NAME
clone, __clone
— spawn new process with
options
LIBRARY
library “libc”
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
Theclone 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 direction 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_SIGHANDis 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: