unshare(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | NOTES | EXAMPLES | AUTHORS | SEE ALSO | REPORTING BUGS | AVAILABILITY

UNSHARE(1)                    User Commands                   UNSHARE(1)

NAME         top

       unshare - run program in new namespaces

SYNOPSIS         top

       unshare [options] [program [arguments]]

DESCRIPTION         top

       The unshare command creates new namespaces (as specified by the
       command-line options described below) and then executes the
       specified program. If program is not given, then "${SHELL}" is
       run (default: /bin/sh).

       By default, a new namespace persists only as long as it has
       member processes. A new namespace can be made persistent even
       when it has no member processes by bind mounting
       /proc/pid/ns/type files to a filesystem path. A namespace that
       has been made persistent in this way can subsequently be entered
       with nsenter(1) even after the program terminates (except PID
       namespaces where a permanently running init process is required).
       Once a persistent namespace is no longer needed, it can be
       unpersisted by using umount(8) to remove the bind mount. See the
       EXAMPLES section for more details.

       unshare since util-linux version 2.36 uses
       /proc/[pid]/ns/pid_for_children and
       /proc/[pid]/ns/time_for_children files for persistent PID and
       TIME namespaces. This change requires Linux kernel 4.17 or newer.

       The following types of namespaces can be created with unshare:

       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).

           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 uts_namespaces(7).

       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
           ipc_namespaces(7).

       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 network_namespaces(7).

       PID namespace
           Children will have a distinct set of PID-to-process mappings
           from their parent. For further details, see
           pid_namespaces(7).

       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).

       user namespace
           The process will have a distinct set of UIDs, GIDs and
           capabilities. For further details, see user_namespaces(7).

       time namespace
           The process can have a distinct view of CLOCK_MONOTONIC
           and/or CLOCK_BOOTTIME which can be changed using
           /proc/self/timens_offsets. For further details, see
           time_namespaces(7).

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 must be located on a mount whose propagation type is not
           shared (or an error results). 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 a
           persistent namespace is created by a bind mount. (Creation of
           a persistent PID namespace will fail if the --fork option is
           not also specified.)

           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.

       -T, --time[=file]
           Unshare the time namespace. If file is specified, then a
           persistent namespace is created by a bind mount. The
           --monotonic and --boottime options can be used to specify the
           corresponding offset in the time namespace.

       -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. Note that when unshare is waiting for
           the child process, then it ignores SIGINT and SIGTERM and
           does not forward any signals to the child. It is necessary to
           send signals to the child process.

       --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).

       --map-user=uid|name
           Run the program only after the current effective user ID has
           been mapped to uid. If this option is specified multiple
           times, the last occurrence takes precedence. This option
           implies --user.

       --map-group=gid|name
           Run the program only after the current effective group ID has
           been mapped to gid. If this option is specified multiple
           times, the last occurrence takes precedence. This option
           implies --setgroups=deny and --user.

       -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. This option
           is equivalent to --map-user=0 --map-group=0.

       -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. This option is equivalent to
           --map-user=$(id -ru) --map-group=$(id -rg).

       --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.

       --monotonic offset
           Set the offset of CLOCK_MONOTONIC which will be used in the
           entered time namespace. This option requires unsharing a time
           namespace with --time.

       --boottime offset
           Set the offset of CLOCK_BOOTTIME which will be used in the
           entered time namespace. This option requires unsharing a time
           namespace with --time.

       -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

       The following command creates a PID namespace, using --fork to
       ensure that the executed command is performed in a child process
       that (being the first process in the namespace) has PID 1. The
       --mount-proc option ensures that a new mount namespace is also
       simultaneously created and that a new proc(5) filesystem is
       mounted that contains information corresponding to the new PID
       namespace. When the readlink command terminates, the new
       namespaces are automatically torn down.

           # unshare --fork --pid --mount-proc readlink /proc/self
           1

       As an unprivileged user, create a new user namespace where the
       user’s credentials are mapped to the root IDs inside the
       namespace:

           $ id -u; id -g
           1000
           1000
           $ unshare --user --map-root-user \
                   sh -c ''whoami; cat /proc/self/uid_map /proc/self/gid_map''
           root
                    0       1000          1
                    0       1000          1

       The first of the following commands creates a new persistent UTS
       namespace and modifies the hostname as seen in that namespace.
       The namespace is then entered with nsenter(1) in order to display
       the modified hostname; this step demonstrates that the UTS
       namespace continues to exist even though the namespace had no
       member processes after the unshare command terminated. The
       namespace is then destroyed by removing the bind mount.

           # touch /root/uts-ns
           # unshare --uts=/root/uts-ns hostname FOO
           # nsenter --uts=/root/uts-ns hostname
           FOO
           # umount /root/uts-ns

       The following commands establish a persistent mount namespace
       referenced by the bind mount /root/namespaces/mnt. In order to
       ensure that the creation of that bind mount succeeds, the parent
       directory (/root/namespaces) is made a bind mount whose
       propagation type is not shared.

           # mount --bind /root/namespaces /root/namespaces
           # mount --make-private /root/namespaces
           # touch /root/namespaces/mnt
           # unshare --mount=/root/namespaces/mnt

       The following commands demonstrate the use of the --kill-child
       option when creating a PID namespace, in order to ensure that
       when unshare is killed, all of the processes within the PID
       namespace are killed.

           # set +m                # Don't print job status messages

           # unshare --pid --fork --mount-proc --kill-child -- \

                  bash --norc -c ''(sleep 555 &) && (ps a &) && sleep 999'' &
           [1] 53456
           #     PID TTY      STAT   TIME COMMAND
                 1 pts/3    S+     0:00 sleep 999
                 3 pts/3    S+     0:00 sleep 555
                 5 pts/3    R+     0:00 ps a

           # ps h -o 'comm' $! # Show that background job is unshare(1)
           unshare
           # kill $! # Kill unshare(1)
           # pidof sleep

       The pidof(1) command prints no output, because the sleep
       processes have been killed. More precisely, when the sleep
       process that has PID 1 in the namespace (i.e., the namespace’s
       init process) was killed, this caused all other processes in the
       namespace to be killed. By contrast, a similar series of commands
       where the --kill-child option is not used shows that when unshare
       terminates, the processes in the PID namespace are not killed:

           # unshare --pid --fork --mount-proc -- \

                  bash --norc -c ''(sleep 555 &) && (ps a &) && sleep 999'' &
           [1] 53479
           #     PID TTY      STAT   TIME COMMAND
                 1 pts/3    S+     0:00 sleep 999
                 3 pts/3    S+     0:00 sleep 555
                 5 pts/3    R+     0:00 ps a

           # kill $!
           # pidof sleep
           53482 53480

       The following example demonstrates the creation of a time
       namespace where the boottime clock is set to a point several
       years in the past:

           # uptime -p             # Show uptime in initial time namespace
           up 21 hours, 30 minutes
           # unshare --time --fork --boottime 300000000 uptime -p
           up 9 years, 28 weeks, 1 day, 2 hours, 50 minutes

AUTHORS         top

       Mikhail Gusarov <dottedmag@dottedmag.net>, Karel Zak
       <kzak@redhat.com>

SEE ALSO         top

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

REPORTING BUGS         top

       For bug reports, use the issue tracker at
       https://github.com/karelzak/util-linux/issues.

AVAILABILITY         top

       The unshare command is part of the util-linux package which can
       be downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>. 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
       2021-06-20. (At that time, the date of the most recent commit
       that was found in the repository was 2021-06-18.) If you discover
       any rendering problems in this HTML version 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 manual page),
       send a mail to man-pages@man7.org

util-linux 2.37.109-b366e69    2021-06-20                     UNSHARE(1)

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