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@(#)vfork.2 6.2 (Berkeley) 06/30/85
int pid;
Vfork returns 0 in the child's context and (later) the pid of the child in the parent's context.
Vfork can normally be used just like fork. It does not work, however, to return while running in the childs context from the procedure that called vfork since the eventual return from vfork would then return to a no longer existent stack frame. Be careful, also, to call _exit rather than exit if you can't execve , since exit will flush and close standard I/O channels, and thereby mess up the parent processes standard I/O data structures. (Even with fork it is wrong to call exit since buffered data would then be flushed twice.)
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 s are allowed and input attempts result in an end-of-file indication.