NAME

       vfork — create a new process without copying the address space

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

       #include <unistd.h>

       pid_t
       vfork(void);

DESCRIPTION

       Since  this  function  is  hard  to  use  correctly  from  application software, it is recommended to use
       posix_spawn(3) or fork(2) instead.

       The vfork() system call can be used to create new processes without fully copying the  address  space  of
       the  old  process, which is inefficient in a paged environment.  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 process's address space and the calling thread's stack until
       a  call  to  execve(2)  or  an  exit (either by a call to _exit(2) or abnormally).  The calling thread is
       suspended while the child is using its resources.  Other threads continue to run.

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

       Many problems can occur when replacing fork(2) with vfork().  For example, it does  not  work  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 existent stack frame.  Also, changing process  state  which
       is  partially  implemented in user space such as signal handlers with libthr(3) will corrupt the parent's
       state.

       Be careful, also, to call _exit(2) rather than exit(3) if you cannot execve(2), since exit(3) will  flush
       and  close  standard I/O channels, and thereby mess up the parent processes standard I/O data structures.
       (Even with fork(2) it is wrong to call exit(3) since buffered data would then be flushed twice.)

RETURN VALUES

       Same as for fork(2).

SEE ALSO

       _exit(2), execve(2), fork(2), rfork(2), sigaction(2), wait(2), exit(3), posix_spawn(3)

HISTORY

       The vfork() system call appeared in 3BSD.

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.

Debian                                            May 22, 2016                                          VFORK(2)