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"
45 .Op Fl l u Ar username | Fl U Ar username
46 .Ar path hostname ip-number command ...
50 utility imprisons a process and all future descendants.
52 The options are as follows:
53 .Bl -tag -width ".Fl u Ar username"
55 Output the jail identifier of the newly created jail.
57 Run program in the clean environment.
58 The environment is discarded except for
59 .Ev HOME , SHELL , TERM
65 are set to the target login's default values.
67 is set to the target login.
69 is imported from the current environment.
70 The environment variables from the login class capability database for the
71 target login are also set.
73 The user name from host environment as whom the
77 The user name from jailed environment as whom the
81 Directory which is to be the root of the prison.
83 Hostname of the prison.
85 IP number assigned to the prison.
87 Pathname of the program which is to be executed.
90 Jails are typically set up using one of two philosophies: either to
91 constrain a specific application (possibly running with privilege), or
93 .Dq "virtual system image"
94 running a variety of daemons and services.
95 In both cases, a fairly complete file system install of
98 required, so as to provide the necessary command line tools, daemons,
99 libraries, application configuration files, etc.
100 However, for a virtual server configuration, a fair amount of
101 additional work is required so as to configure the
104 This manual page documents the configuration steps necessary to support
105 either of these steps, although the configuration steps may be
106 refined based on local requirements.
110 man page for further details.
112 .Ss "Setting up a Jail Directory Tree"
113 To set up a jail directory tree containing an entire
115 distribution, the following
117 command script can be used:
122 make world DESTDIR=$D
123 make distribution DESTDIR=$D
124 mount_devfs devfs $D/dev
127 NOTE: It is important that only appropriate device nodes in devfs be
128 exposed to a jail; access to disk devices in the jail may permit processes
129 in the jail to bypass the jail sandboxing by modifying files outside of
133 for information on how to use devfs rules to limit access to entries
134 in the per-jail devfs.
136 In many cases this example would put far more in the jail than needed.
137 In the other extreme case a jail might contain only one file:
138 the executable to be run in the jail.
140 We recommend experimentation and caution that it is a lot easier to
143 jail and remove things until it stops working,
144 than it is to start with a
146 jail and add things until it works.
147 .Ss "Setting Up a Jail"
148 Do what was described in
149 .Sx "Setting Up a Jail Directory Tree"
150 to build the jail directory tree.
151 For the sake of this example, we will
152 assume you built it in
153 .Pa /data/jail/192.168.11.100 ,
154 named for the jailed IP address.
155 Substitute below as needed with your
156 own directory, IP address, and hostname.
157 .Ss "Setting up the Host Environment"
158 First, you will want to set up your real system's environment to be
160 For consistency, we will refer to the parent box as the
161 .Dq "host environment" ,
162 and to the jailed virtual machine as the
163 .Dq "jail environment" .
164 Since jail is implemented using IP aliases, one of the first things to do
165 is to disable IP services on the host system that listen on all local
166 IP addresses for a service.
167 If a network service is present in the host environment that binds all
168 available IP addresses rather than specific IP addresses, it may service
169 requests sent to jail IP addresses.
172 to only listen on the
173 appropriate IP address, and so forth.
176 in the host environment:
177 .Bd -literal -offset indent
179 inetd_flags="-wW -a 192.168.11.23"
184 is the native IP address for the host system, in this example.
185 Daemons that run out of
187 can be easily set to use only the specified host IP address.
189 will need to be manually configured\(emfor some this is possible through
192 flags entries; for others it is necessary to modify per-application
193 configuration files, or to recompile the applications.
194 The following frequently deployed services must have their individual
195 configuration files modified to limit the application to listening
196 to a specific IP address:
200 it is necessary to modify
201 .Pa /etc/ssh/sshd_config .
205 it is necessary to modify
206 .Pa /etc/mail/sendmail.cf .
210 it is necessary to modify
211 .Pa /etc/namedb/named.conf .
213 In addition, a number of services must be recompiled in order to run
214 them in the host environment.
215 This includes most applications providing services using
222 In general, applications for which it is not possible to specify which
223 IP address to bind should not be run in the host environment unless they
224 should also service requests sent to jail IP addresses.
226 NFS from the host environment may also cause confusion, and cannot be
227 easily reconfigured to use only specific IPs, as some NFS services are
228 hosted directly from the kernel.
229 Any third-party network software running
230 in the host environment should also be checked and configured so that it
231 does not bind all IP addresses, which would result in those services' also
232 appearing to be offered by the jail environments.
235 these daemons have been disabled or fixed in the host environment, it is
236 best to reboot so that all daemons are in a known state, to reduce the
237 potential for confusion later (such as finding that when you send mail
238 to a jail, and its sendmail is down, the mail is delivered to the host,
240 .Ss "Configuring the Jail"
241 Start any jail for the first time without configuring the network
242 interface so that you can clean it up a little and set up accounts.
244 with any machine (virtual or not) you will need to set a root password, time
246 Some of these steps apply only if you intend to run a full virtual server
247 inside the jail; others apply both for constraining a particular application
248 or for running a virtual server.
250 Start a shell in the jail:
252 .Dl "jail /data/jail/192.168.11.100 testhostname 192.168.11.100 /bin/sh"
254 Assuming no errors, you will end up with a shell prompt within the jail.
256 .Pa /usr/sbin/sysinstall
257 and do the post-install configuration to set various configuration options,
258 or perform these actions manually by editing
262 .Bl -bullet -offset indent -compact
266 to quell startup warnings about missing fstab (virtual server only)
268 Disable the port mapper
270 .Li rpcbind_enable="NO" )
271 (virtual server only)
275 so that name resolution within the jail will work correctly
283 Disable interface configuration to quell startup warnings about
285 .Pq Li network_interfaces=""
286 (virtual server only)
288 Set a root password, probably different from the real host system
292 Add accounts for users in the jail environment
294 Install any packages the environment requires
297 You may also want to perform any package-specific configuration (web servers,
298 SSH servers, etc), patch up
300 so it logs as you would like, etc.
301 If you are not using a virtual server, you may wish to modify
303 in the host environment to listen on the syslog socket in the jail
304 environment; in this example, the syslog socket would be stored in
305 .Pa /data/jail/192.168.11.100/var/run/log .
307 Exit from the shell, and the jail will be shut down.
308 .Ss "Starting the Jail"
309 You are now ready to restart the jail and bring up the environment with
310 all of its daemons and other programs.
311 If you are running a single application in the jail, substitute the
312 command used to start the application for
314 in the examples below.
315 To start a virtual server environment,
317 is run to launch various daemons and services.
318 To do this, first bring up the
319 virtual host interface, and then start the jail's
321 script from within the jail.
323 NOTE: If you plan to allow untrusted users to have root access inside the
324 jail, you may wish to consider setting the
325 .Va security.jail.set_hostname_allowed
326 sysctl variable to 0.
327 Please see the management discussion later in this document as to why this
329 If you do decide to set this variable,
330 it must be set before starting any jails, and once each boot.
331 .Bd -literal -offset indent
332 ifconfig ed0 inet alias 192.168.11.100/32
333 mount -t procfs proc /data/jail/192.168.11.100/proc
334 jail /data/jail/192.168.11.100 testhostname 192.168.11.100 \\
338 A few warnings will be produced, because most
340 configuration variables cannot be set from within the jail, as they are
341 global across all jails and the host environment.
342 However, it should all
344 You should be able to see
347 and other processes running within the jail using
351 flag appearing beside jailed processes.
352 To see an active list of jails, use the
355 You should also be able to
357 to the hostname or IP address of the jailed environment, and log
358 in using the accounts you created previously.
360 It is possible to have jails started at boot time.
365 for more information.
368 jail script provides a flexible system to start/stop jails:
372 /etc/rc.d/jail start myjail
373 /etc/rc.d/jail stop myjail
375 .Ss "Managing the Jail"
376 Normal machine shutdown commands, such as
381 cannot be used successfully within the jail.
382 To kill all processes in a
383 jail, you may log into the jail and, as root, use one of the following
384 commands, depending on what you want to accomplish:
386 .Bd -literal -offset indent
395 signals to all processes in the jail from within the jail.
397 the intended use of the jail, you may also want to run
399 from within the jail.
400 To kill processes from outside the jail, use the
402 utility in conjunction with the one of the
407 .Pa /proc/ Ns Ar pid Ns Pa /status
408 file contains, as its last field, the hostname of the jail in which the
411 to indicate that the process is not running within a jail.
416 flag for processes in a jail.
417 However, the hostname for a jail may be, by
418 default, modified from within the jail, so the
420 status entry is unreliable by default.
421 To disable the setting of the hostname
422 from within a jail, set the
423 .Va security.jail.set_hostname_allowed
424 sysctl variable in the host environment to 0, which will affect all jails.
425 You can have this sysctl set on each boot using
427 Just add the following line to
428 .Pa /etc/sysctl.conf :
430 .Dl security.jail.set_hostname_allowed=0
432 You can also list/kill processes based on their jail ID.
433 To show processes and their jail ID, use the following command:
435 .Dl "ps ax -o pid,jid,args"
437 To show and then kill processes in jail number 3 use the following commands:
438 .Bd -literal -offset indent
445 .Ss "Sysctl MIB Entries"
446 Certain aspects of the jail containments environment may be modified from
447 the host environment using
450 Currently, these variables affect all jails on the system, although in
451 the future this functionality may be finer grained.
453 .It Va security.jail.allow_raw_sockets
454 This MIB entry determines whether or not prison root is allowed to
456 Setting this MIB to 1 allows utilities like
460 to operate inside the prison.
462 is set, the source IP addresses are enforced to comply
463 with the IP address bound to the jail, regardless of whether or not
466 flag has been set on the socket.
467 Since raw sockets can be used to configure
468 and interact with various network subsystems, extra caution should be used
469 where privileged access to jails is given out to untrusted parties.
471 by default this option is disabled.
472 .It Va security.jail.enforce_statfs
473 This MIB entry determines which information processes in a jail are
474 able to get about mount-points.
475 It affects the behaviour of the following syscalls:
481 (as well as similar compatibility syscalls).
482 When set to 0, all mount-points are available without any restrictions.
483 When set to 1, only mount-points below the jail's chroot directory are
485 In addition to that, the path to the jail's chroot directory is removed
486 from the front of their pathnames.
487 When set to 2 (default), above syscalls can operate only on a mount-point
488 where the jail's chroot directory is located.
489 .It Va security.jail.set_hostname_allowed
490 This MIB entry determines whether or not processes within a jail are
491 allowed to change their hostname via
495 In the current jail implementation, the ability to set the hostname from
496 within the jail can impact management tools relying on the accuracy of jail
499 As such, this should be disabled in environments where privileged access to
500 jails is given out to untrusted parties.
501 .It Va security.jail.socket_unixiproute_only
502 The jail functionality binds an IPv4 address to each jail, and limits
503 access to other network addresses in the IPv4 space that may be available
504 in the host environment.
505 However, jail is not currently able to limit access to other network
506 protocol stacks that have not had jail functionality added to them.
507 As such, by default, processes within jails may only access protocols
508 in the following domains:
509 .Dv PF_LOCAL , PF_INET ,
512 permitting them access to
515 IPv4 addresses, and routing sockets.
516 To enable access to other domains, this MIB variable may be set to
518 .It Va security.jail.sysvipc_allowed
519 This MIB entry determines whether or not processes within a jail have access
520 to System V IPC primitives.
521 In the current jail implementation, System V primitives share a single
522 namespace across the host and jail environments, meaning that processes
523 within a jail would be able to communicate with (and potentially interfere
524 with) processes outside of the jail, and in other jails.
525 As such, this functionality is disabled by default, but can be enabled
526 by setting this MIB entry to 1.
527 .It Va security.jail.chflags_allowed
528 This MIB entry determines how a privileged user inside a jail will be
531 If zero, such users are treated as unprivileged, and are unable to set
532 or clear system file flags; if non-zero, such users are treated as
533 privileged, and may manipulate system file flags subject to the usual
535 .Va kern.securelevel .
538 There are currently two MIB related variables that have per-jail settings.
539 Changes to these variables by a jailed process do not effect the host
540 environment, only the jail environment.
577 The jail feature was written by
578 .An Poul-Henning Kamp
580 .Pa http://www.rndassociates.com/
581 who contributed it to
585 wrote the extended documentation, found a few bugs, added
586 a few new features, and cleaned up the userland jail environment.
588 Jail currently lacks the ability to allow access to
589 specific jail information via
593 Similarly, it might be a good idea to add an
594 address alias flag such that daemons listening on all IPs
596 will not bind on that address, which would facilitate building a safe
597 host environment such that host daemons do not impose on services offered
599 Currently, the simplest answer is to minimize services
600 offered on the host, possibly limiting it to services offered from
602 which is easily configurable.