2004-11-03 13:51:07 +00:00
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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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2006-02-15 23:15:29 +00:00
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.\" and Copyright (c) Michael Kerrisk, 2001, 2002, 2005
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2004-11-03 13:51:07 +00:00
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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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2007-04-12 22:42:49 +00:00
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.\" Added CLONE_PARENT and revised entire page remove ambiguity
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2004-11-03 13:51:07 +00:00
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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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2005-05-17 15:06:30 +00:00
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.\" Renamed "__clone" to "clone" (which is the prototype in <sched.h>)
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2004-11-03 13:51:07 +00:00
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.\" various other minor tidy ups and clarifications.
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2007-09-20 06:52:22 +00:00
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.\" Modified 26 Jun 2001 by Michael Kerrisk <mtk.manpages@gmail.com>
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2007-06-08 09:56:56 +00:00
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.\" Updated notes for 2.4.7+ behavior of CLONE_THREAD
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2007-09-20 06:52:22 +00:00
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.\" Modified 15 Oct 2002 by Michael Kerrisk <mtk.manpages@gmail.com>
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2004-11-03 13:51:07 +00:00
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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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2007-12-22 22:43:42 +00:00
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.\" Modified 2004-09-10 - added CLONE_PARENT_SETTID etc. - aeb.
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2007-06-08 09:56:56 +00:00
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.\" 2005-04-12, mtk, noted the PID caching behavior of NPTL's getpid()
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2005-04-12 08:11:06 +00:00
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.\" wrapper under BUGS.
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2005-05-17 15:06:30 +00:00
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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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2008-11-19 13:12:00 +00:00
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.\" 2008-11-18, mtk, order CLONE_* flags alphabetically
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.\" 2008-11-18, mtk, document CLONE_NEWPID
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2008-11-19 15:55:24 +00:00
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.\" 2008-11-19, mtk, document CLONE_NEWUTS
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2008-11-19 19:15:25 +00:00
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.\" 2008-11-19, mtk, document CLONE_NEWIPC
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2008-11-19 22:31:32 +00:00
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.\" 2008-11-19, Jens Axboe, mtk, document CLONE_IO
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2004-11-03 13:51:07 +00:00
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.\"
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2007-08-05 09:39:05 +00:00
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.\" FIXME Document CLONE_NEWUSER, which is new in 2.6.23
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.\" (also supported for unshare()?)
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2008-11-19 22:32:03 +00:00
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.\" FIXME . 2.6.25 marks the unused CLONE_STOPPED as obsolete, and it will
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2008-02-11 09:02:41 +00:00
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.\" probably be removed in the future.
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2007-06-28 06:26:09 +00:00
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.\"
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2009-07-18 04:16:12 +00:00
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.TH CLONE 2 2009-07-18 "Linux" "Linux Programmer's Manual"
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2004-11-03 13:51:07 +00:00
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.SH NAME
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2007-06-19 20:09:36 +00:00
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clone, __clone2 \- create a child process
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2004-11-03 13:51:07 +00:00
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.SH SYNOPSIS
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2006-05-31 22:16:55 +00:00
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.nf
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2007-07-08 12:11:40 +00:00
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.B #define _GNU_SOURCE
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.\" Actually _BSD_SOURCE || _SVID_SOURCE
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.\" See http://sources.redhat.com/bugzilla/show_bug.cgi?id=4749
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2004-11-03 13:51:07 +00:00
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.B #include <sched.h>
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2006-05-31 22:16:55 +00:00
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2006-12-04 05:25:49 +00:00
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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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2009-06-21 13:02:21 +00:00
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.BI " /* pid_t *" ptid ", struct user_desc *" tls \
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2006-12-04 05:25:49 +00:00
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", pid_t *" ctid " */ );"
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2006-05-31 22:16:55 +00:00
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.fi
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2004-11-03 13:51:07 +00:00
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.SH DESCRIPTION
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2005-06-30 08:58:03 +00:00
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.BR clone ()
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creates a new process, in a manner similar to
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2004-11-03 13:51:07 +00:00
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.BR fork (2).
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2007-05-28 11:07:05 +00:00
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It is actually a library function layered on top of the underlying
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2005-10-19 06:54:38 +00:00
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.BR clone ()
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2004-11-03 13:51:07 +00:00
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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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2007-09-20 16:26:31 +00:00
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.B sys_clone
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2004-11-03 13:51:07 +00:00
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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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2007-04-12 22:42:49 +00:00
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these calls
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2004-11-03 13:51:07 +00:00
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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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2007-04-12 22:42:49 +00:00
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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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2004-11-03 13:51:07 +00:00
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below.)
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The main use of
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2005-06-30 08:58:03 +00:00
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.BR clone ()
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2004-11-03 13:51:07 +00:00
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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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2007-04-12 22:42:49 +00:00
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.BR clone (),
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2004-11-03 13:51:07 +00:00
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it executes the function
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application
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2007-04-12 22:42:49 +00:00
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.IR fn ( arg ).
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2004-11-03 13:51:07 +00:00
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(This differs from
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2007-04-12 22:42:49 +00:00
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.BR fork (2),
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2004-11-03 13:51:07 +00:00
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where execution continues in the child from the point
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2007-04-12 22:42:49 +00:00
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of the
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.BR fork (2)
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2004-11-03 13:51:07 +00:00
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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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2007-04-12 22:42:49 +00:00
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When the
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2004-11-03 13:51:07 +00:00
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.IR fn ( arg )
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2007-04-12 22:42:49 +00:00
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function application returns, the child process terminates.
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The integer returned by
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2004-11-03 13:51:07 +00:00
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.I fn
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2007-04-12 22:42:49 +00:00
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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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2004-11-03 13:51:07 +00:00
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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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2007-04-12 22:42:49 +00:00
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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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2004-11-03 13:51:07 +00:00
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it is not possible for the child process to execute in the
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2007-04-12 22:42:49 +00:00
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same stack as the calling process.
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The calling process must therefore
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2004-11-03 13:51:07 +00:00
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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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2005-06-30 08:58:03 +00:00
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.BR clone ().
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2004-11-03 13:51:07 +00:00
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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
|
2005-05-17 15:06:30 +00:00
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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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2004-11-03 13:51:07 +00:00
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.BR SIGCHLD ,
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then the parent process must specify the
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2007-04-12 22:42:49 +00:00
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.B __WALL
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or
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2004-11-03 13:51:07 +00:00
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.B __WCLONE
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2007-04-12 22:42:49 +00:00
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options when waiting for the child with
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.BR wait (2).
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2004-11-03 13:51:07 +00:00
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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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2005-05-17 15:06:30 +00:00
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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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2004-11-03 13:51:07 +00:00
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and the child process:
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.TP
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2008-11-18 21:20:54 +00:00
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.BR CLONE_CHILD_CLEARTID " (since Linux 2.5.49)"
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Erase child thread ID at location
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2009-06-21 13:02:21 +00:00
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.I ctid
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2008-11-18 21:20:54 +00:00
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in child memory when the child exits, and do a wakeup on the futex
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at that address.
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The address involved may be changed by the
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.BR set_tid_address (2)
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system call.
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This is used by threading libraries.
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.TP
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.BR CLONE_CHILD_SETTID " (since Linux 2.5.49)"
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Store child thread ID at location
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2009-06-21 13:02:21 +00:00
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.I ctid
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2008-11-18 21:20:54 +00:00
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in child memory.
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.TP
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.B CLONE_FILES
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2004-11-03 13:51:07 +00:00
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If
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2008-11-18 21:20:54 +00:00
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.B CLONE_FILES
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is set, the calling process and the child process share the same file
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descriptor table.
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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,
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or changes its associated flags (using the
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.BR fcntl (2)
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.B F_SETFD
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operation), the other process is also affected.
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2004-11-03 13:51:07 +00:00
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If
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2008-11-18 21:20:54 +00:00
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.B CLONE_FILES
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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
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.BR clone ().
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(The duplicated file descriptors in the child refer to the
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same open file descriptions (see
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.BR open (2))
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as the corresponding file descriptors in the calling process.)
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Subsequent operations that open or close file descriptors,
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or change file descriptor flags,
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performed by either the calling
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process or the child process do not affect the other process.
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2004-11-03 13:51:07 +00:00
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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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2008-09-23 05:22:43 +00:00
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is set, the caller and the child process share the same file system
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2007-04-12 22:42:49 +00:00
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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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2004-11-03 13:51:07 +00:00
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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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2005-06-30 08:58:03 +00:00
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performed by the calling process or the child process also affects the
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2004-11-03 13:51:07 +00:00
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other process.
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2007-04-12 22:42:49 +00:00
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If
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2004-11-03 13:51:07 +00:00
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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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2005-06-30 08:58:03 +00:00
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.BR clone ()
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2004-11-03 13:51:07 +00:00
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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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2008-11-20 14:59:15 +00:00
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.BR CLONE_IO " (since Linux 2.6.25)"
|
2008-11-19 22:29:03 +00:00
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If
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.B CLONE_IO
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is set, then the new process shares an I/O context with
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the calling process.
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If this flag is not set, then (as with
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.BR fork (2))
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the new process has its own I/O context.
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.\" The following based on text from Jens Axboe
|
2008-11-26 02:44:53 +00:00
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The I/O context is the I/O scope of the disk scheduler (i.e,
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2008-11-19 22:29:03 +00:00
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what the I/O scheduler uses to model scheduling of a process's I/O).
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If processes share the same I/O context,
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they are treated as one by the I/O scheduler.
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As a consequence, they get to share disk time.
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For some I/O schedulers,
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.\" the anticipatory and CFQ scheduler
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if two processes share an I/O context,
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they will be allowed to interleave their disk access.
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If several threads are doing I/O on behalf of the same process
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.RB ( aio_read (3),
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for instance), they should employ
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.BR CLONE_IO
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to get better I/O performance.
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.\" with CFQ and AS.
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If the kernel is not configured with the
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.B CONFIG_BLOCK
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option, this flag is a no-op.
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.TP
|
2009-07-18 04:16:12 +00:00
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.BR CLONE_NEWIPC " (since Linux 2.6.19)"
|
2008-11-19 19:15:25 +00:00
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If
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.B CLONE_NEWIPC
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is set, then create the process in a new IPC namespace.
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If this flag is not set, then (as with
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.BR fork (2)),
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the process is created in the same IPC namespace as
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the calling process.
|
2008-11-20 14:54:34 +00:00
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This flag is intended for the implementation of containers.
|
2008-11-19 19:15:25 +00:00
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An IPC namespace consists of the set of identifiers for
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System V IPC objects.
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(These objects are created using
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.BR msgctl (2),
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.BR semctl (2),
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and
|
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.BR shmctl (2)).
|
2009-09-28 08:31:09 +00:00
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Objects created in an IPC namespace are visible to all other processes
|
2008-11-19 19:15:25 +00:00
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that are members of that namespace,
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but are not visible to processes in other IPC namespaces.
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|
2008-11-20 16:21:41 +00:00
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When an IPC namespace is destroyed
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(i.e, when the last process that is a member of the namespace terminates),
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all IPC objects in the namespace are automatically destroyed.
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|
2008-11-19 19:15:25 +00:00
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Use of this flag requires: a kernel configured with the
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.B CONFIG_SYSVIPC
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and
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.B CONFIG_IPC_NS
|
2008-11-20 17:15:56 +00:00
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|
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options and that the process be privileged
|
2008-11-19 19:15:25 +00:00
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.RB ( CAP_SYS_ADMIN ).
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This flag can't be specified in conjunction with
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|
|
.BR CLONE_SYSVSEM .
|
|
|
|
.TP
|
2008-11-20 17:15:23 +00:00
|
|
|
.BR CLONE_NEWNET " (since Linux 2.6.24)"
|
|
|
|
(The implementation of this flag is not yet complete,
|
|
|
|
but probably will be mostly complete by about Linux 2.6.28.)
|
|
|
|
|
|
|
|
If
|
|
|
|
.B CLONE_NEWNET
|
|
|
|
is set, then create the process in a new network namespace.
|
|
|
|
If this flag is not set, then (as with
|
|
|
|
.BR fork (2)),
|
|
|
|
the process is created in the same network namespace as
|
|
|
|
the calling process.
|
|
|
|
This flag is intended for the implementation of containers.
|
|
|
|
|
|
|
|
A network namespace provides an isolated view of the networking stack
|
|
|
|
(network device interfaces, IPv4 and IPv6 protocol stacks,
|
|
|
|
IP routing tables, firewall rules, the
|
|
|
|
.I /proc/net
|
|
|
|
and
|
|
|
|
.I /sys/class/net
|
|
|
|
directory trees, sockets, etc.).
|
|
|
|
A physical network device can live in exactly one
|
|
|
|
network namespace.
|
|
|
|
A virtual network device ("veth") pair provides a pipe-like abstraction
|
|
|
|
that can be used to create tunnels between network namespaces,
|
|
|
|
and can be used to create a bridge to a physical network device
|
|
|
|
in another namespace.
|
|
|
|
|
2008-11-25 14:46:46 +00:00
|
|
|
When a network namespace is freed
|
|
|
|
(i.e., when the last process in the namespace terminates),
|
|
|
|
its physical network devices are moved back to the
|
|
|
|
initial network namespace (not to the parent of the process).
|
|
|
|
|
2008-11-20 17:15:23 +00:00
|
|
|
Use of this flag requires: a kernel configured with the
|
|
|
|
.B CONFIG_NET_NS
|
|
|
|
option and that the process be privileged
|
2008-11-20 18:19:15 +00:00
|
|
|
.RB ( CAP_SYS_ADMIN ).
|
2008-11-20 17:15:23 +00:00
|
|
|
.TP
|
2006-05-31 22:16:55 +00:00
|
|
|
.BR CLONE_NEWNS " (since Linux 2.4.19)"
|
2008-11-20 16:04:07 +00:00
|
|
|
Start the child in a new mount namespace.
|
2004-11-03 13:51:07 +00:00
|
|
|
|
2008-11-20 16:04:07 +00:00
|
|
|
Every process lives in a mount namespace.
|
2007-04-12 22:42:49 +00:00
|
|
|
The
|
2004-11-03 13:51:07 +00:00
|
|
|
.I namespace
|
|
|
|
of a process is the data (the set of mounts) describing the file hierarchy
|
2007-04-12 22:42:49 +00:00
|
|
|
as seen by that process.
|
|
|
|
After a
|
2004-11-03 13:51:07 +00:00
|
|
|
.BR fork (2)
|
|
|
|
or
|
2007-11-24 10:10:39 +00:00
|
|
|
.BR clone ()
|
2004-11-03 13:51:07 +00:00
|
|
|
where the
|
|
|
|
.B CLONE_NEWNS
|
2008-11-20 16:04:07 +00:00
|
|
|
flag is not set, the child lives in the same mount
|
2008-11-19 19:23:47 +00:00
|
|
|
namespace as the parent.
|
2004-11-03 13:51:07 +00:00
|
|
|
The system calls
|
|
|
|
.BR mount (2)
|
|
|
|
and
|
|
|
|
.BR umount (2)
|
2008-11-20 16:04:07 +00:00
|
|
|
change the mount namespace of the calling process, and hence affect
|
2004-11-03 13:51:07 +00:00
|
|
|
all processes that live in the same namespace, but do not affect
|
2008-11-20 16:04:07 +00:00
|
|
|
processes in a different mount namespace.
|
2004-11-03 13:51:07 +00:00
|
|
|
|
|
|
|
After a
|
2007-11-24 10:10:39 +00:00
|
|
|
.BR clone ()
|
2004-11-03 13:51:07 +00:00
|
|
|
where the
|
|
|
|
.B CLONE_NEWNS
|
2008-11-20 16:04:07 +00:00
|
|
|
flag is set, the cloned child is started in a new mount namespace,
|
2004-11-03 13:51:07 +00:00
|
|
|
initialized with a copy of the namespace of the parent.
|
|
|
|
|
2007-06-20 22:15:34 +00:00
|
|
|
Only a privileged process (one having the \fBCAP_SYS_ADMIN\fP capability)
|
2004-11-03 13:51:07 +00:00
|
|
|
may specify the
|
|
|
|
.B CLONE_NEWNS
|
|
|
|
flag.
|
|
|
|
It is not permitted to specify both
|
|
|
|
.B CLONE_NEWNS
|
|
|
|
and
|
|
|
|
.B CLONE_FS
|
|
|
|
in the same
|
2005-10-19 06:54:38 +00:00
|
|
|
.BR clone ()
|
2004-11-03 13:51:07 +00:00
|
|
|
call.
|
|
|
|
.TP
|
2008-11-19 13:12:00 +00:00
|
|
|
.BR CLONE_NEWPID " (since Linux 2.6.24)"
|
|
|
|
.\" This explanation draws a lot of details from
|
|
|
|
.\" http://lwn.net/Articles/259217/
|
|
|
|
.\" Authors: Pavel Emelyanov <xemul@openvz.org>
|
|
|
|
.\" and Kir Kolyshkin <kir@openvz.org>
|
|
|
|
.\"
|
|
|
|
.\" The primary kernel commit is 30e49c263e36341b60b735cbef5ca37912549264
|
|
|
|
.\" Author: Pavel Emelyanov <xemul@openvz.org>
|
|
|
|
If
|
2008-11-19 15:44:22 +00:00
|
|
|
.B CLONE_NEWPID
|
2008-11-19 13:12:00 +00:00
|
|
|
is set, then create the process in a new PID namespace.
|
|
|
|
If this flag is not set, then (as with
|
|
|
|
.BR fork (2)),
|
|
|
|
the process is created in the same PID namespace as
|
|
|
|
the calling process.
|
2008-11-20 14:54:34 +00:00
|
|
|
This flag is intended for the implementation of containers.
|
2008-11-19 13:12:00 +00:00
|
|
|
|
|
|
|
A PID namespace provides an isolated environment for PIDs:
|
|
|
|
PIDs in a new namespace start at 1,
|
|
|
|
somewhat like a standalone system, and calls to
|
|
|
|
.BR fork (2),
|
|
|
|
.BR vfork (2),
|
|
|
|
or
|
|
|
|
.BR clone (2)
|
2008-11-25 15:46:37 +00:00
|
|
|
will produce processes with PIDs that are unique within the namespace.
|
2008-11-19 13:12:00 +00:00
|
|
|
|
|
|
|
The first process created in a new namespace
|
|
|
|
(i.e., the process created using the
|
|
|
|
.BR CLONE_NEWPID
|
|
|
|
flag) has the PID 1, and is the "init" process for the namespace.
|
|
|
|
Children that are orphaned within the namespace will be reparented
|
|
|
|
to this process rather than
|
|
|
|
.BR init (8).
|
|
|
|
Unlike the traditional
|
|
|
|
.B init
|
|
|
|
process, the "init" process of a PID namespace can terminate,
|
|
|
|
and if it does, all of the processes in the namespace are terminated.
|
|
|
|
|
|
|
|
PID namespaces form a hierarchy.
|
2009-09-27 07:26:26 +00:00
|
|
|
When a new PID namespace is created,
|
2008-11-25 15:12:06 +00:00
|
|
|
the processes in that namespace are visible
|
2008-11-19 13:12:00 +00:00
|
|
|
in the PID namespace of the process that created the new namespace;
|
|
|
|
analogously, if the parent PID namespace is itself
|
|
|
|
the child of another PID namespace,
|
2008-11-25 15:12:06 +00:00
|
|
|
then processes in the child and parent PID namespaces will both be
|
2008-11-19 13:12:00 +00:00
|
|
|
visible in the grandparent PID namespace.
|
|
|
|
Conversely, the processes in the "child" PID namespace do not see
|
2008-11-25 15:46:37 +00:00
|
|
|
the processes in the parent namespace.
|
2008-11-19 13:12:00 +00:00
|
|
|
The existence of a namespace hierarchy means that each process
|
|
|
|
may now have multiple PIDs:
|
2008-11-25 15:46:37 +00:00
|
|
|
one for each namespace in which it is visible;
|
|
|
|
each of these PIDs is unique within the corresponding namespace.
|
2008-11-19 13:12:00 +00:00
|
|
|
(A call to
|
|
|
|
.BR getpid (2)
|
|
|
|
always returns the PID associated with the namespace in which
|
2008-11-25 16:27:34 +00:00
|
|
|
the process lives.)
|
2008-11-19 13:12:00 +00:00
|
|
|
|
|
|
|
After creating the new namespace,
|
|
|
|
it is useful for the child to change its root directory
|
|
|
|
and mount a new procfs instance at
|
|
|
|
.I /proc
|
|
|
|
so that tools such as
|
|
|
|
.BR ps (1)
|
|
|
|
work correctly.
|
|
|
|
.\" mount -t proc proc /proc
|
2008-11-25 15:12:06 +00:00
|
|
|
(If
|
|
|
|
.BR CLONE_NEWNS
|
|
|
|
is also included in
|
|
|
|
.IR flags ,
|
|
|
|
then it isn't necessary to change the root directory:
|
2008-11-25 15:48:27 +00:00
|
|
|
a new procfs instance can be mounted directly over
|
2008-11-25 15:12:06 +00:00
|
|
|
.IR /proc .)
|
2008-11-19 13:12:00 +00:00
|
|
|
|
|
|
|
Use of this flag requires: a kernel configured with the
|
|
|
|
.B CONFIG_PID_NS
|
2008-11-20 17:15:56 +00:00
|
|
|
option and that the process be privileged
|
2008-11-19 15:45:26 +00:00
|
|
|
.RB ( CAP_SYS_ADMIN ).
|
2008-11-19 13:12:00 +00:00
|
|
|
This flag can't be specified in conjunction with
|
|
|
|
.BR CLONE_THREAD .
|
|
|
|
.TP
|
2008-11-19 15:55:24 +00:00
|
|
|
.BR CLONE_NEWUTS " (since Linux 2.6.19)"
|
|
|
|
If
|
|
|
|
.B CLONE_NEWUTS
|
2008-11-24 23:12:13 +00:00
|
|
|
is set, then create the process in a new UTS namespace,
|
|
|
|
whose identifiers are initialized by duplicating the identifiers
|
|
|
|
from the UTS namespace of the calling process.
|
2008-11-19 15:55:24 +00:00
|
|
|
If this flag is not set, then (as with
|
|
|
|
.BR fork (2)),
|
|
|
|
the process is created in the same UTS namespace as
|
|
|
|
the calling process.
|
2008-11-20 14:54:34 +00:00
|
|
|
This flag is intended for the implementation of containers.
|
2008-11-19 15:55:24 +00:00
|
|
|
|
|
|
|
A UTS namespace is the set of identifiers returned by
|
|
|
|
.BR uname (2);
|
|
|
|
among these, the domain name and the host name can be modified by
|
|
|
|
.BR setdomainname (2)
|
|
|
|
and
|
|
|
|
.BR
|
|
|
|
.BR sethostname (2),
|
|
|
|
respectively.
|
2009-09-28 08:31:09 +00:00
|
|
|
Changes made to the identifiers in a UTS namespace
|
|
|
|
are visible to all other processes in the same namespace,
|
2008-11-19 15:55:24 +00:00
|
|
|
but are not visible to processes in other UTS namespaces.
|
|
|
|
|
|
|
|
Use of this flag requires: a kernel configured with the
|
|
|
|
.B CONFIG_UTS_NS
|
2008-11-20 17:15:56 +00:00
|
|
|
option and that the process be privileged
|
2008-11-19 15:55:24 +00:00
|
|
|
.RB ( CAP_SYS_ADMIN ).
|
|
|
|
.TP
|
2008-11-18 21:20:54 +00:00
|
|
|
.BR CLONE_PARENT " (since Linux 2.3.12)"
|
|
|
|
If
|
|
|
|
.B CLONE_PARENT
|
|
|
|
is set, then the parent of the new child (as returned by
|
|
|
|
.BR getppid (2))
|
|
|
|
will be the same as that of the calling process.
|
|
|
|
|
|
|
|
If
|
|
|
|
.B CLONE_PARENT
|
|
|
|
is not set, then (as with
|
|
|
|
.BR fork (2))
|
|
|
|
the child's parent is the calling process.
|
|
|
|
|
|
|
|
Note that it is the parent process, as returned by
|
|
|
|
.BR getppid (2),
|
|
|
|
which is signaled when the child terminates, so that
|
|
|
|
if
|
|
|
|
.B CLONE_PARENT
|
|
|
|
is set, then the parent of the calling process, rather than the
|
|
|
|
calling process itself, will be signaled.
|
|
|
|
.TP
|
|
|
|
.BR CLONE_PARENT_SETTID " (since Linux 2.5.49)"
|
|
|
|
Store child thread ID at location
|
2009-06-21 13:02:21 +00:00
|
|
|
.I ptid
|
2008-11-18 21:20:54 +00:00
|
|
|
in parent and child memory.
|
|
|
|
(In Linux 2.5.32-2.5.48 there was a flag
|
|
|
|
.B CLONE_SETTID
|
|
|
|
that did this.)
|
|
|
|
.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
|
|
|
|
.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_SETTLS " (since Linux 2.5.32)"
|
|
|
|
The
|
|
|
|
.I newtls
|
|
|
|
argument is the new TLS (Thread Local Storage) descriptor.
|
|
|
|
(See
|
|
|
|
.BR set_thread_area (2).)
|
|
|
|
.TP
|
2004-11-03 13:51:07 +00:00
|
|
|
.B CLONE_SIGHAND
|
|
|
|
If
|
|
|
|
.B CLONE_SIGHAND
|
2008-09-23 05:22:43 +00:00
|
|
|
is set, the calling process and the child process share the same table of
|
2007-04-12 22:42:49 +00:00
|
|
|
signal handlers.
|
|
|
|
If the calling process or child process calls
|
2004-11-03 13:51:07 +00:00
|
|
|
.BR sigaction (2)
|
2007-04-12 22:42:49 +00:00
|
|
|
to change the behavior associated with a signal, the behavior is
|
|
|
|
changed in the other process as well.
|
|
|
|
However, the calling process and child
|
2004-11-03 13:51:07 +00:00
|
|
|
processes still have distinct signal masks and sets of pending
|
2007-04-12 22:42:49 +00:00
|
|
|
signals.
|
|
|
|
So, one of them may block or unblock some signals using
|
2004-11-03 13:51:07 +00:00
|
|
|
.BR sigprocmask (2)
|
|
|
|
without affecting the other process.
|
|
|
|
|
|
|
|
If
|
|
|
|
.B CLONE_SIGHAND
|
|
|
|
is not set, the child process inherits a copy of the signal handlers
|
|
|
|
of the calling process at the time
|
2005-06-30 08:58:03 +00:00
|
|
|
.BR clone ()
|
2007-04-12 22:42:49 +00:00
|
|
|
is called.
|
|
|
|
Calls to
|
2004-11-03 13:51:07 +00:00
|
|
|
.BR sigaction (2)
|
|
|
|
performed later by one of the processes have no effect on the other
|
|
|
|
process.
|
2006-02-16 04:00:49 +00:00
|
|
|
|
|
|
|
Since Linux 2.6.0-test6,
|
|
|
|
.I flags
|
|
|
|
must also include
|
|
|
|
.B CLONE_VM
|
|
|
|
if
|
|
|
|
.B CLONE_SIGHAND
|
|
|
|
is specified
|
2004-11-03 13:51:07 +00:00
|
|
|
.TP
|
2005-05-10 16:48:27 +00:00
|
|
|
.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.
|
2008-04-14 13:03:17 +00:00
|
|
|
|
|
|
|
.I "From Linux 2.6.25 this flag is deprecated."
|
|
|
|
You probably never wanted to use it,
|
2008-04-25 09:53:45 +00:00
|
|
|
you certainly shouldn't be using it, and soon it will go away.
|
2008-11-08 02:32:57 +00:00
|
|
|
.\" glibc 2.8 removed this defn from bits/sched.h
|
2005-05-10 16:48:27 +00:00
|
|
|
.TP
|
2008-11-18 21:20:54 +00:00
|
|
|
.BR CLONE_SYSVSEM " (since Linux 2.5.10)"
|
2004-11-03 13:51:07 +00:00
|
|
|
If
|
2008-11-18 21:20:54 +00:00
|
|
|
.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.
|
2004-11-03 13:51:07 +00:00
|
|
|
.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.
|
2005-05-17 15:06:30 +00:00
|
|
|
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.
|
2004-11-03 13:51:07 +00:00
|
|
|
|
2005-05-17 15:06:30 +00:00
|
|
|
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.
|
2007-04-12 22:42:49 +00:00
|
|
|
Since Linux 2.4, calls to
|
2004-11-03 13:51:07 +00:00
|
|
|
.BR getpid (2)
|
2005-05-17 15:06:30 +00:00
|
|
|
return the TGID of the caller.
|
|
|
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|
|
|
|
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).
|
|
|
|
|
2007-04-12 22:42:49 +00:00
|
|
|
When a call is made to
|
2005-05-17 15:06:30 +00:00
|
|
|
.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.
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|
|
This thread is the
|
|
|
|
.I leader
|
|
|
|
of the new thread group.
|
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|
|
A new thread created with
|
|
|
|
.B CLONE_THREAD
|
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|
|
has the same parent process as the caller of
|
|
|
|
.BR clone ()
|
2007-04-12 22:42:49 +00:00
|
|
|
(i.e., like
|
2005-05-17 15:06:30 +00:00
|
|
|
.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
|
2007-04-12 22:42:49 +00:00
|
|
|
.B CLONE_THREAD
|
2005-05-17 15:06:30 +00:00
|
|
|
thread terminates, the thread that created it using
|
|
|
|
.BR clone ()
|
|
|
|
is not sent a
|
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|
|
.B SIGCHLD
|
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|
|
(or other termination) signal;
|
|
|
|
nor can the status of such a thread be obtained
|
|
|
|
using
|
|
|
|
.BR wait (2).
|
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|
|
(The thread is said to be
|
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|
|
.IR detached .)
|
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|
|
2005-05-17 16:21:20 +00:00
|
|
|
After all of the threads in a thread group terminate
|
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|
|
the parent process of the thread group is sent a
|
2005-05-17 15:06:30 +00:00
|
|
|
.B SIGCHLD
|
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|
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(or other termination) signal.
|
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|
|
If any of the threads in a thread group performs an
|
|
|
|
.BR execve (2),
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|
|
then all threads other than the thread group leader are terminated,
|
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|
|
and the new program is executed in the thread group leader.
|
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|
|
2005-06-02 10:22:34 +00:00
|
|
|
If one of the threads in a thread group creates a child using
|
|
|
|
.BR fork (2),
|
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|
|
then any thread in the group can
|
|
|
|
.BR wait (2)
|
|
|
|
for that child.
|
|
|
|
|
2005-06-30 08:58:03 +00:00
|
|
|
Since Linux 2.5.35,
|
2005-05-17 15:06:30 +00:00
|
|
|
.I flags
|
|
|
|
must also include
|
|
|
|
.B CLONE_SIGHAND
|
|
|
|
if
|
|
|
|
.B CLONE_THREAD
|
|
|
|
is specified.
|
2005-05-17 16:21:20 +00:00
|
|
|
|
|
|
|
Signals may be sent to a thread group as a whole (i.e., a TGID) using
|
|
|
|
.BR kill (2),
|
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|
|
or to a specific thread (i.e., TID) using
|
|
|
|
.BR tgkill (2).
|
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|
|
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.
|
|
|
|
|
2005-05-18 08:29:38 +00:00
|
|
|
Each thread has its own signal mask, as set by
|
2005-05-17 16:21:20 +00:00
|
|
|
.BR sigprocmask (2),
|
2006-02-16 04:55:18 +00:00
|
|
|
but signals can be pending either: for the whole process
|
2005-05-17 16:21:20 +00:00
|
|
|
(i.e., deliverable to any member of the thread group),
|
|
|
|
when sent with
|
2006-02-16 04:55:18 +00:00
|
|
|
.BR kill (2);
|
2005-05-17 16:21:20 +00:00
|
|
|
or for an individual thread, when sent with
|
|
|
|
.BR tgkill (2).
|
2005-05-18 08:29:38 +00:00
|
|
|
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.
|
2005-05-17 16:21:20 +00:00
|
|
|
|
2007-04-12 22:42:49 +00:00
|
|
|
If
|
2005-05-17 16:21:20 +00:00
|
|
|
.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.
|
2007-04-12 22:42:49 +00:00
|
|
|
If multiple threads in a group are waiting to accept the same signal using
|
2005-05-17 16:21:20 +00:00
|
|
|
.BR sigwaitinfo (2),
|
|
|
|
the kernel will arbitrarily select one of these threads
|
2007-04-12 22:42:49 +00:00
|
|
|
to receive a signal sent using
|
2005-05-17 16:21:20 +00:00
|
|
|
.BR kill (2).
|
2005-05-10 16:48:27 +00:00
|
|
|
.TP
|
2008-11-18 21:20:54 +00:00
|
|
|
.BR CLONE_UNTRACED " (since Linux 2.5.46)"
|
2005-05-10 16:48:27 +00:00
|
|
|
If
|
2008-11-18 21:20:54 +00:00
|
|
|
.B CLONE_UNTRACED
|
|
|
|
is specified, then a tracing process cannot force
|
|
|
|
.B CLONE_PTRACE
|
|
|
|
on this child process.
|
2004-11-03 13:51:07 +00:00
|
|
|
.TP
|
2008-11-18 21:20:54 +00:00
|
|
|
.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.
|
2004-11-03 13:51:07 +00:00
|
|
|
.TP
|
2008-11-18 21:20:54 +00:00
|
|
|
.B CLONE_VM
|
|
|
|
If
|
|
|
|
.B CLONE_VM
|
|
|
|
is set, the calling process and the child process 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).
|
2004-11-03 13:51:07 +00:00
|
|
|
.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
|
2007-04-12 22:42:49 +00:00
|
|
|
call.
|
|
|
|
Thus,
|
2004-11-03 13:51:07 +00:00
|
|
|
.B sys_clone
|
|
|
|
only requires the
|
|
|
|
.I flags
|
2007-04-12 22:42:49 +00:00
|
|
|
and
|
2004-11-03 13:51:07 +00:00
|
|
|
.I child_stack
|
2007-04-12 22:42:49 +00:00
|
|
|
arguments, which have the same meaning as for
|
|
|
|
.BR clone ().
|
2004-11-03 13:51:07 +00:00
|
|
|
(Note that the order of these arguments differs from
|
2007-04-12 22:42:49 +00:00
|
|
|
.BR clone ().)
|
2004-11-03 13:51:07 +00:00
|
|
|
|
2007-04-12 22:42:49 +00:00
|
|
|
Another difference for
|
2004-11-03 13:51:07 +00:00
|
|
|
.B sys_clone
|
|
|
|
is that the
|
|
|
|
.I child_stack
|
2007-04-12 22:42:49 +00:00
|
|
|
argument may be zero, in which case copy-on-write semantics ensure that the
|
2004-11-03 13:51:07 +00:00
|
|
|
child gets separate copies of stack pages when either process modifies
|
2007-04-12 22:42:49 +00:00
|
|
|
the stack.
|
|
|
|
In this case, for correct operation, the
|
2004-11-03 13:51:07 +00:00
|
|
|
.B CLONE_VM
|
|
|
|
option should not be specified.
|
|
|
|
|
2009-06-21 13:30:21 +00:00
|
|
|
In Linux 2.4 and earlier,
|
|
|
|
.BR clone ()
|
|
|
|
does not take arguments
|
|
|
|
.IR ptid ,
|
|
|
|
.IR tls ,
|
|
|
|
and
|
2009-10-17 04:39:02 +00:00
|
|
|
.IR ctid .
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH "RETURN VALUE"
|
2007-05-11 23:07:02 +00:00
|
|
|
.\" gettid(2) returns current->pid;
|
|
|
|
.\" getpid(2) returns current->tgid;
|
2004-11-03 13:51:07 +00:00
|
|
|
On success, the thread ID of the child process is returned
|
2007-04-12 22:42:49 +00:00
|
|
|
in the caller's thread of execution.
|
2008-07-12 11:01:09 +00:00
|
|
|
On failure, \-1 is returned
|
2004-11-03 13:51:07 +00:00
|
|
|
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
|
2007-05-16 04:32:48 +00:00
|
|
|
was not.
|
|
|
|
(Since Linux 2.6.0-test6.)
|
2004-11-03 13:51:07 +00:00
|
|
|
.TP
|
|
|
|
.B EINVAL
|
|
|
|
.B CLONE_THREAD
|
|
|
|
was specified, but
|
|
|
|
.B CLONE_SIGHAND
|
2008-06-28 04:57:20 +00:00
|
|
|
was not.
|
|
|
|
(Since Linux 2.5.35.)
|
2006-02-16 04:00:49 +00:00
|
|
|
.\" .TP
|
|
|
|
.\" .B EINVAL
|
|
|
|
.\" Precisely one of
|
|
|
|
.\" .B CLONE_DETACHED
|
|
|
|
.\" and
|
|
|
|
.\" .B CLONE_THREAD
|
2008-06-28 04:57:20 +00:00
|
|
|
.\" was specified.
|
|
|
|
.\" (Since Linux 2.6.0-test6.)
|
2004-11-03 13:51:07 +00:00
|
|
|
.TP
|
|
|
|
.B EINVAL
|
|
|
|
Both
|
|
|
|
.B CLONE_FS
|
|
|
|
and
|
|
|
|
.B CLONE_NEWNS
|
|
|
|
were specified in
|
|
|
|
.IR flags .
|
|
|
|
.TP
|
|
|
|
.B EINVAL
|
2008-11-19 13:12:00 +00:00
|
|
|
Both
|
2008-11-19 19:15:25 +00:00
|
|
|
.B CLONE_NEWIPC
|
|
|
|
and
|
|
|
|
.B CLONE_SYSVSEM
|
|
|
|
were specified in
|
|
|
|
.IR flags .
|
|
|
|
.TP
|
|
|
|
.B EINVAL
|
|
|
|
Both
|
2008-11-19 13:12:00 +00:00
|
|
|
.BR CLONE_NEWPID
|
|
|
|
and
|
|
|
|
.BR CLONE_THREAD
|
|
|
|
were specified in
|
|
|
|
.IR flags .
|
|
|
|
.TP
|
|
|
|
.B EINVAL
|
2007-04-12 22:42:49 +00:00
|
|
|
Returned by
|
2005-06-30 08:58:03 +00:00
|
|
|
.BR clone ()
|
2007-04-12 22:42:49 +00:00
|
|
|
when a zero value is specified for
|
2004-11-03 13:51:07 +00:00
|
|
|
.IR child_stack .
|
|
|
|
.TP
|
2008-11-19 15:01:38 +00:00
|
|
|
.B EINVAL
|
2008-11-19 19:15:25 +00:00
|
|
|
.BR CLONE_NEWIPC
|
|
|
|
was specified in
|
|
|
|
.IR flags ,
|
|
|
|
but the kernel was not configured with the
|
|
|
|
.B CONFIG_SYSVIPC
|
|
|
|
and
|
|
|
|
.BR CONFIG_IPC_NS
|
|
|
|
options.
|
|
|
|
.TP
|
|
|
|
.B EINVAL
|
2008-11-20 17:15:23 +00:00
|
|
|
.BR CLONE_NEWNET
|
|
|
|
was specified in
|
|
|
|
.IR flags ,
|
|
|
|
but the kernel was not configured with the
|
|
|
|
.B CONFIG_NET_NS
|
|
|
|
option.
|
|
|
|
.TP
|
|
|
|
.B EINVAL
|
2008-11-19 15:01:38 +00:00
|
|
|
.BR CLONE_NEWPID
|
|
|
|
was specified in
|
|
|
|
.IR flags ,
|
|
|
|
but the kernel was not configured with the
|
|
|
|
.B CONFIG_PID_NS
|
|
|
|
option.
|
|
|
|
.TP
|
2008-11-19 15:55:24 +00:00
|
|
|
.B EINVAL
|
|
|
|
.BR CLONE_NEWUTS
|
|
|
|
was specified in
|
|
|
|
.IR flags ,
|
|
|
|
but the kernel was not configured with the
|
|
|
|
.B CONFIG_UTS
|
|
|
|
option.
|
|
|
|
.TP
|
2004-11-03 13:51:07 +00:00
|
|
|
.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
|
2008-11-19 19:15:25 +00:00
|
|
|
.BR CLONE_NEWIPC ,
|
2008-11-20 17:15:23 +00:00
|
|
|
.BR CLONE_NEWNET ,
|
2008-11-19 15:55:24 +00:00
|
|
|
.BR CLONE_NEWNS ,
|
|
|
|
.BR CLONE_NEWPID ,
|
2008-11-19 13:12:00 +00:00
|
|
|
or
|
2008-11-19 15:55:24 +00:00
|
|
|
.BR CLONE_NEWUTS
|
2007-06-20 22:15:34 +00:00
|
|
|
was specified by a non-root process (process without \fBCAP_SYS_ADMIN\fP).
|
2004-11-03 13:51:07 +00:00
|
|
|
.TP
|
|
|
|
.B EPERM
|
|
|
|
.B CLONE_PID
|
|
|
|
was specified by a process other than process 0.
|
2007-05-16 04:53:05 +00:00
|
|
|
.SH VERSIONS
|
2004-11-03 13:51:07 +00:00
|
|
|
There is no entry for
|
2005-06-30 08:58:03 +00:00
|
|
|
.BR clone ()
|
2007-05-16 04:53:05 +00:00
|
|
|
in libc5.
|
|
|
|
glibc2 provides
|
2005-06-30 08:58:03 +00:00
|
|
|
.BR clone ()
|
2004-11-03 13:51:07 +00:00
|
|
|
as described in this manual page.
|
2007-05-18 16:06:42 +00:00
|
|
|
.SH "CONFORMING TO"
|
|
|
|
The
|
|
|
|
.BR clone ()
|
|
|
|
and
|
|
|
|
.B sys_clone
|
2007-12-25 21:28:09 +00:00
|
|
|
calls are Linux-specific and should not be used in programs
|
2007-05-18 16:06:42 +00:00
|
|
|
intended to be portable.
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH NOTES
|
2005-05-17 15:06:30 +00:00
|
|
|
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
|
2007-04-12 22:42:49 +00:00
|
|
|
.B CLONE_PARENT
|
2005-05-17 15:06:30 +00:00
|
|
|
flag (as in kernel 2.6).
|
2004-11-03 13:51:07 +00:00
|
|
|
|
2007-04-12 22:42:49 +00:00
|
|
|
For a while there was
|
|
|
|
.B CLONE_DETACHED
|
2006-09-04 06:57:17 +00:00
|
|
|
(introduced in 2.5.32):
|
2007-04-12 22:42:49 +00:00
|
|
|
parent wants no child-exit signal.
|
2006-09-04 06:57:17 +00:00
|
|
|
In 2.6.2 the need to give this
|
2007-04-12 22:42:49 +00:00
|
|
|
together with
|
|
|
|
.B CLONE_THREAD
|
2006-09-04 06:57:17 +00:00
|
|
|
disappeared.
|
|
|
|
This flag is still defined, but has no effect.
|
|
|
|
|
2007-12-24 17:31:35 +00:00
|
|
|
On i386,
|
2006-02-03 03:32:38 +00:00
|
|
|
.BR clone ()
|
|
|
|
should not be called through vsyscall, but directly through
|
|
|
|
.IR "int $0x80" .
|
2006-12-04 05:25:49 +00:00
|
|
|
|
2007-07-08 16:06:51 +00:00
|
|
|
On ia64, a different system call is used:
|
2006-12-04 05:25:49 +00:00
|
|
|
.nf
|
|
|
|
|
2007-06-19 20:09:36 +00:00
|
|
|
.BI "int __clone2(int (*" "fn" ")(void *), "
|
|
|
|
.BI " void *" child_stack_base ", size_t " stack_size ,
|
|
|
|
.BI " int " flags ", void *" "arg" ", ... "
|
2009-06-21 13:02:21 +00:00
|
|
|
.BI " /* pid_t *" ptid ", struct user_desc *" tls \
|
2006-12-04 05:25:49 +00:00
|
|
|
", pid_t *" ctid " */ );"
|
|
|
|
.fi
|
|
|
|
.PP
|
|
|
|
The
|
2007-06-19 20:09:36 +00:00
|
|
|
.BR __clone2 ()
|
2007-04-12 22:42:49 +00:00
|
|
|
system call operates in the same way as
|
2006-12-04 05:25:49 +00:00
|
|
|
.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 .
|
2005-04-12 08:11:06 +00:00
|
|
|
.SH BUGS
|
|
|
|
Versions of the GNU C library that include the NPTL threading library
|
2007-04-12 22:42:49 +00:00
|
|
|
contain a wrapper function for
|
2007-05-11 23:07:02 +00:00
|
|
|
.BR getpid (2)
|
2005-04-12 08:11:06 +00:00
|
|
|
that performs caching of PIDs.
|
2008-09-23 03:04:49 +00:00
|
|
|
This caching relies on support in the glibc wrapper for
|
|
|
|
.BR clone (),
|
|
|
|
but as currently implemented,
|
|
|
|
the cache may not be up to date in some circumstances.
|
|
|
|
In particular,
|
|
|
|
if a signal is delivered to the child immediately after the
|
|
|
|
.BR clone ()
|
|
|
|
call, then a call to
|
|
|
|
.BR getpid ()
|
|
|
|
in a handler for the signal may return the PID
|
|
|
|
of the calling process ("the parent"),
|
2008-11-18 21:21:47 +00:00
|
|
|
if the clone wrapper has not yet had a chance to update the PID
|
2008-09-23 03:04:49 +00:00
|
|
|
cache in the child.
|
|
|
|
(This discussion ignores the case where the child was created using
|
2008-09-25 07:50:14 +00:00
|
|
|
.BR CLONE_THREAD ,
|
2008-09-23 03:04:49 +00:00
|
|
|
when
|
|
|
|
.BR getpid ()
|
|
|
|
.I should
|
|
|
|
return the same value in the child and in the process that called
|
|
|
|
.BR clone (),
|
2008-09-23 04:55:29 +00:00
|
|
|
since the caller and the child are in the same thread group.
|
2008-09-23 04:58:51 +00:00
|
|
|
The stale-cache problem also does not occur if the
|
2008-09-23 04:55:29 +00:00
|
|
|
.I flags
|
|
|
|
argument includes
|
|
|
|
.BR CLONE_VM .)
|
2008-09-23 03:04:49 +00:00
|
|
|
To get the truth, it may be necessary to use code such as the following:
|
2005-04-12 08:11:06 +00:00
|
|
|
.nf
|
|
|
|
|
|
|
|
#include <syscall.h>
|
|
|
|
|
|
|
|
pid_t mypid;
|
|
|
|
|
|
|
|
mypid = syscall(SYS_getpid);
|
|
|
|
.fi
|
2008-09-23 03:04:49 +00:00
|
|
|
.\" See also the following bug reports
|
|
|
|
.\" https://bugzilla.redhat.com/show_bug.cgi?id=417521
|
|
|
|
.\" http://sourceware.org/bugzilla/show_bug.cgi?id=6910
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH "SEE ALSO"
|
|
|
|
.BR fork (2),
|
2005-04-11 15:03:38 +00:00
|
|
|
.BR futex (2),
|
2004-11-03 13:51:07 +00:00
|
|
|
.BR getpid (2),
|
|
|
|
.BR gettid (2),
|
2005-04-11 15:10:47 +00:00
|
|
|
.BR set_thread_area (2),
|
2005-04-11 15:03:38 +00:00
|
|
|
.BR set_tid_address (2),
|
2005-04-11 15:10:47 +00:00
|
|
|
.BR tkill (2),
|
2006-03-20 21:29:29 +00:00
|
|
|
.BR unshare (2),
|
2004-11-03 13:51:07 +00:00
|
|
|
.BR wait (2),
|
2005-06-07 12:35:32 +00:00
|
|
|
.BR capabilities (7),
|
|
|
|
.BR pthreads (7)
|