Updated: 2022/Sep/29

Please read Privacy Policy. It's for your privacy.

VFORK(2)                      System Calls Manual                     VFORK(2)

     vfork - spawn new process in a virtual memory efficient way

     Standard C Library (libc, -lc)

     #include <unistd.h>


     The vfork system call creates a new process that does not have a new
     virtual address space, but rather shares address space with the parent,
     thus avoiding potentially expensive copy-on-write operations normally
     associated with creating a new process.  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's memory and thread of control until a call to execve(2) or an
     exit (either by a call to _exit(2) or abnormally).  The parent process is
     suspended while the child is using its resources.

     The vfork system call returns 0 in the child's context and (later) the
     pid of the child in the parent's context.

     The vfork system call can normally be used just like fork(2).  It does
     not work, however, 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 existing stack frame.  Be careful, also,
     to call _exit(2) rather than exit(3) if you can't execve(2), since
     exit(3) will flush and close standard I/O channels, and thereby mess up
     the standard I/O data structures in the parent process.  (Even with
     fork(2) it is wrong to call exit(3) since buffered data would then be
     flushed twice.)

     Same as for fork(2).

     Same as for fork(2).

     execve(2), fork(2), sigaction(2), wait(2), posix_spawn(3)

     The vfork() function call appeared in 3.0BSD.  In 4.4BSD, the semantics
     were changed to only suspend the parent and not share the address space.
     The original semantics were reintroduced in NetBSD 1.4.

     Portable applications should not depend on the memory sharing semantics
     of vfork() as implementations exist that implement vfork() as plain

     To avoid a possible deadlock situation, processes that are children in
     the middle of a vfork() are never sent SIGTSTP, SIGTTOU or SIGTTIN
     signals; rather, output or ioctl(2) calls are allowed and input attempts
     result in an end-of-file indication.

     New applications should prefer posix_spawn(3) over vfork followed by

NetBSD 9.99                      June 9, 2021                      NetBSD 9.99