• NAME
  
  unshare - disassociate parts of the process execution context
• SYNOPSIS
  

  
   #define _GNU_SOURCE
  
  
   #include <sched.h>
  
   int unshare(int  flags );
  

• DESCRIPTION
  
  unshare ()
  allows a process to disassociate parts of its execution
  context 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 execution 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 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.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  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
  context 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 particular, 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 3.19 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/.
  

Current Users: 31 © 1999-2009 PenguinSoft. All trademarks and copyrights on this page are owned by their respective companies. Linux is a trademark of Linus Torvalds.