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fork(2) [opendarwin man page]

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

Check Out this Related Man Page

vfork(2)							System Calls Manual							  vfork(2)

NAME
vfork - spawn new process; share virtual memory SYNOPSIS
REMARKS
is a higher performance version of that is provided on some systems where a performance advantage can be attained. If the calling process is multi-threaded, the newly created child process will only contain one thread. This one thread will be a copy of the thread calling differs from only in that the child process can share code and data with the calling process (parent process). This speeds cloning activ- ity significantly at a risk to the integrity of the parent process if is misused. The use of for any purpose except as a prelude to an immediate or is not supported. Any program that relies upon the differences between and is not portable across HP-UX systems. All HP-UX implementations must provide the entry but it is permissible for them to treat it identically to On some implementations the two are not distinguished because the implementation is as efficient as possible. Other versions may do the same to avoid the overhead of sup- porting two similar calls. DESCRIPTION
can be used to create new processes without fully copying the address space of the old process. If a forked process is simply going to do an (see exec(2)), the data space copied from the parent to the child by is not used. This is particularly inefficient in a paged environ- ment, making particularly useful. Depending upon the size of the parent's data space, can give a significant performance improvement over differs from in that the child borrows the parent's memory and thread of control until a call to or an exit (either by a call to or abnor- mally (see exec(2) and exit(2)). The parent process is suspended while the child is using its resources. returns 0 in the child's context and (later) the pid of the child in the parent's context. can normally be used just like It does not work, however, to return while running in the child's context from the procedure which called since the eventual return from would then return to a no longer existent stack frame. The window begins at the call and ends when the child completes its call. RETURN VALUE
Upon successful completion, 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, no child process is created, and is set to indicate the error. ERRORS
fails and no child process is created if any of the following conditions are encountered: The system-wide limit on the total number of processes under execution would be exceeded. The system-imposed limit on the total number of processes under execution by a single user would be exceeded. DEPENDENCIES
Servers Process times for the parent and child processes within the window may be inaccurate. Parent and child processes share the same stack space within the window. If the size of the stack has been changed within this win- dow by the child process (return from or call to a function, for example), it is likely that the parent and child processes will be killed with signal or In the window, a call to (see signal(2) that installs a catching function can affect handling of the signal by the parent. The par- ent is not affected if the handling is being set to or or if is used (see sigaction(2)). AUTHOR
was developed by the University of California, Berkeley. SEE ALSO
exec(2), exit(2), fork(2), sigaction(2), wait(2). vfork(2)

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