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CLONE(2)                  Linux Programmer's Manual                 CLONE(2)

NAME         top

       clone, __clone2 - create a child process

SYNOPSIS         top

       /* Prototype for the glibc wrapper function */

       #include <sched.h>

       int clone(int (*fn)(void *), void *child_stack,
                 int flags, void *arg, ...
                 /* pid_t *ptid, struct user_desc *tls, pid_t *ctid */ );

       /* Prototype for the raw system call */

       long clone(unsigned long flags, void *child_stack,
                 void *ptid, void *ctid,
                 struct pt_regs *regs);

   Feature Test Macro Requirements for glibc wrapper function (see
   feature_test_macros(7)):

       clone():
           Since glibc 2.14:
               _GNU_SOURCE
           Before glibc 2.14:
               _BSD_SOURCE || _SVID_SOURCE
                   /* _GNU_SOURCE also suffices */

DESCRIPTION         top

       clone() creates a new process, in a manner similar to fork(2).

       This page describes both the glibc clone() wrapper function and the
       underlying system call on which it is based.  The main text describes
       the wrapper function; the differences for the raw system call are
       described toward the end of this page.

       Unlike fork(2), clone() allows the child process to share parts of
       its execution context with the calling process, such as the memory
       space, the table of file descriptors, and the table of signal
       handlers.  (Note that on this manual page, "calling process" normally
       corresponds to "parent process".  But see the description of
       CLONE_PARENT below.)

       The main use of clone() is to implement threads: multiple threads of
       control in a program that run concurrently in a shared memory space.

       When the child process is created with clone(), it executes the
       function fn(arg).  (This differs from fork(2), where execution
       continues in the child from the point of the fork(2) call.)  The fn
       argument is a pointer to a function that is called by the child
       process at the beginning of its execution.  The arg argument is
       passed to the fn function.

       When the fn(arg) function application returns, the child process
       terminates.  The integer returned by fn is the exit code for the
       child process.  The child process may also terminate explicitly by
       calling exit(2) or after receiving a fatal signal.

       The child_stack argument specifies the location of the stack used by
       the child process.  Since the child and calling process may share
       memory, it is not possible for the child process to execute in the
       same stack as the calling process.  The calling process must
       therefore set up memory space for the child stack and pass a pointer
       to this space to clone().  Stacks grow downward on all processors
       that run Linux (except the HP PA processors), so child_stack usually
       points to the topmost address of the memory space set up for the
       child stack.

       The low byte of flags contains the number of the termination signal
       sent to the parent when the child dies.  If this signal is specified
       as anything other than SIGCHLD, then the parent process must specify
       the __WALL or __WCLONE options when waiting for the child with
       wait(2).  If no signal is specified, then the parent process is not
       signaled when the child terminates.

       flags may also be bitwise-or'ed with zero or more of the following
       constants, in order to specify what is shared between the calling
       process and the child process:

       CLONE_CHILD_CLEARTID (since Linux 2.5.49)
              Erase child thread ID at location ctid in child memory when
              the child exits, and do a wakeup on the futex at that address.
              The address involved may be changed by the set_tid_address(2)
              system call.  This is used by threading libraries.

       CLONE_CHILD_SETTID (since Linux 2.5.49)
              Store child thread ID at location ctid in child memory.

       CLONE_FILES (since Linux 2.0)
              If CLONE_FILES is set, the calling process and the child
              process share the same file descriptor table.  Any file
              descriptor created by the calling process or by the child
              process is also valid in the other process.  Similarly, if one
              of the processes closes a file descriptor, or changes its
              associated flags (using the fcntl(2) F_SETFD operation), the
              other process is also affected.

              If CLONE_FILES is not set, the child process inherits a copy
              of all file descriptors opened in the calling process at the
              time of clone().  (The duplicated file descriptors in the
              child refer to the same open file descriptions (see open(2))
              as the corresponding file descriptors in the calling process.)
              Subsequent operations that open or close file descriptors, or
              change file descriptor flags, performed by either the calling
              process or the child process do not affect the other process.

       CLONE_FS (since Linux 2.0)
              If CLONE_FS is set, the caller and the child process share the
              same filesystem information.  This includes the root of the
              filesystem, the current working directory, and the umask.  Any
              call to chroot(2), chdir(2), or umask(2) performed by the
              calling process or the child process also affects the other
              process.

              If CLONE_FS is not set, the child process works on a copy of
              the filesystem information of the calling process at the time
              of the clone() call.  Calls to chroot(2), chdir(2), umask(2)
              performed later by one of the processes do not affect the
              other process.

       CLONE_IO (since Linux 2.6.25)
              If CLONE_IO is set, then the new process shares an I/O context
              with the calling process.  If this flag is not set, then (as
              with fork(2)) the new process has its own I/O context.

              The I/O context is the I/O scope of the disk scheduler (i.e,
              what the I/O scheduler uses to model scheduling of a process's
              I/O).  If processes share the same I/O context, they are
              treated as one by the I/O scheduler.  As a consequence, they
              get to share disk time.  For some I/O schedulers, if two
              processes share an I/O context, they will be allowed to
              interleave their disk access.  If several threads are doing
              I/O on behalf of the same process (aio_read(3), for instance),
              they should employ CLONE_IO to get better I/O performance.

              If the kernel is not configured with the CONFIG_BLOCK option,
              this flag is a no-op.

       CLONE_NEWIPC (since Linux 2.6.19)
              If CLONE_NEWIPC is set, then create the process in a new IPC
              namespace.  If this flag is not set, then (as with fork(2)),
              the process is created in the same IPC namespace as the
              calling process.  This flag is intended for the implementation
              of containers.

              An IPC namespace provides an isolated view of System V IPC
              objects (see svipc(7)) and (since Linux 2.6.30) POSIX message
              queues (see mq_overview(7)).  The common characteristic of
              these IPC mechanisms is that IPC objects are identified by
              mechanisms other than filesystem pathnames.

              Objects created in an IPC namespace are visible to all other
              processes that are members of that namespace, but are not
              visible to processes in other IPC namespaces.

              When an IPC namespace is destroyed (i.e., when the last
              process that is a member of the namespace terminates), all IPC
              objects in the namespace are automatically destroyed.

              Only a privileged process (CAP_SYS_ADMIN) can employ
              CLONE_NEWIPC.  This flag can't be specified in conjunction
              with CLONE_SYSVSEM.

              For further information on IPC namespaces, see namespaces(7).

       CLONE_NEWNET (since Linux 2.6.24)
              (The implementation of this flag was completed only by about
              kernel version 2.6.29.)

              If CLONE_NEWNET is set, then create the process in a new
              network namespace.  If this flag is not set, then (as with
              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
              /proc/net and /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.

              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).  For further information on network
              namespaces, see namespaces(7).

              Only a privileged process (CAP_SYS_ADMIN) can employ
              CLONE_NEWNET.

       CLONE_NEWNS (since Linux 2.4.19)
              If CLONE_NEWNS is set, the cloned child is started in a new
              mount namespace, initialized with a copy of the namespace of
              the parent.  If CLONE_NEWNS is not set, the child lives in the
              same mount namespace as the parent.

              For further information on mount namespaces, see
              namespaces(7).

              Only a privileged process (CAP_SYS_ADMIN) can employ
              CLONE_NEWNS.  It is not permitted to specify both CLONE_NEWNS
              and CLONE_FS in the same clone() call.

       CLONE_NEWPID (since Linux 2.6.24)
              If CLONE_NEWPID is set, then create the process in a new PID
              namespace.  If this flag is not set, then (as with fork(2))
              the process is created in the same PID namespace as the
              calling process.  This flag is intended for the implementation
              of containers.

              For further information on PID namespaces, see namespaces(7)
              and pid_namespaces(7)

              Only a privileged process (CAP_SYS_ADMIN) can employ
              CLONE_NEWPID.  This flag can't be specified in conjunction
              with CLONE_THREAD or CLONE_PARENT.

       CLONE_NEWUSER
              (This flag first became meaningful for clone() in Linux
              2.6.23, the current clone() semantics were merged in Linux
              3.5, and the final pieces to make the user namespaces
              completely usable were merged in Linux 3.8.)

              If CLONE_NEWUSER is set, then create the process in a new user
              namespace.  If this flag is not set, then (as with fork(2))
              the process is created in the same user namespace as the
              calling process.

              For further information on user namespaces, see namespaces(7)
              and user_namespaces(7)

              Before Linux 3.8, use of CLONE_NEWUSER required that the
              caller have three capabilities: CAP_SYS_ADMIN, CAP_SETUID, and
              CAP_SETGID.  Starting with Linux 3.8, no privileges are needed
              to create a user namespace.

              This flag can't be specified in conjunction with CLONE_THREAD
              or CLONE_PARENT.  For security reasons, CLONE_NEWUSER cannot
              be specified in conjunction with CLONE_FS.

              For further information on user namespaces, see
              user_namespaces(7).

       CLONE_NEWUTS (since Linux 2.6.19)
              If CLONE_NEWUTS 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.
              If this flag is not set, then (as with fork(2)) the process is
              created in the same UTS namespace as the calling process.
              This flag is intended for the implementation of containers.

              A UTS namespace is the set of identifiers returned by
              uname(2); among these, the domain name and the hostname can be
              modified by setdomainname(2) and sethostname(2), respectively.
              Changes made to the identifiers in a UTS namespace are visible
              to all other processes in the same namespace, but are not
              visible to processes in other UTS namespaces.

              Only a privileged process (CAP_SYS_ADMIN) can employ
              CLONE_NEWUTS.

              For further information on UTS namespaces, see namespaces(7).

       CLONE_PARENT (since Linux 2.3.12)
              If CLONE_PARENT is set, then the parent of the new child (as
              returned by getppid(2)) will be the same as that of the
              calling process.

              If CLONE_PARENT is not set, then (as with fork(2)) the child's
              parent is the calling process.

              Note that it is the parent process, as returned by getppid(2),
              which is signaled when the child terminates, so that if
              CLONE_PARENT is set, then the parent of the calling process,
              rather than the calling process itself, will be signaled.

       CLONE_PARENT_SETTID (since Linux 2.5.49)
              Store child thread ID at location ptid in parent and child
              memory.  (In Linux 2.5.32-2.5.48 there was a flag CLONE_SETTID
              that did this.)

       CLONE_PID (obsolete)
              If 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.

       CLONE_PTRACE (since Linux 2.2)
              If CLONE_PTRACE is specified, and the calling process is being
              traced, then trace the child also (see ptrace(2)).

       CLONE_SETTLS (since Linux 2.5.32)
              The newtls argument is the new TLS (Thread Local Storage)
              descriptor.  (See set_thread_area(2).)

       CLONE_SIGHAND (since Linux 2.0)
              If CLONE_SIGHAND is set, the calling process and the child
              process share the same table of signal handlers.  If the
              calling process or child process calls sigaction(2) to change
              the behavior associated with a signal, the behavior is changed
              in the other process as well.  However, the calling process
              and child processes still have distinct signal masks and sets
              of pending signals.  So, one of them may block or unblock some
              signals using sigprocmask(2) without affecting the other
              process.

              If CLONE_SIGHAND is not set, the child process inherits a copy
              of the signal handlers of the calling process at the time
              clone() is called.  Calls to sigaction(2) performed later by
              one of the processes have no effect on the other process.

              Since Linux 2.6.0-test6, flags must also include CLONE_VM if
              CLONE_SIGHAND is specified

       CLONE_STOPPED (since Linux 2.6.0-test2)
              If CLONE_STOPPED is set, then the child is initially stopped
              (as though it was sent a SIGSTOP signal), and must be resumed
              by sending it a SIGCONT signal.

              This flag was deprecated from Linux 2.6.25 onward, and was
              removed altogether in Linux 2.6.38.

       CLONE_SYSVSEM (since Linux 2.5.10)
              If CLONE_SYSVSEM is set, then the child and the calling
              process share a single list of System V semaphore adjustment
              (semadj) values (see semop(2)).  In this case, the shared list
              accumulates semadj values across all processes sharing the
              list, and semaphore adjustments are performed only when the
              last process that is sharing the list terminates (or ceases
              sharing the list using unshare(2)).  If this flag is not set,
              then the child has a separate semadj list that is initially
              empty.

       CLONE_THREAD (since Linux 2.4.0-test8)
              If CLONE_THREAD is set, the child is placed in the same thread
              group as the calling process.  To make the remainder of the
              discussion of CLONE_THREAD more readable, the term "thread" is
              used to refer to the processes within a thread group.

              Thread groups were a feature added in Linux 2.4 to support the
              POSIX threads notion of a set of threads that share a single
              PID.  Internally, this shared PID is the so-called thread
              group identifier (TGID) for the thread group.  Since Linux
              2.4, calls to getpid(2) return the TGID of the caller.

              The threads within a group can be distinguished by their
              (system-wide) unique thread IDs (TID).  A new thread's TID is
              available as the function result returned to the caller of
              clone(), and a thread can obtain its own TID using gettid(2).

              When a call is made to clone() without specifying
              CLONE_THREAD, then the resulting thread is placed in a new
              thread group whose TGID is the same as the thread's TID.  This
              thread is the leader of the new thread group.

              A new thread created with CLONE_THREAD has the same parent
              process as the caller of clone() (i.e., like CLONE_PARENT), so
              that calls to getppid(2) return the same value for all of the
              threads in a thread group.  When a CLONE_THREAD thread
              terminates, the thread that created it using clone() is not
              sent a SIGCHLD (or other termination) signal; nor can the
              status of such a thread be obtained using wait(2).  (The
              thread is said to be detached.)

              After all of the threads in a thread group terminate the
              parent process of the thread group is sent a SIGCHLD (or other
              termination) signal.

              If any of the threads in a thread group performs an execve(2),
              then all threads other than the thread group leader are
              terminated, and the new program is executed in the thread
              group leader.

              If one of the threads in a thread group creates a child using
              fork(2), then any thread in the group can wait(2) for that
              child.

              Since Linux 2.5.35, flags must also include CLONE_SIGHAND if
              CLONE_THREAD is specified (and note that, since Linux
              2.6.0-test6, CLONE_SIGHAND also requires CLONE_VM to be
              included).

              Signals may be sent to a thread group as a whole (i.e., a
              TGID) using kill(2), or to a specific thread (i.e., TID) using
              tgkill(2).

              Signal dispositions and actions are process-wide: if an
              unhandled signal is delivered to a thread, then it will affect
              (terminate, stop, continue, be ignored in) all members of the
              thread group.

              Each thread has its own signal mask, as set by sigprocmask(2),
              but signals can be pending either: for the whole process
              (i.e., deliverable to any member of the thread group), when
              sent with kill(2); or for an individual thread, when sent with
              tgkill(2).  A call to sigpending(2) returns a signal set that
              is the union of the signals pending for the whole process and
              the signals that are pending for the calling thread.

              If kill(2) is used to send a signal to a thread group, and the
              thread group has installed a handler for the signal, then the
              handler will be invoked in exactly one, arbitrarily selected
              member of the thread group that has not blocked the signal.
              If multiple threads in a group are waiting to accept the same
              signal using sigwaitinfo(2), the kernel will arbitrarily
              select one of these threads to receive a signal sent using
              kill(2).

       CLONE_UNTRACED (since Linux 2.5.46)
              If CLONE_UNTRACED is specified, then a tracing process cannot
              force CLONE_PTRACE on this child process.

       CLONE_VFORK (since Linux 2.2)
              If CLONE_VFORK is set, the execution of the calling process is
              suspended until the child releases its virtual memory
              resources via a call to execve(2) or _exit(2) (as with
              vfork(2)).

              If 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.

       CLONE_VM (since Linux 2.0)
              If 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 mmap(2) or munmap(2) by
              the child or calling process also affects the other process.

              If 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
              clone().  Memory writes or file mappings/unmappings performed
              by one of the processes do not affect the other, as with
              fork(2).

   C library/kernel ABI differences
       The raw clone() system call corresponds more closely to fork(2) in
       that execution in the child continues from the point of the call.  As
       such, the fn and arg arguments of the clone() wrapper function are
       omitted.  Furthermore, the argument order changes.  The raw system
       call interface on x86 and many other architectures is roughly:

           long clone(unsigned long flags, void *child_stack,
                      void *ptid, void *ctid,
                      struct pt_regs *regs);

       Another difference for the raw system call is that the child_stack
       argument may be zero, in which case copy-on-write semantics ensure
       that the child gets separate copies of stack pages when either
       process modifies the stack.  In this case, for correct operation, the
       CLONE_VM option should not be specified.

       For some architectures, the order of the arguments for the system
       call differs from that shown above.  On the score, microblaze, ARM,
       ARM 64, PA-RISC, arc, Power PC, xtensa, and MIPS architectures, the
       order of the fourth and fifth arguments is reversed.  On the cris and
       s390 architectures, the order of the first and second arguments is
       reversed.

   blackfin, m68k, and sparc
       The argument-passing conventions on blackfin, m68k, and sparc are
       different from the descriptions above.  For details, see the kernel
       (and glibc) source.

   ia64
       On ia64, a different interface is used:

       int __clone2(int (*fn)(void *),
                    void *child_stack_base, size_t stack_size,
                    int flags, void *arg, ...
                 /* pid_t *ptid, struct user_desc *tls, pid_t *ctid */ );

       The prototype shown above is for the glibc wrapper function; the raw
       system call interface has no fn or arg argument, and changes the
       order of the arguments so that flags is the first argument, and tls
       is the last argument.

       __clone2() operates in the same way as clone(), except that
       child_stack_base points to the lowest address of the child's stack
       area, and stack_size specifies the size of the stack pointed to by
       child_stack_base.

   Linux 2.4 and earlier
       In Linux 2.4 and earlier, clone() does not take arguments ptid, tls,
       and ctid.

RETURN VALUE         top

       On success, the thread ID of the child process is returned in the
       caller's thread of execution.  On failure, -1 is returned in the
       caller's context, no child process will be created, and errno will be
       set appropriately.

ERRORS         top

       EAGAIN Too many processes are already running; see fork(2).

       EINVAL CLONE_SIGHAND was specified, but CLONE_VM was not.  (Since
              Linux 2.6.0-test6.)

       EINVAL CLONE_THREAD was specified, but CLONE_SIGHAND was not.  (Since
              Linux 2.5.35.)

       EINVAL Both CLONE_FS and CLONE_NEWNS were specified in flags.

       EINVAL (since Linux 3.9)
              Both CLONE_NEWUSER and CLONE_FS were specified in flags.

       EINVAL Both CLONE_NEWIPC and CLONE_SYSVSEM were specified in flags.

       EINVAL One (or both) of CLONE_NEWPID or CLONE_NEWUSER and one (or
              both) of CLONE_THREAD or CLONE_PARENT were specified in flags.

       EINVAL Returned by clone() when a zero value is specified for
              child_stack.

       EINVAL CLONE_NEWIPC was specified in flags, but the kernel was not
              configured with the CONFIG_SYSVIPC and CONFIG_IPC_NS options.

       EINVAL CLONE_NEWNET was specified in flags, but the kernel was not
              configured with the CONFIG_NET_NS option.

       EINVAL CLONE_NEWPID was specified in flags, but the kernel was not
              configured with the CONFIG_PID_NS option.

       EINVAL CLONE_NEWUTS was specified in flags, but the kernel was not
              configured with the CONFIG_UTS option.

       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.

       EPERM  CLONE_NEWIPC, CLONE_NEWNET, CLONE_NEWNS, CLONE_NEWPID, or
              CLONE_NEWUTS was specified by an unprivileged process (process
              without CAP_SYS_ADMIN).

       EPERM  CLONE_PID was specified by a process other than process 0.

       EPERM  CLONE_NEWUSER was specified in flags, but either the effective
              user ID or the effective group ID of the caller does not have
              a mapping in the parent namespace (see user_namespaces(7)).

       EPERM (since Linux 3.9)
              CLONE_NEWUSER was specified in flags and the caller is in a
              chroot environment (i.e., the caller's root directory does not
              match the root directory of the mount namespace in which it
              resides).

       EUSERS (since Linux 3.11)
              CLONE_NEWUSER was specified in flags, and the call would cause
              the limit on the number of nested user namespaces to be
              exceeded.  See user_namespaces(7).

VERSIONS         top

       There is no entry for clone() in libc5.  glibc2 provides clone() as
       described in this manual page.

CONFORMING TO         top

       clone() is Linux-specific and should not be used in programs intended
       to be portable.

NOTES         top

       In the kernel 2.4.x series, 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
       CLONE_THREAD flag implied the CLONE_PARENT flag (as in kernel 2.6).

       For a while there was CLONE_DETACHED (introduced in 2.5.32): parent
       wants no child-exit signal.  In 2.6.2 the need to give this together
       with CLONE_THREAD disappeared.  This flag is still defined, but has
       no effect.

       On i386, clone() should not be called through vsyscall, but directly
       through int $0x80.

BUGS         top

       Versions of the GNU C library that include the NPTL threading library
       contain a wrapper function for getpid(2) that performs caching of
       PIDs.  This caching relies on support in the glibc wrapper for
       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 clone() call, then a call to
       getpid(2) in a handler for the signal may return the PID of the
       calling process ("the parent"), if the clone wrapper has not yet had
       a chance to update the PID cache in the child.  (This discussion
       ignores the case where the child was created using CLONE_THREAD, when
       getpid(2) should return the same value in the child and in the
       process that called clone(), since the caller and the child are in
       the same thread group.  The stale-cache problem also does not occur
       if the flags argument includes CLONE_VM.)  To get the truth, it may
       be necessary to use code such as the following:

           #include <syscall.h>

           pid_t mypid;

           mypid = syscall(SYS_getpid);

EXAMPLE         top

       The following program demonstrates the use of clone() to create a
       child process that executes in a separate UTS namespace.  The child
       changes the hostname in its UTS namespace.  Both parent and child
       then display the system hostname, making it possible to see that the
       hostname differs in the UTS namespaces of the parent and child.  For
       an example of the use of this program, see setns(2).

   Program source
       #define _GNU_SOURCE
       #include <sys/wait.h>
       #include <sys/utsname.h>
       #include <sched.h>
       #include <string.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                               } while (0)

       static int              /* Start function for cloned child */
       childFunc(void *arg)
       {
           struct utsname uts;

           /* Change hostname in UTS namespace of child */

           if (sethostname(arg, strlen(arg)) == -1)
               errExit("sethostname");

           /* Retrieve and display hostname */

           if (uname(&uts) == -1)
               errExit("uname");
           printf("uts.nodename in child:  %s\n", uts.nodename);

           /* Keep the namespace open for a while, by sleeping.
              This allows some experimentation--for example, another
              process might join the namespace. */

           sleep(200);

           return 0;           /* Child terminates now */
       }

       #define STACK_SIZE (1024 * 1024)    /* Stack size for cloned child */

       int
       main(int argc, char *argv[])
       {
           char *stack;                    /* Start of stack buffer */
           char *stackTop;                 /* End of stack buffer */
           pid_t pid;
           struct utsname uts;

           if (argc < 2) {
               fprintf(stderr, "Usage: %s <child-hostname>\n", argv[0]);
               exit(EXIT_SUCCESS);
           }

           /* Allocate stack for child */

           stack = malloc(STACK_SIZE);
           if (stack == NULL)
               errExit("malloc");
           stackTop = stack + STACK_SIZE;  /* Assume stack grows downward */

           /* Create child that has its own UTS namespace;
              child commences execution in childFunc() */

           pid = clone(childFunc, stackTop, CLONE_NEWUTS | SIGCHLD, argv[1]);
           if (pid == -1)
               errExit("clone");
           printf("clone() returned %ld\n", (long) pid);

           /* Parent falls through to here */

           sleep(1);           /* Give child time to change its hostname */

           /* Display hostname in parent's UTS namespace. This will be
              different from hostname in child's UTS namespace. */

           if (uname(&uts) == -1)
               errExit("uname");
           printf("uts.nodename in parent: %s\n", uts.nodename);

           if (waitpid(pid, NULL, 0) == -1)    /* Wait for child */
               errExit("waitpid");
           printf("child has terminated\n");

           exit(EXIT_SUCCESS);
       }

SEE ALSO         top

       fork(2), futex(2), getpid(2), gettid(2), kcmp(2), set_thread_area(2),
       set_tid_address(2), setns(2), tkill(2), unshare(2), wait(2),
       capabilities(7), namespaces(7), pthreads(7)

COLOPHON         top

       This page is part of release 3.73 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       http://www.kernel.org/doc/man-pages/.

Linux                            2014-09-21                         CLONE(2)