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2 .\" Copyright (c) 2000 Robert N. M. Watson
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19 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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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 .\" ----------------------------------------------------------------------------
33 .\"
34 .\" $FreeBSD: src/usr.sbin/jail/jail.8,v 1.13.2.15 2003/05/08 13:04:24 maxim Exp $
35 .\" $DragonFly: src/usr.sbin/jail/jail.8,v 1.10 2007/05/17 08:19:03 swildner Exp $
36 .\"
37 .Dd December 12, 2001
38 .Dt JAIL 8
39 .Os
40 .Sh NAME
41 .Nm jail
42 .Nd "imprison process and its descendants"
43 .Sh SYNOPSIS
44 .Nm
45 .Op Fl i
46 .Op Fl l u Ar username | Fl U Ar username
47 .Ar path hostname ip-list command ...
48 .Sh DESCRIPTION
49 The
50 .Nm
51 command imprisons a process and all future descendants.
52 .Pp
53 The options are as follows:
54 .Bl -tag -width ".Fl u Ar username"
55 .It Fl i
56 Output the jail identifier of the newly created jail.
57 .It Fl l
58 Run program in the clean environment.
59 The environment is discarded except for
60 .Ev HOME , SHELL , TERM
61 and
62 .Ev USER .
63 .Ev HOME
64 and
65 .Ev SHELL
66 are set to the target login's default values.
67 .Ev USER
68 is set to the target login.
69 .Ev TERM
70 is imported from the current environment.
71 The environment variables from the login class capability database for the
72 target login are also set.
73 .It Fl u Ar username
74 The user name as whom the
75 .Ar command
76 should run.
77 .It Fl U Ar username
78 The user name from jailed environment as whom the
79 .Ar command
80 should run.
81 .It Ar path
82 Directory which is to be the root of the prison.
83 .It Ar hostname
84 Hostname of the prison.
85 .It Ar ip-list
86 Comma separated IP list assigned to the prison.
87 .It Ar command
88 Pathname of the program which is to be executed.
89 .El
90 .Pp
91 Please see the
92 .Xr jail 2
93 man page for further details.
94 .Sh EXAMPLES
95 .Ss "Setting up a Jail Directory Tree"
96 This example shows how to setup a jail directory tree
97 containing an entire
98 .Dx
99 distribution, provided that you built world before already:
100 .Bd -literal
101 D=/here/is/the/jail
102 cd /usr/src
103 mkdir -p $D
104 make installworld DESTDIR=$D
105 cd etc
106 make distribution DESTDIR=$D -DNO_MAKEDEV_RUN
107 cd $D/dev
108 sh MAKEDEV jail
109 cd $D
110 ln -sf dev/null kernel
111 .Ed
112 .Pp
113 In many cases this example would put far more stuff in the jail than is needed.
114 In the other extreme case a jail might contain only one single file:
115 the executable to be run in the jail.
116 .Pp
117 We recommend experimentation and caution that it is a lot easier to
118 start with a
119 .Dq fat
120 jail and remove things until it stops working,
121 than it is to start with a
122 .Dq thin
123 jail and add things until it works.
124 .Ss "Setting Up a Jail"
125 Do what was described in
126 .Sx "Setting Up a Jail Directory Tree"
127 to build the jail directory tree.
128 For the sake of this example, we will
129 assume you built it in
130 .Pa /data/jail/192.168.11.100 ,
131 named for the external jail IP address.
132 Substitute below as needed with your
133 own directory, IP addresses, and hostname.
134 .Pp
135 First, you will want to set up your real system's environment to be
136 .Dq jail-friendly .
137 For consistency, we will refer to the parent box as the
138 .Dq "host environment" ,
139 and to the jailed virtual machine as the
140 .Dq "jail environment" .
141 Because jail is implemented using IP aliases, one of the first things to do
142 is to disable IP services on the host system that listen on all local
143 IP addresses for a service.
144 This means changing
145 .Xr inetd 8
146 to only listen on the
147 appropriate IP address, and so forth.
148 Add the following to
149 .Pa /etc/rc.conf
150 in the host environment:
151 .Bd -literal -offset indent
152 sendmail_enable="NO"
153 inetd_flags="-wW -a 192.168.11.23"
154 portmap_enable="NO"
155 .Ed
156 .Pp
157 .Li 192.168.11.23
158 is the native IP address for the host system, in this example.
159 Daemons that run out of
160 .Xr inetd 8
161 can be easily set to use only the specified host IP address.
162 Other daemons
163 will need to be manually configured\(emfor some this is possible through
164 the
165 .Xr rc.conf 5
166 flags entries, for others it is not possible without munging
167 the per-application configuration files, or even recompiling.
168 For those
169 applications that cannot specify the IP they run on, it is better to disable
170 them, if possible.
171 .Pp
172 A number of daemons ship with the base system that may have problems when
173 run from outside of a jail in a jail-centric environment.
174 This includes
175 .Xr sendmail 8 ,
176 .Xr named 8 ,
177 and
178 .Xr portmap 8 .
179 While
180 .Xr sendmail 8
181 and
182 .Xr named 8
183 can be configured to listen only on a specific
184 IP using their configuration files, in most cases it is easier to simply
185 run the daemons in jails only, and not in the host environment.
186 Attempting to serve
187 NFS from the host environment may also cause confusion, and cannot be
188 easily reconfigured to use only specific IPs, as some NFS services are
189 hosted directly from the kernel.
190 Any third party network software running
191 in the host environment should also be checked and configured so that it
192 does not bind all IP addresses, which would result in those services also
193 appearing to be offered by the jail environments.
194 .Pp
195 Once
196 these daemons have been disabled or fixed in the host environment, it is
197 best to reboot so that all daemons are in a known state, to reduce the
198 potential for confusion later (such as finding that when you send mail
199 to a jail, and its sendmail is down, the mail is delivered to the host,
200 etc.)
201 .Pp
202 Start any jails for the first time without configuring the network
203 interface so that you can clean it up a little and set up accounts.
204 As
205 with any machine (virtual or not) you will need to set a root password, time
206 zone, etc.
207 .Pp
208 Now start the jail:
209 .Pp
210 .Dl "jail /data/jail/192.168.11.100 testhostname 127.0.0.1,192.168.11.100 /bin/sh"
211 .Pp
212 You will end up with a shell prompt, assuming no errors, within the jail.
213 You can now do the post-install configuration to set various configuration
214 options by editing
215 .Pa /etc/rc.conf ,
216 etc.
217 .Pp
218 .Bl -bullet -offset indent -compact
219 .It
220 Create an empty
221 .Pa /etc/fstab
222 to quell startup warnings about missing fstab
223 .It
224 Disable the port mapper
225 .Pa ( /etc/rc.conf :
226 .Li portmap_enable="NO" )
227 .It
228 Run
229 .Xr newaliases 1
230 to quell
231 .Xr sendmail 8
232 warnings.
233 .It
234 Disable interface configuration to quell startup warnings about
235 .Xr ifconfig 8
236 .Pq Li network_interfaces=""
237 .It
238 Configure
239 .Pa /etc/resolv.conf
240 so that name resolution within the jail will work correctly
241 .It
242 Set a root password, probably different from the real host system
243 .It
244 Set the timezone with
245 .Xr tzsetup 8
246 .It
247 Add accounts for users in the jail environment
248 .It
249 Install any packages that you think the environment requires
250 .El
251 .Pp
252 You may also want to perform any package-specific configuration (web servers,
253 SSH servers, etc), patch up
254 .Pa /etc/syslog.conf
255 so it logs as you would like, etc.
256 .Pp
257 Exit from the shell, and the jail will be shut down.
258 .Ss "Starting the Jail"
259 You are now ready to restart the jail and bring up the environment with
260 all of its daemons and other programs.
261 To do this, first bring up the
262 virtual host interface, and then start the jail's
263 .Pa /etc/rc
264 script from within the jail.
265 .Pp
266 NOTE: If you plan to allow untrusted users to have root access inside the
267 jail, you may wish to consider setting the
268 .Va jail.set_hostname_allowed
269 to 0.
270 Please see the management reasons why this is a good idea.
271 If you do decide to set this variable,
272 it must be set before starting any jails, and once each boot.
273 .Bd -literal -offset indent
274 ifconfig ed0 inet alias 192.168.11.100/32
275 mount -t procfs proc /data/jail/192.168.11.100/proc
276 jail /data/jail/192.168.11.100 testhostname 127.0.0.1,192.168.11.100 \\
277 /bin/sh /etc/rc
278 .Ed
279 .Pp
280 A few warnings will be produced, because most
281 .Xr sysctl 8
282 configuration variables cannot be set from within the jail, as they are
283 global across all jails and the host environment.
284 However, it should all
285 work properly.
286 You should be able to see
287 .Xr inetd 8 ,
288 .Xr syslogd 8 ,
289 and other processes running within the jail using
290 .Xr ps 1 ,
291 with the
292 .Ql J
293 flag appearing beside jailed processes.
294 You should also be able to
295 .Xr telnet 1
296 to the hostname or IP address of the jailed environment, and log
297 in using the accounts you created previously.
298 .Ss "Managing the Jail"
299 Normal machine shutdown commands, such as
300 .Xr halt 8 ,
301 .Xr reboot 8 ,
302 and
303 .Xr shutdown 8 ,
304 cannot be used successfully within the jail.
305 To kill all processes in a
306 jail, you may log into the jail and, as root, use one of the following
307 commands, depending on what you want to accomplish:
308 .Pp
309 .Bd -literal -offset indent
310 kill -TERM -1
311 kill -KILL -1
312 .Ed
313 .Pp
314 This will send the
315 .Dv SIGTERM
316 or
317 .Dv SIGKILL
318 signals to all processes in the jail from within the jail.
319 Depending on
320 the intended use of the jail, you may also want to run
321 .Pa /etc/rc.shutdown
322 from within the jail.
323 Currently there is no way to insert new processes
324 into a jail, so you must first log into the jail before performing these
325 actions.
326 .Pp
327 To kill processes from outside the jail, you must individually identify the
328 PID of each process to be killed.
329 The
330 .Pa /proc/ Ns Ar pid Ns Pa /status
331 file contains, as its last field, the hostname of the jail in which the
332 process runs, or
333 .Dq Li -
334 to indicate that the process is not running within a jail.
335 The
336 .Xr ps 1
337 command also shows a
338 .Ql J
339 flag for processes in a jail.
340 However, the hostname for a jail may be, by
341 default, modified from within the jail, so the
342 .Pa /proc
343 status entry is unreliable by default.
344 To disable the setting of the hostname
345 from within a jail, set the
346 .Va jail.set_hostname_allowed
347 sysctl variable in the host environment to 0, which will affect all jails.
348 You can have this sysctl set on each boot using
349 .Xr sysctl.conf 5 .
350 Just add the following line to
351 .Pa /etc/sysctl.conf :
352 .Pp
353 .Dl jail.set_hostname_allowed=0
354 .Pp
355 In a future version of
356 .Dx ,
357 the mechanisms for managing jails may be
358 more refined.
359 .Ss "Sysctl MIB Entries"
360 Certain aspects of the jail containments environment may be modified from
361 the host environment using
362 .Xr sysctl 8
363 MIB variables.
364 Currently, these variables affect all jails on the system, although in
365 the future this functionality may be finer grained.
366 .Bl -tag -width XXX
367 .It Va jail.set_hostname_allowed
368 This MIB entry determines whether or not processes within a jail are
369 allowed to change their hostname via
370 .Xr hostname 1
371 or
372 .Xr sethostname 3 .
373 In the current jail implementation, the ability to set the hostname from
374 within the jail can impact management tools relying on the accuracy of jail
375 information in
376 .Pa /proc .
377 As such, this should be disabled in environments where privileged access to
378 jails is given out to untrusted parties.
379 .It Va jail.socket_unixiproute_only
380 The jail functionality binds IPv4 and IPv6 addresses to each jail, and limits
381 access to other network addresses in the IPv4 and IPv6 space that may be available
382 in the host environment.
383 However, jail is not currently able to limit access to other network
384 protocol stacks that have not had jail functionality added to them.
385 As such, by default, processes within jails may only access protocols
386 in the following domains:
387 .Dv PF_LOCAL , PF_INET , PF_INET6 ,
388 and
389 .Dv PF_ROUTE ,
390 permitting them access to
391 .Ux
392 domain sockets,
393 IPv4 and IPv6 addresses, and routing sockets.
394 To enable access to other domains, this MIB variable may be set to
395 0.
396 .It Va jail.sysvipc_allowed
397 This MIB entry determines whether or not processes within a jail have access
398 to System V IPC primitives.
399 In the current jail implementation, System V primitives share a single
400 namespace across the host and jail environments, meaning that processes
401 within a jail would be able to communicate with (and potentially interfere
402 with) processes outside of the jail, and in other jails.
403 As such, this functionality is disabled by default, but can be enabled
404 by setting this MIB entry to 1.
405 .El
406 .Sh SEE ALSO
407 .Xr newaliases 1 ,
408 .Xr ps 1 ,
409 .Xr chroot 2 ,
410 .Xr jail 2 ,
411 .Xr procfs 5 ,
412 .Xr rc.conf 5 ,
413 .Xr sysctl.conf 5 ,
414 .Xr halt 8 ,
415 .Xr inetd 8 ,
416 .Xr named 8 ,
417 .Xr portmap 8 ,
418 .Xr pw 8 ,
419 .Xr reboot 8 ,
420 .Xr sendmail 8 ,
421 .Xr shutdown 8 ,
422 .Xr sysctl 8 ,
423 .Xr syslogd 8 ,
424 .Xr tzsetup 8
425 .Sh HISTORY
426 The
427 .Nm
428 command appeared in
429 .Fx 4.0 .
430 .Pp
431 Support for multiple IPs and IPv6 appeared in
432 .Dx
433 1.7.
434 .Sh AUTHORS
435 .An -nosplit
436 The jail feature was written by
437 .An Poul-Henning Kamp
438 for R&D Associates
439 .Pa http://www.rndassociates.com/
440 who contributed it to
441 .Fx .
442 .Pp
443 .An Robert Watson
444 wrote the extended documentation, found a few bugs, added
445 a few new features, and cleaned up the userland jail environment.
446 .Pp
447 .An Victor Balada Diaz
448 wrote the support for multiple IPs and IPv6. Multiple IPs support
449 is based on work done by
450 .An Pawel Jakub Dawidek .
451 .Sh BUGS
452 Jail currently lacks strong management functionality, such as the ability
453 to deliver signals to all processes in a jail, and to allow access to
454 specific jail information via
455 .Xr ps 1
456 as opposed to
457 .Xr procfs 5 .
458 Similarly, it might be a good idea to add an
459 address alias flag such that daemons listening on all IPs
460 .Pq Dv INADDR_ANY
461 will not bind on that address, which would facilitate building a safe
462 host environment such that host daemons do not impose on services offered
463 from within jails.
464 Currently, the simplist answer is to minimize services
465 offered on the host, possibly limiting it to services offered from
466 .Xr inetd 8
467 which is easily configurable.