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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) opera-
tion is to create a new system context 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 modification 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, however, 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 stan-
dard 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 prelude 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
SunOS 5.10 Last change: 8 Nov 2004 1
System Calls vfork(2)
Upon successful completion, vfork() returns 0 to the child
process and returns the process ID of the child process to
the parent process. Otherwise, -1 is returned to the parent
process, no child process is created, 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 processes under execution (either
system-quality or by a single user) would be
exceeded. This limit is determined when the
system is generated.
ENOMEM There is insufficient swap space for the new
process.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Obsolete |
|_____________________________|_____________________________|
| MT-Level | Unsafe |
|_____________________________|_____________________________|
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
SunOS 5.10 Last change: 8 Nov 2004 2
System Calls vfork(2)
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
<unistd.h> is not included in the source calling vfork().
SunOS 5.10 Last change: 8 Nov 2004 3
Man(1) output converted with
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This page was generated on Wed Sep 12 11:27:13 GMT 2007
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