unshare


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 con-
       text 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 exe-
       cution 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_NEWIPC (since Linux 2.6.19)
              This flag has the same effect as the clone(2) CLONE_NEWIPC flag.
              Unshare  the System 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 automati-
              cally  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 network namespace, so that the  calling  process  is
              moved  into a new network namespace which is not shared with any
              previously  existing   process.    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.
              other process.  Use of CLONE_NEWUTS requires  the  CAP_SYS_ADMIN
              capability.

       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 con-
              text 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 particu-
       lar,  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 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.



Linux                             2010-10-30                        UNSHARE(2)
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