unshare Man page

Resume Wikipedia de Cgroups

cgroups (control groups) est une fonctionnalité du noyau Linux pour limiter, compter et isoler l’utilisation des ressources (processeur, mémoire, utilisation disque, etc.).
Ce travail a été initié par des ingénieurs de Google (d’abord Paul Menage et Rohit Seth) en 2006 sous le nom « conteneur de processus» ; à la fin 2007, il a été renommé Control Groups (à cause de la confusion causée par les différentes significations du terme « conteneur » dans le noyau Linux) et intégré à la version 2.6.24 du noyau Linux. Depuis lors, de nombreuses nouvelles fonctionnalités et contrôleurs ont été ajoutés.

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.

The namespaces can optionally be persisted by bind mounting
/proc/[pid]/ns/[type] files to a filesystem path and entered with nsen‐
ter(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 propa‐
gation 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 mes‐
sage queues, semaphore sets and shared memory segments.
(CLONE_NEWIPC flag)

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. (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 capabili‐
ties. (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 persis‐
tent namespace is created by bind mount.

-n, –net[=file] Unshare the network namespace. If file is specified then persis‐
tent 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 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 (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 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 sets mount propagation flag in the new mount names‐
pace. 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 syscall in user namespaces.

setgroups 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 until after GID map has been set. The GID
map is writable by root when setgroups is enabled and GID map
becomes writable by unprivileged processes when setgroups 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.

SEE ALSO

unshare, 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/.

util-linux July 2014 UNSHARE(1)