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CentOS 7.0 - man page for unshare (centos section 2)

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

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 cur-
       rently 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 fol-
       lowing 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 (chroot(2)), cur-
	      rent 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  Sys-
	      tem 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  net-
	      work  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 call-
       ing 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 3.53 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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