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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

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       description of the project, and information about reporting  bugs,  can
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