Provided by: util-linux_2.34-0.1ubuntu9.6_amd64 
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 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).
OPTIONS
-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.
--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 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).
-R,--root=dir
run the command with root directory set to dir.
-w,--wd=dir
change working directory to dir.
-S,--setuid uid
Set the user ID which will be used in the entered namespace.
-G,--setgid gid
Set the group ID which will be used in the entered namespace and drop supplementary groups.
-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 solution, 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-parented
to PID 1.
SEE ALSO
clone(2), unshare(2), namespaces(7), mount(8)
AUTHORS
Mikhail Gusarov
Karel Zak
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)