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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 ...
54 .Op Fl s Ar securelevel
55 .Op Fl l u Ar username | Fl U Ar username
56 .Op Ar path hostname [ip[,..]] command ...
62 utility creates a new jail or modifies an existing jail, optionally
63 imprisoning the current process (and future descendants) inside it.
65 The options are as follows:
66 .Bl -tag -width indent
68 Allow making changes to a dying jail.
74 and add all IP addresses returned by the resolver
77 addresses for this prison.
78 This may affect default address selection for outgoing IPv4 connections
80 The address first returned by the resolver for each address family
81 will be used as primary address.
86 parameters further down for details.
88 Output the jail identifier of the newly created jail.
91 This is deprecated and is equivalent to setting the
97 file, containing jail identifier, path, hostname, IP and
98 command used to start the jail.
100 Run program in the clean environment.
101 The environment is discarded except for
102 .Ev HOME , SHELL , TERM
108 are set to the target login's default values.
110 is set to the target login.
112 is imported from the current environment.
113 The environment variables from the login class capability database for the
114 target login are also set.
115 .It Fl s Ar securelevel
118 MIB entry to the specified value inside the newly created jail.
119 This is deprecated and is equivalent to setting the
123 The user name from host environment as whom the
127 The user name from jailed environment as whom the
136 parameters (if specified) must not refer to an existing jail.
138 Modify an existing jail.
143 parameters must exist and refer to an existing jail.
145 Create a jail if it does not exist, or modify a jail if it does exist.
149 specified by jid or name.
150 All jailed processes are killed, and all children of this jail are also
159 options must be specified.
164 form, following the options.
165 Some parameters are boolean, and do not have a value but are set by the
166 name alone with or without a
172 Any parameters not set will be given default values, often based on the
177 specifies that the current process should enter the new (or modified) jail,
178 and run the specified command.
179 It must be the last parameter specified, because it includes not only
180 the value following the
182 sign, but also passes the rest of the arguments to the command.
184 Instead of supplying named
186 four fixed parameters may be supplied in order on the command line:
196 parameters aren't in this list, this mode will always create a new jail, and
201 options don't apply (and must not exist).
203 Jails have a set a core parameters, and modules can add their own jail
205 The current set of available parameters can be retrieved via
206 .Dq Nm sysctl Fl d Va security.jail.param .
207 The core parameters are:
208 .Bl -tag -width indent
211 This will be assigned automatically to a new jail (or can be explicitly
212 set), and can be used to identify the jail for later modification, or
219 This is an arbitrary string that identifies a jail (except it may not
224 it can be passed to later
232 is supplied, a default is assumed that is the same as the
235 Directory which is to be the root of the prison.
238 (if any) is run from this directory, as are commands from
241 A comma-separated list of IPv4 addresses assigned to the prison.
242 If this is set, the jail is restricted to using only these addresses.
243 Any attempts to use other addresses fail, and attempts to use wildcard
244 addresses silently use the jailed address instead.
245 For IPv4 the first address given will be kept used as the source address
246 in case source address selection on unbound sockets cannot find a better
248 It is only possible to start multiple jails with the same IP address,
249 if none of the jails has more than this single overlapping IP address
252 A boolean option to change the formerly mentioned behaviour and disable
253 IPv4 source address selection for the prison in favour of the primary
254 IPv4 address of the jail.
255 Source address selection is enabled by default for all jails and a
257 setting of a parent jail is not inherited for any child jails.
259 Control the availability of IPv4 addresses.
262 to allow unrestricted access to all system addresses,
264 to restrict addresses via
268 to stop the jail from using IPv4 entirely.
271 parameter implies a value of
273 .It Va ip6.addr , Va ip6.saddrsel , Va ip6
274 A set of IPv6 options for the prison, the counterparts to
281 Hostname of the prison.
282 Other similar parameters are
283 .Va host.domainname ,
288 Set the origin of hostname and related information.
291 to use the system information and
293 for the jail to use the information from the above fields.
294 Setting any of the above fields implies a value of
297 The value of the jail's
300 A jail never has a lower securelevel than the default system, but by
301 setting this parameter it may have a higher one.
302 If the system securelevel is changed, any jail securelevels will be at
305 The number of child jails allowed to be created by this jail (or by
306 other jails under this jail).
307 This limit is zero by default, indicating the jail is not allowed to
310 .Va "Hierarchical Jails"
311 section for more information.
313 The number of descendents of this jail, including its own child jails
314 and any jails created under them.
315 .It Va enforce_statfs
316 This determines which information processes in a jail are able to get
318 It affects the behaviour of the following syscalls:
324 (as well as similar compatibility syscalls).
325 When set to 0, all mount points are available without any restrictions.
326 When set to 1, only mount points below the jail's chroot directory are
328 In addition to that, the path to the jail's chroot directory is removed
329 from the front of their pathnames.
330 When set to 2 (default), above syscalls can operate only on a mount-point
331 where the jail's chroot directory is located.
333 Setting this boolean parameter allows a jail to exist without any
335 Normally, a jail is destroyed as its last process exits.
336 A new jail must have either the
340 pseudo-parameter set.
342 The ID of the cpuset associated with this jail (read-only).
344 This is true if the jail is in the process of shutting down (read-only).
348 of the parent of this jail, or zero if this is a top-level jail
351 Some restrictions of the jail environment may be set on a per-jail
353 With the exception of
354 .Va allow.set_hostname ,
355 these boolean parameters are off by default.
356 .Bl -tag -width indent
357 .It Va allow.set_hostname
358 The jail's hostname may be changed via
363 A process within the jail has access to System V IPC primitives.
364 In the current jail implementation, System V primitives share a single
365 namespace across the host and jail environments, meaning that processes
366 within a jail would be able to communicate with (and potentially interfere
367 with) processes outside of the jail, and in other jails.
368 .It Va allow.raw_sockets
369 The prison root is allowed to create raw sockets.
370 Setting this parameter allows utilities like
374 to operate inside the prison.
375 If this is set, the source IP addresses are enforced to comply
376 with the IP address bound to the jail, regardless of whether or not
379 flag has been set on the socket.
380 Since raw sockets can be used to configure and interact with various
381 network subsystems, extra caution should be used where privileged access
382 to jails is given out to untrusted parties.
384 Normally, privileged users inside a jail are treated as unprivileged by
386 When this parameter is set, such users are treated as privileged, and
387 may manipulate system file flags subject to the usual constraints on
388 .Va kern.securelevel .
390 privileged users inside the jail will be able to mount and unmount file
391 system types marked as jail-friendly.
394 command can be used to find file system types available for mount from
396 This permission is effective only if
398 is set to a value lower than 2.
400 The prison root may administer quotas on the jail's filesystem(s).
401 This includes filesystems that the jail may share with other jails or
402 with non-jailed parts of the system.
403 .It Va allow.socket_af
404 Sockets within a jail are normally restricted to IPv4, IPv6, local
405 (UNIX), and route. This allows access to other protocol stacks that
406 have not had jail functionality added to them.
410 Jails are typically set up using one of two philosophies: either to
411 constrain a specific application (possibly running with privilege), or
413 .Dq "virtual system image"
414 running a variety of daemons and services.
415 In both cases, a fairly complete file system install of
418 required, so as to provide the necessary command line tools, daemons,
419 libraries, application configuration files, etc.
420 However, for a virtual server configuration, a fair amount of
421 additional work is required so as to configure the
424 This manual page documents the configuration steps necessary to support
425 either of these steps, although the configuration steps may be
426 refined based on local requirements.
428 .Ss "Setting up a Jail Directory Tree"
429 To set up a jail directory tree containing an entire
431 distribution, the following
433 command script can be used:
438 make world DESTDIR=$D
439 make distribution DESTDIR=$D
440 mount -t devfs devfs $D/dev
443 NOTE: It is important that only appropriate device nodes in devfs be
444 exposed to a jail; access to disk devices in the jail may permit processes
445 in the jail to bypass the jail sandboxing by modifying files outside of
449 for information on how to use devfs rules to limit access to entries
450 in the per-jail devfs.
451 A simple devfs ruleset for jails is available as ruleset #4 in
452 .Pa /etc/defaults/devfs.rules .
454 In many cases this example would put far more in the jail than needed.
455 In the other extreme case a jail might contain only one file:
456 the executable to be run in the jail.
458 We recommend experimentation and caution that it is a lot easier to
461 jail and remove things until it stops working,
462 than it is to start with a
464 jail and add things until it works.
465 .Ss "Setting Up a Jail"
466 Do what was described in
467 .Sx "Setting Up a Jail Directory Tree"
468 to build the jail directory tree.
469 For the sake of this example, we will
470 assume you built it in
471 .Pa /data/jail/192.0.2.100 ,
472 named for the jailed IP address.
473 Substitute below as needed with your
474 own directory, IP address, and hostname.
475 .Ss "Setting up the Host Environment"
476 First, you will want to set up your real system's environment to be
478 For consistency, we will refer to the parent box as the
479 .Dq "host environment" ,
480 and to the jailed virtual machine as the
481 .Dq "jail environment" .
482 Since jail is implemented using IP aliases, one of the first things to do
483 is to disable IP services on the host system that listen on all local
484 IP addresses for a service.
485 If a network service is present in the host environment that binds all
486 available IP addresses rather than specific IP addresses, it may service
487 requests sent to jail IP addresses if the jail did not bind the port.
490 to only listen on the
491 appropriate IP address, and so forth.
494 in the host environment:
495 .Bd -literal -offset indent
497 inetd_flags="-wW -a 192.0.2.23"
502 is the native IP address for the host system, in this example.
503 Daemons that run out of
505 can be easily set to use only the specified host IP address.
507 will need to be manually configured\(emfor some this is possible through
510 flags entries; for others it is necessary to modify per-application
511 configuration files, or to recompile the applications.
512 The following frequently deployed services must have their individual
513 configuration files modified to limit the application to listening
514 to a specific IP address:
518 it is necessary to modify
519 .Pa /etc/ssh/sshd_config .
523 it is necessary to modify
524 .Pa /etc/mail/sendmail.cf .
528 it is necessary to modify
529 .Pa /etc/namedb/named.conf .
531 In addition, a number of services must be recompiled in order to run
532 them in the host environment.
533 This includes most applications providing services using
540 In general, applications for which it is not possible to specify which
541 IP address to bind should not be run in the host environment unless they
542 should also service requests sent to jail IP addresses.
544 NFS from the host environment may also cause confusion, and cannot be
545 easily reconfigured to use only specific IPs, as some NFS services are
546 hosted directly from the kernel.
547 Any third-party network software running
548 in the host environment should also be checked and configured so that it
549 does not bind all IP addresses, which would result in those services' also
550 appearing to be offered by the jail environments.
553 these daemons have been disabled or fixed in the host environment, it is
554 best to reboot so that all daemons are in a known state, to reduce the
555 potential for confusion later (such as finding that when you send mail
556 to a jail, and its sendmail is down, the mail is delivered to the host,
558 .Ss "Configuring the Jail"
559 Start any jail for the first time without configuring the network
560 interface so that you can clean it up a little and set up accounts.
562 with any machine (virtual or not) you will need to set a root password, time
564 Some of these steps apply only if you intend to run a full virtual server
565 inside the jail; others apply both for constraining a particular application
566 or for running a virtual server.
568 Start a shell in the jail:
569 .Bd -literal -offset indent
570 jail -c path=/data/jail/192.0.2.100 host.hostname=testhostname \\
571 ip4.addr=192.0.2.100 command=/bin/sh
574 Assuming no errors, you will end up with a shell prompt within the jail.
576 .Pa /usr/sbin/sysinstall
577 and do the post-install configuration to set various configuration options,
578 or perform these actions manually by editing
582 .Bl -bullet -offset indent -compact
586 to quell startup warnings about missing fstab (virtual server only)
588 Disable the port mapper
590 .Li rpcbind_enable="NO" )
591 (virtual server only)
595 so that name resolution within the jail will work correctly
603 Disable interface configuration to quell startup warnings about
605 .Pq Li network_interfaces=""
606 (virtual server only)
608 Set a root password, probably different from the real host system
612 Add accounts for users in the jail environment
614 Install any packages the environment requires
617 You may also want to perform any package-specific configuration (web servers,
618 SSH servers, etc), patch up
620 so it logs as you would like, etc.
621 If you are not using a virtual server, you may wish to modify
623 in the host environment to listen on the syslog socket in the jail
624 environment; in this example, the syslog socket would be stored in
625 .Pa /data/jail/192.0.2.100/var/run/log .
627 Exit from the shell, and the jail will be shut down.
628 .Ss "Starting the Jail"
629 You are now ready to restart the jail and bring up the environment with
630 all of its daemons and other programs.
631 If you are running a single application in the jail, substitute the
632 command used to start the application for
634 in the examples below.
635 To start a virtual server environment,
637 is run to launch various daemons and services.
638 To do this, first bring up the
639 virtual host interface, and then start the jail's
641 script from within the jail.
642 .Bd -literal -offset indent
643 ifconfig ed0 inet alias 192.0.2.100/32
644 mount -t procfs proc /data/jail/192.0.2.100/proc
645 jail -c path=/data/jail/192.0.2.100 host.hostname=testhostname \\
646 ip4.addr=192.0.2.100 command=/bin/sh /etc/rc
649 A few warnings will be produced, because most
651 configuration variables cannot be set from within the jail, as they are
652 global across all jails and the host environment.
653 However, it should all
655 You should be able to see
658 and other processes running within the jail using
662 flag appearing beside jailed processes.
663 To see an active list of jails, use the
666 You should also be able to
668 to the hostname or IP address of the jailed environment, and log
669 in using the accounts you created previously.
671 It is possible to have jails started at boot time.
676 for more information.
679 jail script provides a flexible system to start/stop jails:
683 /etc/rc.d/jail start myjail
684 /etc/rc.d/jail stop myjail
686 .Ss "Managing the Jail"
687 Normal machine shutdown commands, such as
692 cannot be used successfully within the jail.
693 To kill all processes in a
694 jail, you may log into the jail and, as root, use one of the following
695 commands, depending on what you want to accomplish:
696 .Bd -literal -offset indent
705 signals to all processes in the jail from within the jail.
707 the intended use of the jail, you may also want to run
709 from within the jail.
710 To kill processes from outside the jail, use the
712 utility in conjunction with the one of the
715 You may also remove the jail with
718 which will killall the jail's processes with
722 .Pa /proc/ Ns Ar pid Ns Pa /status
723 file contains, as its last field, the name of the jail in which the
726 to indicate that the process is not running within a jail.
731 flag for processes in a jail.
733 You can also list/kill processes based on their jail ID.
734 To show processes and their jail ID, use the following command:
736 .Dl "ps ax -o pid,jid,args"
738 To show and then kill processes in jail number 3 use the following commands:
739 .Bd -literal -offset indent
746 .Ss "Jails and File Systems"
747 It is not possible to
751 any file system inside a jail unless the file system is marked
752 jail-friendly, the jail's
754 parameter is set and the jail's
756 parameter is lower than 2.
758 Multiple jails sharing the same file system can influence each other.
759 For example a user in one jail can fill the file system also
760 leaving no space for processes in the other jail.
763 to prevent this will not work either as the file system quotas
764 are not aware of jails but only look at the user and group IDs.
765 This means the same user ID in two jails share the same file
767 One would need to use one file system per jail to make this work.
768 .Ss "Sysctl MIB Entries"
770 .Va security.jail.jailed
771 can be used to determine if a process is running inside a jail (value
772 is one) or not (value is zero).
775 .Va security.jail.max_af_ips
776 determines how may address per address family a prison may have.
779 Some MIB variables have per-jail settings.
780 Changes to these variables by a jailed process do not effect the host
781 environment, only the jail environment.
783 .Va kern.securelevel ,
785 .Va kern.domainname ,
789 .Ss "Hierarchical Jails"
792 parameter, processes within a jail may be able to create jails of their own.
793 These child jails are kept in a hierarchy, with jails only able to see and/or
794 modify the jails they created (or those jails' children).
795 Each jail has a read-only
797 parameter, containing the
799 of the jail that created it; a
801 of 0 indicates the jail is a child of the current jail (or is a top-level
802 jail if the current process isn't jailed).
804 Jailed processes are not allowed to confer greater permissions than they
805 themselves are given, e.g. if a jail is created with
807 it is not able to create a jail with
810 Similarly, such restrictions as
814 may not be bypassed in child jails.
816 A child jail may in turn create its own child jails if its own
818 parameter is set (remember it is zero by default).
819 These jails are visible to and can be modified by their parent and all
822 Jail names reflect this hierarchy, with a full name being an MIB-type string
824 For example, if a base system process creates a jail
826 and a process under that jail creates another jail
828 then the second jail will be seen as
830 in the base system (though it is only seen as
832 to any processes inside jail
834 Jids on the other hand exist in a single space, and each jail must have a
837 Like the names, a child jail's
839 is relative to its creator's own
841 This is by virtue of the child jail being created in the chrooted
842 environment of the first jail.
876 Hierarchical/extensible jails were introduced in
880 The jail feature was written by
881 .An Poul-Henning Kamp
883 .Pa http://www.rndassociates.com/
884 who contributed it to
888 wrote the extended documentation, found a few bugs, added
889 a few new features, and cleaned up the userland jail environment.
892 added multi-IP jail support for IPv4 and IPv6 based on a patch
894 .An Pawel Jakub Dawidek
898 added the extensible jail parameters and hierarchical jails.
900 Jail currently lacks the ability to allow access to
901 specific jail information via
905 Similarly, it might be a good idea to add an
906 address alias flag such that daemons listening on all IPs
908 will not bind on that address, which would facilitate building a safe
909 host environment such that host daemons do not impose on services offered
911 Currently, the simplest answer is to minimize services
912 offered on the host, possibly limiting it to services offered from
914 which is easily configurable.
916 Great care should be taken when managing directories visible within the jail.
917 For example, if a jailed process has its current working directory set to a
918 directory that is moved out of the jail's chroot, then the process may gain
919 access to the file space outside of the jail.
920 It is recommended that directories always be copied, rather than moved, out