sigchld | 易学教程

How To Avoid SIGCHLD error In Bash Script That Uses GNU Parallel

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问题 I'm running a script.sh in a loop. The script contains a parallel wget command. I'm getting the following error: Signal SIGCHLD received, but no signal handler set. The loop looks like this: for i in {1..5}; do /script.sh; done And the line that is causing the error looks like this (omitting options and settings): cat file.txt | parallel -j15 wget Research: I'm not an expert with GNU Parallel, but the script seems to work fine most of the time except when I get the error above. While looking

linux - sleep() of parent process interrupted by child process

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问题 When a child process is fork() ed , then the parent process can wait() for the child process to complete . Suppose , just for experimenting , instead of wait() ing , if we make the parent process sleep() , then why does not it work ? #include <stdio.h> #include <unistd.h> #include <sys/wait.h> int main() { pid_t child_id ; child_id = fork() ; if (child_id == 0) { printf("\nChild process"); printf("\nChild process exiting"); } else { printf("\nParent process"); sleep(10); printf("\nParent

Don't want to remove terminated child process immediately, need to become zombie

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问题 I got below information from SE QUE Explicitly setting the disposition of SIGCHLD to SIG_IGN causes any child process that subsequently terminates to be immediately removed from the system instead of being converted into a zombie. As far I know, to read the child status it is required to have child pid in process table. So it is necessary to have zombie child process in process table to read the child status. So I want to write signal handler which will remove "setting the disposition of

Is there a way to prevent only a specific child from triggering a SIGCHLD?

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问题 I'm writing a debugging utility, and I want to fork a child while preventing that child's termination from triggering a SIGCHLD to its parent. I still want other children to normally cause a SIGCHLD upon termination. I want to do this because I don't want the fork to trigger an existing $SIG{CHLD} handler, but I still want other children to trigger it. That is, I want to isolate my new child and I don't want it to interfere with management of existing children. I'm wary of locally installing

Trapping CHLD signal - ZSH works but ksh/bash/sh don't?

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问题 Here's a sample code where a shell script launches a few jobs in the background and upon receiving the CHLD signal (i.e. the child process termination) it will take some actions... The problem is that if the parent shell script is a ZSH one, it works just fine and traps the CHLD signals, but other shells do not ! why is that? #! /bin/zsh - function foo() { echo "Trapped CHLD signal!" } trap 'foo' CHLD ./child-work1.sh & ./child-work2.sh & ./child-work3.sh & echo 'waiting for the children'

bash restart sub-process using trap SIGCHLD?

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问题 I've seen monitoring programs either in scripts that check process status using 'ps' or 'service status(on Linux)' periodically, or in C/C++ that forks and wait on the process... I wonder if it is possible to use bash with trap and restart the sub-process when SIGCLD received? I have tested a basic suite on RedHat Linux with following idea (and certainly it didn't work...) #!/bin/bash set -o monitor # can someone explain this? discussion on Internet say this is needed trap startProcess

What's the difference between various $SIG{CHLD} values?

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问题 What is the difference between these settings? $SIG{CHLD} = 'IGNORE' $SIG{CHLD} = 'DEFAULT' $SIG{CHLD} = '' $SIG{CHLD} = undef According to "Advanced Programming in the UNIX Environment, 2nd edition", figure 10.1 the default value of SIGCHLD is "ignore." If "ignore" meant "SIG_IGN", then no child would ever be a zombie, and that's not the case. It doesn't get much more clear from there: If the process specifically sets its disposition to SIG_IGN, children of the calling process will not

How can I handle SIGCHLD?

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I need to handle SIGCHLD properly. How can I use it with my existing code. at the moment I cant wait for the child process unless I use 0 instead of WNOHANG|WUNTRACED . status = 0; pid_t child, endID; if(amp == 1) signal( SIGCHLD, SIG_IGN ); child = fork(); if (child < 0) { perror("fork() error\n"); exit(EXIT_FAILURE); } else if (child == 0) { // do sth here perror("error\n"); } else { //sleep(1) If I remove sleep then parent is executed 1st.. why? cnicutar Here is a start (but read below): static void child_handler(int sig) { pid_t pid; int status; /* EEEEXTEERMINAAATE! */ while((pid =

How can I handle SIGCHLD?

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问题 I need to handle SIGCHLD properly. How can I use it with my existing code? at the moment I cant wait for the child process unless I use 0 instead of WNOHANG|WUNTRACED . status = 0; pid_t child, endID; if(amp == 1) signal( SIGCHLD, SIG_IGN ); child = fork(); if (child < 0) { perror(\"fork() error\\n\"); exit(EXIT_FAILURE); } else if (child == 0) { // do sth here perror(\"error\\n\"); } else { //sleep(1) If I remove sleep then parent is executed 1st.. why? 回答1: Here is a start (but read below):