1 .\" Copyright (c) 1992 Drew Eckhardt <drew@cs.colorado.edu>, March 28, 1992
2 .\" and Copyright (c) Michael Kerrisk, 2001, 2002, 2005, 2013
4 .\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
5 .\" May be distributed under the GNU General Public License.
8 .\" Modified by Michael Haardt <michael@moria.de>
9 .\" Modified 24 Jul 1993 by Rik Faith <faith@cs.unc.edu>
10 .\" Modified 21 Aug 1994 by Michael Chastain <mec@shell.portal.com>:
11 .\" New man page (copied from 'fork.2').
12 .\" Modified 10 June 1995 by Andries Brouwer <aeb@cwi.nl>
13 .\" Modified 25 April 1998 by Xavier Leroy <Xavier.Leroy@inria.fr>
14 .\" Modified 26 Jun 2001 by Michael Kerrisk
15 .\" Mostly upgraded to 2.4.x
16 .\" Added prototype for sys_clone() plus description
17 .\" Added CLONE_THREAD with a brief description of thread groups
18 .\" Added CLONE_PARENT and revised entire page remove ambiguity
19 .\" between "calling process" and "parent process"
20 .\" Added CLONE_PTRACE and CLONE_VFORK
21 .\" Added EPERM and EINVAL error codes
22 .\" Renamed "__clone" to "clone" (which is the prototype in <sched.h>)
23 .\" various other minor tidy ups and clarifications.
24 .\" Modified 26 Jun 2001 by Michael Kerrisk <mtk.manpages@gmail.com>
25 .\" Updated notes for 2.4.7+ behavior of CLONE_THREAD
26 .\" Modified 15 Oct 2002 by Michael Kerrisk <mtk.manpages@gmail.com>
27 .\" Added description for CLONE_NEWNS, which was added in 2.4.19
28 .\" Slightly rephrased, aeb.
29 .\" Modified 1 Feb 2003 - added CLONE_SIGHAND restriction, aeb.
30 .\" Modified 1 Jan 2004 - various updates, aeb
31 .\" Modified 2004-09-10 - added CLONE_PARENT_SETTID etc. - aeb.
32 .\" 2005-04-12, mtk, noted the PID caching behavior of NPTL's getpid()
33 .\" wrapper under BUGS.
34 .\" 2005-05-10, mtk, added CLONE_SYSVSEM, CLONE_UNTRACED, CLONE_STOPPED.
35 .\" 2005-05-17, mtk, Substantially enhanced discussion of CLONE_THREAD.
36 .\" 2008-11-18, mtk, order CLONE_* flags alphabetically
37 .\" 2008-11-18, mtk, document CLONE_NEWPID
38 .\" 2008-11-19, mtk, document CLONE_NEWUTS
39 .\" 2008-11-19, mtk, document CLONE_NEWIPC
40 .\" 2008-11-19, Jens Axboe, mtk, document CLONE_IO
42 .TH CLONE 2 2014-09-21 "Linux" "Linux Programmer's Manual"
44 clone, __clone2 \- create a child process
47 /* Prototype for the glibc wrapper function */
51 .BI "int clone(int (*" "fn" ")(void *), void *" child_stack ,
52 .BI " int " flags ", void *" "arg" ", ... "
53 .BI " /* pid_t *" ptid ", struct user_desc *" tls \
54 ", pid_t *" ctid " */ );"
56 /* Prototype for the raw system call */
58 .BI "long clone(unsigned long " flags ", void *" child_stack ,
59 .BI " void *" ptid ", void *" ctid ,
60 .BI " struct pt_regs *" regs );
64 Feature Test Macro Requirements for glibc wrapper function (see
65 .BR feature_test_macros (7)):
76 .\" See http://sources.redhat.com/bugzilla/show_bug.cgi?id=4749
78 _BSD_SOURCE || _SVID_SOURCE
79 /* _GNU_SOURCE also suffices */
85 creates a new process, in a manner similar to
88 This page describes both the glibc
90 wrapper function and the underlying system call on which it is based.
91 The main text describes the wrapper function;
92 the differences for the raw system call
93 are described toward the end of this page.
98 allows the child process to share parts of its execution context with
99 the calling process, such as the memory space, the table of file
100 descriptors, and the table of signal handlers.
101 (Note that on this manual
102 page, "calling process" normally corresponds to "parent process".
103 But see the description of
109 is to implement threads: multiple threads of control in a program that
110 run concurrently in a shared memory space.
112 When the child process is created with
114 it executes the function
118 where execution continues in the child from the point
124 argument is a pointer to a function that is called by the child
125 process at the beginning of its execution.
128 argument is passed to the
134 function application returns, the child process terminates.
135 The integer returned by
137 is the exit code for the child process.
138 The child process may also terminate explicitly by calling
140 or after receiving a fatal signal.
144 argument specifies the location of the stack used by the child process.
145 Since the child and calling process may share memory,
146 it is not possible for the child process to execute in the
147 same stack as the calling process.
148 The calling process must therefore
149 set up memory space for the child stack and pass a pointer to this
152 Stacks grow downward on all processors that run Linux
153 (except the HP PA processors), so
155 usually points to the topmost address of the memory space set up for
160 contains the number of the
161 .I "termination signal"
162 sent to the parent when the child dies.
163 If this signal is specified as anything other than
165 then the parent process must specify the
169 options when waiting for the child with
171 If no signal is specified, then the parent process is not signaled
172 when the child terminates.
175 may also be bitwise-or'ed with zero or more of the following constants,
176 in order to specify what is shared between the calling process
177 and the child process:
179 .BR CLONE_CHILD_CLEARTID " (since Linux 2.5.49)"
180 Erase child thread ID at location
182 in child memory when the child exits, and do a wakeup on the futex
184 The address involved may be changed by the
185 .BR set_tid_address (2)
187 This is used by threading libraries.
189 .BR CLONE_CHILD_SETTID " (since Linux 2.5.49)"
190 Store child thread ID at location
194 .BR CLONE_FILES " (since Linux 2.0)"
197 is set, the calling process and the child process share the same file
199 Any file descriptor created by the calling process or by the child
200 process is also valid in the other process.
201 Similarly, if one of the processes closes a file descriptor,
202 or changes its associated flags (using the
205 operation), the other process is also affected.
209 is not set, the child process inherits a copy of all file descriptors
210 opened in the calling process at the time of
212 (The duplicated file descriptors in the child refer to the
213 same open file descriptions (see
215 as the corresponding file descriptors in the calling process.)
216 Subsequent operations that open or close file descriptors,
217 or change file descriptor flags,
218 performed by either the calling
219 process or the child process do not affect the other process.
221 .BR CLONE_FS " (since Linux 2.0)"
224 is set, the caller and the child process share the same filesystem
226 This includes the root of the filesystem, the current
227 working directory, and the umask.
233 performed by the calling process or the child process also affects the
238 is not set, the child process works on a copy of the filesystem
239 information of the calling process at the time of the
246 performed later by one of the processes do not affect the other process.
248 .BR CLONE_IO " (since Linux 2.6.25)"
251 is set, then the new process shares an I/O context with
253 If this flag is not set, then (as with
255 the new process has its own I/O context.
257 .\" The following based on text from Jens Axboe
258 The I/O context is the I/O scope of the disk scheduler (i.e,
259 what the I/O scheduler uses to model scheduling of a process's I/O).
260 If processes share the same I/O context,
261 they are treated as one by the I/O scheduler.
262 As a consequence, they get to share disk time.
263 For some I/O schedulers,
264 .\" the anticipatory and CFQ scheduler
265 if two processes share an I/O context,
266 they will be allowed to interleave their disk access.
267 If several threads are doing I/O on behalf of the same process
269 for instance), they should employ
271 to get better I/O performance.
274 If the kernel is not configured with the
276 option, this flag is a no-op.
278 .BR CLONE_NEWIPC " (since Linux 2.6.19)"
281 is set, then create the process in a new IPC namespace.
282 If this flag is not set, then (as with
284 the process is created in the same IPC namespace as
286 This flag is intended for the implementation of containers.
288 An IPC namespace provides an isolated view of System\ V IPC objects (see
290 and (since Linux 2.6.30)
291 .\" commit 7eafd7c74c3f2e67c27621b987b28397110d643f
292 .\" https://lwn.net/Articles/312232/
295 .BR mq_overview (7)).
296 The common characteristic of these IPC mechanisms is that IPC
297 objects are identified by mechanisms other than filesystem
300 Objects created in an IPC namespace are visible to all other processes
301 that are members of that namespace,
302 but are not visible to processes in other IPC namespaces.
304 When an IPC namespace is destroyed
305 (i.e., when the last process that is a member of the namespace terminates),
306 all IPC objects in the namespace are automatically destroyed.
308 Only a privileged process
309 .RB ( CAP_SYS_ADMIN )
312 This flag can't be specified in conjunction with
315 For further information on IPC namespaces, see
318 .BR CLONE_NEWNET " (since Linux 2.6.24)"
319 (The implementation of this flag was completed only
320 by about kernel version 2.6.29.)
324 is set, then create the process in a new network namespace.
325 If this flag is not set, then (as with
327 the process is created in the same network namespace as
329 This flag is intended for the implementation of containers.
331 A network namespace provides an isolated view of the networking stack
332 (network device interfaces, IPv4 and IPv6 protocol stacks,
333 IP routing tables, firewall rules, the
337 directory trees, sockets, etc.).
338 A physical network device can live in exactly one
340 A virtual network device ("veth") pair provides a pipe-like abstraction
341 .\" FIXME . Add pointer to veth(4) page when it is eventually completed
342 that can be used to create tunnels between network namespaces,
343 and can be used to create a bridge to a physical network device
344 in another namespace.
346 When a network namespace is freed
347 (i.e., when the last process in the namespace terminates),
348 its physical network devices are moved back to the
349 initial network namespace (not to the parent of the process).
350 For further information on network namespaces, see
353 Only a privileged process
354 .RB ( CAP_SYS_ADMIN )
358 .BR CLONE_NEWNS " (since Linux 2.4.19)"
361 is set, the cloned child is started in a new mount namespace,
362 initialized with a copy of the namespace of the parent.
365 is not set, the child lives in the same mount
366 namespace as the parent.
368 For further information on mount namespaces, see
371 Only a privileged process
372 .RB ( CAP_SYS_ADMIN )
375 It is not permitted to specify both
379 .\" See https://lwn.net/Articles/543273/
384 .BR CLONE_NEWPID " (since Linux 2.6.24)"
385 .\" This explanation draws a lot of details from
386 .\" http://lwn.net/Articles/259217/
387 .\" Authors: Pavel Emelyanov <xemul@openvz.org>
388 .\" and Kir Kolyshkin <kir@openvz.org>
390 .\" The primary kernel commit is 30e49c263e36341b60b735cbef5ca37912549264
391 .\" Author: Pavel Emelyanov <xemul@openvz.org>
394 is set, then create the process in a new PID namespace.
395 If this flag is not set, then (as with
397 the process is created in the same PID namespace as
399 This flag is intended for the implementation of containers.
401 For further information on PID namespaces, see
404 .BR pid_namespaces (7)
406 Only a privileged process
407 .RB ( CAP_SYS_ADMIN )
410 This flag can't be specified in conjunction with
416 (This flag first became meaningful for
421 semantics were merged in Linux 3.5,
422 and the final pieces to make the user namespaces completely usable were
423 merged in Linux 3.8.)
427 is set, then create the process in a new user namespace.
428 If this flag is not set, then (as with
430 the process is created in the same user namespace as the calling process.
432 For further information on user namespaces, see
435 .BR user_namespaces (7)
437 Before Linux 3.8, use of
439 required that the caller have three capabilities:
444 .\" Before Linux 2.6.29, it appears that only CAP_SYS_ADMIN was needed
445 Starting with Linux 3.8,
446 no privileges are needed to create a user namespace.
448 This flag can't be specified in conjunction with
452 For security reasons,
453 .\" commit e66eded8309ebf679d3d3c1f5820d1f2ca332c71
454 .\" https://lwn.net/Articles/543273/
455 .\" The fix actually went into 3.9 and into 3.8.3. However, user namespaces
456 .\" were, for practical purposes, unusable in earlier 3.8.x because of the
457 .\" various filesystems that didn't support userns.
459 cannot be specified in conjunction with
462 For further information on user namespaces, see
463 .BR user_namespaces (7).
465 .BR CLONE_NEWUTS " (since Linux 2.6.19)"
468 is set, then create the process in a new UTS namespace,
469 whose identifiers are initialized by duplicating the identifiers
470 from the UTS namespace of the calling process.
471 If this flag is not set, then (as with
473 the process is created in the same UTS namespace as
475 This flag is intended for the implementation of containers.
477 A UTS namespace is the set of identifiers returned by
479 among these, the domain name and the hostname can be modified by
480 .BR setdomainname (2)
484 Changes made to the identifiers in a UTS namespace
485 are visible to all other processes in the same namespace,
486 but are not visible to processes in other UTS namespaces.
488 Only a privileged process
489 .RB ( CAP_SYS_ADMIN )
493 For further information on UTS namespaces, see
496 .BR CLONE_PARENT " (since Linux 2.3.12)"
499 is set, then the parent of the new child (as returned by
501 will be the same as that of the calling process.
505 is not set, then (as with
507 the child's parent is the calling process.
509 Note that it is the parent process, as returned by
511 which is signaled when the child terminates, so that
514 is set, then the parent of the calling process, rather than the
515 calling process itself, will be signaled.
517 .BR CLONE_PARENT_SETTID " (since Linux 2.5.49)"
518 Store child thread ID at location
520 in parent and child memory.
521 (In Linux 2.5.32-2.5.48 there was a flag
525 .BR CLONE_PID " (obsolete)"
528 is set, the child process is created with the same process ID as
530 This is good for hacking the system, but otherwise
532 Since 2.3.21 this flag can be
533 specified only by the system boot process (PID 0).
534 It disappeared in Linux 2.5.16.
536 .BR CLONE_PTRACE " (since Linux 2.2)"
539 is specified, and the calling process is being traced,
540 then trace the child also (see
543 .BR CLONE_SETTLS " (since Linux 2.5.32)"
546 argument is the new TLS (Thread Local Storage) descriptor.
548 .BR set_thread_area (2).)
550 .BR CLONE_SIGHAND " (since Linux 2.0)"
553 is set, the calling process and the child process share the same table of
555 If the calling process or child process calls
557 to change the behavior associated with a signal, the behavior is
558 changed in the other process as well.
559 However, the calling process and child
560 processes still have distinct signal masks and sets of pending
562 So, one of them may block or unblock some signals using
564 without affecting the other process.
568 is not set, the child process inherits a copy of the signal handlers
569 of the calling process at the time
574 performed later by one of the processes have no effect on the other
577 Since Linux 2.6.0-test6,
585 .BR CLONE_STOPPED " (since Linux 2.6.0-test2)"
588 is set, then the child is initially stopped (as though it was sent a
590 signal), and must be resumed by sending it a
596 from Linux 2.6.25 onward,
599 altogether in Linux 2.6.38.
600 .\" glibc 2.8 removed this defn from bits/sched.h
602 .BR CLONE_SYSVSEM " (since Linux 2.5.10)"
605 is set, then the child and the calling process share
606 a single list of System V semaphore adjustment
610 In this case, the shared list accumulates
612 values across all processes sharing the list,
613 and semaphore adjustments are performed only when the last process
614 that is sharing the list terminates (or ceases sharing the list using
616 If this flag is not set, then the child has a separate
618 list that is initially empty.
620 .BR CLONE_THREAD " (since Linux 2.4.0-test8)"
623 is set, the child is placed in the same thread group as the calling process.
624 To make the remainder of the discussion of
626 more readable, the term "thread" is used to refer to the
627 processes within a thread group.
629 Thread groups were a feature added in Linux 2.4 to support the
630 POSIX threads notion of a set of threads that share a single PID.
631 Internally, this shared PID is the so-called
632 thread group identifier (TGID) for the thread group.
633 Since Linux 2.4, calls to
635 return the TGID of the caller.
637 The threads within a group can be distinguished by their (system-wide)
638 unique thread IDs (TID).
639 A new thread's TID is available as the function result
640 returned to the caller of
642 and a thread can obtain
646 When a call is made to
650 then the resulting thread is placed in a new thread group
651 whose TGID is the same as the thread's TID.
654 of the new thread group.
656 A new thread created with
658 has the same parent process as the caller of
664 return the same value for all of the threads in a thread group.
667 thread terminates, the thread that created it using
671 (or other termination) signal;
672 nor can the status of such a thread be obtained
675 (The thread is said to be
678 After all of the threads in a thread group terminate
679 the parent process of the thread group is sent a
681 (or other termination) signal.
683 If any of the threads in a thread group performs an
685 then all threads other than the thread group leader are terminated,
686 and the new program is executed in the thread group leader.
688 If one of the threads in a thread group creates a child using
690 then any thread in the group can
701 (and note that, since Linux 2.6.0-test6,
707 Signals may be sent to a thread group as a whole (i.e., a TGID) using
709 or to a specific thread (i.e., TID) using
712 Signal dispositions and actions are process-wide:
713 if an unhandled signal is delivered to a thread, then
714 it will affect (terminate, stop, continue, be ignored in)
715 all members of the thread group.
717 Each thread has its own signal mask, as set by
719 but signals can be pending either: for the whole process
720 (i.e., deliverable to any member of the thread group),
723 or for an individual thread, when sent with
727 returns a signal set that is the union of the signals pending for the
728 whole process and the signals that are pending for the calling thread.
732 is used to send a signal to a thread group,
733 and the thread group has installed a handler for the signal, then
734 the handler will be invoked in exactly one, arbitrarily selected
735 member of the thread group that has not blocked the signal.
736 If multiple threads in a group are waiting to accept the same signal using
738 the kernel will arbitrarily select one of these threads
739 to receive a signal sent using
742 .BR CLONE_UNTRACED " (since Linux 2.5.46)"
745 is specified, then a tracing process cannot force
747 on this child process.
749 .BR CLONE_VFORK " (since Linux 2.2)"
752 is set, the execution of the calling process is suspended
753 until the child releases its virtual memory
754 resources via a call to
763 is not set, then both the calling process and the child are schedulable
764 after the call, and an application should not rely on execution occurring
765 in any particular order.
767 .BR CLONE_VM " (since Linux 2.0)"
770 is set, the calling process and the child process run in the same memory
772 In particular, memory writes performed by the calling process
773 or by the child process are also visible in the other process.
774 Moreover, any memory mapping or unmapping performed with
778 by the child or calling process also affects the other process.
782 is not set, the child process runs in a separate copy of the memory
783 space of the calling process at the time of
785 Memory writes or file mappings/unmappings performed by one of the
786 processes do not affect the other, as with
788 .SS C library/kernel ABI differences
791 system call corresponds more closely to
793 in that execution in the child continues from the point of the
801 wrapper function are omitted.
802 Furthermore, the argument order changes.
803 The raw system call interface on x86 and many other architectures is roughly:
807 .BI "long clone(unsigned long " flags ", void *" child_stack ,
808 .BI " void *" ptid ", void *" ctid ,
809 .BI " struct pt_regs *" regs );
813 Another difference for the raw system call is that the
815 argument may be zero, in which case copy-on-write semantics ensure that the
816 child gets separate copies of stack pages when either process modifies
818 In this case, for correct operation, the
820 option should not be specified.
822 For some architectures, the order of the arguments for the system call
823 differs from that shown above.
824 On the score, microblaze, ARM, ARM 64, PA-RISC, arc, Power PC, xtensa,
825 and MIPS architectures,
826 the order of the fourth and fifth arguments is reversed.
827 On the cris and s390 architectures,
828 the order of the first and second arguments is reversed.
829 .SS blackfin, m68k, and sparc
830 The argument-passing conventions on
831 blackfin, m68k, and sparc are different from the descriptions above.
832 For details, see the kernel (and glibc) source.
834 On ia64, a different interface is used:
837 .BI "int __clone2(int (*" "fn" ")(void *), "
838 .BI " void *" child_stack_base ", size_t " stack_size ,
839 .BI " int " flags ", void *" "arg" ", ... "
840 .BI " /* pid_t *" ptid ", struct user_desc *" tls \
841 ", pid_t *" ctid " */ );"
844 The prototype shown above is for the glibc wrapper function;
845 the raw system call interface has no
849 argument, and changes the order of the arguments so that
851 is the first argument, and
853 is the last argument.
856 operates in the same way as
860 points to the lowest address of the child's stack area,
863 specifies the size of the stack pointed to by
864 .IR child_stack_base .
865 .SS Linux 2.4 and earlier
866 In Linux 2.4 and earlier,
868 does not take arguments
874 .\" gettid(2) returns current->pid;
875 .\" getpid(2) returns current->tgid;
876 On success, the thread ID of the child process is returned
877 in the caller's thread of execution.
878 On failure, \-1 is returned
879 in the caller's context, no child process will be created, and
881 will be set appropriately.
885 Too many processes are already running; see
893 (Since Linux 2.6.0-test6.)
900 (Since Linux 2.5.35.)
904 .\" .B CLONE_DETACHED
908 .\" (Since Linux 2.6.0-test6.)
911 .\" commit e66eded8309ebf679d3d3c1f5820d1f2ca332c71
919 .BR EINVAL " (since Linux 3.9)"
950 when a zero value is specified for
957 but the kernel was not configured with the
967 but the kernel was not configured with the
975 but the kernel was not configured with the
983 but the kernel was not configured with the
988 Cannot allocate sufficient memory to allocate a task structure for the
989 child, or to copy those parts of the caller's context that need to be
999 was specified by an unprivileged process (process without \fBCAP_SYS_ADMIN\fP).
1003 was specified by a process other than process 0.
1009 but either the effective user ID or the effective group ID of the caller
1010 does not have a mapping in the parent namespace (see
1011 .BR user_namespaces (7)).
1013 .BR EPERM " (since Linux 3.9)"
1014 .\" commit 3151527ee007b73a0ebd296010f1c0454a919c7d
1015 .B CLONE_NEWUSER was specified in
1017 and the caller is in a chroot environment
1018 .\" FIXME What is the rationale for this restriction?
1019 (i.e., the caller's root directory does not match the root directory
1020 of the mount namespace in which it resides).
1022 .BR EUSERS " (since Linux 3.11)"
1026 and the call would cause the limit on the number of
1027 nested user namespaces to be exceeded.
1029 .BR user_namespaces (7).
1031 There is no entry for
1036 as described in this manual page.
1039 is Linux-specific and should not be used in programs
1040 intended to be portable.
1042 In the kernel 2.4.x series,
1044 generally does not make the parent of the new thread the same
1045 as the parent of the calling process.
1046 However, for kernel versions 2.4.7 to 2.4.18 the
1050 flag (as in kernel 2.6).
1052 For a while there was
1054 (introduced in 2.5.32):
1055 parent wants no child-exit signal.
1056 In 2.6.2 the need to give this
1060 This flag is still defined, but has no effect.
1064 should not be called through vsyscall, but directly through
1067 Versions of the GNU C library that include the NPTL threading library
1068 contain a wrapper function for
1070 that performs caching of PIDs.
1071 This caching relies on support in the glibc wrapper for
1073 but as currently implemented,
1074 the cache may not be up to date in some circumstances.
1076 if a signal is delivered to the child immediately after the
1078 call, then a call to
1080 in a handler for the signal may return the PID
1081 of the calling process ("the parent"),
1082 if the clone wrapper has not yet had a chance to update the PID
1084 (This discussion ignores the case where the child was created using
1089 return the same value in the child and in the process that called
1091 since the caller and the child are in the same thread group.
1092 The stale-cache problem also does not occur if the
1096 To get the truth, it may be necessary to use code such as the following:
1099 #include <syscall.h>
1103 mypid = syscall(SYS_getpid);
1105 .\" See also the following bug reports
1106 .\" https://bugzilla.redhat.com/show_bug.cgi?id=417521
1107 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=6910
1109 The following program demonstrates the use of
1111 to create a child process that executes in a separate UTS namespace.
1112 The child changes the hostname in its UTS namespace.
1113 Both parent and child then display the system hostname,
1114 making it possible to see that the hostname
1115 differs in the UTS namespaces of the parent and child.
1116 For an example of the use of this program, see
1121 #include <sys/wait.h>
1122 #include <sys/utsname.h>
1129 #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \\
1132 static int /* Start function for cloned child */
1133 childFunc(void *arg)
1137 /* Change hostname in UTS namespace of child */
1139 if (sethostname(arg, strlen(arg)) == \-1)
1140 errExit("sethostname");
1142 /* Retrieve and display hostname */
1144 if (uname(&uts) == \-1)
1146 printf("uts.nodename in child: %s\\n", uts.nodename);
1148 /* Keep the namespace open for a while, by sleeping.
1149 This allows some experimentation\-\-for example, another
1150 process might join the namespace. */
1154 return 0; /* Child terminates now */
1157 #define STACK_SIZE (1024 * 1024) /* Stack size for cloned child */
1160 main(int argc, char *argv[])
1162 char *stack; /* Start of stack buffer */
1163 char *stackTop; /* End of stack buffer */
1168 fprintf(stderr, "Usage: %s <child\-hostname>\\n", argv[0]);
1172 /* Allocate stack for child */
1174 stack = malloc(STACK_SIZE);
1177 stackTop = stack + STACK_SIZE; /* Assume stack grows downward */
1179 /* Create child that has its own UTS namespace;
1180 child commences execution in childFunc() */
1182 pid = clone(childFunc, stackTop, CLONE_NEWUTS | SIGCHLD, argv[1]);
1185 printf("clone() returned %ld\\n", (long) pid);
1187 /* Parent falls through to here */
1189 sleep(1); /* Give child time to change its hostname */
1191 /* Display hostname in parent\(aqs UTS namespace. This will be
1192 different from hostname in child\(aqs UTS namespace. */
1194 if (uname(&uts) == \-1)
1196 printf("uts.nodename in parent: %s\\n", uts.nodename);
1198 if (waitpid(pid, NULL, 0) == \-1) /* Wait for child */
1200 printf("child has terminated\\n");
1211 .BR set_thread_area (2),
1212 .BR set_tid_address (2),
1217 .BR capabilities (7),
1221 This page is part of release 3.75 of the Linux
1224 A description of the project,
1225 information about reporting bugs,
1226 and the latest version of this page,
1228 \%http://www.kernel.org/doc/man\-pages/.