NAME
vfork —
spawn new process and block
parent
SYNOPSIS
#include
<unistd.h>
pid_t
vfork(void);
DESCRIPTION
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.
RETURN VALUES
Same as for fork(2).
SEE ALSO
HISTORY
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.
BUGS
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.