FORK(2)FORK(2)NAME
fork, vfork - create a new process
SYNOPSIS
#include <sys/types.h>
pid_t fork(void);
DESCRIPTION
The fork function causes creation of a new process (vfork is another
name for fork). The new process (child process) is an exact copy of
the calling process except for the following:
The child process has a unique process ID.
The child process has a different parent process ID (i.e., the
process ID of the parent process).
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.
The child processes resource utilizations are set to 0; see
setrlimit(2).
For POSIX applications the following differences between the child and
parent process also apply:
File locks previously set by the parent are not inherited by the child.
Pending alarms are cleared for the child process.
The set of pending signals for the child process is initialized to the
empty set.
RETURN VALUE
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
The fork function will fail and no child process will be created if one
or more of the following are true:
[EAGAIN] The system-imposed limit on the total number of
processes under execution would be exceeded.
[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 ALSOexecve(2), wait(2)
August 1, 1992 FORK(2)
