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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (c) 1992 Drew Eckhardt <drew@cs.colorado.edu>, March 28, 1992
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.\" and Copyright (c) Michael Kerrisk, 2001, 2002, 2005
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.\" May be distributed under the GNU General Public License.
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.\" Modified by Michael Haardt <michael@moria.de>
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.\" Modified 24 Jul 1993 by Rik Faith <faith@cs.unc.edu>
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.\" Modified 21 Aug 1994 by Michael Chastain <mec@shell.portal.com>:
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.\" New man page (copied from 'fork.2').
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.\" Modified 10 June 1995 by Andries Brouwer <aeb@cwi.nl>
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.\" Modified 25 April 1998 by Xavier Leroy <Xavier.Leroy@inria.fr>
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.\" Modified 26 Jun 2001 by Michael Kerrisk
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.\" Mostly upgraded to 2.4.x
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.\" Added prototype for sys_clone() plus description
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.\" Added CLONE_THREAD with a brief description of thread groups
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.\" Added CLONE_PARENT and revised entire page remove ambiguity
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.\" between "calling process" and "parent process"
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.\" Added CLONE_PTRACE and CLONE_VFORK
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.\" Added EPERM and EINVAL error codes
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.\" Renamed "__clone" to "clone" (which is the prototype in <sched.h>)
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.\" various other minor tidy ups and clarifications.
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.\" Modified 26 Jun 2001 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Updated notes for 2.4.7+ behavior of CLONE_THREAD
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.\" Modified 15 Oct 2002 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Added description for CLONE_NEWNS, which was added in 2.4.19
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.\" Slightly rephrased, aeb.
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.\" Modified 1 Feb 2003 - added CLONE_SIGHAND restriction, aeb.
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.\" Modified 1 Jan 2004 - various updates, aeb
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.\" Modified 2004-09-10 - added CLONE_PARENT_SETTID etc - aeb.
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.\" 2005-04-12, mtk, noted the PID caching behavior of NPTL's getpid()
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.\" wrapper under BUGS.
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.\" 2005-05-10, mtk, added CLONE_SYSVSEM, CLONE_UNTRACED, CLONE_STOPPED.
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.\" 2005-05-17, mtk, Substantially enhanced discussion of CLONE_THREAD.
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.\"
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.TH CLONE 2 2007-06-01 "Linux" "Linux Programmer's Manual"
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.SH NAME
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clone, __clone2 \- create a child process
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.SH SYNOPSIS
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.nf
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.B #include <sched.h>
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.BI "int clone(int (*" "fn" ")(void *), void *" child_stack ,
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.BI " int " flags ", void *" "arg" ", ... "
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.BI " /* pid_t *" pid ", struct user_desc *" tls \
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", pid_t *" ctid " */ );"
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.fi
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.SH DESCRIPTION
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.BR clone ()
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creates a new process, in a manner similar to
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.BR fork (2).
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It is actually a library function layered on top of the underlying
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.BR clone ()
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system call, hereinafter referred to as
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.BR sys_clone .
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A description of
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.BR sys_clone
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is given towards the end of this page.
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Unlike
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.BR fork (2),
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these calls
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allow the child process to share parts of its execution context with
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the calling process, such as the memory space, the table of file
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descriptors, and the table of signal handlers.
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(Note that on this manual
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page, "calling process" normally corresponds to "parent process".
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But see the description of
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.B CLONE_PARENT
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below.)
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The main use of
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.BR clone ()
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is to implement threads: multiple threads of control in a program that
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run concurrently in a shared memory space.
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When the child process is created with
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.BR clone (),
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it executes the function
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application
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.IR fn ( arg ).
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(This differs from
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.BR fork (2),
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where execution continues in the child from the point
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of the
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.BR fork (2)
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call.)
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The
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.I fn
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argument is a pointer to a function that is called by the child
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process at the beginning of its execution.
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The
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.I arg
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argument is passed to the
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.I fn
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function.
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When the
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.IR fn ( arg )
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function application returns, the child process terminates.
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The integer returned by
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.I fn
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is the exit code for the child process.
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The child process may also terminate explicitly by calling
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.BR exit (2)
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or after receiving a fatal signal.
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The
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.I child_stack
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argument specifies the location of the stack used by the child process.
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Since the child and calling process may share memory,
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it is not possible for the child process to execute in the
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same stack as the calling process.
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The calling process must therefore
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set up memory space for the child stack and pass a pointer to this
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space to
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.BR clone ().
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Stacks grow downwards on all processors that run Linux
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(except the HP PA processors), so
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.I child_stack
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usually points to the topmost address of the memory space set up for
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the child stack.
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The low byte of
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.I flags
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contains the number of the
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.I "termination signal"
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sent to the parent when the child dies.
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If this signal is specified as anything other than
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.BR SIGCHLD ,
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then the parent process must specify the
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.B __WALL
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or
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.B __WCLONE
|
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options when waiting for the child with
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.BR wait (2).
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If no signal is specified, then the parent process is not signaled
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when the child terminates.
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.I flags
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may also be bitwise-or'ed with zero or more of the following constants,
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in order to specify what is shared between the calling process
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and the child process:
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.TP
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.BR CLONE_PARENT " (since Linux 2.3.12)"
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If
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.B CLONE_PARENT
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is set, then the parent of the new child (as returned by
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.BR getppid (2))
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will be the same as that of the calling process.
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If
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.B CLONE_PARENT
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is not set, then (as with
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.BR fork (2))
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the child's parent is the calling process.
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|
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Note that it is the parent process, as returned by
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.BR getppid (2),
|
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which is signaled when the child terminates, so that
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if
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.B CLONE_PARENT
|
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is set, then the parent of the calling process, rather than the
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|
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calling process itself, will be signaled.
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.TP
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.B CLONE_FS
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If
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.B CLONE_FS
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is set, the caller and the child processes share the same file system
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information.
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This includes the root of the file system, the current
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working directory, and the umask.
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Any call to
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.BR chroot (2),
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.BR chdir (2),
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or
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.BR umask (2)
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performed by the calling process or the child process also affects the
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other process.
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If
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.B CLONE_FS
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is not set, the child process works on a copy of the file system
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information of the calling process at the time of the
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.BR clone ()
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call.
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Calls to
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.BR chroot (2),
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.BR chdir (2),
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||||||
.BR umask (2)
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||||||
performed later by one of the processes do not affect the other process.
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.TP
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.B CLONE_FILES
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If
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.B CLONE_FILES
|
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is set, the calling process and the child processes share the same file
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descriptor table.
|
|
||||||
Any file descriptor created by the calling process or by the child
|
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||||||
process is also valid in the other process.
|
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Similarly, if one of the processes closes a file descriptor,
|
|
||||||
or changes its associated flags (using the
|
|
||||||
.BR fcntl (2)
|
|
||||||
.B F_SETFD
|
|
||||||
operation), the other process is also affected.
|
|
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|
|
||||||
If
|
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||||||
.B CLONE_FILES
|
|
||||||
is not set, the child process inherits a copy of all file descriptors
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|
||||||
opened in the calling process at the time of
|
|
||||||
.BR clone ().
|
|
||||||
(The duplicated file descriptors in the child refer to the
|
|
||||||
same open file descriptions (see
|
|
||||||
.BR open (2))
|
|
||||||
as the corresponding file descriptors in the calling process.)
|
|
||||||
Subsequent operations that open or close file descriptors,
|
|
||||||
or change file descriptor flags,
|
|
||||||
performed by either the calling
|
|
||||||
process or the child process do not affect the other process.
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.TP
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.BR CLONE_NEWNS " (since Linux 2.4.19)"
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|
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Start the child in a new namespace.
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|
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Every process lives in a namespace.
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The
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|
||||||
.I namespace
|
|
||||||
of a process is the data (the set of mounts) describing the file hierarchy
|
|
||||||
as seen by that process.
|
|
||||||
After a
|
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.BR fork (2)
|
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or
|
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.BR clone (2)
|
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where the
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|
||||||
.B CLONE_NEWNS
|
|
||||||
flag is not set, the child lives in the same namespace as the parent.
|
|
||||||
The system calls
|
|
||||||
.BR mount (2)
|
|
||||||
and
|
|
||||||
.BR umount (2)
|
|
||||||
change the namespace of the calling process, and hence affect
|
|
||||||
all processes that live in the same namespace, but do not affect
|
|
||||||
processes in a different namespace.
|
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|
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||||||
After a
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|
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.BR clone (2)
|
|
||||||
where the
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.B CLONE_NEWNS
|
|
||||||
flag is set, the cloned child is started in a new namespace,
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initialized with a copy of the namespace of the parent.
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|
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Only a privileged process (one having the \fBCAP_SYS_ADMIN\fP capability)
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|
||||||
may specify the
|
|
||||||
.B CLONE_NEWNS
|
|
||||||
flag.
|
|
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It is not permitted to specify both
|
|
||||||
.B CLONE_NEWNS
|
|
||||||
and
|
|
||||||
.B CLONE_FS
|
|
||||||
in the same
|
|
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.BR clone ()
|
|
||||||
call.
|
|
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.TP
|
|
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.B CLONE_SIGHAND
|
|
||||||
If
|
|
||||||
.B CLONE_SIGHAND
|
|
||||||
is set, the calling process and the child processes share the same table of
|
|
||||||
signal handlers.
|
|
||||||
If the calling process or child process calls
|
|
||||||
.BR sigaction (2)
|
|
||||||
to change the behavior associated with a signal, the behavior is
|
|
||||||
changed in the other process as well.
|
|
||||||
However, the calling process and child
|
|
||||||
processes still have distinct signal masks and sets of pending
|
|
||||||
signals.
|
|
||||||
So, one of them may block or unblock some signals using
|
|
||||||
.BR sigprocmask (2)
|
|
||||||
without affecting the other process.
|
|
||||||
|
|
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If
|
|
||||||
.B CLONE_SIGHAND
|
|
||||||
is not set, the child process inherits a copy of the signal handlers
|
|
||||||
of the calling process at the time
|
|
||||||
.BR clone ()
|
|
||||||
is called.
|
|
||||||
Calls to
|
|
||||||
.BR sigaction (2)
|
|
||||||
performed later by one of the processes have no effect on the other
|
|
||||||
process.
|
|
||||||
|
|
||||||
Since Linux 2.6.0-test6,
|
|
||||||
.I flags
|
|
||||||
must also include
|
|
||||||
.B CLONE_VM
|
|
||||||
if
|
|
||||||
.B CLONE_SIGHAND
|
|
||||||
is specified
|
|
||||||
.TP
|
|
||||||
.B CLONE_PTRACE
|
|
||||||
If
|
|
||||||
.B CLONE_PTRACE
|
|
||||||
is specified, and the calling process is being traced,
|
|
||||||
then trace the child also (see
|
|
||||||
.BR ptrace (2)).
|
|
||||||
.TP
|
|
||||||
.BR CLONE_UNTRACED " (since Linux 2.5.46)"
|
|
||||||
If
|
|
||||||
.B CLONE_UNTRACED
|
|
||||||
is specified, then a tracing process cannot force
|
|
||||||
.B CLONE_PTRACE
|
|
||||||
on this child process.
|
|
||||||
.TP
|
|
||||||
.BR CLONE_STOPPED " (since Linux 2.6.0-test2)"
|
|
||||||
If
|
|
||||||
.B CLONE_STOPPED
|
|
||||||
is set, then the child is initially stopped (as though it was sent a
|
|
||||||
.B SIGSTOP
|
|
||||||
signal), and must be resumed by sending it a
|
|
||||||
.B SIGCONT
|
|
||||||
signal.
|
|
||||||
.TP
|
|
||||||
.B CLONE_VFORK
|
|
||||||
If
|
|
||||||
.B CLONE_VFORK
|
|
||||||
is set, the execution of the calling process is suspended
|
|
||||||
until the child releases its virtual memory
|
|
||||||
resources via a call to
|
|
||||||
.BR execve (2)
|
|
||||||
or
|
|
||||||
.BR _exit (2)
|
|
||||||
(as with
|
|
||||||
.BR vfork (2)).
|
|
||||||
|
|
||||||
If
|
|
||||||
.B CLONE_VFORK
|
|
||||||
is not set then both the calling process and the child are schedulable
|
|
||||||
after the call, and an application should not rely on execution occurring
|
|
||||||
in any particular order.
|
|
||||||
.TP
|
|
||||||
.B CLONE_VM
|
|
||||||
If
|
|
||||||
.B CLONE_VM
|
|
||||||
is set, the calling process and the child processes run in the same memory
|
|
||||||
space.
|
|
||||||
In particular, memory writes performed by the calling process
|
|
||||||
or by the child process are also visible in the other process.
|
|
||||||
Moreover, any memory mapping or unmapping performed with
|
|
||||||
.BR mmap (2)
|
|
||||||
or
|
|
||||||
.BR munmap (2)
|
|
||||||
by the child or calling process also affects the other process.
|
|
||||||
|
|
||||||
If
|
|
||||||
.B CLONE_VM
|
|
||||||
is not set, the child process runs in a separate copy of the memory
|
|
||||||
space of the calling process at the time of
|
|
||||||
.BR clone ().
|
|
||||||
Memory writes or file mappings/unmappings performed by one of the
|
|
||||||
processes do not affect the other, as with
|
|
||||||
.BR fork (2).
|
|
||||||
.TP
|
|
||||||
.BR CLONE_PID " (obsolete)"
|
|
||||||
If
|
|
||||||
.B CLONE_PID
|
|
||||||
is set, the child process is created with the same process ID as
|
|
||||||
the calling process.
|
|
||||||
This is good for hacking the system, but otherwise
|
|
||||||
of not much use.
|
|
||||||
Since 2.3.21 this flag can be
|
|
||||||
specified only by the system boot process (PID 0).
|
|
||||||
It disappeared in Linux 2.5.16.
|
|
||||||
.TP
|
|
||||||
.BR CLONE_THREAD " (since Linux 2.4.0-test8)"
|
|
||||||
If
|
|
||||||
.B CLONE_THREAD
|
|
||||||
is set, the child is placed in the same thread group as the calling process.
|
|
||||||
To make the remainder of the discussion of
|
|
||||||
.B CLONE_THREAD
|
|
||||||
more readable, the term "thread" is used to refer to the
|
|
||||||
processes within a thread group.
|
|
||||||
|
|
||||||
Thread groups were a feature added in Linux 2.4 to support the
|
|
||||||
POSIX threads notion of a set of threads that share a single PID.
|
|
||||||
Internally, this shared PID is the so-called
|
|
||||||
thread group identifier (TGID) for the thread group.
|
|
||||||
Since Linux 2.4, calls to
|
|
||||||
.BR getpid (2)
|
|
||||||
return the TGID of the caller.
|
|
||||||
|
|
||||||
The threads within a group can be distinguished by their (system-wide)
|
|
||||||
unique thread IDs (TID).
|
|
||||||
A new thread's TID is available as the function result
|
|
||||||
returned to the caller of
|
|
||||||
.BR clone (),
|
|
||||||
and a thread can obtain
|
|
||||||
its own TID using
|
|
||||||
.BR gettid (2).
|
|
||||||
|
|
||||||
When a call is made to
|
|
||||||
.BR clone ()
|
|
||||||
without specifying
|
|
||||||
.BR CLONE_THREAD ,
|
|
||||||
then the resulting thread is placed in a new thread group
|
|
||||||
whose TGID is the same as the thread's TID.
|
|
||||||
This thread is the
|
|
||||||
.I leader
|
|
||||||
of the new thread group.
|
|
||||||
|
|
||||||
A new thread created with
|
|
||||||
.B CLONE_THREAD
|
|
||||||
has the same parent process as the caller of
|
|
||||||
.BR clone ()
|
|
||||||
(i.e., like
|
|
||||||
.BR CLONE_PARENT ),
|
|
||||||
so that calls to
|
|
||||||
.BR getppid (2)
|
|
||||||
return the same value for all of the threads in a thread group.
|
|
||||||
When a
|
|
||||||
.B CLONE_THREAD
|
|
||||||
thread terminates, the thread that created it using
|
|
||||||
.BR clone ()
|
|
||||||
is not sent a
|
|
||||||
.B SIGCHLD
|
|
||||||
(or other termination) signal;
|
|
||||||
nor can the status of such a thread be obtained
|
|
||||||
using
|
|
||||||
.BR wait (2).
|
|
||||||
(The thread is said to be
|
|
||||||
.IR detached .)
|
|
||||||
|
|
||||||
After all of the threads in a thread group terminate
|
|
||||||
the parent process of the thread group is sent a
|
|
||||||
.B SIGCHLD
|
|
||||||
(or other termination) signal.
|
|
||||||
|
|
||||||
If any of the threads in a thread group performs an
|
|
||||||
.BR execve (2),
|
|
||||||
then all threads other than the thread group leader are terminated,
|
|
||||||
and the new program is executed in the thread group leader.
|
|
||||||
|
|
||||||
If one of the threads in a thread group creates a child using
|
|
||||||
.BR fork (2),
|
|
||||||
then any thread in the group can
|
|
||||||
.BR wait (2)
|
|
||||||
for that child.
|
|
||||||
|
|
||||||
Since Linux 2.5.35,
|
|
||||||
.I flags
|
|
||||||
must also include
|
|
||||||
.B CLONE_SIGHAND
|
|
||||||
if
|
|
||||||
.B CLONE_THREAD
|
|
||||||
is specified.
|
|
||||||
|
|
||||||
Signals may be sent to a thread group as a whole (i.e., a TGID) using
|
|
||||||
.BR kill (2),
|
|
||||||
or to a specific thread (i.e., TID) using
|
|
||||||
.BR tgkill (2).
|
|
||||||
|
|
||||||
Signal dispositions and actions are process-wide:
|
|
||||||
if an unhandled signal is delivered to a thread, then
|
|
||||||
it will affect (terminate, stop, continue, be ignored in)
|
|
||||||
all members of the thread group.
|
|
||||||
|
|
||||||
Each thread has its own signal mask, as set by
|
|
||||||
.BR sigprocmask (2),
|
|
||||||
but signals can be pending either: for the whole process
|
|
||||||
(i.e., deliverable to any member of the thread group),
|
|
||||||
when sent with
|
|
||||||
.BR kill (2);
|
|
||||||
or for an individual thread, when sent with
|
|
||||||
.BR tgkill (2).
|
|
||||||
A call to
|
|
||||||
.BR sigpending (2)
|
|
||||||
returns a signal set that is the union of the signals pending for the
|
|
||||||
whole process and the signals that are pending for the calling thread.
|
|
||||||
|
|
||||||
If
|
|
||||||
.BR kill (2)
|
|
||||||
is used to send a signal to a thread group,
|
|
||||||
and the thread group has installed a handler for the signal, then
|
|
||||||
the handler will be invoked in exactly one, arbitrarily selected
|
|
||||||
member of the thread group that has not blocked the signal.
|
|
||||||
If multiple threads in a group are waiting to accept the same signal using
|
|
||||||
.BR sigwaitinfo (2),
|
|
||||||
the kernel will arbitrarily select one of these threads
|
|
||||||
to receive a signal sent using
|
|
||||||
.BR kill (2).
|
|
||||||
.TP
|
|
||||||
.BR CLONE_SYSVSEM " (since Linux 2.5.10)"
|
|
||||||
If
|
|
||||||
.B CLONE_SYSVSEM
|
|
||||||
is set, then the child and the calling process share
|
|
||||||
a single list of System V semaphore undo values (see
|
|
||||||
.BR semop (2)).
|
|
||||||
If this flag is not set, then the child has a separate undo list,
|
|
||||||
which is initially empty.
|
|
||||||
.TP
|
|
||||||
.BR CLONE_SETTLS " (since Linux 2.5.32)"
|
|
||||||
The
|
|
||||||
.I newtls
|
|
||||||
parameter is the new TLS (Thread Local Storage) descriptor.
|
|
||||||
(See
|
|
||||||
.BR set_thread_area (2).)
|
|
||||||
.TP
|
|
||||||
.BR CLONE_PARENT_SETTID " (since Linux 2.5.49)"
|
|
||||||
Store child thread ID at location
|
|
||||||
.I parent_tidptr
|
|
||||||
in parent and child memory.
|
|
||||||
(In Linux 2.5.32-2.5.48 there was a flag
|
|
||||||
.BR CLONE_SETTID
|
|
||||||
that did this.)
|
|
||||||
.TP
|
|
||||||
.BR CLONE_CHILD_SETTID " (since Linux 2.5.49)"
|
|
||||||
Store child thread ID at location
|
|
||||||
.I child_tidptr
|
|
||||||
in child memory.
|
|
||||||
.TP
|
|
||||||
.BR CLONE_CHILD_CLEARTID " (since Linux 2.5.49)"
|
|
||||||
Erase child thread ID at location
|
|
||||||
.I child_tidptr
|
|
||||||
in child memory when the child exits, and do a wakeup on the futex
|
|
||||||
at that address.
|
|
||||||
The address involved may be changed by the
|
|
||||||
.BR set_tid_address (2)
|
|
||||||
system call.
|
|
||||||
This is used by threading libraries.
|
|
||||||
.SS "sys_clone"
|
|
||||||
The
|
|
||||||
.B sys_clone
|
|
||||||
system call corresponds more closely to
|
|
||||||
.BR fork (2)
|
|
||||||
in that execution in the child continues from the point of the
|
|
||||||
call.
|
|
||||||
Thus,
|
|
||||||
.B sys_clone
|
|
||||||
only requires the
|
|
||||||
.I flags
|
|
||||||
and
|
|
||||||
.I child_stack
|
|
||||||
arguments, which have the same meaning as for
|
|
||||||
.BR clone ().
|
|
||||||
(Note that the order of these arguments differs from
|
|
||||||
.BR clone ().)
|
|
||||||
|
|
||||||
Another difference for
|
|
||||||
.B sys_clone
|
|
||||||
is that the
|
|
||||||
.I child_stack
|
|
||||||
argument may be zero, in which case copy-on-write semantics ensure that the
|
|
||||||
child gets separate copies of stack pages when either process modifies
|
|
||||||
the stack.
|
|
||||||
In this case, for correct operation, the
|
|
||||||
.B CLONE_VM
|
|
||||||
option should not be specified.
|
|
||||||
|
|
||||||
Since Linux 2.5.49 the system call has five parameters.
|
|
||||||
The two new parameters are
|
|
||||||
.I parent_tidptr
|
|
||||||
which points to the location (in parent and child memory) where
|
|
||||||
the child thread ID will be written in case
|
|
||||||
.B CLONE_PARENT_SETTID
|
|
||||||
was specified, and
|
|
||||||
.I child_tidptr
|
|
||||||
which points to the location (in child memory) where the child thread ID
|
|
||||||
will be written in case
|
|
||||||
.B CLONE_CHILD_SETTID
|
|
||||||
was specified.
|
|
||||||
.SH "RETURN VALUE"
|
|
||||||
.\" gettid(2) returns current->pid;
|
|
||||||
.\" getpid(2) returns current->tgid;
|
|
||||||
On success, the thread ID of the child process is returned
|
|
||||||
in the caller's thread of execution.
|
|
||||||
On failure, a \-1 will be returned
|
|
||||||
in the caller's context, no child process will be created, and
|
|
||||||
.I errno
|
|
||||||
will be set appropriately.
|
|
||||||
.SH ERRORS
|
|
||||||
.TP
|
|
||||||
.B EAGAIN
|
|
||||||
Too many processes are already running.
|
|
||||||
.TP
|
|
||||||
.B EINVAL
|
|
||||||
.B CLONE_SIGHAND
|
|
||||||
was specified, but
|
|
||||||
.B CLONE_VM
|
|
||||||
was not.
|
|
||||||
(Since Linux 2.6.0-test6.)
|
|
||||||
.TP
|
|
||||||
.B EINVAL
|
|
||||||
.B CLONE_THREAD
|
|
||||||
was specified, but
|
|
||||||
.B CLONE_SIGHAND
|
|
||||||
was not. (Since Linux 2.5.35.)
|
|
||||||
.\" .TP
|
|
||||||
.\" .B EINVAL
|
|
||||||
.\" Precisely one of
|
|
||||||
.\" .B CLONE_DETACHED
|
|
||||||
.\" and
|
|
||||||
.\" .B CLONE_THREAD
|
|
||||||
.\" was specified. (Since Linux 2.6.0-test6.)
|
|
||||||
.TP
|
|
||||||
.B EINVAL
|
|
||||||
Both
|
|
||||||
.B CLONE_FS
|
|
||||||
and
|
|
||||||
.B CLONE_NEWNS
|
|
||||||
were specified in
|
|
||||||
.IR flags .
|
|
||||||
.TP
|
|
||||||
.B EINVAL
|
|
||||||
Returned by
|
|
||||||
.BR clone ()
|
|
||||||
when a zero value is specified for
|
|
||||||
.IR child_stack .
|
|
||||||
.TP
|
|
||||||
.B ENOMEM
|
|
||||||
Cannot allocate sufficient memory to allocate a task structure for the
|
|
||||||
child, or to copy those parts of the caller's context that need to be
|
|
||||||
copied.
|
|
||||||
.TP
|
|
||||||
.B EPERM
|
|
||||||
.B CLONE_NEWNS
|
|
||||||
was specified by a non-root process (process without \fBCAP_SYS_ADMIN\fP).
|
|
||||||
.TP
|
|
||||||
.B EPERM
|
|
||||||
.B CLONE_PID
|
|
||||||
was specified by a process other than process 0.
|
|
||||||
.SH VERSIONS
|
|
||||||
There is no entry for
|
|
||||||
.BR clone ()
|
|
||||||
in libc5.
|
|
||||||
glibc2 provides
|
|
||||||
.BR clone ()
|
|
||||||
as described in this manual page.
|
|
||||||
.SH "CONFORMING TO"
|
|
||||||
The
|
|
||||||
.BR clone ()
|
|
||||||
and
|
|
||||||
.B sys_clone
|
|
||||||
calls are Linux specific and should not be used in programs
|
|
||||||
intended to be portable.
|
|
||||||
.SH NOTES
|
|
||||||
In the kernel 2.4.x series,
|
|
||||||
.B CLONE_THREAD
|
|
||||||
generally does not make the parent of the new thread the same
|
|
||||||
as the parent of the calling process.
|
|
||||||
However, for kernel versions 2.4.7 to 2.4.18 the
|
|
||||||
.B CLONE_THREAD
|
|
||||||
flag implied the
|
|
||||||
.B CLONE_PARENT
|
|
||||||
flag (as in kernel 2.6).
|
|
||||||
|
|
||||||
For a while there was
|
|
||||||
.B CLONE_DETACHED
|
|
||||||
(introduced in 2.5.32):
|
|
||||||
parent wants no child-exit signal.
|
|
||||||
In 2.6.2 the need to give this
|
|
||||||
together with
|
|
||||||
.B CLONE_THREAD
|
|
||||||
disappeared.
|
|
||||||
This flag is still defined, but has no effect.
|
|
||||||
|
|
||||||
On x86,
|
|
||||||
.BR clone ()
|
|
||||||
should not be called through vsyscall, but directly through
|
|
||||||
.IR "int $0x80" .
|
|
||||||
|
|
||||||
On IA-64, a different system call is used:
|
|
||||||
.nf
|
|
||||||
|
|
||||||
.BI "int __clone2(int (*" "fn" ")(void *), "
|
|
||||||
.BI " void *" child_stack_base ", size_t " stack_size ,
|
|
||||||
.BI " int " flags ", void *" "arg" ", ... "
|
|
||||||
.BI " /* pid_t *" pid ", struct user_desc *" tls \
|
|
||||||
", pid_t *" ctid " */ );"
|
|
||||||
.fi
|
|
||||||
.PP
|
|
||||||
The
|
|
||||||
.BR __clone2 ()
|
|
||||||
system call operates in the same way as
|
|
||||||
.BR clone (),
|
|
||||||
except that
|
|
||||||
.I child_stack_base
|
|
||||||
points to the lowest address of the child's stack area,
|
|
||||||
and
|
|
||||||
.I stack_size
|
|
||||||
specifies the size of the stack pointed to by
|
|
||||||
.IR child_stack_base .
|
|
||||||
.SH BUGS
|
|
||||||
Versions of the GNU C library that include the NPTL threading library
|
|
||||||
contain a wrapper function for
|
|
||||||
.BR getpid (2)
|
|
||||||
that performs caching of PIDs.
|
|
||||||
In programs linked against such libraries, calls to
|
|
||||||
.BR getpid (2)
|
|
||||||
may return the same value, even when the threads were not created using
|
|
||||||
.B CLONE_THREAD
|
|
||||||
(and thus are not in the same thread group).
|
|
||||||
To get the truth, it may be necessary to use code such as the following
|
|
||||||
.nf
|
|
||||||
|
|
||||||
#include <syscall.h>
|
|
||||||
|
|
||||||
pid_t mypid;
|
|
||||||
|
|
||||||
mypid = syscall(SYS_getpid);
|
|
||||||
.fi
|
|
||||||
.SH "SEE ALSO"
|
|
||||||
.BR fork (2),
|
|
||||||
.BR futex (2),
|
|
||||||
.BR getpid (2),
|
|
||||||
.BR gettid (2),
|
|
||||||
.BR set_thread_area (2),
|
|
||||||
.BR set_tid_address (2),
|
|
||||||
.BR tkill (2),
|
|
||||||
.BR unshare (2),
|
|
||||||
.BR wait (2),
|
|
||||||
.BR capabilities (7),
|
|
||||||
.BR pthreads (7)
|
|
Loading…
Reference in New Issue