unshare
NAME
unshare - disassociate parts of the process execution context
SYNOPSIS
#include <sched.h> I int unshare(int flags );
DESCRIPTION
R 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 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
R 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
CLONE_NEWNS
This flag has the
same
effect as the
clone(2)
CLONE_NEWNS
flag.
Unshare the 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
R 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
EPERM
flags
specified
CLONE_NEWNS
but the calling process was not privileged (did not have the
CAP_SYS_ADMIN
capability).
ENOMEM
Cannot allocate sufficient memory to copy parts of caller's
context that need to be unshared.
EINVAL
An invalid bit was specified in
R flags .
VERSIONS
The
R unshare ()
system call was added to Linux in kernel 2.6.16.
CONFORMING TO
The
R 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
R unshare ().
In particular, as at kernel 2.6.16,
R unshare ()
does not implement flags that reverse the effects of
R CLONE_SIGHAND ,
R CLONE_SYSVSEM ,
R CLONE_THREAD ,
or
R CLONE_VM .
Such functionality may be added in the future, if required.
