clone(2) [netbsd man page]

CLONE(2)						      BSD System Calls Manual							  CLONE(2)

NAME

     clone, __clone -- spawn new process with options

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sched.h>

     pid_t
     clone(int (*func)(void *arg), void *stack, int flags, void *arg);

     pid_t
     __clone(int (*func)(void *arg), void *stack, int flags, void *arg);

DESCRIPTION

     The clone system call (and associated library support code) creates a new process in a way that allows the caller to specify several options
     for the new process creation.

     Unlike fork(2) or vfork(2), in which the child process returns to the call site, clone causes the child process to begin execution at the
     function specified by func.  The argument arg is passed to the entry point, as a means for the parent to provide context to the child.  The
     stack pointer for the child process will be set to stack.	Note that the clone interface requires that the application know the stack direc-
     tion for the architecture, and that the caller initialize the stack argument as appropriate for the stack direction.

     The flags argument specifies several options that control how the child process is created.  The lower 8 bits of flags specify the signal
     that is to be sent to the parent when the child exits.  The following flags may also be specified by bitwise-or'ing them with the signal
     value:

       CLONE_VM       Share the virtual address space with the parent.	The address space is shared in the same way as vfork(2).

       CLONE_FS       Share the ``file system information'' with the parent.  This include the current working directory and file creation mask.

       CLONE_FILES    Share the file descriptor table with the parent.

       CLONE_SIGHAND  Share the signal handler set with the parent.  Note that the signal mask is never shared between the parent and the child,
		      even if CLONE_SIGHAND is set.

       CLONE_VFORK    Preserve the synchronization semantics of vfork(2); the parent blocks until the child exits.

     The clone call returns the pid of the child in the parent's context.  The child is provided no return value, since it begins execution at a
     different address.

     If the child process's entry point returns, the value it returns is passed to _exit(2), and the child process exits.  Note that if the child
     process wants to exit directly, it should use _exit(2), and not exit(3), since exit(3) will flush and close standard I/O channels, and
     thereby corrupt the parent process's standard I/O data structures (even with fork(2) it is wrong to call exit(3) since buffered data would
     then be flushed twice).

     Note that clone is not intended to be used for new native NetBSD applications.  It is provided as a means to port software originally written
     for the Linux operating system to NetBSD.

RETURN VALUES

     Same as for fork(2).

ERRORS

     Same as for fork(2).

SEE ALSO

     chdir(2), chroot(2), fork(2), sigaction(2), sigprocmask(2), umask(2), vfork(2), wait(2)

HISTORY

     The clone() function call appeared in NetBSD 1.6.	It is compatible with the Linux function call of the same name with respect to the
     described options.

BUGS

     The NetBSD implementation of clone() does not implement the following flags that are present in the Linux implementation:

	   o   CLONE_CHILD_CLEARTID
	   o   CLONE_CHILD_SETTID
	   o   CLONE_IO
	   o   CLONE_NEWIPC
	   o   CLONE_NEWNET
	   o   CLONE_NEWNS
	   o   CLONE_NEWPID
	   o   CLONE_NEWUTS
	   o   CLONE_PARENT
	   o   CLONE_PARENT_SETTID
	   o   CLONE_PID
	   o   CLONE_PTRACE
	   o   CLONE_SETTLS
	   o   CLONE_STOPPED
	   o   CLONE_SYSVSEM
	   o   CLONE_THREAD
	   o   CLONE_UNTRACED

BSD
								    May 4, 2010 							       BSD

Check Out this Related Man Page

VFORK(2)						      BSD System Calls Manual							  VFORK(2)

NAME

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

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

     pid_t
     vfork(void);

DESCRIPTION

     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 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(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.)

RETURN VALUES

     Same as for fork(2).

ERRORS

     Same as for fork(2).

SEE ALSO

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

HISTORY

     The vfork() function call appeared in 3.0BSD.  In 4.4BSD, the semantics were changed to only suspend the parent.  The original semantics were
     reintroduced in NetBSD 1.4.

BUGS

     Users should not depend on the memory sharing semantics of vfork() as other ways of speeding up the fork process may be developed in the
     future.

     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.

BSD
								  January 3, 1998							       BSD

Linux and UNIX Man Pages

clone(2) [netbsd man page]

Check Out this Related Man Page