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Top Forums UNIX for Beginners Questions & Answers Question about global environment variables & fork() exec() Post 303027558 by bodisha on Tuesday 18th of December 2018 02:06:02 PM
Old 12-18-2018
Question about global environment variables & fork() exec()

Hello... And thanks in advance for any help anyone can offer me on my question! I've been doing a lot of reading to try and find my answer... But I haven't had any luck


What I'm trying to understand is where a child process inherits global environment variables from? I understand the exec() system call overwrites environment variable created by the fork()... But how does exec() cause global environment variables to be included with a newly created child process if all the environment variables are overwritten? My best guess is that global environment variables are somehow excluded from being overwritten... But I can't confirm this

Also... when does the fork() assign a PID to a child process? Before or after it copies itself into a new region of memory?

Thanks to everyone for any assistance!

Last edited by bodisha; 12-18-2018 at 04:21 PM..
 

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ENV(3)							     Library Functions Manual							    ENV(3)

NAME
env - environment variables SYNOPSIS
bind #e /env /env/var1 /env/var2 ... DESCRIPTION
The env device serves a one-level directory containing files with arbitrary names and contents. The intention is that the file name is the name of an environment variable (see rc(1)), and the content is the variable's current value. When a fork(2) system call creates a new process, both the parent and the child continue to see exactly the same files in the env device: changes made in either process can be noticed by the other. In contrast, an rfork system call with the RFENVG bit set (see fork(2)) causes a split: initially both process groups see the same environment files, but any changes made in one process group cannot be noticed by the other. An rfork with RFCENVG splits and then clears the environment. SEE ALSO
rc(1), fork(2) SOURCE
/sys/src/9/port/devenv.c BUGS
A write starting at an offset after the current extent of a file yields an error instead of zero filling. ENV(3)
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