NAME
fork - create a new process

SYNOPSIS
pid_t fork()

DESCRIPTION
Fork causes creation of a new process. 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 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.

The child processes resource utilizations are set to 0; see
setrlimit(2)*.

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
Fork 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. 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.