2 .\" Copyright (c) 2000, 2003 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)
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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 .\" ----------------------------------------------------------------------------
41 .Nd "imprison process and its descendants"
46 .Op Fl l u Ar username | Fl U Ar username
47 .Ar path hostname ip-number command ...
51 utility imprisons a process and all future descendants.
53 The options are as follows:
54 .Bl -tag -width ".Fl u Ar username"
56 Output the jail identifier of the newly created jail.
58 Write a JidFile, like a PidFile, containing jailid, path, hostname, ip and
59 command used to start the jail.
61 Run program in the clean environment.
62 The environment is discarded except for
63 .Ev HOME , SHELL , TERM
69 are set to the target login's default values.
71 is set to the target login.
73 is imported from the current environment.
74 The environment variables from the login class capability database for the
75 target login are also set.
77 The user name from host environment as whom the
81 The user name from jailed environment as whom the
85 Directory which is to be the root of the prison.
87 Hostname of the prison.
89 IP number assigned to the prison.
91 Pathname of the program which is to be executed.
94 Jails are typically set up using one of two philosophies: either to
95 constrain a specific application (possibly running with privilege), or
97 .Dq "virtual system image"
98 running a variety of daemons and services.
99 In both cases, a fairly complete file system install of
102 required, so as to provide the necessary command line tools, daemons,
103 libraries, application configuration files, etc.
104 However, for a virtual server configuration, a fair amount of
105 additional work is required so as to configure the
108 This manual page documents the configuration steps necessary to support
109 either of these steps, although the configuration steps may be
110 refined based on local requirements.
114 man page for further details.
116 .Ss "Setting up a Jail Directory Tree"
117 To set up a jail directory tree containing an entire
119 distribution, the following
121 command script can be used:
126 make world DESTDIR=$D
127 make distribution DESTDIR=$D
128 mount_devfs devfs $D/dev
131 NOTE: It is important that only appropriate device nodes in devfs be
132 exposed to a jail; access to disk devices in the jail may permit processes
133 in the jail to bypass the jail sandboxing by modifying files outside of
137 for information on how to use devfs rules to limit access to entries
138 in the per-jail devfs.
140 In many cases this example would put far more in the jail than needed.
141 In the other extreme case a jail might contain only one file:
142 the executable to be run in the jail.
144 We recommend experimentation and caution that it is a lot easier to
147 jail and remove things until it stops working,
148 than it is to start with a
150 jail and add things until it works.
151 .Ss "Setting Up a Jail"
152 Do what was described in
153 .Sx "Setting Up a Jail Directory Tree"
154 to build the jail directory tree.
155 For the sake of this example, we will
156 assume you built it in
157 .Pa /data/jail/192.168.11.100 ,
158 named for the jailed IP address.
159 Substitute below as needed with your
160 own directory, IP address, and hostname.
161 .Ss "Setting up the Host Environment"
162 First, you will want to set up your real system's environment to be
164 For consistency, we will refer to the parent box as the
165 .Dq "host environment" ,
166 and to the jailed virtual machine as the
167 .Dq "jail environment" .
168 Since jail is implemented using IP aliases, one of the first things to do
169 is to disable IP services on the host system that listen on all local
170 IP addresses for a service.
171 If a network service is present in the host environment that binds all
172 available IP addresses rather than specific IP addresses, it may service
173 requests sent to jail IP addresses.
176 to only listen on the
177 appropriate IP address, and so forth.
180 in the host environment:
181 .Bd -literal -offset indent
183 inetd_flags="-wW -a 192.168.11.23"
188 is the native IP address for the host system, in this example.
189 Daemons that run out of
191 can be easily set to use only the specified host IP address.
193 will need to be manually configured\(emfor some this is possible through
196 flags entries; for others it is necessary to modify per-application
197 configuration files, or to recompile the applications.
198 The following frequently deployed services must have their individual
199 configuration files modified to limit the application to listening
200 to a specific IP address:
204 it is necessary to modify
205 .Pa /etc/ssh/sshd_config .
209 it is necessary to modify
210 .Pa /etc/mail/sendmail.cf .
214 it is necessary to modify
215 .Pa /etc/namedb/named.conf .
217 In addition, a number of services must be recompiled in order to run
218 them in the host environment.
219 This includes most applications providing services using
226 In general, applications for which it is not possible to specify which
227 IP address to bind should not be run in the host environment unless they
228 should also service requests sent to jail IP addresses.
230 NFS from the host environment may also cause confusion, and cannot be
231 easily reconfigured to use only specific IPs, as some NFS services are
232 hosted directly from the kernel.
233 Any third-party network software running
234 in the host environment should also be checked and configured so that it
235 does not bind all IP addresses, which would result in those services' also
236 appearing to be offered by the jail environments.
239 these daemons have been disabled or fixed in the host environment, it is
240 best to reboot so that all daemons are in a known state, to reduce the
241 potential for confusion later (such as finding that when you send mail
242 to a jail, and its sendmail is down, the mail is delivered to the host,
244 .Ss "Configuring the Jail"
245 Start any jail for the first time without configuring the network
246 interface so that you can clean it up a little and set up accounts.
248 with any machine (virtual or not) you will need to set a root password, time
250 Some of these steps apply only if you intend to run a full virtual server
251 inside the jail; others apply both for constraining a particular application
252 or for running a virtual server.
254 Start a shell in the jail:
256 .Dl "jail /data/jail/192.168.11.100 testhostname 192.168.11.100 /bin/sh"
258 Assuming no errors, you will end up with a shell prompt within the jail.
260 .Pa /usr/sbin/sysinstall
261 and do the post-install configuration to set various configuration options,
262 or perform these actions manually by editing
266 .Bl -bullet -offset indent -compact
270 to quell startup warnings about missing fstab (virtual server only)
272 Disable the port mapper
274 .Li rpcbind_enable="NO" )
275 (virtual server only)
279 so that name resolution within the jail will work correctly
287 Disable interface configuration to quell startup warnings about
289 .Pq Li network_interfaces=""
290 (virtual server only)
292 Set a root password, probably different from the real host system
296 Add accounts for users in the jail environment
298 Install any packages the environment requires
301 You may also want to perform any package-specific configuration (web servers,
302 SSH servers, etc), patch up
304 so it logs as you would like, etc.
305 If you are not using a virtual server, you may wish to modify
307 in the host environment to listen on the syslog socket in the jail
308 environment; in this example, the syslog socket would be stored in
309 .Pa /data/jail/192.168.11.100/var/run/log .
311 Exit from the shell, and the jail will be shut down.
312 .Ss "Starting the Jail"
313 You are now ready to restart the jail and bring up the environment with
314 all of its daemons and other programs.
315 If you are running a single application in the jail, substitute the
316 command used to start the application for
318 in the examples below.
319 To start a virtual server environment,
321 is run to launch various daemons and services.
322 To do this, first bring up the
323 virtual host interface, and then start the jail's
325 script from within the jail.
327 NOTE: If you plan to allow untrusted users to have root access inside the
328 jail, you may wish to consider setting the
329 .Va security.jail.set_hostname_allowed
330 sysctl variable to 0.
331 Please see the management discussion later in this document as to why this
333 If you do decide to set this variable,
334 it must be set before starting any jails, and once each boot.
335 .Bd -literal -offset indent
336 ifconfig ed0 inet alias 192.168.11.100/32
337 mount -t procfs proc /data/jail/192.168.11.100/proc
338 jail /data/jail/192.168.11.100 testhostname 192.168.11.100 \\
342 A few warnings will be produced, because most
344 configuration variables cannot be set from within the jail, as they are
345 global across all jails and the host environment.
346 However, it should all
348 You should be able to see
351 and other processes running within the jail using
355 flag appearing beside jailed processes.
356 To see an active list of jails, use the
359 You should also be able to
361 to the hostname or IP address of the jailed environment, and log
362 in using the accounts you created previously.
364 It is possible to have jails started at boot time.
369 for more information.
372 jail script provides a flexible system to start/stop jails:
376 /etc/rc.d/jail start myjail
377 /etc/rc.d/jail stop myjail
379 .Ss "Managing the Jail"
380 Normal machine shutdown commands, such as
385 cannot be used successfully within the jail.
386 To kill all processes in a
387 jail, you may log into the jail and, as root, use one of the following
388 commands, depending on what you want to accomplish:
390 .Bd -literal -offset indent
399 signals to all processes in the jail from within the jail.
401 the intended use of the jail, you may also want to run
403 from within the jail.
404 To kill processes from outside the jail, use the
406 utility in conjunction with the one of the
411 .Pa /proc/ Ns Ar pid Ns Pa /status
412 file contains, as its last field, the hostname of the jail in which the
415 to indicate that the process is not running within a jail.
420 flag for processes in a jail.
421 However, the hostname for a jail may be, by
422 default, modified from within the jail, so the
424 status entry is unreliable by default.
425 To disable the setting of the hostname
426 from within a jail, set the
427 .Va security.jail.set_hostname_allowed
428 sysctl variable in the host environment to 0, which will affect all jails.
429 You can have this sysctl set on each boot using
431 Just add the following line to
432 .Pa /etc/sysctl.conf :
434 .Dl security.jail.set_hostname_allowed=0
436 You can also list/kill processes based on their jail ID.
437 To show processes and their jail ID, use the following command:
439 .Dl "ps ax -o pid,jid,args"
441 To show and then kill processes in jail number 3 use the following commands:
442 .Bd -literal -offset indent
449 .Ss "Sysctl MIB Entries"
450 Certain aspects of the jail containments environment may be modified from
451 the host environment using
454 Currently, these variables affect all jails on the system, although in
455 the future this functionality may be finer grained.
457 .It Va security.jail.allow_raw_sockets
458 This MIB entry determines whether or not prison root is allowed to
460 Setting this MIB to 1 allows utilities like
464 to operate inside the prison.
466 is set, the source IP addresses are enforced to comply
467 with the IP address bound to the jail, regardless of whether or not
470 flag has been set on the socket.
471 Since raw sockets can be used to configure
472 and interact with various network subsystems, extra caution should be used
473 where privileged access to jails is given out to untrusted parties.
475 by default this option is disabled.
476 .It Va security.jail.enforce_statfs
477 This MIB entry determines which information processes in a jail are
478 able to get about mount-points.
479 It affects the behaviour of the following syscalls:
485 (as well as similar compatibility syscalls).
486 When set to 0, all mount-points are available without any restrictions.
487 When set to 1, only mount-points below the jail's chroot directory are
489 In addition to that, the path to the jail's chroot directory is removed
490 from the front of their pathnames.
491 When set to 2 (default), above syscalls can operate only on a mount-point
492 where the jail's chroot directory is located.
493 .It Va security.jail.set_hostname_allowed
494 This MIB entry determines whether or not processes within a jail are
495 allowed to change their hostname via
499 In the current jail implementation, the ability to set the hostname from
500 within the jail can impact management tools relying on the accuracy of jail
503 As such, this should be disabled in environments where privileged access to
504 jails is given out to untrusted parties.
505 .It Va security.jail.socket_unixiproute_only
506 The jail functionality binds an IPv4 address to each jail, and limits
507 access to other network addresses in the IPv4 space that may be available
508 in the host environment.
509 However, jail is not currently able to limit access to other network
510 protocol stacks that have not had jail functionality added to them.
511 As such, by default, processes within jails may only access protocols
512 in the following domains:
513 .Dv PF_LOCAL , PF_INET ,
516 permitting them access to
519 IPv4 addresses, and routing sockets.
520 To enable access to other domains, this MIB variable may be set to
522 .It Va security.jail.sysvipc_allowed
523 This MIB entry determines whether or not processes within a jail have access
524 to System V IPC primitives.
525 In the current jail implementation, System V primitives share a single
526 namespace across the host and jail environments, meaning that processes
527 within a jail would be able to communicate with (and potentially interfere
528 with) processes outside of the jail, and in other jails.
529 As such, this functionality is disabled by default, but can be enabled
530 by setting this MIB entry to 1.
531 .It Va security.jail.chflags_allowed
532 This MIB entry determines how a privileged user inside a jail will be
535 If zero, such users are treated as unprivileged, and are unable to set
536 or clear system file flags; if non-zero, such users are treated as
537 privileged, and may manipulate system file flags subject to the usual
539 .Va kern.securelevel .
542 There are currently two MIB related variables that have per-jail settings.
543 Changes to these variables by a jailed process do not effect the host
544 environment, only the jail environment.
581 The jail feature was written by
582 .An Poul-Henning Kamp
584 .Pa http://www.rndassociates.com/
585 who contributed it to
589 wrote the extended documentation, found a few bugs, added
590 a few new features, and cleaned up the userland jail environment.
592 Jail currently lacks the ability to allow access to
593 specific jail information via
597 Similarly, it might be a good idea to add an
598 address alias flag such that daemons listening on all IPs
600 will not bind on that address, which would facilitate building a safe
601 host environment such that host daemons do not impose on services offered
603 Currently, the simplest answer is to minimize services
604 offered on the host, possibly limiting it to services offered from
606 which is easily configurable.