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 executes the specified program. 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. 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 (CLONE_NEWNS flag), 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). 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. (CLONE_NEWUTS flag) IPC namespace The process will have an independent namespace for System V message queues, semaphore sets and shared memory segments. (CLONE_NEWIPC flag) 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. (CLONE_NEWNET flag) pid namespace Children will have a distinct set of PID-to-process mappings from their parent. (CLONE_NEWPID flag) 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. (CLONE_NEWCGROUP flag) user namespace The process will have a distinct set of UIDs, GIDs and capabilities. (CLONE_NEWUSER flag) See clone(2) for the exact semantics of the flags.
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.
--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) syscall 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.
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.
SEE ALSO
unshare(2), clone(2), 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 ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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