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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | NOTES | EXAMPLES | SEE ALSO | AUTHORS | AVAILABILITY | COLOPHON |
UNSHARE(1) User Commands UNSHARE(1)
unshare - run program with some namespaces unshared from parent
unshare [options] [program [arguments]]
Unshares the indicated namespaces from the parent process and then
executes the specified program. If program is not given, then
``${SHELL}'' is run (default: /bin/sh).
The namespaces can optionally be made persistent by bind mounting
/proc/pid/ns/type files to a filesystem path and entered with
nsenter(1) even after the program terminates (except PID namespaces
where permanently running init process is required). Once a
persistent namespace is no longer needed, it can be unpersisted with
umount(8). See the EXAMPLES section for more details.
The namespaces to be unshared are indicated via options. Unshareable
namespaces are:
mount namespace
Mounting and unmounting filesystems will not affect the rest
of the system, except for filesystems which are explicitly
marked as shared (with mount --make-shared; see
/proc/self/mountinfo or findmnt -o+PROPAGATION for the shared
flags). For further details, see mount_namespaces(7) and the
discussion of the CLONE_NEWNS flag in clone(2).
unshare since util-linux version 2.27 automatically sets
propagation to private in a new mount namespace to make sure
that the new namespace is really unshared. It's possible to
disable this feature with option --propagation unchanged.
Note that private is the kernel default.
UTS namespace
Setting hostname or domainname will not affect the rest of the
system. For further details, see namespaces(7) and the
discussion of the CLONE_NEWUTS flag in clone(2).
IPC namespace
The process will have an independent namespace for POSIX
message queues as well as System V message queues, semaphore
sets and shared memory segments. For further details, see
namespaces(7) and the discussion of the CLONE_NEWIPC flag in
clone(2).
network namespace
The process will have independent IPv4 and IPv6 stacks, IP
routing tables, firewall rules, the /proc/net and
/sys/class/net directory trees, sockets, etc. For further
details, see namespaces(7) and the discussion of the
CLONE_NEWNET flag in clone(2).
PID namespace
Children will have a distinct set of PID-to-process mappings
from their parent. For further details, see pid_namespaces(7)
and the discussion of the CLONE_NEWPID flag in clone(2).
cgroup namespace
The process will have a virtualized view of /proc/self/cgroup,
and new cgroup mounts will be rooted at the namespace cgroup
root. For further details, see cgroup_namespaces(7) and the
discussion of the CLONE_NEWCGROUP flag in clone(2).
user namespace
The process will have a distinct set of UIDs, GIDs and
capabilities. For further details, see user_namespaces(7) and
the discussion of the CLONE_NEWUSER flag in clone(2).
-i, --ipc[=file]
Unshare the IPC namespace. If file is specified, then a
persistent namespace is created by a bind mount.
-m, --mount[=file]
Unshare the mount namespace. If file is specified, then a
persistent namespace is created by a bind mount. Note that
file has to be located on a filesystem with the propagation
flag set to private. Use the command findmnt -o+PROPAGATION
when not sure about the current setting. See also the
examples below.
-n, --net[=file]
Unshare the network namespace. If file is specified, then a
persistent namespace is created by a bind mount.
-p, --pid[=file]
Unshare the PID namespace. If file is specified then
persistent namespace is created by a bind mount. See also the
--fork and --mount-proc options.
-u, --uts[=file]
Unshare the UTS namespace. If file is specified, then a
persistent namespace is created by a bind mount.
-U, --user[=file]
Unshare the user namespace. If file is specified, then a
persistent namespace is created by a bind mount.
-C, --cgroup[=file]
Unshare the cgroup namespace. If file is specified then
persistent namespace is created by bind mount.
-f, --fork
Fork the specified program as a child process of unshare
rather than running it directly. This is useful when creating
a new PID namespace.
--mount-proc[=mountpoint]
Just before running the program, mount the proc filesystem at
mountpoint (default is /proc). This is useful when creating a
new PID namespace. It also implies creating a new mount
namespace since the /proc mount would otherwise mess up
existing programs on the system. The new proc filesystem is
explicitly mounted as private (with MS_PRIVATE|MS_REC).
-r, --map-root-user
Run the program only after the current effective user and
group IDs have been mapped to the superuser UID and GID in the
newly created user namespace. This makes it possible to
conveniently gain capabilities needed to manage various
aspects of the newly created namespaces (such as configuring
interfaces in the network namespace or mounting filesystems in
the mount namespace) even when run unprivileged. As a mere
convenience feature, it does not support more sophisticated
use cases, such as mapping multiple ranges of UIDs and GIDs.
This option implies --setgroups=deny.
--propagation private|shared|slave|unchanged
Recursively set the mount propagation flag in the new mount
namespace. The default is to set the propagation to private.
It is possible to disable this feature with the argument
unchanged. The option is silently ignored when the mount
namespace (--mount) is not requested.
--setgroups allow|deny
Allow or deny the setgroups(2) system call in a user
namespace.
To be able to call setgroups(2), the calling process must at
least have CAP_SETGID. But since Linux 3.19 a further
restriction applies: the kernel gives permission to call
setgroups(2) only after the GID map (/proc/pid/gid_map) has
been set. The GID map is writable by root when setgroups(2)
is enabled (i.e. allow, the default), and the GID map becomes
writable by unprivileged processes when setgroups(2) is
permanently disabled (with deny).
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.
The proc and sysfs filesystems mounting as root in a user namespace
have to be restricted so that a less privileged user can not get more
access to sensitive files that a more privileged user made
unavailable. In short the rule for proc and sysfs is as close to a
bind mount as possible.
# unshare --fork --pid --mount-proc readlink /proc/self
1
Establish a PID namespace, ensure we're PID 1 in it against a
newly mounted procfs instance.
$ unshare --map-root-user --user sh -c whoami
root
Establish a user namespace as an unprivileged user with a root
user within it.
# touch /root/uts-ns
# unshare --uts=/root/uts-ns hostname FOO
# nsenter --uts=/root/uts-ns hostname
FOO
# umount /root/uts-ns
Establish a persistent UTS namespace, and modify the hostname.
The namespace is then entered with nsenter. The namespace is
destroyed by unmounting the bind reference.
# mount --bind /root/namespaces /root/namespaces
# mount --make-private /root/namespaces
# touch /root/namespaces/mnt
# unshare --mount=/root/namespaces/mnt
Establish a persistent mount namespace referenced by the bind
mount /root/namespaces/mnt. This example shows a portable
solution, because it makes sure that the bind mount is created
on a shared filesystem.
clone(2), unshare(2), namespaces(7), mount(8)
Mikhail Gusarov ⟨dottedmag@dottedmag.net⟩
Karel Zak ⟨kzak@redhat.com⟩
The unshare command is part of the util-linux package and is
available from https://www.kernel.org/pub/linux/utils/util-linux/.
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found at
⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
bug report for this manual page, send it to
util-linux@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2017-07-05. If you discover any rendering problems in this HTML ver‐
sion of the page, or you believe there is a better or more up-to-date
source for the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original man‐
ual page), send a mail to man-pages@man7.org
util-linux February 2016 UNSHARE(1)
Pages that refer to this page: unshare(2), cgroup_namespaces(7), mount_namespaces(7), namespaces(7), findmnt(8), lsns(8)