2 .\" Copyright (c) 2000 Robert N. M. Watson
3 .\" All rights reserved.
5 .\" Redistribution and use in source and binary forms, with or without
6 .\" modification, are permitted provided that the following conditions
8 .\" 1. Redistributions of source code must retain the above copyright
9 .\" notice, this list of conditions and the following disclaimer.
10 .\" 2. Redistributions in binary form must reproduce the above copyright
11 .\" notice, this list of conditions and the following disclaimer in the
12 .\" documentation and/or other materials provided with the distribution.
14 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 .\" ----------------------------------------------------------------------------
28 .\" "THE BEER-WARE LICENSE" (Revision 42):
29 .\" <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
30 .\" can do whatever you want with this stuff. If we meet some day, and you think
31 .\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
32 .\" ----------------------------------------------------------------------------
40 .Nd "imprison process and its descendants"
44 .Op Fl l u Ar username | Fl U Ar username
45 .Ar path hostname ip-list command ...
49 command imprisons a process and all future descendants.
51 The options are as follows:
52 .Bl -tag -width ".Fl u Ar username"
54 Output the jail identifier of the newly created jail.
56 Run program in the clean environment.
57 The environment is discarded except for
58 .Ev HOME , SHELL , TERM
64 are set to the target login's default values.
66 is set to the target login.
68 is imported from the current environment.
69 The environment variables from the login class capability database for the
70 target login are also set.
72 The user name as whom the
76 The user name from jailed environment as whom the
80 Directory which is to be the root of the prison.
82 Hostname of the prison.
84 Comma separated IP list assigned to the prison.
86 Pathname of the program which is to be executed.
91 man page for further details.
93 .Ss "Setting Up a Jail Directory Tree"
94 This example shows how to setup a jail directory tree
97 distribution, provided that you built world before already:
102 make installworld DESTDIR=$D
104 make distribution DESTDIR=$D
106 ln -sf dev/null boot/kernel
109 In many cases this example would put far more stuff in the jail than is needed.
110 In the other extreme case a jail might contain only one single file:
111 the executable to be run in the jail.
113 We recommend experimentation and caution that it is a lot easier to
116 jail and remove things until it stops working,
117 than it is to start with a
119 jail and add things until it works.
120 .Ss "Setting Up a Jail"
121 Do what was described in
122 .Sx "Setting Up a Jail Directory Tree"
123 to build the jail directory tree.
124 For the sake of this example, we will
125 assume you built it in
126 .Pa /data/jail/192.168.11.100 ,
127 named for the external jail IP address.
128 Substitute below as needed with your
129 own directory, IP addresses, and hostname.
131 First, you will want to set up your real system's environment to be
133 For consistency, we will refer to the parent box as the
134 .Dq "host environment" ,
135 and to the jailed virtual machine as the
136 .Dq "jail environment" .
137 Generally speaking making a system jail-friendly does not require much
139 .Va jail.defaults.allow_listen_override
141 This will allow all listen sockets inside the jail to overload
142 and override wildcard listen sockets on the host.
143 This methodology works extremely well as long as you restrict the IPs you
144 pass into the jail to avoid any security concerns, which typically means
145 making at least two IP aliases for each jail that you create (an external
146 IP and a localhost IP).
148 If you do not want to allow listener socket overloading, you must modify
149 services you intend to leave running on the host system to listen only on
150 specific IPs and not all IPs, or generally only run services inside your
151 jails that do not conflict with services on the host system.
152 This can be difficult and is not recommended.
154 Common services include:
165 For the purposes of our examples below,
167 is the host IP and we create aliases
170 In addition, we leave
172 on the host only and create aliases
176 Start any jails for the first time without configuring the network
177 interface so that you can clean it up a little and set up accounts.
179 with any machine (virtual or not) you will need to set a root password, time
182 To set the jail up for real you need to ifconfig some interface aliases.
183 and set jail defaults. Here is an example:
185 .Dl "sysctl jail.defaults.net_raw_sockets=1"
186 .Dl "sysctl jail.defaults.allow_listen_override=1"
187 .Dl "ifconfig lo0 127.0.0.2 alias"
188 .Dl "ifconfig em0 192.168.11.100 netmask 255.255.255.0 alias"
190 From within your jail you can generally run services normally. Just use
192 normally. Do not inform services that localhost is 127.0.0.2.
193 The kernel will automatically remap 'localhost' (e.g. 127.0.0.1) to the
194 localhost IP you specify for the jail. The kernel will also map the jail's
195 localhost IP back to 127.0.0.1 in the
202 Listen sockets can be overloaded between jails and between the host and its
203 jails. You can continue to use services that listen on the wildcard *.*
204 socket normally on both the host and its jails if you set the
205 .Va allow_listen_override
206 flag to 1, and jailed listen sockets will override any host listen sockets
207 listening on the wildcard address for the allowed jail IPs.
210 also allows you to overload specific ports, but the jailed service will
211 not receive any connections if the host is also specifically listening
212 on the addr/port pair that the jail is using. If multiple jails are listening
213 on the same addr/port pair (as specified by the jail's IP list), and the
214 host is not, then only one jail will receive connections on that pair.
216 In otherwords, it is still a good idea to give each jail its own local
217 and non-local IP address rather than have jails share.
221 .Dl "jail /data/jail/192.168.11.100 testhostname 127.0.0.2,192.168.11.100 /bin/sh"
223 You will end up with a shell prompt, assuming no errors, within the jail.
224 You can now do the post-install configuration to set various configuration
229 .Bl -bullet -offset indent -compact
231 Disable the port mapper
233 .Li rpcbind_enable="NO" )
241 Disable interface configuration to quell startup warnings about
243 .Pq Li network_interfaces=""
247 so that name resolution within the jail will work correctly
249 Set a root password, probably different from the real host system
251 Set the timezone with
254 Add accounts for users in the jail environment
256 Install any packages that you think the environment requires
259 You may also want to perform any package-specific configuration (web servers,
260 SSH servers, etc), patch up
262 so it logs as you would like, etc.
264 Exit from the shell, and the jail will be shut down.
265 .Ss "Starting the Jail"
266 You are now ready to restart the jail and bring up the environment with
267 all of its daemons and other programs.
268 To do this, first bring up the
269 virtual host interface, and then start the jail's
271 script from within the jail.
273 NOTE: If you plan to allow untrusted users to have root access inside the
274 jail, you may wish to consider setting the
275 .Va jail.defaults.set_hostname_allowed
277 Please see the management reasons why this is a good idea.
278 If you do decide to set this variable,
279 it must be set before starting any jails, and once each boot.
280 .Bd -literal -offset indent
281 sysctl jail.defaults.net_raw_sockets=1
282 sysctl jail.defaults.allow_listen_override=1
283 ifconfig em0 inet alias 192.168.11.100/32
284 ifconfig lo0 inet alias 127.0.0.2
285 mount -t procfs proc /data/jail/192.168.11.100/proc
286 jail /data/jail/192.168.11.100 testhostname 127.0.0.2,192.168.11.100 \\
290 A few warnings will be produced, because most
292 configuration variables cannot be set from within the jail, as they are
293 global across all jails and the host environment.
294 However, it should all
296 You should be able to see
299 and other processes running within the jail using
303 flag appearing beside jailed processes.
304 You should also be able to
306 to the hostname or IP address of the jailed environment, and log
307 in using the accounts you created previously.
308 .Ss "Managing the Jail"
309 Normal machine shutdown commands, such as
314 cannot be used successfully within the jail.
315 To kill all processes in a
316 jail, you may log into the jail and, as root, use one of the following
317 commands, depending on what you want to accomplish:
318 .Bd -literal -offset indent
327 signals to all processes in the jail from within the jail.
329 the intended use of the jail, you may also want to run
331 from within the jail.
332 Currently there is no way to insert new processes
333 into a jail, so you must first log into the jail before performing these
336 To kill processes from outside the jail, you must individually identify the
337 PID of each process to be killed.
339 .Pa /proc/ Ns Ar pid Ns Pa /status
340 file contains, as its last field, the hostname of the jail in which the
343 to indicate that the process is not running within a jail.
348 flag for processes in a jail.
349 However, the hostname for a jail may be, by
350 default, modified from within the jail, so the
352 status entry is unreliable by default.
353 To disable the setting of the hostname
354 from within a jail, set the
355 .Va jail.set_hostname_allowed
356 sysctl variable in the host environment to 0, which will affect all jails.
357 You can have this sysctl set on each boot using
359 Just add the following line to
360 .Pa /etc/sysctl.conf :
362 .Dl jail.defaults.set_hostname_allowed=0
364 In a future version of
366 the mechanisms for managing jails may be
368 .Ss "Sysctl MIB Entries"
369 Certain aspects of the jail containments environment may be modified from
370 the host environment using
373 For each jail there will be the same set of MIB variables as shown below but
376 which allows control of every jail individually.
377 The values of the variables under
379 will be copied to the per-jail MIB variables upon creation thus serving as
380 a kind of system-wide template.
382 .It Va jail.defaults.allow_raw_sockets
383 This MIB entry determines whether or not prison root is allowed to
385 Setting this MIB to 1 allows utilities like
389 to operate inside the prison.
390 If this MIB is set, the source IP addresses are enforced to comply
391 with the IP address bound to the jail, regardless of whether or not the
393 flag has been set on the socket. Because raw sockets can be used to configure
394 and interact with various network subsystems, extra caution should be used
395 where privileged access to jails is given out to untrusted parties.
396 As such, this option is disabled by default.
397 .It Va jail.defaults.chflags_allowed
398 This MIB entry determines how a privileged user inside a jail will be
401 If zero, such users are treated as unprivileged, and are unable to set
402 or clear system file flags; if non-zero, such users are treated as
403 privileged, and may manipulate system file flags subject to the usual
405 .Va kern.securelevel .
407 This read-only MIB entry can be used to determine if a process is running
408 inside a jail (value is 1) or not (value is 0).
409 .It Va jail.defaults.set_hostname_allowed
410 This MIB entry determines whether or not processes within a jail are
411 allowed to change their hostname via
415 In the current jail implementation, the ability to set the hostname from
416 within the jail can impact management tools relying on the accuracy of jail
419 As such, this should be disabled in environments where privileged access to
420 jails is given out to untrusted parties.
421 .It Va jail.defaults.allow_listen_override
422 This feature allows both the host and your jails to overload services on
424 If enabled, the services in the jails will override wildcarded services on
425 the host for the jail's IP list.
426 As a safety mechanism, any services the host specifically binds to an IP
427 will not be overridden. The host has visibility to all jail IPs but
428 jails only have visibility to their specific IPs.
429 .It Va jail.defaults.socket_unixiproute_only
430 The jail functionality binds IPv4 and IPv6 addresses to each jail, and limits
431 access to other network addresses in the IPv4 and IPv6 space that may be available
432 in the host environment.
433 However, jail is not currently able to limit access to other network
434 protocol stacks that have not had jail functionality added to them.
435 As such, by default, processes within jails may only access protocols
436 in the following domains:
437 .Dv PF_LOCAL , PF_INET , PF_INET6 ,
440 permitting them access to
443 IPv4 and IPv6 addresses, and routing sockets.
444 To enable access to other domains, this MIB variable may be set to 0.
445 .It Va jail.defaults.sysvipc_allowed
446 This MIB entry determines whether or not processes within a jail have access
447 to System V IPC primitives.
448 In the current jail implementation, System V primitives share a single
449 namespace across the host and jail environments, meaning that processes
450 within a jail would be able to communicate with (and potentially interfere
451 with) processes outside of the jail, and in other jails.
452 As such, this functionality is disabled by default, but can be enabled
453 by setting this MIB entry to 1.
482 Support for multiple IPs and IPv6 appeared in
487 The jail feature was originally written by
488 .An Poul-Henning Kamp
490 .Pa http://www.rndassociates.com/
491 who contributed it to
495 wrote the extended documentation, found a few bugs, added
496 a few new features, and cleaned up the userland jail environment.
498 .An Victor Balada Diaz
499 wrote the support for multiple IPs and IPv6. Multiple IPs support
500 is based on work done by
501 .An Pawel Jakub Dawidek .
504 added port overloading to make configuration easier.
506 Jail currently lacks strong management functionality, such as the ability
507 to deliver signals to all processes in a jail, and to allow access to
508 specific jail information via
512 Similarly, it might be a good idea to add an
513 address alias flag such that daemons listening on all IPs
515 will not bind on that address, which would facilitate building a safe
516 host environment such that host daemons do not impose on services offered
518 Currently, the simplest answer is to minimize services
519 offered on the host, possibly limiting it to services offered from
521 which is easily configurable.