UNSHARE
Section: Linux Programmer's Manual (2)
Updated: 2013-04-17
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NAME
unshare - disassociate parts of the process execution context
SYNOPSIS
#include <sched.h>
int unshare(int flags);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
unshare():
-
- Since glibc 2.14:
-
_GNU_SOURCE
-
-
Before glibc 2.14:
_BSD_SOURCE || _SVID_SOURCE
/* _GNU_SOURCE also suffices */
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 filesystem attributes, so that the calling process
no longer shares its root directory
(chroot(2)),
current directory
(chdir(2)),
or umask
(umask(2))
attributes with any other process.
- 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 automatically 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.
Use of
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.
- CLONE_NEWUTS (since Linux 2.6.19)
-
This flag has the same effect as the
clone(2)
CLONE_NEWUTS
flag.
Unshare the UTS IPC namespace,
so that the calling process has a private copy of the
UTS namespace which is not shared with any other process.
Use of
CLONE_NEWUTS
requires the
CAP_SYS_ADMIN
capability.
- CLONE_SYSVSEM (since Linux 2.6.26)
-
This flag reverses the effect of the
clone(2)
CLONE_SYSVSEM
flag.
Unshare System V semaphore undo values,
so that the calling process has a private copy
which is not shared with any other process.
Use of
CLONE_SYSVSEM
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
context 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 particular, as at kernel 3.8,
unshare()
does not implement flags that reverse the effects of
CLONE_SIGHAND,
CLONE_THREAD,
or
CLONE_VM.
Such functionality may be added in the future, if required.
SEE ALSO
clone(2),
fork(2),
kcmp(2),
setns(2),
vfork(2)
Documentation/unshare.txt
in the Linux kernel source tree
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
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Time: 02:54:46 GMT, September 18, 2014