man > unshare(1)

UNSHARE(1)                                  User Commands                                 UNSHARE(1)

NAME
       unshare - run program in new namespaces

SYNOPSIS
       unshare [options] [program [arguments]]

DESCRIPTION
       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
       -i, --ipc[=file]
           Create a new IPC namespace. If file is specified, then the namespace is made persistent
           by creating a bind mount at file.

       -m, --mount[=file]
           Create a new mount namespace. If file is specified, then the namespace is made persistent
           by creating a bind mount at file. 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]
           Create a new network namespace. If file is specified, then the namespace is made
           persistent by creating a bind mount at file.

       -p, --pid[=file]
           Create a new PID namespace. If file is specified, then the namespace is made persistent
           by creating a bind mount at file. (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]
           Create a new UTS namespace. If file is specified, then the namespace is made persistent
           by creating a bind mount at file.

       -U, --user[=file]
           Create a new user namespace. If file is specified, then the namespace is made persistent
           by creating a bind mount at file.

       -C, --cgroup[=file]
           Create a new cgroup namespace. If file is specified, then the namespace is made
           persistent by creating a bind mount at file.

       -T, --time[=file]
           Create a new time namespace. If file is specified, then the namespace is made persistent
           by creating a bind mount at file. 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-users=inneruid:outeruid:count|auto
           Run the program only after the block of user IDs of size count beginning at outeruid has
           been mapped to the block of user IDs beginning at inneruid. This mapping is created with
           newuidmap(1). If the range of user IDs overlaps with the mapping specified by --map-user,
           then a "hole" will be removed from the mapping. This may result in the highest user ID of
           the mapping not being mapped. The special value auto will map the first block of user IDs
           owned by the effective user from /etc/subuid to a block starting at user ID 0. If this
           option is specified multiple times, the last occurrence takes precedence. This option
           implies --user.

           Before util-linux version 2.39, this option expected a comma-separated argument of the
           form outeruid,inneruid,count but that format is now deprecated for consistency with the
           ordering used in /proc/[pid]/uid_map and the X-mount.idmap mount option.

       --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.

       --map-groups=innergid:outergid:count|auto
           Run the program only after the block of group IDs of size count beginning at outergid has
           been mapped to the block of group IDs beginning at innergid. This mapping is created with
           newgidmap(1). If the range of group IDs overlaps with the mapping specified by
           --map-group, then a "hole" will be removed from the mapping. This may result in the
           highest group ID of the mapping not being mapped. The special value auto will map the
           first block of user IDs owned by the effective user from /etc/subgid to a block starting
           at group ID 0. If this option is specified multiple times, the last occurrence takes
           precedence. This option implies --user.

           Before util-linux version 2.39, this option expected a comma-separated argument of the
           form outergid,innergid,count but that format is now deprecated for consistency with the
           ordering used in /proc/[pid]/gid_map and the X-mount.idmap mount option.

       --map-auto
           Map the first block of user IDs owned by the effective user from /etc/subuid to a block
           starting at user ID 0. In the same manner, also map the first block of group IDs owned by
           the effective group from /etc/subgid to a block starting at group ID 0. This option is
           intended to handle the common case where the first block of subordinate user and group
           IDs can map the whole user and group ID space. This option is equivalent to specifying
           --map-users=auto and --map-groups=auto.

       -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.

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

       -V, --version
           Print version 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 cannot 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
       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(1) 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

       As an unprivileged user, create a user namespace where the first 65536 IDs are all mapped,
       and the user’s credentials are mapped to the root IDs inside the namespace. The map is
       determined by the subordinate IDs assigned in subuid(5) and subgid(5). Demonstrate this
       mapping by creating a file with user ID 1 and group ID 1. For brevity, only the user ID
       mappings are shown:

           $ id -u
           1000
           $ cat /etc/subuid
           1000:100000:65536
           $ unshare --user --map-auto --map-root-user
           # id -u
           0
           # cat /proc/self/uid_map
                    0       1000          1
                    1     100000      65535
           # touch file; chown 1:1 file
           # ls -ln --time-style=+ file
           -rw-r--r-- 1 1 1 0  file
           # exit
           $ ls -ln --time-style=+ file
           -rw-r--r-- 1 100000 100000 0  file

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

SEE ALSO
       newuidmap(1), newgidmap(1), clone(2), unshare(2), namespaces(7), mount(8)

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

AVAILABILITY
       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/>.

util-linux 2.39.3                            2023-11-21                                   UNSHARE(1)