| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
UNSHARE(2) Linux Programmer's Manual UNSHARE(2)
unshare - disassociate parts of the process execution context
#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 */
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 (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.
On success, zero returned. On failure, -1 is returned and errno is
set to indicate the error.
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.
The unshare() system call was added to Linux in kernel 2.6.16.
The unshare() system call is Linux-specific.
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.
clone(2), fork(2), kcmp(2), setns(2), vfork(2)
Documentation/unshare.txt in the Linux kernel source tree
This page is part of release 3.51 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 2013-04-17 UNSHARE(2)
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