NAME | SYNOPSIS | DESCRIPTION | OPTIONS | NOTES | EXAMPLES | SEE ALSO | AUTHORS | AVAILABILITY | COLOPHON

UNSHARE(1)                      User Commands                     UNSHARE(1)

NAME         top

       unshare - run program with some namespaces unshared from parent

SYNOPSIS         top

       unshare [options] [program [arguments]]

DESCRIPTION         top

       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         top

       -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) 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).

       -V, --version
              Display version information and exit.

       -h, --help
              Display help text and exit.

NOTES         top

       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         top

       # 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         top

       clone(2), unshare(2), namespaces(7), mount(8)

AUTHORS         top

       Mikhail Gusarov ⟨dottedmag@dottedmag.net⟩
       Karel Zak ⟨kzak@redhat.com⟩

AVAILABILITY         top

       The unshare command is part of the util-linux package and is
       available from https://www.kernel.org/pub/linux/utils/util-linux/.

COLOPHON         top

       This page is part of the util-linux (a random collection of Linux
       utilities) project.  Information about the project can be found at 
       ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.  If you have a
       bug report for this manual page, send it to
       util-linux@vger.kernel.org.  This page was obtained from the
       project's upstream Git repository 
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2017-09-15.  If you discover any rendering problems in this HTML ver‐
       sion of the page, or you believe there is a better or more up-to-date
       source for the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original man‐
       ual page), send a mail to man-pages@man7.org

util-linux                      February 2016                     UNSHARE(1)

Pages that refer to this page: unshare(2)cgroup_namespaces(7)mount_namespaces(7)namespaces(7)findmnt(8)lsns(8)