unshare

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
       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.

       --keep-caps
              When the --user option is given, ensure that capabilities
              granted in the user namespace are preserved in the child
              process.

       --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 and --user.

       -c, --map-current-user
              Run the program only after the current effective user and group
              IDs have been mapped to the same UID and GID in the newly
              created user namespace. This option implies --setgroups=deny and
              --user.

       --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/.



util-linux                       February 2016                      UNSHARE(1)