fork - create a new process
fork() causes creation of a new process. The new process
is an exact copy of the calling process (parent process) except for the
+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
These descriptors reference the same underlying
that, for instance, file pointers in file objects
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
newly created processes as well as to set up
+o The child process' resource utilizations are set
to 0; see
+o All interval timers are cleared; see setitimer(2).
In general, the child process should call _exit(2) rather
Otherwise, any stdio buffers that exist both in the parent
and child will
be flushed twice. Similarly, _exit(2) should be used to
atexit(3) routines from being called twice (once in the parent and once
in the child).
Upon successful completion, fork() returns a value of 0 to
the child process
and returns the process ID of the child process to the
Otherwise, a value of -1 is returned to the parent
child process is created, and the global variable errno is
set to indicate
fork() will fail and no child process will be created if:
[EAGAIN] The system-imposed limit on the total number of
execution would be exceeded. This limit is configuration-dependent.
[EAGAIN] The limit RLIMIT_NPROC on the total number of processes under
execution by the user ID would be exceeded.
[ENOMEM] There is insufficient swap space for the new process.
execve(2), setrlimit(2), wait(2)
The fork() function conforms to IEEE Std 1003.1-1990
A fork() function call appeared in Version 2 AT&T UNIX.
OpenBSD 3.6 June 4, 1993
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