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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | NOTES | EXAMPLES | AUTHORS | SEE ALSO | REPORTING BUGS | AVAILABILITY |
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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]
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|all
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 unshare was run unprivileged. 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. Use --map-users multiple times to map more than one
block of user IDs. 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. The special
value all will create a pass-through map for every user ID
available in the parent namespace. 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|all
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 unshare was run unprivileged. 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. Use --map-groups multiple times to map more than one
block of group IDs. 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. The special
value all will create a pass-through map for every group ID
available in the parent namespace. 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.
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.
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
Mikhail Gusarov <dottedmag@dottedmag.net>, Karel Zak
<kzak@redhat.com>
newuidmap(1), newgidmap(1), clone(2), unshare(2), namespaces(7),
mount(8)
For bug reports, use the issue tracker at
https://github.com/util-linux/util-linux/issues.
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
2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-06-10.) 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 2.39.1041-8a7c 2023-12-22 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)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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