a flag telling it to send a SIGUSR1 in reply and send a SIGUSR2 when it is done executing. Then i could keep a count of signals. Maybe that would be *easier*. Or perhaps a count of all child processes and just a termination signal to decrement the counter.
I'm looking for a way in Perl to be able to take a list of servers, ssh multiple commands to it and store the results. If I do this process serially, sometimes one server will hang the whole script and if it doesn't, it still takes hours to complete.
I'm thinking what I need to do is make a parent loop that calls out a separate process that passes the server name to the child sub process and then executes all the commands I have defined in its own process. If one server 'hangs', at least that won't stop the script from doing all the other servers in the list.
I'm guessing using the fork() command would serve me best, however, all the online descriptions I have found have been vague at best.
I have written a simple script which has to find required patterns from a bunch of files ( where each file is around 2 GB each,which contain the output of seq 1 10000000000000) on an 8 core machine.I am current forking 6 child processes which run simultaneously on 6 cores of the processor & have to search for the required pattern in 6 different files & inform the parent process when a pattern is found using a PIPE.
The problem is,when a child process is done reading a text file looking for a pattern,it is becoming a zombie process.It exits cleanly when i put a $SIG{CHLD} = "IGNORE"; in the script.Can any one tell me whats going on & how do i improve the communication between child and parent processes?
Code:
#!/bin/perl
use strict;
[code]...
What happens to a child process that dies and has no parent process to wait for it and what's bad about this?
View 2 Replies View RelatedI 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]....
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.
View 1 Replies View RelatedI have setgid permission on my home directory (/home/XXXX) the permission look like below.
Code:
drwxrws--- 2 toshi jadu 4096 Apr 26 16:54 getset
If I create new directory in this getset folder the permission of getset folder could not inherit.
Code:
#cd getset
#mkdir test2
#ls |grep test2
drwxr-s--- 2 toshi jadu 4096 Apr 26 16:56 test2
As I know the setgid utility allow to inherit the permission from parent directory to child directory.
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
I'm in a nested shell trying to use disown to re-root myself as well as a child. Looks like this:
Code:
# echo $$
1234
# disown 1234
disown: job not found: 1234
# disown $$
disown: job not found: 1234
# pgrep mychild
2222
# disown 2222
disown: job not found: 2222
This is in zsh. The goal is to have process 1 (the root of all processes) to become the parent.
I have a transparent proxy Squid-3.0 on Slackware 12.2. I used cron to restart squid every day at 7:30 AM (just /path.to.squid/squid -k kill && /path.to.squid/squid) Some days ago I saw in /var/log/messages that Squid was killed but haven't started. I started it manually and everything was OK. But today everything repeated. And the log file is interesting. I tried to find about it on http://squid-cache.org/ but al in vain. This is from /var/log/messages :
Code:
May 24 07:30:02 konura squid[17188]: Squid Parent: child process 17199 exited due to signal 9
May 24 07:30:02 konura squid[19038]: Squid Parent: child process 19040 started
May 24 07:30:03 konura squid[19038]: Squid Parent: child process 19040 exited with status 1
May 24 07:30:06 konura squid[19038]: Squid Parent: child process 19045 started
[code]....
I need to say that I haven't edited the config file for a long time, but this problem started to happen. ADDED, Solved: I'm not sure, but maybe I found the decision. I deleted about 400 mb of Sarg logs from /var partition. And now squid runs well. Besides, before deleting old logs, 'crontab -e' and 'pkgtool' didn't work And the system wrote me that it's no space left on device. At the same time, 'df -h' showed me that all partitions had enough free space. Seems strange, but that's it. After deleting old proxy statistics, generated by Sarg (this is about 400 mb) 1)squid runs OK and 2)there are no more that annoying messages about abscence of free space.
I've written a simple server in linux used fork to create a FIFO pipe.The server create two FIFO pipe.One for server read data from client and write data to client.Then another pipe for client read data from server and write data to server.When the server read data from a client used server-pipe and then write data to client.But ,if the client no read open the pipe,the server side write will be crashed because of a broken-pipe SIGPIPE. How to check whether the read side is opened?Or,how to catch the SIGPIPE,and then my server will still execute on,not crashed!!
View 5 Replies View RelatedI 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]....
I want to check all the child processes attached to a specific process. Say for a example; my process is a java process. Then I wanna know what are the processes attached to that java process. At the moment I use the command # ps aux|grep java; this gives the details about the currently running java process. So I can kill the whole java process using #kill -9 {pid} ...but there are sub processes attached (I guess child processes) to java process. I wanna view all of them & kill whatever the process I like not the whole thing. I'm using Red hat 5 enterprise edition. and currently a weblogic application server is running on that.
View 2 Replies View RelatedI work on Linux for ARM processor for cable modem. There is a tool that I have written (as the job demands) that sends/storms customized UDP packets using raw sockets. I form the packet from scratch so that we have the flexibility to play with different options. This tool is mainly for stress testing routers.I actually have multiple interfaces created. Each interface will obtain IP addresses using DHCP. This is done in order to make the modem behave as virtual customer premises equipment (vcpe).
When the system comes up, I start those processes that are asked to. Every process that I start will continuously send packets. So process 0 will send packets using interface 0 and so on. Each of these processes that send packets would allow configuration (change in UDP parameters and other options at run time). Thats the reason I decide to have separate processes. I start these processes using fork and excec from the provisioning processes of the modem. The problem now is that each process takes up a lot of memory. Starting just 3 such processes, causes the system to crash and reboot.
I have tried the following:-
1-I have always assumed that pushing more code to the Shared Libraries will. when I tried moving many functions into shared library and keeping minimum code in the processes, it made no difference to my surprise.
2-I also removed all arrays and made them use the heap. However it made no difference. This maybe because the processes runs continuously and it makes no difference if it is stack or heap?
3-I suspect the process from I where I call the fork is huge and that is the reason for the processes that I make result being huge. I am not sure how else I could go about. say process A is huge -> I start process B by forking and excec. B inherits A's memory area. So now I do this -> A starts C which inturn starts B will also not help as C still inherits A?. I used vfork as an alternative which did not help either. I do wonder why.
I have a situation where I have several screen (/usr/bin/screen) sessions running. 2 of the screen sessions (ps1 and ps2) run a script that launched SipP with specific parameters. 1 script starts SipP and has it make 50 calls where the other makes only 20 calls. However The script is configured where we can change how many calls it makes if needed.
So the problem is, due to issues with SipP, we must restart everything every 12 hours (at maximum). So I am trying to work out scripts to stop the SipP processes cleanly. In order to do so I need to figure out which SipP process is spawned by which screen. i.e. which sipp was started by screen session ps1, and which one was started by screen session ps2.
Now I can do ps -ef | grep <number of calls configured> to find out but then I would have to change my stop script every time we reconfigure how many calls are made, and have a separate stop script for each screen session. I would much rather be able to send the screen name as a parameter to the stop script and have it work no matter how many calls SipP is configured to make.Also your standard kill -1 <PID> does not shutdown SipP cleanly. So working out those details is a bit more tricky. Anyone know how I can determine what processes are spawned from a specific screen session?
Im wondering if there is a simple way to protect environment variables to be changed by child processes?
View 1 Replies View Relatedhow I could save all of the mail sendmail processes to a named pipe?
View 5 Replies View RelatedCode:
#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.