|VFORK(2)||System Calls Manual||VFORK(2)|
LIBRARY¶Standard C Library (libc, -lc)
vfork() system call can be used to
create new processes without fully copying the address space of the old
process, which is inefficient in a paged environment. It is useful when the
purpose of fork(2) would have been to create a new system
context for an execve(2). The
vfork() system call differs from
fork(2) in that the child borrows the parent process's
address space and the calling thread's stack until a call to
execve(2) or an exit (either by a call to
_exit(2) or abnormally). The calling thread is suspended
while the child is using its resources. Other threads continue to run.
vfork() system call returns 0 in the
child's context and (later) the pid of the child in the parent's
Many problems can occur when replacing fork(2)
vfork(). For example, it does not work to
return while running in the child's context from the procedure that called
vfork() since the eventual return from
vfork() would then return to a no longer existent
stack frame. Also, changing process state which is partially implemented in
user space such as signal handlers with libthr(3) will
corrupt the parent's state.
Be careful, also, to call _exit(2) rather than exit(3) if you cannot execve(2), since exit(3) will flush and close standard I/O channels, and thereby mess up the parent processes standard I/O data structures. (Even with fork(2) it is wrong to call exit(3) since buffered data would then be flushed twice.)
RETURN VALUES¶Same as for fork(2).
SEE ALSO¶_exit(2), execve(2), fork(2), rfork(2), sigaction(2), wait(2), exit(3), posix_spawn(3)
vfork() system call appeared in 3BSD.
BUGS¶To avoid a possible deadlock situation, processes that are children in the middle of a
vfork() are never sent
SIGTTINsignals; rather, output or ioctl(2) calls are allowed and input attempts result in an end-of-file indication.
|May 22, 2016||Linux 4.9.0-9-amd64|