Question about global environment variables & fork() exec() Post: 303027558

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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

12-18-2018

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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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LEARN ABOUT BSD

fork

FORK(3F)																  FORK(3F)

NAME

       fork - create a copy of this process

SYNOPSIS

       integer function fork()

DESCRIPTION

       Fork  creates  a  copy  of  the	calling  process.   The only distinction between the 2 processes is that the value returned to one of them
       (referred to as the `parent' process) will be the process id of the copy.  The copy is usually referred to as  the  `child'  process.   The
       value returned to the `child' process will be zero.

       All logical units open for writing are flushed before the fork to avoid duplication of the contents of I/O buffers in the external file(s).

       If the returned value is negative, it indicates an error and will be the negation of the system error code.  See perror(3F).

       A corresponding exec routine has not been provided because there is no satisfactory way to retain open logical units across the exec.  How-
       ever, the usual function of fork/exec can be performed using system(3F).

FILES

       /usr/lib/libU77.a

SEE ALSO

       fork(2), wait(3F), kill(3F), system(3F), perror(3F)

4.2 Berkeley Distribution					   May 27, 1986 							  FORK(3F)

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