UNSHARE(1) User Commands UNSHARE(1)
NAME
unshare - run program with some namespaces unshared from parent
SYNOPSIS
unshare [options] [program [arguments]]
DESCRIPTION
Unshares the indicated namespaces from the parent process and then exe-
cutes 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 propa-
gation 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 discus-
sion 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 rout-
ing tables, firewall rules, the /proc/net and /sys/class/net
directory trees, sockets, etc. For further details, see names-
paces(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 capabili-
ties. For further details, see user_namespaces(7) and the dis-
cussion of the CLONE_NEWUSER flag in clone(2).
OPTIONS
-i, --ipc[=file]
Unshare the IPC namespace. If file is specified, then a persis-
tent namespace is created by a bind mount.
-m, --mount[=file]
Unshare the mount namespace. If file is specified, then a per-
sistent 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 persis-
tent namespace is created by a bind mount.
-U, --user[=file]
Unshare the user namespace. If file is specified, then a per-
sistent namespace is created by a bind mount.
-C, --cgroup[=file]
Unshare the cgroup namespace. If file is specified then persis-
tent 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.
--kill-child[=signame]
When unshare terminates, have signame be sent to the forked
child process. Combined with --pid this allows for an easy and
reliable killing of the entire process tree below unshare. If
not given, signame defaults to SIGKILL. This option implies
--fork.
--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 names-
pace since the /proc mount would otherwise mess up existing pro-
grams 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 net-
work 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 --set-
groups=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 names-
pace (--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 restric-
tion 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 unpriv-
ileged processes when setgroups(2) is permanently disabled (with
deny).
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.
NOTES
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.
EXAMPLES
# 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 solu-
tion, because it makes sure that the bind mount is created on a
shared filesystem.
# unshare -pf --kill-child -- bash -c (sleep 999 &) && sleep 1000 &
# pid=$!
# kill $pid
Reliable killing of subprocesses of the program. When unshare
gets killed, everything below it gets killed as well. Without
it, the children of program would have orphaned and been re-par-
ented to PID 1.
SEE ALSO
clone(2), unshare(2), namespaces(7), mount(8)
AUTHORS
Mikhail Gusarov <dottedmag AT dottedmag.net>
Karel Zak <kzak AT redhat.com>
AVAILABILITY
The unshare command is part of the util-linux package and is available
from https://www.kernel.org/pub/linux/utils/util-linux/.
util-linux February 2016 UNSHARE(1)
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