__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

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

NAME

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

SYNOPSIS

     #include <unistd.h>

     pid_t
     vfork(void);

DESCRIPTION

     Vfork() can be used to create new processes without fully copying the address space of the old process, which is horrendously 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.  Vfork() differs
     from fork 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.

     Vfork() returns 0 in the child's context and (later) the pid of the child in the parent's context.

     Vfork() can normally be used just like fork.  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 rather than exit if you can't execve, since exit will flush and close standard I/O channels, and thereby mess up the parent processes
     standard I/O data structures.  (Even with fork it is wrong to call exit since buffered data would then be flushed twice.)

SEE ALSO

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

ERRORS

     The vfork() system call will fail for any of the reasons described in the fork man page.  In addition, it will fail if:

     [EINVAL]		A system call other than _exit() or execve() (or libc functions that make no system calls other than those) is called fol-
			lowing calling a vfork() call.

BUGS

     This system call will be eliminated when proper system sharing mechanisms are implemented.  Users should not depend on the memory sharing
     semantics of vfork as it will, in that case, be made synonymous to fork.

     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.

HISTORY

     The vfork() function call appeared in 3.0BSD.

4th Berkeley Distribution					   June 4, 1993 					 4th Berkeley Distribution

Linux and UNIX Man Pages

__clone(2) [netbsd man page]

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