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



NAME
       unshare - disassociate parts of the process execution context

SYNOPSIS
       #define _GNU_SOURCE
       #include <&lt;sched.h>&gt;

       int unshare(int flags);

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 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 file
              system attributes, so that the calling process no longer  shares
              its  root directory, current directory, or umask attributes with
              any other process.  chroot(2), chdir(2), or umask(2)

       CLONE_NEWNS
              This flag has the same effect as the clone(2) CLONE_NEWNS  flag.
              Unshare the 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.

       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  flags  specified  CLONE_NEWNS  but  the  calling process was not
              privileged (did not have the CAP_SYS_ADMIN capability).

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 2.6.16,  unshare()  does  not  implement  flags  that
       reverse  the  effects of CLONE_SIGHAND, CLONE_SYSVSEM, CLONE_THREAD, or
       CLONE_VM.  Such functionality may be added in the future, if required.

SEE ALSO
       clone(2), fork(2), vfork(2), Documentation/unshare.txt

COLOPHON
       This page is part of release 3.05 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                             2007-07-26                        UNSHARE(2)