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 ⟨dottedmag@dottedmag.net⟩
Karel Zak ⟨kzak@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/.