fork(2) [plan9 man page]

FORK(2) 							System Calls Manual							   FORK(2)

NAME

       fork, rfork - manipulate process resources

SYNOPSIS

       #include <u.h>
       #include <libc.h>

       int fork(void)

       int rfork(int flags)

DESCRIPTION

       Forking	is  the  only way new processes are created.  The flags argument to rfork selects which resources of the invoking process (parent)
       are shared by the new process (child) or initialized to their default values.  The resources include the file name  space,  the	open  file
       descriptor table (which, when shared, permits processes to open and close files for other processes), the set of environment variables (see
       env(3)), the note group (the set of processes that receive notes written to a member's notepg file; see proc(3)), and open files.  Flags is
       the logical OR of some subset of

       RFPROC If set a new process is created; otherwise changes affect the current process.

       RFNOWAIT
	      If  set, the child process will be dissociated from the parent. Upon exit the child will leave no Waitmsg (see wait(2)) for the par-
	      ent to collect.

       RFNAMEG
	      If set, the new process inherits a copy of the parent's name space; otherwise the new process shares the parent's name  space.   The
	      tag space for rendezvous(2) is considered part of the name space.  Is mutually exclusive with RFCNAMEG.

       RFCNAMEG
	      If  set, the new process starts with a clean name space. A new name space must be built from a mount of an open file descriptor.	Is
	      mutually exclusive with RFNAMEG.

       RFENVG If set, the environment variables are copied; otherwise the two processes share environment variables.  Is mutually  exclusive  with
	      RFCENVG.

       RFCENVG
	      If set, the new process starts with an empty environment.  Is mutually exclusive with RFENVG.

       RFNOTEG
	      Each  process  is  a  member of a group of processes that all receive notes when a note is written to any of their notepg files (see
	      proc(3)).  The group of a new process is by default the same as its parent, but if  RFNOTEG  is  set  (regardless  of  RFPROC),  the
	      process becomes the first in a new group, isolated from previous processes.

       RFFDG  If set, the invoker's file descriptor table (see intro(2)) is copied; otherwise the two processes share a single table.

       RFCFDG If set, the new process starts with a clean file descriptor table.  Is mutually exclusive with RFFDG.

       RFMEM  If set, the kernel will mark segments of type data and bss as shared. The child will then inherit all the shared segments the parent
	      process owns. Other segment types will be unaffected.  Subsequent forks by the parent will then propagate the shared  data  and  bss
	      between children.  The stack segment is always split.  May be set only with RFPROC.

       File descriptors in a shared file descriptor table are kept open until either they are explicitly closed or all processes sharing the table
       exit.

       If RFPROC is set, the value returned in the parent process is the process id of the child process; the value returned in the child is zero.
       Without	RFPROC,  the  return value is zero.  Process ids range from 1 to the maximum integer (int) value.  Rfork will sleep, if necessary,
       until required process resources are available.

       Fork is just a call of rfork(RFFDG|RFPROC).

SOURCE

       /sys/src/libc/9syscall
       /sys/src/libc/9sys/fork.c

SEE ALSO

       intro(2), proc(3),

DIAGNOSTICS

       These functions set errstr.

																	   FORK(2)

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FORK(2) 						      BSD System Calls Manual							   FORK(2)

NAME

     fork -- create a new process

SYNOPSIS

     #include <sys/types.h>
     #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 or write 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 processes resource utilizations are set to 0; see setrlimit(2).

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-
			dependent.

     [EAGAIN]		The system-imposed limit MAXUPRC (<sys/param.h>) on the total number of processes under execution by a single user would
			be exceeded.

     [ENOMEM]		There is insufficient swap space for the new process.

SEE ALSO

     execve(2), wait(2)

HISTORY

     A fork() function call appeared in Version 6 AT&T UNIX.

4th Berkeley Distribution					   June 4, 1993 					 4th Berkeley Distribution

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fork(2) [plan9 man page]

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