1UNSHARE(1) User Commands UNSHARE(1)
2
6 unshare - run program in new namespaces
7
9 unshare [options] [program [arguments]]
10
12 The unshare command creates new namespaces (as specified by the
13 command-line options described below) and then executes the specified
14 program. If program is not given, then "${SHELL}" is run (default:
15 /bin/sh).
16 By default, a new namespace persists only as long as it has member
18 processes. A new namespace can be made persistent even when it has no
19 member processes by bind mounting /proc/pid/ns/type files to a
20 filesystem path. A namespace that has been made persistent in this way
21 can subsequently be entered with nsenter(1) even after the program
22 terminates (except PID namespaces where a permanently running init
23 process is required). Once a persistent namespace is no longer needed,
24 it can be unpersisted by using umount(8) to remove the bind mount. See
25 the EXAMPLES section for more details.
26 unshare since util-linux version 2.36 uses
28 /proc/[pid]/ns/pid_for_children and /proc/[pid]/ns/time_for_children
29 files for persistent PID and TIME namespaces. This change requires
30 Linux kernel 4.17 or newer.
31 The following types of namespaces can be created with unshare:
33 mount namespace
35 Mounting and unmounting filesystems will not affect the rest of the
36 system, except for filesystems which are explicitly marked as
37 shared (with mount --make-shared; see /proc/self/mountinfo or
38 findmnt -o+PROPAGATION for the shared flags). For further details,
39 see mount_namespaces(7).
40 unshare since util-linux version 2.27 automatically sets
42 propagation to private in a new mount namespace to make sure that
43 the new namespace is really unshared. It’s possible to disable this
44 feature with option --propagation unchanged. Note that private is
45 the kernel default.
46 UTS namespace
48 Setting hostname or domainname will not affect the rest of the
49 system. For further details, see uts_namespaces(7).
50 IPC namespace
52 The process will have an independent namespace for POSIX message
53 queues as well as System V message queues, semaphore sets and
54 shared memory segments. For further details, see ipc_namespaces(7).
55 network namespace
57 The process will have independent IPv4 and IPv6 stacks, IP routing
58 tables, firewall rules, the /proc/net and /sys/class/net directory
59 trees, sockets, etc. For further details, see
60 network_namespaces(7).
61 PID namespace
63 Children will have a distinct set of PID-to-process mappings from
64 their parent. For further details, see pid_namespaces(7).
65 cgroup namespace
67 The process will have a virtualized view of /proc/self/cgroup, and
68 new cgroup mounts will be rooted at the namespace cgroup root. For
69 further details, see cgroup_namespaces(7).
70 user namespace
72 The process will have a distinct set of UIDs, GIDs and
73 capabilities. For further details, see user_namespaces(7).
74 time namespace
76 The process can have a distinct view of CLOCK_MONOTONIC and/or
77 CLOCK_BOOTTIME which can be changed using
78 /proc/self/timens_offsets. For further details, see
79 time_namespaces(7).
80
82 -i, --ipc[=file]
83 Create a new IPC namespace. If file is specified, then the
84 namespace is made persistent by creating a bind mount at file.
85 -m, --mount[=file]
87 Create a new mount namespace. If file is specified, then the
88 namespace is made persistent by creating a bind mount at file. Note
89 that file must be located on a mount whose propagation type is not
90 shared (or an error results). Use the command findmnt
91 -o+PROPAGATION when not sure about the current setting. See also
92 the examples below.
93 -n, --net[=file]
95 Create a new network namespace. If file is specified, then the
96 namespace is made persistent by creating a bind mount at file.
97 -p, --pid[=file]
99 Create a new PID namespace. If file is specified, then the
100 namespace is made persistent by creating a bind mount at file.
101 (Creation of a persistent PID namespace will fail if the --fork
102 option is not also specified.)
103 See also the --fork and --mount-proc options.
105 -u, --uts[=file]
107 Create a new UTS namespace. If file is specified, then the
108 namespace is made persistent by creating a bind mount at file.
109 -U, --user[=file]
111 Create a new user namespace. If file is specified, then the
112 namespace is made persistent by creating a bind mount at file.
113 -C, --cgroup[=file]
115 Create a new cgroup namespace. If file is specified, then the
116 namespace is made persistent by creating a bind mount at file.
117 -T, --time[=file]
119 Create a new time namespace. If file is specified, then the
120 namespace is made persistent by creating a bind mount at file. The
121 --monotonic and --boottime options can be used to specify the
122 corresponding offset in the time namespace.
123 -f, --fork
125 Fork the specified program as a child process of unshare rather
126 than running it directly. This is useful when creating a new PID
127 namespace. Note that when unshare is waiting for the child process,
128 then it ignores SIGINT and SIGTERM and does not forward any signals
129 to the child. It is necessary to send signals to the child process.
130 --keep-caps
132 When the --user option is given, ensure that capabilities granted
133 in the user namespace are preserved in the child process.
134 --kill-child[=signame]
136 When unshare terminates, have signame be sent to the forked child
137 process. Combined with --pid this allows for an easy and reliable
138 killing of the entire process tree below unshare. If not given,
139 signame defaults to SIGKILL. This option implies --fork.
140 --mount-proc[=mountpoint]
142 Just before running the program, mount the proc filesystem at
143 mountpoint (default is /proc). This is useful when creating a new
144 PID namespace. It also implies creating a new mount namespace since
145 the /proc mount would otherwise mess up existing programs on the
146 system. The new proc filesystem is explicitly mounted as private
147 (with MS_PRIVATE|MS_REC).
148 --map-user=uid|name
150 Run the program only after the current effective user ID has been
151 mapped to uid. If this option is specified multiple times, the last
152 occurrence takes precedence. This option implies --user.
153 --map-users=outeruid,inneruid,count|auto
155 Run the program only after the block of user IDs of size count
156 beginning at outeruid has been mapped to the block of user IDs
157 beginning at inneruid. This mapping is created with newuidmap(1).
158 If the range of user IDs overlaps with the mapping specified by
159 --map-user, then a "hole" will be removed from the mapping. This
160 may result in the highest user ID of the mapping not being mapped.
161 The special value auto will map the first block of user IDs owned
162 by the effective user from /etc/subuid to a block starting at user
163 ID 0. If this option is specified multiple times, the last
164 occurrence takes precedence. This option implies --user.
165 --map-group=gid|name
167 Run the program only after the current effective group ID has been
168 mapped to gid. If this option is specified multiple times, the last
169 occurrence takes precedence. This option implies --setgroups=deny
170 and --user.
171 --map-groups=outergid,innergid,count|auto
173 Run the program only after the block of group IDs of size count
174 beginning at outergid has been mapped to the block of group IDs
175 beginning at innergid. This mapping is created with newgidmap(1).
176 If the range of group IDs overlaps with the mapping specified by
177 --map-group, then a "hole" will be removed from the mapping. This
178 may result in the highest group ID of the mapping not being mapped.
179 The special value auto will map the first block of user IDs owned
180 by the effective user from /etc/subgid to a block starting at group
181 ID 0. If this option is specified multiple times, the last
182 occurrence takes precedence. This option implies --user.
183 --map-auto
185 Map the first block of user IDs owned by the effective user from
186 /etc/subuid to a block starting at user ID 0. In the same manner,
187 also map the first block of group IDs owned by the effective group
188 from /etc/subgid to a block starting at group ID 0. This option is
189 intended to handle the common case where the first block of
190 subordinate user and group IDs can map the whole user and group ID
191 space. This option is equivalent to specifying --map-users=auto and
192 --map-groups=auto.
193 -r, --map-root-user
195 Run the program only after the current effective user and group IDs
196 have been mapped to the superuser UID and GID in the newly created
197 user namespace. This makes it possible to conveniently gain
198 capabilities needed to manage various aspects of the newly created
199 namespaces (such as configuring interfaces in the network namespace
200 or mounting filesystems in the mount namespace) even when run
201 unprivileged. As a mere convenience feature, it does not support
202 more sophisticated use cases, such as mapping multiple ranges of
203 UIDs and GIDs. This option implies --setgroups=deny and --user.
204 This option is equivalent to --map-user=0 --map-group=0.
205 -c, --map-current-user
207 Run the program only after the current effective user and group IDs
208 have been mapped to the same UID and GID in the newly created user
209 namespace. This option implies --setgroups=deny and --user. This
210 option is equivalent to --map-user=$(id -ru) --map-group=$(id -rg).
211 --propagation private|shared|slave|unchanged
213 Recursively set the mount propagation flag in the new mount
214 namespace. The default is to set the propagation to private. It is
215 possible to disable this feature with the argument unchanged. The
216 option is silently ignored when the mount namespace (--mount) is
217 not requested.
218 --setgroups allow|deny
220 Allow or deny the setgroups(2) system call in a user namespace.
221 To be able to call setgroups(2), the calling process must at least
223 have CAP_SETGID. But since Linux 3.19 a further restriction
224 applies: the kernel gives permission to call setgroups(2) only
225 after the GID map (/proc/pid*/gid_map*) has been set. The GID map
226 is writable by root when setgroups(2) is enabled (i.e., allow, the
227 default), and the GID map becomes writable by unprivileged
228 processes when setgroups(2) is permanently disabled (with deny).
229 -R, --root=dir
231 run the command with root directory set to dir.
232 -w, --wd=dir
234 change working directory to dir.
235 -S, --setuid uid
237 Set the user ID which will be used in the entered namespace.
238 -G, --setgid gid
240 Set the group ID which will be used in the entered namespace and
241 drop supplementary groups.
242 --monotonic offset
244 Set the offset of CLOCK_MONOTONIC which will be used in the entered
245 time namespace. This option requires unsharing a time namespace
246 with --time.
247 --boottime offset
249 Set the offset of CLOCK_BOOTTIME which will be used in the entered
250 time namespace. This option requires unsharing a time namespace
251 with --time.
252 -h, --help
254 Display help text and exit.
255 -V, --version
257 Print version and exit.
258
260 The proc and sysfs filesystems mounting as root in a user namespace
261 have to be restricted so that a less privileged user cannot get more
262 access to sensitive files that a more privileged user made unavailable.
263 In short the rule for proc and sysfs is as close to a bind mount as
264 possible.
265
267 The following command creates a PID namespace, using --fork to ensure
268 that the executed command is performed in a child process that (being
269 the first process in the namespace) has PID 1. The --mount-proc option
270 ensures that a new mount namespace is also simultaneously created and
271 that a new proc(5) filesystem is mounted that contains information
272 corresponding to the new PID namespace. When the readlink(1) command
273 terminates, the new namespaces are automatically torn down.
274 # unshare --fork --pid --mount-proc readlink /proc/self
276 1
277 As an unprivileged user, create a new user namespace where the user’s
279 credentials are mapped to the root IDs inside the namespace:
280 $ id -u; id -g
282 1000
283 1000
284 $ unshare --user --map-root-user \
285 sh -c ''whoami; cat /proc/self/uid_map /proc/self/gid_map''
286 root
287 0 1000 1
288 0 1000 1
289 As an unprivileged user, create a user namespace where the first 65536
291 IDs are all mapped, and the user’s credentials are mapped to the root
292 IDs inside the namespace. The map is determined by the subordinate IDs
293 assigned in subuid(5) and subgid(5). Demonstrate this mapping by
294 creating a file with user ID 1 and group ID 1. For brevity, only the
295 user ID mappings are shown:
296 $ id -u
298 1000
299 $ cat /etc/subuid
300 1000:100000:65536
301 $ unshare --user --map-auto --map-root-user
302 # id -u
303 0
304 # cat /proc/self/uid_map
305 0 1000 1
306 1 100000 65535
307 # touch file; chown 1:1 file
308 # ls -ln --time-style=+ file
309 -rw-r--r-- 1 1 1 0 file
310 # exit
311 $ ls -ln --time-style=+ file
312 -rw-r--r-- 1 100000 100000 0 file
313 The first of the following commands creates a new persistent UTS
315 namespace and modifies the hostname as seen in that namespace. The
316 namespace is then entered with nsenter(1) in order to display the
317 modified hostname; this step demonstrates that the UTS namespace
318 continues to exist even though the namespace had no member processes
319 after the unshare command terminated. The namespace is then destroyed
320 by removing the bind mount.
321 # touch /root/uts-ns
323 # unshare --uts=/root/uts-ns hostname FOO
324 # nsenter --uts=/root/uts-ns hostname
325 FOO
326 # umount /root/uts-ns
327 The following commands establish a persistent mount namespace
329 referenced by the bind mount /root/namespaces/mnt. In order to ensure
330 that the creation of that bind mount succeeds, the parent directory
331 (/root/namespaces) is made a bind mount whose propagation type is not
332 shared.
333 # mount --bind /root/namespaces /root/namespaces
335 # mount --make-private /root/namespaces
336 # touch /root/namespaces/mnt
337 # unshare --mount=/root/namespaces/mnt
338 The following commands demonstrate the use of the --kill-child option
340 when creating a PID namespace, in order to ensure that when unshare is
341 killed, all of the processes within the PID namespace are killed.
342 # set +m # Don't print job status messages
344 # unshare --pid --fork --mount-proc --kill-child -- \
347 bash --norc -c ''(sleep 555 &) && (ps a &) && sleep 999'' &
350 [1] 53456
351 # PID TTY STAT TIME COMMAND
352 1 pts/3 S+ 0:00 sleep 999
353 3 pts/3 S+ 0:00 sleep 555
354 5 pts/3 R+ 0:00 ps a
355 # ps h -o 'comm' $! # Show that background job is unshare(1)
357 unshare
358 # kill $! # Kill unshare(1)
359 # pidof sleep
360 The pidof(1) command prints no output, because the sleep processes have
362 been killed. More precisely, when the sleep process that has PID 1 in
363 the namespace (i.e., the namespace’s init process) was killed, this
364 caused all other processes in the namespace to be killed. By contrast,
365 a similar series of commands where the --kill-child option is not used
366 shows that when unshare terminates, the processes in the PID namespace
367 are not killed:
368 # unshare --pid --fork --mount-proc -- \
370 bash --norc -c ''(sleep 555 &) && (ps a &) && sleep 999'' &
373 [1] 53479
374 # PID TTY STAT TIME COMMAND
375 1 pts/3 S+ 0:00 sleep 999
376 3 pts/3 S+ 0:00 sleep 555
377 5 pts/3 R+ 0:00 ps a
378 # kill $!
380 # pidof sleep
381 53482 53480
382 The following example demonstrates the creation of a time namespace
384 where the boottime clock is set to a point several years in the past:
385 # uptime -p # Show uptime in initial time namespace
387 up 21 hours, 30 minutes
388 # unshare --time --fork --boottime 300000000 uptime -p
389 up 9 years, 28 weeks, 1 day, 2 hours, 50 minutes
390
392 Mikhail Gusarov <dottedmag@dottedmag.net>, Karel Zak <kzak@redhat.com>
393
395 newuidmap(1) newgidmap(1) clone(2), unshare(2), namespaces(7), mount(8)
396
398 For bug reports, use the issue tracker at
399 https://github.com/util-linux/util-linux/issues.
400
402 The unshare command is part of the util-linux package which can be
403 downloaded from Linux Kernel Archive
404 <https://www.kernel.org/pub/linux/utils/util-linux/>.
405util-linux 2.38.1 2022-05-11 UNSHARE(1)