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UNSHARE(2)		   Linux Programmers Manual		   UNSHARE(2)

       unshare - disassociate parts of the process execution context

       #define _GNU_SOURCE

       int unshare(int flags);

       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:

	      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.

	      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)

	      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  pro
	      cess.   Specifying  this	flag automatically implies CLONE_FS as

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

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

       EINVAL An invalid bit was specified in flags.

       ENOMEM Cannot allocate sufficient memory to copy parts of callers 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).

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

       The unshare() system call is Linux-specific.

       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.

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

       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)

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