unshare - Online in the Cloud

PROGRAM:

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 persisted by bind mounting /proc/[pid]/ns/[type] files to
a filesystem path and entered with nsenter(1) even after program terminates. Once a
persistent namespace is no longer needed it can be unpersisted with umount(8). See
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
the new mount namespace to make sure that the new namespace is really unshared.
This feature is possible to disable by 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)

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 persistent namespace is
created by bind mount.

-m, --mount[=file]
Unshare the mount namespace. If file is specified then persistent namespace is
created by bind mount.

-n, --net[=file]
Unshare the network namespace. If file is specified then persistent namespace is
created by bind mount.

-p, --pid[=file]
Unshare the pid namespace. If file is specified then persistent namespace is
created by bind mount. See also the --fork and --mount-proc options.

-u, --uts[=file]
Unshare the UTS namespace. If file is specified then persistent namespace is
created by bind mount.

-U, --user[=file]
Unshare the user 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 (by 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 sets mount propagation flag in the new mount namespace. The default is
to set the propagation to private, this feature is possible to disable by unchanged
argument. The options is silently ignored when mount namespace (--mount) is not
requested.

--setgroups allow|deny
Allow or deny setgroups(2) syscall in user namespaces.

setgroups(2) is only callable with CAP_SETGID and CAP_SETGID in a user namespace
(since Linux 3.19) does not give you permission to call setgroups(2) until after
GID map has been set. The GID map is writable by root when setgroups(2) is enabled
and GID map becomes writable by unprivileged processes when setgroups(2) is
permanently disabled.

-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 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 hostanme FOO
# nsenter --uts=/root/uts-ns hostname
FOO
# umount /root/uts-ns
Establish a persistent UTS namespace, modify hostname. The namespace maybe later
entered by nsenter. The namespace is destroyed by umount the bind reference.

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