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 pro-
       cesses.  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  capabil-
              ity).

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_SIG-
       HAND, 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 3.25 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)