03-21-2006
here's
You welcome, and there're no stupid questions, we learn sofisticated system with some 30+ years of development...
Generally as far as I learned there are only two ways for making unix process and here they are:
1. The special processes: these are processes that are created under system boot time and they are created by some programing tricks and special methods, it is not UNIX yet, it is a midway. Depending of version of unix it is may be just init process or there are may be two-three with some memory-disk swapping "abnormal" deamon that system will not let you kill.
2. The normal processes: as we desribed above, and ALL the processes use the same scheme. It allows in a turn to command processes in a similar way, by sending signals to them (you always can get a list of signals available for your system with "kill -l" command). It also implyes the so called "standard process lifespan".
Generally speaking, yes all processes including init use the same scheme for replicating, by the end of their lifespan, process passes so called "zombi" phase and thankfully to the scheme, init takes care to remove the proceses that had not been removed properly by their own parent processes (in a case when parent process was terminated before child process).
Hope it helps.
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FORK(2) BSD System Calls Manual FORK(2)
NAME
fork -- create a new process
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
pid_t
fork(void);
DESCRIPTION
fork() causes creation of a new process. The new process (child process) is an exact copy of the calling process (parent process) except for
the following:
o The child process has a unique process ID.
o The child process has a different parent process ID (i.e., the process ID of the parent process).
o The child process has its own copy of the parent's descriptors. These descriptors reference the same underlying objects, so that,
for instance, file pointers in file objects are shared between the child and the parent, so that an lseek(2) on a descriptor in the
child process can affect a subsequent read(2) or write(2) by the parent. This descriptor copying is also used by the shell to
establish standard input and output for newly created processes as well as to set up pipes.
o The child process' resource utilizations are set to 0; see setrlimit(2).
In general, the child process should call _exit(2) rather than exit(3). Otherwise, any stdio buffers that exist both in the parent and child
will be flushed twice. Similarly, _exit(2) should be used to prevent atexit(3) routines from being called twice (once in the parent and once
in the child).
In case of a threaded program, only the thread calling fork() is still running in the child processes.
Child processes of a threaded program have additional restrictions, a child must only call functions that are async-signal-safe. Very few
functions are asynchronously safe and applications should make sure they call exec(3) as soon as possible.
RETURN VALUES
Upon successful completion, fork() returns a value of 0 to the child process and returns the process ID of the child process to the parent
process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to
indicate the error.
ERRORS
fork() will fail and no child process will be created if:
[EAGAIN] The system-imposed limit on the total number of processes under execution would be exceeded. This limit is configuration-depen-
dent.
[EAGAIN] The limit RLIMIT_NPROC on the total number of processes under execution by this user id would be exceeded.
[ENOMEM] There is insufficient swap space for the new process.
SEE ALSO
execve(2), setrlimit(2), vfork(2), wait(2), pthread_atfork(3)
STANDARDS
The fork() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').
HISTORY
A fork() system call appeared in Version 6 AT&T UNIX.
BSD
June 10, 2004 BSD