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



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  pro-
              cess.  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 execu-
       tion 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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-11-20                        UNSHARE(2)