unshare


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 con-
       text 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 exe-
       cution 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  automati-
              cally  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
              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 call-
              ing 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 con-
              text 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 particu-
       lar, as at kernel 3.8, unshare() does not implement flags that  reverse
       the  effects  of  CLONE_SIGHAND, CLONE_THREAD, or CLONE_VM.  Such func-
       tionality 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 3.54 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/.



Linux                             2013-04-17                        UNSHARE(2)
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