NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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

NAME         top

       unshare - disassociate parts of the process execution context

SYNOPSIS         top

       #include <sched.h>

       int unshare(int flags);

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

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

DESCRIPTION         top

       unshare() allows a process to disassociate parts of its execution
       context that are currently being shared with other processes.  Part
       of the execution context, such as the mount namespace, is shared
       implicitly when a new process is created using fork(2) or vfork(2),
       while other parts, such as virtual memory, may be shared by explicit
       request when creating a process using clone(2).

       The main use of unshare() is to allow a process to control its shared
       execution context without creating a new process.

       The flags argument is a bit mask that specifies which parts of the
       execution context should be unshared.  This argument is specified by
       ORing together zero or more of the following constants:

       CLONE_FILES
              Reverse the effect of the clone(2) CLONE_FILES flag.  Unshare
              the file descriptor table, so that the calling process no
              longer shares its file descriptors with any other process.

       CLONE_FS
              Reverse the effect of the clone(2) CLONE_FS flag.  Unshare
              filesystem attributes, so that the calling process no longer
              shares its root directory (chroot(2)), current directory
              (chdir(2)), or umask (umask(2)) attributes with any other
              process.

       CLONE_NEWIPC (since Linux 2.6.19)
              This flag has the same effect as the clone(2) CLONE_NEWIPC
              flag.  Unshare the System V IPC namespace, so that the calling
              process has a private copy of the System V IPC namespace which
              is not shared with any other process.  Specifying this flag
              automatically implies CLONE_SYSVSEM as well.  Use of
              CLONE_NEWIPC requires the CAP_SYS_ADMIN capability.

       CLONE_NEWNET (since Linux 2.6.24)
              This flag has the same effect as the clone(2) CLONE_NEWNET
              flag.  Unshare the network namespace, so that the calling
              process is moved into a new network namespace which is not
              shared with any previously existing process.  Use of
              CLONE_NEWNET requires the CAP_SYS_ADMIN capability.

       CLONE_NEWNS
              This flag has the same effect as the clone(2) CLONE_NEWNS
              flag.  Unshare the mount namespace, so that the calling
              process has a private copy of its namespace which is not
              shared with any other process.  Specifying this flag
              automatically implies CLONE_FS as well.  Use of CLONE_NEWNS
              requires the CAP_SYS_ADMIN capability.

       CLONE_NEWUTS (since Linux 2.6.19)
              This flag has the same effect as the clone(2) CLONE_NEWUTS
              flag.  Unshare the UTS IPC namespace, so that the calling
              process has a private copy of the UTS namespace which is not
              shared with any other process.  Use of CLONE_NEWUTS requires
              the CAP_SYS_ADMIN capability.

       CLONE_SYSVSEM (since Linux 2.6.26)
              This flag reverses the effect of the clone(2) CLONE_SYSVSEM
              flag.  Unshare System V semaphore undo values, so that the
              calling process has a private copy which is not shared with
              any other process.  Use of CLONE_SYSVSEM requires the
              CAP_SYS_ADMIN capability.

       If flags is specified as zero, then unshare() is a no-op; no changes
       are made to the calling process's execution context.

RETURN VALUE         top

       On success, zero returned.  On failure, -1 is returned and errno is
       set to indicate the error.

ERRORS         top

       EINVAL An invalid bit was specified in flags.

       ENOMEM Cannot allocate sufficient memory to copy parts of caller's
              context that need to be unshared.

       EPERM  The calling process did not have the required privileges for
              this operation.

VERSIONS         top

       The unshare() system call was added to Linux in kernel 2.6.16.

CONFORMING TO         top

       The unshare() system call is Linux-specific.

NOTES         top

       Not all of the process attributes that can be shared when a new
       process is created using clone(2) can be unshared using unshare().
       In particular, as at kernel 3.8, unshare() does not implement flags
       that reverse the effects of CLONE_SIGHAND, CLONE_THREAD, or CLONE_VM.
       Such functionality may be added in the future, if required.

SEE ALSO         top

       clone(2), fork(2), kcmp(2), setns(2), vfork(2)

       Documentation/unshare.txt in the Linux kernel source tree

COLOPHON         top

       This page is part of release 3.71 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                            2013-04-17                       UNSHARE(2)