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NAME

       unshare - disassociate parts of the process execution context

SYNOPSIS

       #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

       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

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

ERRORS

       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

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

CONFORMING TO

       The unshare() system call is Linux-specific.

NOTES

       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

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

       Documentation/unshare.txt in the Linux kernel source tree

COLOPHON

       This page is part of release 3.65 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



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