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

NAME

       unshare - disassociate parts of the process execution context

SYNOPSIS

       define _GNU_SOURCE	      /* See feature_test_macros(7) */
       #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 pri-
	      vate 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 par-
       ticular, 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 3.27 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								    2010-09-10								UNSHARE(2)