Updated: 2022/Sep/29

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CLONE(2)                      System Calls Manual                     CLONE(2)

NAME
     clone, __clone - spawn new process with options

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #define _GNU_SOURCE

     #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 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_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:

           ⊕   CLONE_CHILD_CLEARTID
           ⊕   CLONE_CHILD_SETTID
           ⊕   CLONE_IO
           ⊕   CLONE_NEWIPC
           ⊕   CLONE_NEWNET
           ⊕   CLONE_NEWNS
           ⊕   CLONE_NEWPID
           ⊕   CLONE_NEWUTS
           ⊕   CLONE_PARENT
           ⊕   CLONE_PARENT_SETTID
           ⊕   CLONE_PTRACE
           ⊕   CLONE_SETTLS
           ⊕   CLONE_SYSVSEM
           ⊕   CLONE_THREAD
           ⊕   CLONE_UNTRACED

NetBSD 10.99                    August 1, 2022                    NetBSD 10.99