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vfork(2)                         System Calls                         vfork(2)



NAME
       vfork - spawn new process in a virtual memory efficient way

SYNOPSIS
       #include <unistd.h>

       pid_t vfork(void);

DESCRIPTION
       The  vfork()  function  creates a new process without fully copying the
       address space of the old process. This function is useful in  instances
       where the purpose of a fork(2) operation is to create a new system con-
       text for an execve() operation (see exec(2)).

       Unlike with the fork() function, the child process borrows the parent's
       memory  and  thread  of  control  until  a  call to execve() or an exit
       (either abnormally or by a call to _exit() (see exit(2)). Any modifica-
       tion  made  during this time to any part of memory in the child process
       is reflected in the parent process on return from vfork().  The  parent
       process is suspended while the child is using its resources.

       In  a  multithreaded  application,   vfork() borrows only the thread of
       control that called vfork() in the parent; that is, the child  contains
       only one thread. The use of vfork() in multithreaded applications, how-
       ever, is unsafe due to race conditons that can cause the child  process
       to  become  deadlocked and consequently block both the child and parent
       process from execution indefinitely.

       The vfork() function can normally be used the same way as  fork().  The
       procedure that called vfork(), however, should not return while running
       in the child's context, since the eventual return from vfork()  in  the
       parent  would  be  to  a stack frame that no longer exists. The _exit()
       function should be used in favor of exit(3C) if unable  to  perform  an
       execve()  operation,  since exit() will invoke all functions registered
       by atexit(3C) and will flush and close standard I/O  channels,  thereby
       corrupting the parent process's standard I/O data structures. Care must
       be taken in the child process not to modify any global  or  local  data
       that affects the behavior of the parent process on return from vfork(),
       unless such an effect is intentional.

       The vfork() function is deprecated. Its sole legitimate use as  a  pre-
       lude  to  an  immediate  call to a function from the exec family can be
       achieved safely by posix_spawn(3C) or posix_spawnp(3C).

RETURN VALUES
       Upon successful completion, vfork() returns  0 to the child process and
       returns the process ID of the child process to the parent process. Oth-
       erwise, -1 is returned to the parent process, no child process is  cre-
       ated, and errno is set to indicate the error.

ERRORS
       The vfork() function will fail if:

       EAGAIN          The  system-imposed  limit  on the total number of pro-
                       cesses under execution (either system-quality or  by  a
                       single  user)  would  be exceeded. This limit is deter-
                       mined when the system is generated.



       ENOMEM          There is insufficient swap space for the new process.



ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:


       tab()    allbox;    cw(2.750000i)|     cw(2.750000i)     lw(2.750000i)|
       lw(2.750000i).   ATTRIBUTE TYPEATTRIBUTE VALUE Interface StabilityObso-
       lete MT-LevelUnsafe


SEE ALSO
       exec(2),   exit(2),   fork(2),    ioctl(2),    atexit(3C),    exit(3C),
       posix_spawn(3C),     posix_spawnp(3C),    signal.h(3HEAD),    wait(3C),
       attributes(5), standards(5)

NOTES
       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 ioctls are allowed and input attempts  result  in  an
       EOF indication.

       To forstall parent memory corruption due to race conditions with signal
       handling, vfork() treats signal handlers in the child  process  in  the
       same  manner  as the exec(2) functions: signals set to be caught by the
       parent process are set to the default action  (SIG_DFL)  in  the  child
       process  (see signal.h(3HEAD)).  Any attempt to set a signal handler in
       the child before execve() to anything other than SIG_DFL or SIG_IGN  is
       disallowed and results in setting the handler to SIG_DFL.

       On  some  systems,  the  implementation of vfork() causes the parent to
       inherit register values from the child. This can  create  problems  for
       certain  optimizing  compilers  if  <&lt;unistd.h>&gt;  is  not included in the
       source calling vfork().



SunOS 5.10                        8 Nov 2004                          vfork(2)