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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | NOTES | EXAMPLES | AUTHORS | SEE ALSO | AVAILABILITY | COLOPHON |
UNSHARE(1) User Commands UNSHARE(1)
unshare - run program in new namespaces
unshare [options] [program [arguments]]
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).
-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.
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.
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 con‐
tinues 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 refer‐
enced 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 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
Mikhail Gusarov ⟨dottedmag@dottedmag.net⟩
Karel Zak ⟨kzak@redhat.com⟩
clone(2), unshare(2), namespaces(7), mount(8)
The unshare command is part of the util-linux package and is
available from 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
2020-08-13. (At that time, the date of the most recent commit that
was found in the repository was 2020-08-12.) 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 February 2016 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)