2 .\" Copyright (c) 2000, 2003 Robert N. M. Watson
3 .\" Copyright (c) 2008 James Gritton
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29 .\" "THE BEER-WARE LICENSE" (Revision 42):
30 .\" <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
31 .\" can do whatever you want with this stuff. If we meet some day, and you think
32 .\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
33 .\" ----------------------------------------------------------------------------
42 .Nd "create or modify a system jail"
47 .Op Fl l u Ar username | Fl U Ar username
49 .Op Ar parameter=value ...
55 .Op Fl s Ar securelevel
56 .Op Fl l u Ar username | Fl U Ar username
57 .Op Ar path hostname [ip[,..]] command ...
64 utility creates a new jail or modifies an existing jail, optionally
65 imprisoning the current process (and future descendants) inside it.
67 The options are as follows:
68 .Bl -tag -width indent
70 Allow making changes to a
78 and add all IP addresses returned by the resolver
81 addresses for this prison.
82 This may affect default address selection for outgoing IPv4 connections
84 The address first returned by the resolver for each address family
85 will be used as primary address.
90 parameters further down for details.
92 Output the jail identifier of the newly created jail.
95 This is deprecated and is equivalent to setting the
101 file, containing jail identifier, path, hostname, IP and
102 command used to start the jail.
104 Run program in the clean environment.
105 The environment is discarded except for
106 .Ev HOME , SHELL , TERM
112 are set to the target login's default values.
114 is set to the target login.
116 is imported from the current environment.
117 The environment variables from the login class capability database for the
118 target login are also set.
119 .It Fl s Ar securelevel
122 MIB entry to the specified value inside the newly created jail.
123 This is deprecated and is equivalent to setting the
127 The user name from host environment as whom the
131 The user name from jailed environment as whom the
140 parameters (if specified) must not refer to an existing jail.
142 Modify an existing jail.
147 parameters must exist and refer to an existing jail.
149 Create a jail if it does not exist, or modify a jail if it does exist.
153 specified by jid or name.
154 All jailed processes are killed, and all children of this jail are also
163 options must be specified.
168 form, following the options.
169 Some parameters are boolean, and do not have a value but are set by the
170 name alone with or without a
176 Any parameters not set will be given default values, often based on the
181 specifies that the current process should enter the new (or modified) jail,
182 and run the specified command.
183 It must be the last parameter specified, because it includes not only
184 the value following the
186 sign, but also passes the rest of the arguments to the command.
188 Instead of supplying named
190 four fixed parameters may be supplied in order on the command line:
200 parameters aren't in this list, this mode will always create a new jail, and
205 options don't apply (and must not exist).
207 Jails have a set a core parameters, and modules can add their own jail
209 The current set of available parameters can be retrieved via
210 .Dq Nm sysctl Fl d Va security.jail.param .
211 The core parameters are:
212 .Bl -tag -width indent
215 This will be assigned automatically to a new jail (or can be explicitly
216 set), and can be used to identify the jail for later modification, or
223 This is an arbitrary string that identifies a jail (except it may not
228 it can be passed to later
236 is supplied, a default is assumed that is the same as the
239 Directory which is to be the root of the prison.
242 (if any) is run from this directory, as are commands from
245 A comma-separated list of IPv4 addresses assigned to the prison.
246 If this is set, the jail is restricted to using only these address.
247 Any attempts to use other addresses fail, and attempts to use wildcard
248 addresses silently use the jailed address instead.
249 For IPv4 the first address given will be kept used as the source address
250 in case source address selection on unbound sockets cannot find a better
252 It is only possible to start multiple jails with the same IP address,
253 if none of the jails has more than this single overlapping IP address
256 Control the availablity of IPv4 addresses.
259 to allow unrestricted access to all system addresses,
261 to restrict addresses via
265 to stop the jail from using IPv4 entirely.
268 parameter implies a value of
270 .It Va ip6.addr , Va ip6
271 A list of IPv6 addresses assigned to the prison, the counterpart to
277 Hostname of the prison.
278 Other similar parameters are
279 .Va host.domainname ,
284 Set the origin of hostname and related information.
287 to use the system information and
289 for the jail to use the information from the above fields.
290 Setting any of the above fields implies a value of
293 The value of the jail's
296 A jail never has a lower securelevel than the default system, but by
297 setting this parameter it may have a higher one.
298 If the system securelevel is changed, any jail securelevels will be at
301 The number of child jails allowed to be created by this jail (or by
302 other jails under this jail).
303 This limit is zero by default, indicating the jail is not allowed to
306 .Va "Hierarchical Jails"
307 section for more information.
309 The number of descendents of this jail, including its own child jails
310 and any jails created under them.
311 .It Va enforce_statfs
312 This determines which information processes in a jail are able to get
314 It affects the behaviour of the following syscalls:
320 (as well as similar compatibility syscalls).
321 When set to 0, all mount points are available without any restrictions.
322 When set to 1, only mount points below the jail's chroot directory are
324 In addition to that, the path to the jail's chroot directory is removed
325 from the front of their pathnames.
326 When set to 2 (default), above syscalls can operate only on a mount-point
327 where the jail's chroot directory is located.
329 Setting this boolean parameter allows a jail to exist without any
331 Normally, a jail is destroyed as its last process exits.
332 A new jail must have either the
336 pseudo-parameter set.
338 The ID of the cpuset associated with this jail (read-only).
340 This is true if the jail is in the process of shutting down (read-only).
344 of the parent of this jail, or zero if this is a top-level jail
347 Some restrictions of the jail environment may be set on a per-jail
349 With the exception of
350 .Va allow.set_hostname ,
351 these boolean parameters are off by default.
352 .Bl -tag -width indent
353 .It Va allow.set_hostname
354 The jail's hostname may be changed via
359 A process within the jail has access to System V IPC primitives.
360 In the current jail implementation, System V primitives share a single
361 namespace across the host and jail environments, meaning that processes
362 within a jail would be able to communicate with (and potentially interfere
363 with) processes outside of the jail, and in other jails.
364 .It Va allow.raw_sockets
365 The prison root is allowed to create raw sockets.
366 Setting this parameter allows utilities like
370 to operate inside the prison.
371 If this is set, the source IP addresses are enforced to comply
372 with the IP address bound to the jail, regardless of whether or not
375 flag has been set on the socket.
376 Since raw sockets can be used to configure and interact with various
377 network subsystems, extra caution should be used where privileged access
378 to jails is given out to untrusted parties.
380 Normally, priveleged users inside a jail are treated as unprivileged by
382 When this parameter is set, such users are treated as privileged, and
383 may manipulate system file flags subject to the usual constraints on
384 .Va kern.securelevel .
386 privileged users inside the jail will be able to mount and unmount file
387 system types marked as jail-friendly.
390 command can be used to find file system types available for mount from
393 The prison root may administer quotas on the jail's filesystem(s).
394 This includes filesystems that the jail may share with other jails or
395 with non-jailed parts of the system.
396 .It Va allow.socket_af
397 Sockets within a jail are normally restricted to IPv4, IPv6, local
398 (UNIX), and route. This allows access to other protocol stacks that
399 have not had jail functionality added to them.
403 Jails are typically set up using one of two philosophies: either to
404 constrain a specific application (possibly running with privilege), or
406 .Dq "virtual system image"
407 running a variety of daemons and services.
408 In both cases, a fairly complete file system install of
411 required, so as to provide the necessary command line tools, daemons,
412 libraries, application configuration files, etc.
413 However, for a virtual server configuration, a fair amount of
414 additional work is required so as to configure the
417 This manual page documents the configuration steps necessary to support
418 either of these steps, although the configuration steps may be
419 refined based on local requirements.
421 .Ss "Setting up a Jail Directory Tree"
422 To set up a jail directory tree containing an entire
424 distribution, the following
426 command script can be used:
431 make world DESTDIR=$D
432 make distribution DESTDIR=$D
433 mount -t devfs devfs $D/dev
436 NOTE: It is important that only appropriate device nodes in devfs be
437 exposed to a jail; access to disk devices in the jail may permit processes
438 in the jail to bypass the jail sandboxing by modifying files outside of
442 for information on how to use devfs rules to limit access to entries
443 in the per-jail devfs.
444 A simple devfs ruleset for jails is available as ruleset #4 in
445 .Pa /etc/defaults/devfs.rules .
447 In many cases this example would put far more in the jail than needed.
448 In the other extreme case a jail might contain only one file:
449 the executable to be run in the jail.
451 We recommend experimentation and caution that it is a lot easier to
454 jail and remove things until it stops working,
455 than it is to start with a
457 jail and add things until it works.
458 .Ss "Setting Up a Jail"
459 Do what was described in
460 .Sx "Setting Up a Jail Directory Tree"
461 to build the jail directory tree.
462 For the sake of this example, we will
463 assume you built it in
464 .Pa /data/jail/192.0.2.100 ,
465 named for the jailed IP address.
466 Substitute below as needed with your
467 own directory, IP address, and hostname.
468 .Ss "Setting up the Host Environment"
469 First, you will want to set up your real system's environment to be
471 For consistency, we will refer to the parent box as the
472 .Dq "host environment" ,
473 and to the jailed virtual machine as the
474 .Dq "jail environment" .
475 Since jail is implemented using IP aliases, one of the first things to do
476 is to disable IP services on the host system that listen on all local
477 IP addresses for a service.
478 If a network service is present in the host environment that binds all
479 available IP addresses rather than specific IP addresses, it may service
480 requests sent to jail IP addresses if the jail did not bind the port.
483 to only listen on the
484 appropriate IP address, and so forth.
487 in the host environment:
488 .Bd -literal -offset indent
490 inetd_flags="-wW -a 192.0.2.23"
495 is the native IP address for the host system, in this example.
496 Daemons that run out of
498 can be easily set to use only the specified host IP address.
500 will need to be manually configured\(emfor some this is possible through
503 flags entries; for others it is necessary to modify per-application
504 configuration files, or to recompile the applications.
505 The following frequently deployed services must have their individual
506 configuration files modified to limit the application to listening
507 to a specific IP address:
511 it is necessary to modify
512 .Pa /etc/ssh/sshd_config .
516 it is necessary to modify
517 .Pa /etc/mail/sendmail.cf .
521 it is necessary to modify
522 .Pa /etc/namedb/named.conf .
524 In addition, a number of services must be recompiled in order to run
525 them in the host environment.
526 This includes most applications providing services using
533 In general, applications for which it is not possible to specify which
534 IP address to bind should not be run in the host environment unless they
535 should also service requests sent to jail IP addresses.
537 NFS from the host environment may also cause confusion, and cannot be
538 easily reconfigured to use only specific IPs, as some NFS services are
539 hosted directly from the kernel.
540 Any third-party network software running
541 in the host environment should also be checked and configured so that it
542 does not bind all IP addresses, which would result in those services' also
543 appearing to be offered by the jail environments.
546 these daemons have been disabled or fixed in the host environment, it is
547 best to reboot so that all daemons are in a known state, to reduce the
548 potential for confusion later (such as finding that when you send mail
549 to a jail, and its sendmail is down, the mail is delivered to the host,
551 .Ss "Configuring the Jail"
552 Start any jail for the first time without configuring the network
553 interface so that you can clean it up a little and set up accounts.
555 with any machine (virtual or not) you will need to set a root password, time
557 Some of these steps apply only if you intend to run a full virtual server
558 inside the jail; others apply both for constraining a particular application
559 or for running a virtual server.
561 Start a shell in the jail:
563 .Bd -literal -offset indent
564 jail path=/data/jail/192.0.2.100 host.hostname=testhostname \\
565 ip4.addr=192.0.2.100 command=/bin/sh
568 Assuming no errors, you will end up with a shell prompt within the jail.
570 .Pa /usr/sbin/sysinstall
571 and do the post-install configuration to set various configuration options,
572 or perform these actions manually by editing
576 .Bl -bullet -offset indent -compact
580 to quell startup warnings about missing fstab (virtual server only)
582 Disable the port mapper
584 .Li rpcbind_enable="NO" )
585 (virtual server only)
589 so that name resolution within the jail will work correctly
597 Disable interface configuration to quell startup warnings about
599 .Pq Li network_interfaces=""
600 (virtual server only)
602 Set a root password, probably different from the real host system
606 Add accounts for users in the jail environment
608 Install any packages the environment requires
611 You may also want to perform any package-specific configuration (web servers,
612 SSH servers, etc), patch up
614 so it logs as you would like, etc.
615 If you are not using a virtual server, you may wish to modify
617 in the host environment to listen on the syslog socket in the jail
618 environment; in this example, the syslog socket would be stored in
619 .Pa /data/jail/192.0.2.100/var/run/log .
621 Exit from the shell, and the jail will be shut down.
622 .Ss "Starting the Jail"
623 You are now ready to restart the jail and bring up the environment with
624 all of its daemons and other programs.
625 If you are running a single application in the jail, substitute the
626 command used to start the application for
628 in the examples below.
629 To start a virtual server environment,
631 is run to launch various daemons and services.
632 To do this, first bring up the
633 virtual host interface, and then start the jail's
635 script from within the jail.
636 .Bd -literal -offset indent
637 ifconfig ed0 inet alias 192.0.2.100/32
638 mount -t procfs proc /data/jail/192.0.2.100/proc
639 jail path=/data/jail/192.0.2.100 host.hostname=testhostname \\
640 ip4.addr=192.0.2.100 command=/bin/sh /etc/rc
643 A few warnings will be produced, because most
645 configuration variables cannot be set from within the jail, as they are
646 global across all jails and the host environment.
647 However, it should all
649 You should be able to see
652 and other processes running within the jail using
656 flag appearing beside jailed processes.
657 To see an active list of jails, use the
660 You should also be able to
662 to the hostname or IP address of the jailed environment, and log
663 in using the accounts you created previously.
665 It is possible to have jails started at boot time.
670 for more information.
673 jail script provides a flexible system to start/stop jails:
677 /etc/rc.d/jail start myjail
678 /etc/rc.d/jail stop myjail
680 .Ss "Managing the Jail"
681 Normal machine shutdown commands, such as
686 cannot be used successfully within the jail.
687 To kill all processes in a
688 jail, you may log into the jail and, as root, use one of the following
689 commands, depending on what you want to accomplish:
691 .Bd -literal -offset indent
700 signals to all processes in the jail from within the jail.
702 the intended use of the jail, you may also want to run
704 from within the jail.
705 To kill processes from outside the jail, use the
707 utility in conjunction with the one of the
710 You may also remove the jail with
713 which will killall the jail's processes with
717 .Pa /proc/ Ns Ar pid Ns Pa /status
718 file contains, as its last field, the name of the jail in which the
721 to indicate that the process is not running within a jail.
726 flag for processes in a jail.
728 You can also list/kill processes based on their jail ID.
729 To show processes and their jail ID, use the following command:
731 .Dl "ps ax -o pid,jid,args"
733 To show and then kill processes in jail number 3 use the following commands:
734 .Bd -literal -offset indent
741 .Ss "Jails and File Systems"
742 It is not possible to
746 any file system inside a jail unless the file system is marked
747 jail-friendly and the jail's
751 Multiple jails sharing the same file system can influence each other.
752 For example a user in one jail can fill the file system also
753 leaving no space for processes in the other jail.
756 to prevent this will not work either as the file system quotas
757 are not aware of jails but only look at the user and group IDs.
758 This means the same user ID in two jails share the same file
760 One would need to use one file system per jail to make this work.
761 .Ss "Sysctl MIB Entries"
763 .Va security.jail.jailed
764 can be used to determine if a process is running inside a jail (value
765 is one) or not (value is zero).
768 .Va security.jail.max_af_ips
769 determines how may address per address family a prison may have.
772 Some MIB variables have per-jail settings.
773 Changes to these variables by a jailed process do not effect the host
774 environment, only the jail environment.
776 .Va kern.securelevel ,
778 .Va kern.domainname ,
782 .Ss "Hierarchical Jails"
785 parameter, processes within a jail may be able to create jails of their own.
786 These child jails are kept in a hierarchy, with jails only able to see and/or
787 modify the jails they created (or those jails' children).
788 Each jail has a read-only
790 parameter, containing the
792 of the jail that created it; a
794 of 0 indicates the jail is a child of the current jail (or is a top-level
795 jail if the current process isn't jailed).
797 Jailed processes are not allowed to confer greater permissions than they
798 themselves are given, e.g. if a jail is created with
800 it is not able to create a jail with
803 Similarly, such restrictions as
807 may not be bypassed in child jails.
809 A child jail may in turn create its own child jails if its own
811 parameter is set (remember it is zero by default).
812 These jails are visible to and can be modified by their parent and all
815 Jail names reflect this hierarchy, with a full name being an MIB-type string
817 For example, if a base system process creates a jail
819 and a process under that jail creates another jail
821 then the second jail will be seen as
823 in the base system (though it is only seen as
825 to any processes inside jail
827 Jids on the other hand exist in a single space, and each jail must have a
830 Like the names, a child jail's
832 is relative to its creator's own
834 This is by virtue of the child jail being created in the chrooted
835 environment of the first jail.
869 Hierarchical/extensible jails were introduced in
873 The jail feature was written by
874 .An Poul-Henning Kamp
876 .Pa http://www.rndassociates.com/
877 who contributed it to
881 wrote the extended documentation, found a few bugs, added
882 a few new features, and cleaned up the userland jail environment.
885 added multi-IP jail support for IPv4 and IPv6 based on a patch
887 .An Pawel Jakub Dawidek
891 added the extensible jail parameters and hierchical jails.
893 Jail currently lacks the ability to allow access to
894 specific jail information via
898 Similarly, it might be a good idea to add an
899 address alias flag such that daemons listening on all IPs
901 will not bind on that address, which would facilitate building a safe
902 host environment such that host daemons do not impose on services offered
904 Currently, the simplest answer is to minimize services
905 offered on the host, possibly limiting it to services offered from
907 which is easily configurable.