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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FORK(2) System Calls Manual FORK(2)
NAME
fork - spawn new process
SYNOPSIS
fork( )
DESCRIPTION
Fork is the only way new processes are created. The new process's core image is a copy of that of the caller of fork. The only distinc-
tion is the fact that the value returned in the old (parent) process contains the process ID of the new (child) process, while the value
returned in the child is 0. Process ID's range from 1 to 30,000. This process ID is used by wait(2).
Files open before the fork are shared, and have a common read-write pointer. In particular, this is the way that standard input and output
files are passed and also how pipes are set up.
SEE ALSO
wait(2), exec(2)
DIAGNOSTICS
Returns -1 and fails to create a process if: there is inadequate swap space, the user is not super-user and has too many processes, or the
system's process table is full. Only the super-user can take the last process-table slot.
ASSEMBLER
(fork = 2.)
sys fork
(new process return)
(old process return, new process ID in r0)
The return locations in the old and new process differ by one word. The C-bit is set in the old process if a new process could not be cre-
ated.
FORK(2)