VFORK(2) BSD System Calls Manual VFORK(2)
vfork -- spawn new process and block parent
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 dimin-
ished. 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() 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 2.9BSD with the additional seman-
tics 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.
BSD March 28, 2017 BSD