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  direc-
              tory 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.

       --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  cre-
              ated 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

       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.

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)