waitpid

Why is Perl's $? returning the wrong value for the exit code of a forked process?

由 [亡魂溺海] 提交于 2019-12-19 03:13:08
问题 Consider this trivial example of fork()ing then waiting for a child to die in Perl: #!/usr/bin/perl use strict; use warnings; if (fork() == 0) { exit(1); } waitpid(-1,0); print $?; Running the script on Solaris 10 I get this result: $ perl test.pl 256 I suspect the values of are being shifted upwards because when I do exit(2) in the child, the output becomes 512 . I can't seem to find this documented in perl's waitpid. Is this a bug on my system or am I doing something wrong? 回答1: It's

Determine pid of terminated process

由 萝らか妹 提交于 2019-12-18 13:25:50
问题 I'm trying to figure out what the pid is of a process that sent the SIGCHLD signal, and I want to do this in a signal handler I created for SIGCHLD. How would I do this? I'm trying: int pid = waitpid(-1, NULL, WNOHANG); because I want to wait for any child process that is spawned. 回答1: If you use waitpid() more or less as shown, you will be told the PID of one of the child processes that has died — usually that will be the only process that has died, but if you get a flurry of them, you might

Test cases in C for WIFSIGNALED, WIFSTOPPED, WIFCONTINUED

由 旧城冷巷雨未停 提交于 2019-12-13 15:09:59
问题 I'm playing with waitpid() and signal() and I'm looking for reliable test cases for returning WIFSIGNALED(status) = WIFSTOPPED(status) = WIFCONTINUED (status) = true but can't find any... Care to tell me how can I make sure those return true so I can debug my code? Also, a few hints about what signals should I catch with signal() to test those macros would be helpful... 回答1: #include <errno.h> #include <signal.h> #include <stdio.h> #include <stdlib.h> #include <sys/wait.h> #include <unistd.h>

How to get the return value of child process to its parent which was created using exec?

由 拥有回忆 提交于 2019-12-11 15:45:21
问题 I have seen similar questions here and here. The answers suggest to use WEXITSTATUS. But according to man page of WAIT(2), it has a limitation. It says: WEXITSTATUS(wstatus) returns the exit status of the child. This consists of the least significant 8 bits of the status argument that the child specified in a call to exit(3) or _exit(2) or as the argument for a return statement in main(). This macro should be employed only if WIFEXITED returned true. So, if the child returns a value larger

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

由 无人久伴 提交于 2019-12-11 10:04:18
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

What does signal(SIGCHLD, SIG_DFL); mean?

由 走远了吗. 提交于 2019-12-10 11:28:17
问题 I am not handling SIGCHLD in my code. Still my process is removed immediately after termination. I want it to become zombie process. If I set SIGCHLD to SIGDFT then, will it work? How do I set SIGCHLD to SIGDFT? I want process to become zombie, so I can read the child status in parent after waitpid. 回答1: From your question history you seem to be tying yourself in knots over this. Here is the outline on how this works: The default disposition of SIGCHLD is ignore. In other words, if you do

Why does Linux program that derefrences (char*)0 not always segfault?

由 蹲街弑〆低调 提交于 2019-12-09 13:01:43
问题 I'm testing code that is designed to detect when a child process has segfaulted. Imagine my surprised when this code does not always segfault: #include <stdio.h> int main() { char *p = (char *)(unsigned long)0; putchar(*p); return 0; } I'm running under a Debian Linux 2.6.26 kernel; my shell is the AT&T ksh93 from the Debian ksh package, Version M 93s+ 2008-01-31. Sometimes this program segfault but otherwise it simply terminates silently with a nonzero exit status but no message. My signal

Which one to choose waitpid/wait/waitid?

由 假如想象 提交于 2019-12-08 07:32:56
问题 I want to use execl in child process after doing fork. execl will execute the script which will take around 120 seconds of time. I tried almost all the combination with waitpid, wait and waitid with different argument (0, WNOHANG, etc.,) but in all case I am getting -1 return value. So I want to know in which wait function I need to use when? So I can concentrate in one wait function to make it work. One more interesting thing which I observed from my logs is that when I am doing nothing in

Monitoring and restarting child process when fails/exits

由 做~自己de王妃 提交于 2019-12-07 18:11:15
问题 I've created a rudimentary example of monitoring a child process and restarting it when it fails or exits. What is the preferred/more robust method of doing this? Is it good practice to continuously poll for a change in status? My understanding is that I should utilize something like SIGCHLD but have been unable to find any good examples. I'm an embedded C coder mainly and this is my first attempt at trying to understand fork() .The purpose of this code will eventually be to monitor a call to

What does signal(SIGCHLD, SIG_DFL); mean?

由 邮差的信 提交于 2019-12-06 13:28:20
I am not handling SIGCHLD in my code. Still my process is removed immediately after termination. I want it to become zombie process. If I set SIGCHLD to SIGDFT then, will it work? How do I set SIGCHLD to SIGDFT? I want process to become zombie, so I can read the child status in parent after waitpid. From your question history you seem to be tying yourself in knots over this. Here is the outline on how this works: The default disposition of SIGCHLD is ignore. In other words, if you do nothing, the signal is ignored but the zombie exists in the process table. This why you can wait on it at any
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