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

       unshare - disassociate parts of the process execution context

       #define _GNU_SOURCE
       #include <sched.h>

       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 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:

	      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  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

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

       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 3.22 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				  2008-11-20			    UNSHARE(2)

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