Manpage of CLONE

CLONE

Section: Linux Programmer's Manual (2)
Updated: 2016-07-17
Index
 

NAME

clone, __clone2 - create a child process  

SYNOPSIS

/* Prototype for the glibc wrapper function */

#define _GNU_SOURCE#include <sched.h>int clone(int (*fn)(void *), void *child_stack,          int flags, void *arg, ...           /* pid_t *ptid, void *newtls, pid_t *ctid */ );/* For the prototype of the raw system call, see NOTES */
 

DESCRIPTION

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_PARENTbelow.)

One 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 fnargument is a pointer to a function that is called by the child process at the beginning of its execution. The argargument is passed to the fnfunction.

When the fn(arg) function application returns, the child process terminates. The integer returned by fnis 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_stackargument 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_stackusually points to the topmost address of the memory space set up for the child stack.

The low byte of flagscontains the number of the termination signalsent to the parent when the child dies. If this signal is specified as anything other than SIGCHLD, then the parent process must specify the __WALLor __WCLONEoptions when waiting for the child with wait(2). If no signal is specified, then the parent process is not signaled when the child terminates.

flagsmay 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 the child thread ID at the location ctidin 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 the child thread ID at the location ctidin the child's memory.
CLONE_FILES (since Linux 2.0)
If CLONE_FILESis 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_SETFDoperation), the other process is also affected. If a process sharing a file descriptor table calls execve(2), its file descriptor table is duplicated (unshared).

If CLONE_FILESis not set, the child process inherits a copy of all file descriptors opened in the calling process at the time of clone(). 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. Note, however, that the duplicated file descriptors in the child refer to the same open file descriptions as the corresponding file descriptors in the calling process, and thus share file offsets and files status flags (see open(2)).

CLONE_FS (since Linux 2.0)
If CLONE_FSis 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_FSis 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_IOis 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_IOto get better I/O performance.

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

CLONE_NEWCGROUP (since Linux 4.6)
Create the process in a new cgroup namespace. If this flag is not set, then (as with fork(2)) the process is created in the same cgroup namespaces as the calling process. This flag is intended for the implementation of containers.

For further information on cgroup namespaces, see cgroup_namespaces(7).

Only a privileged process (CAP_SYS_ADMIN) can employ CLONE_NEWCGROUP.

CLONE_NEWIPC (since Linux 2.6.19)
If CLONE_NEWIPCis 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_NEWNETis 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/netand /sys/class/netdirectory 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_NEWNSis set, the cloned child is started in a new mount namespace, initialized with a copy of the namespace of the parent. If CLONE_NEWNSis not set, the child lives in the same mount namespace as the parent.

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

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

CLONE_NEWPID (since Linux 2.6.24)
If CLONE_NEWPIDis 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_THREADor 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_NEWUSERis 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_NEWUSERrequired 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_THREADor CLONE_PARENT. For security reasons, CLONE_NEWUSERcannot 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_NEWUTSis 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_PARENTis 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_PARENTis 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_PARENTis 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 the child thread ID at the location ptidin the parent's memory. (In Linux 2.5.32-2.5.48 there was a flag CLONE_SETTIDthat did this.)
CLONE_PID (obsolete)
If CLONE_PIDis 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. Since then, the kernel silently ignores it without error.
CLONE_PTRACE (since Linux 2.2)
If CLONE_PTRACEis specified, and the calling process is being traced, then trace the child also (see ptrace(2)).
CLONE_SETTLS (since Linux 2.5.32)
The TLS (Thread Local Storage) descriptor is set to newtls.

The interpretation of newtlsand the resulting effect is architecture dependent. On x86, newtlsis interpreted as a struct user_desc *(See set_thread_area(2)). On x86_64 it is the new value to be set for the %fs base register (See the ARCH_SET_FSargument to arch_prctl(2)). On architectures with a dedicated TLS register, it is the new value of that register.

CLONE_SIGHAND (since Linux 2.0)
If CLONE_SIGHANDis 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_SIGHANDis 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, flagsmust also include CLONE_VMif CLONE_SIGHANDis specified

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

This flag was deprecatedfrom Linux 2.6.25 onward, and was removedaltogether in Linux 2.6.38. Since then, the kernel silently ignores it without error. Starting with Linux 4.6, the same bit was reused for the CLONE_NEWCGROUPflag.

CLONE_SYSVSEM (since Linux 2.5.10)
If CLONE_SYSVSEMis 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 semadjvalues 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 semadjlist that is initially empty.
CLONE_THREAD (since Linux 2.4.0-test8)
If CLONE_THREADis set, the child is placed in the same thread group as the calling process. To make the remainder of the discussion of CLONE_THREADmore 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 leaderof the new thread group.

A new thread created with CLONE_THREADhas 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_THREADthread 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, flagsmust also include CLONE_SIGHANDif CLONE_THREADis specified (and note that, since Linux 2.6.0-test6, CLONE_SIGHANDalso requires CLONE_VMto 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_UNTRACEDis specified, then a tracing process cannot force CLONE_PTRACEon this child process.
CLONE_VFORK (since Linux 2.2)
If CLONE_VFORKis 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_VFORKis 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_VMis 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_VMis 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 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 fnand argarguments of the clone() wrapper function are omitted. Furthermore, the argument order changes. In addition, there are variations across architectures.

The raw system call interface on x86-64 and some other architectures (including sh, tile, and alpha) is roughly:

long clone(unsigned long flags, void *child_stack,           int *ptid, int *ctid,           unsigned long newtls);

On x86-32, and several other common architectures (including score, ARM, ARM 64, PA-RISC, arc, Power PC, xtensa, and MIPS), the order of the last two arguments is reversed:

long clone(unsigned long flags, void *child_stack,          int *ptid, unsigned long newtls,          int *ctid);

On the cris and s390 architectures, the order of the first two arguments is reversed:

long clone(void *child_stack, unsigned long flags,           int *ptid, int *ctid,           unsigned long newtls);

On the microblaze architecture, an additional argument is supplied:

long clone(unsigned long flags, void *child_stack,           int stack_size,         /* Size of stack */
           int *ptid, int *ctid,           unsigned long newtls);

Another difference for the raw system call is that the child_stackargument 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_VMoption should not be specified.  

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 fnor argargument, and changes the order of the arguments so that flagsis the first argument, and tlsis the last argument.

__clone2() operates in the same way as clone(), except that child_stack_basepoints to the lowest address of the child's stack area, and stack_sizespecifies 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

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 errnowill be set appropriately.  

ERRORS

EAGAIN
Too many processes are already running; see fork(2).
EINVAL
CLONE_SIGHANDwas specified, but CLONE_VMwas not. (Since Linux 2.6.0-test6.)
EINVAL
CLONE_THREADwas specified, but CLONE_SIGHANDwas not. (Since Linux 2.5.35.)
EINVAL
Both CLONE_FSand CLONE_NEWNSwere specified in flags.
EINVAL (since Linux 3.9)
Both CLONE_NEWUSERand CLONE_FSwere specified in flags.
EINVAL
Both CLONE_NEWIPCand CLONE_SYSVSEMwere specified in flags.
EINVAL
One (or both) of CLONE_NEWPIDor CLONE_NEWUSERand one (or both) of CLONE_THREADor CLONE_PARENTwere specified in flags.
EINVAL
Returned by the glibc clone() wrapper function when fnor child_stackis specified as NULL.
EINVAL
CLONE_NEWIPCwas specified in flags, but the kernel was not configured with the CONFIG_SYSVIPCand CONFIG_IPC_NSoptions.
EINVAL
CLONE_NEWNETwas specified in flags, but the kernel was not configured with the CONFIG_NET_NSoption.
EINVAL
CLONE_NEWPIDwas specified in flags, but the kernel was not configured with the CONFIG_PID_NSoption.
EINVAL
CLONE_NEWUTSwas specified in flags, but the kernel was not configured with the CONFIG_UTSoption.
EINVAL
child_stackis not aligned to a suitable boundary for this architecture. For example, on aarch64, child_stackmust be a multiple of 16.
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_NEWUTSwas specified by an unprivileged process (process without CAP_SYS_ADMIN).
EPERM
CLONE_PIDwas specified by a process other than process 0.
EPERM
CLONE_NEWUSERwas 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_NEWUSERwas specified in flagsand 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).
ERESTARTNOINTR (since Linux 2.6.17)
System call was interrupted by a signal and will be restarted. (This can be seen only during a trace.)
EUSERS (since Linux 3.11)
CLONE_NEWUSERwas 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

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

CONFORMING TO

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

NOTES

The kcmp(2) system call can be used to test whether two processes share various resources such as a file descriptor table, System V semaphore undo operations, or a virtual address space.

In the kernel 2.4.x series, CLONE_THREADgenerally 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_THREADflag implied the CLONE_PARENTflag (as in kernel 2.6).

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

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

BUGS

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) shouldreturn 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 flagsargument 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

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 parentaqs UTS namespace. This will be
       different from hostname in childaqs 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

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)


 

Index

NAME
SYNOPSIS
DESCRIPTION
C library/kernel differences
blackfin, m68k, and sparc
ia64
Linux 2.4 and earlier
RETURN VALUE
ERRORS
VERSIONS
CONFORMING TO
NOTES
BUGS
EXAMPLE
Program source
SEE ALSO

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