vfork —
spawn new process and block parent
#include
<unistd.h>
pid_t
vfork(
void);
vfork() was originally used to create new
processes without fully copying the address space of the old process, which is
horrendously inefficient in a paged environment. It was useful when the
purpose of
fork(2) would have been
to create a new system context for an
execve(2). Since
fork(2) is now efficient, even in
the above case, the need for
vfork() has
diminished.
vfork() differs from
fork(2) in that the parent is
suspended until the child makes a call to
execve(2) or an exit (either by
a call to
_exit(2) or
abnormally). In addition, fork handlers established using
pthread_atfork(3) are
not called when a multithreaded program calls
vfork().
vfork() returns 0 in the child's context and
(later) the PID of the child in the parent's context.
Same as for
fork(2).
execve(2),
fork(2),
sigaction(2),
wait(2)
The
vfork() function call appeared in
3.0BSD with the additional semantics that the child
process ran in the memory of the parent until it called
execve(2) or exited. That
sharing of memory was removed in
4.4BSD, leaving just
the semantics of blocking the parent until the child calls
execve(2) or exits. On many
other systems the original behavior has been restored, making this interface
particularly unportable.
To avoid a possible deadlock situation, processes that are children in the
middle of a
vfork() are never sent
SIGTTOU or
SIGTTIN signals; rather, output or
ioctl(2) calls are allowed and
input attempts result in an end-of-file indication.
![[OpenBSD]](/openbsd.gif){kind=small}