# Bash 的 unshare 命令

unshare [OPTION]... [CMD [ARG]...]

$ sudo unshare -p -f --mount-proc       # 创建新的 PID 命名空间，运行 /bin/bash
# ps -afx                               # 查看进程树
    PID TTY      STAT   TIME COMMAND
      1 pts/4    S      0:00 -bash
     16 pts/4    R+     0:00 ps -afx

$ sudo unshare -n bash
# ip addr
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

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 <[email protected]>, Karel Zak <[email protected]>

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)