xref: /freebsd/usr.sbin/jail/jail.8 (revision 864c53ead899f7838cd2e1cca3b485a4a82f5cdc)
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2.\" Copyright (c) 2008-2012 James Gritton
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26.\" $FreeBSD$
27.\"
28.Dd May 16, 2014
29.Dt JAIL 8
30.Os
31.Sh NAME
32.Nm jail
33.Nd "manage system jails"
34.Sh SYNOPSIS
35.Nm
36.Op Fl dhilqv
37.Op Fl J Ar jid_file
38.Op Fl u Ar username
39.Op Fl U Ar username
40.Op Fl cmr
41.Ar param Ns = Ns Ar value ...
42.Op Cm command Ns = Ns Ar command ...
43.Nm
44.Op Fl dqv
45.Op Fl f Ar conf_file
46.Op Fl p Ar limit
47.Op Fl cmr
48.Op Ar jail
49.Nm
50.Op Fl qv
51.Op Fl f Ar conf_file
52.Op Fl rR
53.Op Cm * | Ar jail ...
54.Nm
55.Op Fl dhilqv
56.Op Fl J Ar jid_file
57.Op Fl u Ar username
58.Op Fl U Ar username
59.Op Fl n Ar jailname
60.Op Fl s Ar securelevel
61.Op Ar path hostname [ Ar ip Ns [ Ns Ar ,... Ns ]] Ar command ...
62.Sh DESCRIPTION
63The
64.Nm
65utility creates new jails, or modifies or removes existing jails.
66A jail
67.Pq or Dq prison
68is specified via parameters on the command line, or in the
69.Xr jail.conf 5
70file.
71.Pp
72At least one of the options
73.Fl c ,
74.Fl m
75or
76.Fl r
77must be specified.
78These options are used alone or in combination to describe the operation to
79perform:
80.Bl -tag -width indent
81.It Fl c
82Create a new jail.
83The jail
84.Va jid
85and
86.Va name
87parameters (if specified on the command line)
88must not refer to an existing jail.
89.It Fl m
90Modify an existing jail.
91One of the
92.Va jid
93or
94.Va name
95parameters must exist and refer to an existing jail.
96Some parameters may not be changed on a running jail.
97.It Fl r
98Remove the
99.Ar jail
100specified by jid or name.
101All jailed processes are killed, and all jails that are
102children of this jail are also
103removed.
104.It Fl rc
105Restart an existing jail.
106The jail is first removed and then re-created, as if
107.Dq Nm Fl r
108and
109.Dq Nm Fl c
110were run in succession.
111.It Fl cm
112Create a jail if it does not exist, or modify the jail if it does exist.
113.It Fl mr
114Modify an existing jail.
115The jail may be restarted if necessary to modify parameters than could
116not otherwise be changed.
117.It Fl cmr
118Create a jail if it doesn't exist, or modify (and possibly restart) the
119jail if it does exist.
120.El
121.Pp
122Other available options are:
123.Bl -tag -width indent
124.It Fl d
125Allow making changes to a dying jail, equivalent to the
126.Va allow.dying
127parameter.
128.It Fl f Ar conf_file
129Use configuration file
130.Ar conf_file
131instead of the default
132.Pa /etc/jail.conf .
133.It Fl h
134Resolve the
135.Va host.hostname
136parameter (or
137.Va hostname )
138and add all IP addresses returned by the resolver
139to the list of addresses for this jail.
140This is equivalent to the
141.Va ip_hostname
142parameter.
143.It Fl i
144Output (only) the jail identifier of the newly created jail(s).
145This implies the
146.Fl q
147option.
148.It Fl J Ar jid_file
149Write a
150.Ar jid_file
151file, containing the parameters used to start the jail.
152.It Fl l
153Run commands in a clean environment.
154This is deprecated and is equivalent to the exec.clean parameter.
155.It Fl n Ar jailname
156Set the jail's name.
157This is deprecated and is equivalent to the
158.Va name
159parameter.
160.It Fl p Ar limit
161Limit the number of commands from
162.Va  exec.*
163that can run simultaneously.
164.It Fl q
165Suppress the message printed whenever a jail is created, modified or removed.
166Only error messages will be printed.
167.It Fl R
168A variation of the
169.Fl r
170option that removes an existing jail without using the configuration file.
171No removal-related parameters for this jail will be used \(em the jail will
172simply be removed.
173.It Fl s Ar securelevel
174Set the
175.Va kern.securelevel
176MIB entry to the specified value inside the newly created jail.
177This is deprecated and is equivalent to the
178.Va securelevel
179parameter.
180.It Fl u Ar username
181The user name from host environment as whom jailed commands should run.
182This is deprecated and is equivalent to the
183.Va exec.jail_user
184and
185.Va exec.system_jail_user
186parameters.
187.It Fl U Ar username
188The user name from the jailed environment as whom jailed commands should run.
189This is deprecated and is equivalent to the
190.Va exec.jail_user
191parameter.
192.It Fl v
193Print a message on every operation, such as running commands and
194mounting filesystems.
195.El
196.Pp
197If no arguments are given after the options, the operation (except
198remove) will be performed on all jails specified in the
199.Xr jail.conf 5
200file.
201A single argument of a jail name will operate only on the specified jail.
202The
203.Fl r
204and
205.Fl R
206options can also remove running jails that aren't in the
207.Xr jail.conf 5
208file, specified by name or jid.
209.Pp
210An argument of
211.Dq *
212is a wildcard that will operate on all jails, regardless of whether
213they appear in
214.Xr jail.conf 5 ;
215this is the surest way for
216.Fl r
217to remove all jails.
218If hierarchical jails exist, a partial-matching wildcard definition may
219be specified.
220For example, an argument of
221.Dq foo.*
222would apply to jails with names like
223.Dq foo.bar
224and
225.Dq foo.bar.baz .
226.Pp
227A jail may be specified with parameters directly on the command line.
228In this case, the
229.Xr jail.conf 5
230file will not be used.
231For backward compatibility, the command line may also have four fixed
232parameters, without names:
233.Ar path ,
234.Ar hostname ,
235.Ar ip ,
236and
237.Ar command .
238This mode will always create a new jail, and the
239.Fl c
240and
241.Fl m
242options do not apply (and must not be present).
243.Ss Jail Parameters
244Parameters in the
245.Xr jail.conf 5
246file, or on the command line, are generally of the form
247.Dq name=value .
248Some parameters are boolean, and do not have a value but are set by the
249name alone with or without a
250.Dq no
251prefix, e.g.
252.Va persist
253or
254.Va nopersist .
255They can also be given the values
256.Dq true
257and
258.Dq false .
259Other parameters may have more than one value, specified as a
260comma-separated list or with
261.Dq +=
262in the configuration file (see
263.Xr jail.conf 5
264for details).
265.Pp
266The
267.Nm
268utility recognizes two classes of parameters.
269There are the true jail
270parameters that are passed to the kernel when the jail is created,
271which can be seen with
272.Xr jls 8 ,
273and can (usually) be changed with
274.Dq Nm Fl m .
275Then there are pseudo-parameters that are only used by
276.Nm
277itself.
278.Pp
279Jails have a set a core parameters, and kernel modules can add their own
280jail parameters.
281The current set of available parameters can be retrieved via
282.Dq Nm sysctl Fl d Va security.jail.param .
283Any parameters not set will be given default values, often based on the
284current environment.
285The core parameters are:
286.Bl -tag -width indent
287.It Va jid
288The jail identifier.
289This will be assigned automatically to a new jail (or can be explicitly
290set), and can be used to identify the jail for later modification, or
291for such commands as
292.Xr jls 8
293or
294.Xr jexec 8 .
295.It Va name
296The jail name.
297This is an arbitrary string that identifies a jail (except it may not
298contain a
299.Sq \&. ) .
300Like the
301.Va jid ,
302it can be passed to later
303.Nm
304commands, or to
305.Xr jls 8
306or
307.Xr jexec 8 .
308If no
309.Va name
310is supplied, a default is assumed that is the same as the
311.Va jid .
312The
313.Va name
314parameter is implied by the
315.Xr jail.conf 5
316file format, and need not be explicitly set when using the configuration
317file.
318.It Va path
319The directory which is to be the root of the jail.
320Any commands run inside the jail, either by
321.Nm
322or from
323.Xr jexec 8 ,
324are run from this directory.
325.It Va ip4.addr
326A list of IPv4 addresses assigned to the jail.
327If this is set, the jail is restricted to using only these addresses.
328Any attempts to use other addresses fail, and attempts to use wildcard
329addresses silently use the jailed address instead.
330For IPv4 the first address given will be used as the source address
331when source address selection on unbound sockets cannot find a better
332match.
333It is only possible to start multiple jails with the same IP address
334if none of the jails has more than this single overlapping IP address
335assigned to itself.
336.It Va ip4.saddrsel
337A boolean option to change the formerly mentioned behaviour and disable
338IPv4 source address selection for the jail in favour of the primary
339IPv4 address of the jail.
340Source address selection is enabled by default for all jails and the
341.Va ip4.nosaddrsel
342setting of a parent jail is not inherited for any child jails.
343.It Va ip4
344Control the availability of IPv4 addresses.
345Possible values are
346.Dq inherit
347to allow unrestricted access to all system addresses,
348.Dq new
349to restrict addresses via
350.Va ip4.addr ,
351and
352.Dq disable
353to stop the jail from using IPv4 entirely.
354Setting the
355.Va ip4.addr
356parameter implies a value of
357.Dq new .
358.It Va ip6.addr , Va ip6.saddrsel , Va ip6
359A set of IPv6 options for the jail, the counterparts to
360.Va ip4.addr ,
361.Va ip4.saddrsel
362and
363.Va ip4
364above.
365.It vnet
366Create the jail with its own virtual network stack,
367with its own network interfaces, addresses, routing table, etc.
368The kernel must have been compiled with the
369.Sy VIMAGE option
370for this to be available.
371Possible values are
372.Dq inherit
373to use the system network stack, possibly with restricted IP addresses,
374and
375.Dq new
376to create a new network stack.
377.It Va host.hostname
378The hostname of the jail.
379Other similar parameters are
380.Va host.domainname ,
381.Va host.hostuuid
382and
383.Va host.hostid .
384.It Va host
385Set the origin of hostname and related information.
386Possible values are
387.Dq inherit
388to use the system information and
389.Dq new
390for the jail to use the information from the above fields.
391Setting any of the above fields implies a value of
392.Dq new .
393.It Va securelevel
394The value of the jail's
395.Va kern.securelevel
396sysctl.
397A jail never has a lower securelevel than its parent system, but by
398setting this parameter it may have a higher one.
399If the system securelevel is changed, any jail securelevels will be at
400least as secure.
401.It Va devfs_ruleset
402The number of the devfs ruleset that is enforced for mounting devfs in
403this jail.
404A value of zero (default) means no ruleset is enforced.
405Descendant jails inherit the parent jail's devfs ruleset enforcement.
406Mounting devfs inside a jail is possible only if the
407.Va allow.mount
408and
409.Va allow.mount.devfs
410permissions are effective and
411.Va enforce_statfs
412is set to a value lower than 2.
413Devfs rules and rulesets cannot be viewed or modified from inside a jail.
414.Pp
415NOTE: It is important that only appropriate device nodes in devfs be
416exposed to a jail; access to disk devices in the jail may permit processes
417in the jail to bypass the jail sandboxing by modifying files outside of
418the jail.
419See
420.Xr devfs 8
421for information on how to use devfs rules to limit access to entries
422in the per-jail devfs.
423A simple devfs ruleset for jails is available as ruleset #4 in
424.Pa /etc/defaults/devfs.rules .
425.It Va children.max
426The number of child jails allowed to be created by this jail (or by
427other jails under this jail).
428This limit is zero by default, indicating the jail is not allowed to
429create child jails.
430See the
431.Sx "Hierarchical Jails"
432section for more information.
433.It Va children.cur
434The number of descendants of this jail, including its own child jails
435and any jails created under them.
436.It Va enforce_statfs
437This determines what information processes in a jail are able to get
438about mount points.
439It affects the behaviour of the following syscalls:
440.Xr statfs 2 ,
441.Xr fstatfs 2 ,
442.Xr getfsstat 2 ,
443and
444.Xr fhstatfs 2
445(as well as similar compatibility syscalls).
446When set to 0, all mount points are available without any restrictions.
447When set to 1, only mount points below the jail's chroot directory are
448visible.
449In addition to that, the path to the jail's chroot directory is removed
450from the front of their pathnames.
451When set to 2 (default), above syscalls can operate only on a mount-point
452where the jail's chroot directory is located.
453.It Va persist
454Setting this boolean parameter allows a jail to exist without any
455processes.
456Normally, a command is run as part of jail creation, and then the jail
457is destroyed as its last process exits.
458A new jail must have either the
459.Va persist
460parameter or
461.Va exec.start
462or
463.Va command
464pseudo-parameter set.
465.It Va cpuset.id
466The ID of the cpuset associated with this jail (read-only).
467.It Va dying
468This is true if the jail is in the process of shutting down (read-only).
469.It Va parent
470The
471.Va jid
472of the parent of this jail, or zero if this is a top-level jail
473(read-only).
474.It Va allow.*
475Some restrictions of the jail environment may be set on a per-jail
476basis.
477With the exception of
478.Va allow.set_hostname ,
479these boolean parameters are off by default.
480.Bl -tag -width indent
481.It Va allow.set_hostname
482The jail's hostname may be changed via
483.Xr hostname 1
484or
485.Xr sethostname 3 .
486.It Va allow.sysvipc
487A process within the jail has access to System V IPC primitives.
488In the current jail implementation, System V primitives share a single
489namespace across the host and jail environments, meaning that processes
490within a jail would be able to communicate with (and potentially interfere
491with) processes outside of the jail, and in other jails.
492.It Va allow.raw_sockets
493The jail root is allowed to create raw sockets.
494Setting this parameter allows utilities like
495.Xr ping 8
496and
497.Xr traceroute 8
498to operate inside the jail.
499If this is set, the source IP addresses are enforced to comply
500with the IP address bound to the jail, regardless of whether or not
501the
502.Dv IP_HDRINCL
503flag has been set on the socket.
504Since raw sockets can be used to configure and interact with various
505network subsystems, extra caution should be used where privileged access
506to jails is given out to untrusted parties.
507.It Va allow.chflags
508Normally, privileged users inside a jail are treated as unprivileged by
509.Xr chflags 2 .
510When this parameter is set, such users are treated as privileged, and
511may manipulate system file flags subject to the usual constraints on
512.Va kern.securelevel .
513.It Va allow.mount
514privileged users inside the jail will be able to mount and unmount file
515system types marked as jail-friendly.
516The
517.Xr lsvfs 1
518command can be used to find file system types available for mount from
519within a jail.
520This permission is effective only if
521.Va enforce_statfs
522is set to a value lower than 2.
523.It Va allow.mount.devfs
524privileged users inside the jail will be able to mount and unmount the
525devfs file system.
526This permission is effective only together with
527.Va allow.mount
528and only when
529.Va enforce_statfs
530is set to a value lower than 2.
531The devfs ruleset should be restricted from the default by using the
532.Va devfs_ruleset
533option.
534.It Va allow.mount.nullfs
535privileged users inside the jail will be able to mount and unmount the
536nullfs file system.
537This permission is effective only together with
538.Va allow.mount
539and only when
540.Va enforce_statfs
541is set to a value lower than 2.
542.It Va allow.mount.procfs
543privileged users inside the jail will be able to mount and unmount the
544procfs file system.
545This permission is effective only together with
546.Va allow.mount
547and only when
548.Va enforce_statfs
549is set to a value lower than 2.
550.It Va allow.mount.tmpfs
551privileged users inside the jail will be able to mount and unmount the
552tmpfs file system.
553This permission is effective only together with
554.Va allow.mount
555and only when
556.Va enforce_statfs
557is set to a value lower than 2.
558.It Va allow.mount.zfs
559privileged users inside the jail will be able to mount and unmount the
560ZFS file system.
561This permission is effective only together with
562.Va allow.mount
563and only when
564.Va enforce_statfs
565is set to a value lower than 2.
566See
567.Xr zfs 8
568for information on how to configure the ZFS filesystem to operate from
569within a jail.
570.It Va allow.quotas
571The jail root may administer quotas on the jail's filesystem(s).
572This includes filesystems that the jail may share with other jails or
573with non-jailed parts of the system.
574.It Va allow.socket_af
575Sockets within a jail are normally restricted to IPv4, IPv6, local
576(UNIX), and route.  This allows access to other protocol stacks that
577have not had jail functionality added to them.
578.El
579.El
580.Pp
581There are pseudo-parameters that are not passed to the kernel, but are
582used by
583.Nm
584to set up the jail environment, often by running specified commands
585when jails are created or removed.
586The
587.Va exec.*
588command parameters are
589.Xr sh 1
590command lines that are run in either the system or jail environment.
591They may be given multiple values, which run would the specified
592commands in sequence.
593All commands must succeed (return a zero exit status), or the jail will
594not be created or removed, as appropriate.
595.Pp
596The pseudo-parameters are:
597.Bl -tag -width indent
598.It Va exec.prestart
599Command(s) to run in the system environment before a jail is created.
600.It Va exec.start
601Command(s) to run in the jail environment when a jail is created.
602A typical command to run is
603.Dq sh /etc/rc .
604.It Va command
605A synonym for
606.Va exec.start
607for use when specifying a jail directly on the command line.
608Unlike other parameters whose value is a single string,
609.Va command
610uses the remainder of the
611.Nm
612command line as its own arguments.
613.It Va exec.poststart
614Command(s) to run in the system environment after a jail is created,
615and after any
616.Va exec.start
617commands have completed.
618.It Va exec.prestop
619Command(s) to run in the system environment before a jail is removed.
620.It Va exec.stop
621Command(s) to run in the jail environment before a jail is removed,
622and after any
623.Va exec.prestop
624commands have completed.
625A typical command to run is
626.Dq sh /etc/rc.shutdown .
627.It Va exec.poststop
628Command(s) to run in the system environment after a jail is removed.
629.It Va exec.clean
630Run commands in a clean environment.
631The environment is discarded except for
632.Ev HOME , SHELL , TERM
633and
634.Ev USER .
635.Ev HOME
636and
637.Ev SHELL
638are set to the target login's default values.
639.Ev USER
640is set to the target login.
641.Ev TERM
642is imported from the current environment.
643The environment variables from the login class capability database for the
644target login are also set.
645.It Va exec.jail_user
646The user to run commands as, when running in the jail environment.
647The default is to run the commands as the current user.
648.It Va exec.system_jail_user
649This boolean option looks for the
650.Va exec.jail_user
651in the system
652.Xr passwd 5
653file, instead of in the jail's file.
654.It Va exec.system_user
655The user to run commands as, when running in the system environment.
656The default is to run the commands as the current user.
657.It Va exec.timeout
658The maximum amount of time to wait for a command to complete.
659If a command is still running after this many seconds have passed,
660the jail will not be created or removed, as appropriate.
661.It Va exec.consolelog
662A file to direct command output (stdout and stderr) to.
663.It Va exec.fib
664The FIB (routing table) to set when running commands inside the jail.
665.It Va stop.timeout
666The maximum amount of time to wait for a jail's processes to exit
667after sending them a
668.Dv SIGTERM
669signal (which happens after the
670.Va exec.stop
671commands have completed).
672After this many seconds have passed, the jail will be removed, which
673will kill any remaining processes.
674If this is set to zero, no
675.Dv SIGTERM
676is sent and the jail is immediately removed.
677The default is 10 seconds.
678.It Va interface
679A network interface to add the jail's IP addresses
680.Va ( ip4.addr
681and
682.Va ip6.addr )
683to.
684An alias for each address will be added to the interface before the
685jail is created, and will be removed from the interface after the
686jail is removed.
687.It Va ip4.addr
688In addition to the IP addresses that are passed to the kernel, an
689interface and/or a netmask may also be specified, in the form
690.Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar netmask .
691If an interface is given before the IP address, an alias for the address
692will be added to that interface, as it is with the
693.Va interface
694parameter.
695If a netmask in either dotted-quad or CIDR form is given
696after an IP address, it will be used when adding the IP alias.
697.It Va ip6.addr
698In addition to the IP addresses that are passed to the kernel,
699an interface and/or a prefix may also be specified, in the form
700.Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar prefix .
701.It Va vnet.interface
702A network interface to give to a vnet-enabled jail after is it created.
703The interface will automatically be released when the jail is removed.
704.It Va ip_hostname
705Resolve the
706.Va host.hostname
707parameter and add all IP addresses returned by the resolver
708to the list of addresses
709.Po Va ip4.addr
710or
711.Va ip6.addr Pc
712for this jail.
713This may affect default address selection for outgoing IPv4 connections
714from jails.
715The address first returned by the resolver for each address family
716will be used as the primary address.
717.It Va mount
718A filesystem to mount before creating the jail (and to unmount after
719removing it), given as a single
720.Xr fstab 5
721line.
722.It Va mount.fstab
723An
724.Xr fstab 5
725format file containing filesystems to mount before creating a jail.
726.It Va mount.devfs
727Mount a
728.Xr devfs 5
729filesystem on the chrooted
730.Pa /dev
731directory, and apply the ruleset in the
732.Va devfs_ruleset
733parameter (or a default of ruleset 4: devfsrules_jail)
734to restrict the devices visible inside the jail.
735.It Va mount.fdescfs
736Mount a
737.Xr fdescfs 5
738filesystem on the chrooted
739.Pa /dev/fd
740directory.
741.It Va allow.dying
742Allow making changes to a
743.Va dying
744jail.
745.It Va depend
746Specify a jail (or jails) that this jail depends on.
747Any such jails must be fully created, up to the last
748.Va exec.poststart
749command, before any action will taken to create this jail.
750When jails are removed the opposite is true:
751this jail must be fully removed, up to the last
752.Va exec.poststop
753command, before the jail(s) it depends on are stopped.
754.El
755.Sh EXAMPLES
756Jails are typically set up using one of two philosophies: either to
757constrain a specific application (possibly running with privilege), or
758to create a
759.Dq "virtual system image"
760running a variety of daemons and services.
761In both cases, a fairly complete file system install of
762.Fx
763is
764required, so as to provide the necessary command line tools, daemons,
765libraries, application configuration files, etc.
766However, for a virtual server configuration, a fair amount of
767additional work is required so as to replace the
768.Dq boot
769process.
770This manual page documents the configuration steps necessary to support
771either of these steps, although the configuration steps may need to be
772refined based on local requirements.
773.Ss "Setting up a Jail Directory Tree"
774To set up a jail directory tree containing an entire
775.Fx
776distribution, the following
777.Xr sh 1
778command script can be used:
779.Bd -literal
780D=/here/is/the/jail
781cd /usr/src
782mkdir -p $D
783make world DESTDIR=$D
784make distribution DESTDIR=$D
785.Ed
786.Pp
787In many cases this example would put far more in the jail than needed.
788In the other extreme case a jail might contain only one file:
789the executable to be run in the jail.
790.Pp
791We recommend experimentation, and caution that it is a lot easier to
792start with a
793.Dq fat
794jail and remove things until it stops working,
795than it is to start with a
796.Dq thin
797jail and add things until it works.
798.Ss "Setting Up a Jail"
799Do what was described in
800.Sx "Setting Up a Jail Directory Tree"
801to build the jail directory tree.
802For the sake of this example, we will
803assume you built it in
804.Pa /data/jail/testjail ,
805for a jail named
806.Dq testjail .
807Substitute below as needed with your
808own directory, IP address, and hostname.
809.Ss "Setting up the Host Environment"
810First, set up the real system's environment to be
811.Dq jail-friendly .
812For consistency, we will refer to the parent box as the
813.Dq "host environment" ,
814and to the jailed virtual machine as the
815.Dq "jail environment" .
816Since jails are implemented using IP aliases, one of the first things to do
817is to disable IP services on the host system that listen on all local
818IP addresses for a service.
819If a network service is present in the host environment that binds all
820available IP addresses rather than specific IP addresses, it may service
821requests sent to jail IP addresses if the jail did not bind the port.
822This means changing
823.Xr inetd 8
824to only listen on the
825appropriate IP address, and so forth.
826Add the following to
827.Pa /etc/rc.conf
828in the host environment:
829.Bd -literal -offset indent
830sendmail_enable="NO"
831inetd_flags="-wW -a 192.0.2.23"
832rpcbind_enable="NO"
833.Ed
834.Pp
835.Li 192.0.2.23
836is the native IP address for the host system, in this example.
837Daemons that run out of
838.Xr inetd 8
839can be easily configured to use only the specified host IP address.
840Other daemons
841will need to be manually configured \(em for some this is possible through
842.Xr rc.conf 5
843flags entries; for others it is necessary to modify per-application
844configuration files, or to recompile the application.
845The following frequently deployed services must have their individual
846configuration files modified to limit the application to listening
847to a specific IP address:
848.Pp
849To configure
850.Xr sshd 8 ,
851it is necessary to modify
852.Pa /etc/ssh/sshd_config .
853.Pp
854To configure
855.Xr sendmail 8 ,
856it is necessary to modify
857.Pa /etc/mail/sendmail.cf .
858.Pp
859For
860.Xr named 8 ,
861it is necessary to modify
862.Pa /etc/namedb/named.conf .
863.Pp
864In addition, a number of services must be recompiled in order to run
865them in the host environment.
866This includes most applications providing services using
867.Xr rpc 3 ,
868such as
869.Xr rpcbind 8 ,
870.Xr nfsd 8 ,
871and
872.Xr mountd 8 .
873In general, applications for which it is not possible to specify which
874IP address to bind should not be run in the host environment unless they
875should also service requests sent to jail IP addresses.
876Attempting to serve
877NFS from the host environment may also cause confusion, and cannot be
878easily reconfigured to use only specific IPs, as some NFS services are
879hosted directly from the kernel.
880Any third-party network software running
881in the host environment should also be checked and configured so that it
882does not bind all IP addresses, which would result in those services also
883appearing to be offered by the jail environments.
884.Pp
885Once
886these daemons have been disabled or fixed in the host environment, it is
887best to reboot so that all daemons are in a known state, to reduce the
888potential for confusion later (such as finding that when you send mail
889to a jail, and its sendmail is down, the mail is delivered to the host,
890etc.).
891.Ss "Configuring the Jail"
892Start any jail for the first time without configuring the network
893interface so that you can clean it up a little and set up accounts.
894As
895with any machine (virtual or not), you will need to set a root password, time
896zone, etc.
897Some of these steps apply only if you intend to run a full virtual server
898inside the jail; others apply both for constraining a particular application
899or for running a virtual server.
900.Pp
901Start a shell in the jail:
902.Bd -literal -offset indent
903jail -c path=/data/jail/testjail mount.devfs \\
904	host.hostname=testhostname ip4.addr=192.0.2.100 \\
905	command=/bin/sh
906.Ed
907.Pp
908Assuming no errors, you will end up with a shell prompt within the jail.
909You can now run
910.Pa /usr/sbin/sysinstall
911and do the post-install configuration to set various configuration options,
912or perform these actions manually by editing
913.Pa /etc/rc.conf ,
914etc.
915.Pp
916.Bl -bullet -offset indent -compact
917.It
918Configure
919.Pa /etc/resolv.conf
920so that name resolution within the jail will work correctly.
921.It
922Run
923.Xr newaliases 1
924to quell
925.Xr sendmail 8
926warnings.
927.It
928Set a root password, probably different from the real host system.
929.It
930Set the timezone.
931.It
932Add accounts for users in the jail environment.
933.It
934Install any packages the environment requires.
935.El
936.Pp
937You may also want to perform any package-specific configuration (web servers,
938SSH servers, etc), patch up
939.Pa /etc/syslog.conf
940so it logs as you would like, etc.
941If you are not using a virtual server, you may wish to modify
942.Xr syslogd 8
943in the host environment to listen on the syslog socket in the jail
944environment; in this example, the syslog socket would be stored in
945.Pa /data/jail/testjail/var/run/log .
946.Pp
947Exit from the shell, and the jail will be shut down.
948.Ss "Starting the Jail"
949You are now ready to restart the jail and bring up the environment with
950all of its daemons and other programs.
951Create an entry for the jail in
952.Pa /etc/jail.conf :
953.Bd -literal -offset indent
954testjail {
955	path = /tmp/jail/testjail;
956	mount.devfs;
957	host.hostname = testhostname;
958	ip4.addr = 192.0.2.100;
959	interface = ed0;
960	exec.start = "/bin/sh /etc/rc";
961	exec.stop = "/bin/sh /etc/rc.shutdown";
962}
963.Ed
964.Pp
965To start a virtual server environment,
966.Pa /etc/rc
967is run to launch various daemons and services, and
968.Pa /etc/rc.shutdown
969is run to shut them down when the jail is removed.
970If you are running a single application in the jail,
971substitute the command used to start the application for
972.Dq /bin/sh /etc/rc ;
973there may be some script available to cleanly shut down the application,
974or it may be sufficient to go without a stop command, and have
975.Nm
976send
977.Dv SIGTERM
978to the application.
979.Pp
980Start the jail by running:
981.Bd -literal -offset indent
982jail -c testjail
983.Ed
984.Pp
985A few warnings may be produced; however, it should all work properly.
986You should be able to see
987.Xr inetd 8 ,
988.Xr syslogd 8 ,
989and other processes running within the jail using
990.Xr ps 1 ,
991with the
992.Ql J
993flag appearing beside jailed processes.
994To see an active list of jails, use
995.Xr jls 8 .
996If
997.Xr sshd 8
998is enabled in the jail environment, you should be able to
999.Xr ssh 1
1000to the hostname or IP address of the jailed environment, and log
1001in using the accounts you created previously.
1002.Pp
1003It is possible to have jails started at boot time.
1004Please refer to the
1005.Dq jail_*
1006variables in
1007.Xr rc.conf 5
1008for more information.
1009.Ss "Managing the Jail"
1010Normal machine shutdown commands, such as
1011.Xr halt 8 ,
1012.Xr reboot 8 ,
1013and
1014.Xr shutdown 8 ,
1015cannot be used successfully within the jail.
1016To kill all processes from within a jail, you may use one of the
1017following commands, depending on what you want to accomplish:
1018.Bd -literal -offset indent
1019kill -TERM -1
1020kill -KILL -1
1021.Ed
1022.Pp
1023This will send the
1024.Dv SIGTERM
1025or
1026.Dv SIGKILL
1027signals to all processes in the jail \(em be careful not to run this from
1028the host environment!
1029Once all of the jail's processes have died, unless the jail was created
1030with the
1031.Va persist
1032parameter, the jail will be removed.
1033Depending on
1034the intended use of the jail, you may also want to run
1035.Pa /etc/rc.shutdown
1036from within the jail.
1037.Pp
1038To shut down the jail from the outside, simply remove it with
1039.Nm
1040.Ar -r ,
1041which will run any commands specified by
1042.Va exec.stop ,
1043and then send
1044.Dv SIGTERM
1045and eventually
1046.Dv SIGKILL
1047to any remaining jailed processes.
1048.Pp
1049The
1050.Pa /proc/ Ns Ar pid Ns Pa /status
1051file contains, as its last field, the name of the jail in which the
1052process runs, or
1053.Dq Li -
1054to indicate that the process is not running within a jail.
1055The
1056.Xr ps 1
1057command also shows a
1058.Ql J
1059flag for processes in a jail.
1060.Pp
1061You can also list/kill processes based on their jail ID.
1062To show processes and their jail ID, use the following command:
1063.Pp
1064.Dl "ps ax -o pid,jid,args"
1065.Pp
1066To show and then kill processes in jail number 3 use the following commands:
1067.Bd -literal -offset indent
1068pgrep -lfj 3
1069pkill -j 3
1070.Ed
1071or:
1072.Pp
1073.Dl "killall -j 3"
1074.Ss "Jails and File Systems"
1075It is not possible to
1076.Xr mount 8
1077or
1078.Xr umount 8
1079any file system inside a jail unless the file system is marked
1080jail-friendly, the jail's
1081.Va allow.mount
1082parameter is set, and the jail's
1083.Va enforce_statfs
1084parameter is lower than 2.
1085.Pp
1086Multiple jails sharing the same file system can influence each other.
1087For example, a user in one jail can fill the file system,
1088leaving no space for processes in the other jail.
1089Trying to use
1090.Xr quota 1
1091to prevent this will not work either, as the file system quotas
1092are not aware of jails but only look at the user and group IDs.
1093This means the same user ID in two jails share a single file
1094system quota.
1095One would need to use one file system per jail to make this work.
1096.Ss "Sysctl MIB Entries"
1097The read-only entry
1098.Va security.jail.jailed
1099can be used to determine if a process is running inside a jail (value
1100is one) or not (value is zero).
1101.Pp
1102The variable
1103.Va security.jail.max_af_ips
1104determines how may address per address family a jail may have.
1105The default is 255.
1106.Pp
1107Some MIB variables have per-jail settings.
1108Changes to these variables by a jailed process do not affect the host
1109environment, only the jail environment.
1110These variables are
1111.Va kern.securelevel ,
1112.Va kern.hostname ,
1113.Va kern.domainname ,
1114.Va kern.hostid ,
1115and
1116.Va kern.hostuuid .
1117.Ss "Hierarchical Jails"
1118By setting a jail's
1119.Va children.max
1120parameter, processes within a jail may be able to create jails of their own.
1121These child jails are kept in a hierarchy, with jails only able to see and/or
1122modify the jails they created (or those jails' children).
1123Each jail has a read-only
1124.Va parent
1125parameter, containing the
1126.Va jid
1127of the jail that created it; a
1128.Va jid
1129of 0 indicates the jail is a child of the current jail (or is a top-level
1130jail if the current process isn't jailed).
1131.Pp
1132Jailed processes are not allowed to confer greater permissions than they
1133themselves are given, e.g., if a jail is created with
1134.Va allow.nomount ,
1135it is not able to create a jail with
1136.Va allow.mount
1137set.
1138Similarly, such restrictions as
1139.Va ip4.addr
1140and
1141.Va securelevel
1142may not be bypassed in child jails.
1143.Pp
1144A child jail may in turn create its own child jails if its own
1145.Va children.max
1146parameter is set (remember it is zero by default).
1147These jails are visible to and can be modified by their parent and all
1148ancestors.
1149.Pp
1150Jail names reflect this hierarchy, with a full name being an MIB-type string
1151separated by dots.
1152For example, if a base system process creates a jail
1153.Dq foo ,
1154and a process under that jail creates another jail
1155.Dq bar ,
1156then the second jail will be seen as
1157.Dq foo.bar
1158in the base system (though it is only seen as
1159.Dq bar
1160to any processes inside jail
1161.Dq foo ) .
1162Jids on the other hand exist in a single space, and each jail must have a
1163unique jid.
1164.Pp
1165Like the names, a child jail's
1166.Va path
1167appears relative to its creator's own
1168.Va path .
1169This is by virtue of the child jail being created in the chrooted
1170environment of the first jail.
1171.Sh SEE ALSO
1172.Xr killall 1 ,
1173.Xr lsvfs 1 ,
1174.Xr newaliases 1 ,
1175.Xr pgrep 1 ,
1176.Xr pkill 1 ,
1177.Xr ps 1 ,
1178.Xr quota 1 ,
1179.Xr jail_set 2 ,
1180.Xr devfs 5 ,
1181.Xr fdescfs 5 ,
1182.Xr jail.conf 5 ,
1183.Xr procfs 5 ,
1184.Xr rc.conf 5 ,
1185.Xr sysctl.conf 5 ,
1186.Xr chroot 8 ,
1187.Xr devfs 8 ,
1188.Xr halt 8 ,
1189.Xr inetd 8 ,
1190.Xr jexec 8 ,
1191.Xr jls 8 ,
1192.Xr mount 8 ,
1193.Xr named 8 ,
1194.Xr reboot 8 ,
1195.Xr rpcbind 8 ,
1196.Xr sendmail 8 ,
1197.Xr shutdown 8 ,
1198.Xr sysctl 8 ,
1199.Xr syslogd 8 ,
1200.Xr umount 8
1201.Sh HISTORY
1202The
1203.Nm
1204utility appeared in
1205.Fx 4.0 .
1206Hierarchical/extensible jails were introduced in
1207.Fx 8.0 .
1208The configuration file was introduced in
1209.Fx 9.1 .
1210.Sh AUTHORS
1211.An -nosplit
1212The jail feature was written by
1213.An Poul-Henning Kamp
1214for R&D Associates
1215.Pa http://www.rndassociates.com/
1216who contributed it to
1217.Fx .
1218.Pp
1219.An Robert Watson
1220wrote the extended documentation, found a few bugs, added
1221a few new features, and cleaned up the userland jail environment.
1222.Pp
1223.An Bjoern A. Zeeb
1224added multi-IP jail support for IPv4 and IPv6 based on a patch
1225originally done by
1226.An Pawel Jakub Dawidek
1227for IPv4.
1228.Pp
1229.An James Gritton
1230added the extensible jail parameters, hierarchical jails,
1231and the configuration file.
1232.Sh BUGS
1233It might be a good idea to add an
1234address alias flag such that daemons listening on all IPs
1235.Pq Dv INADDR_ANY
1236will not bind on that address, which would facilitate building a safe
1237host environment such that host daemons do not impose on services offered
1238from within jails.
1239Currently, the simplest answer is to minimize services
1240offered on the host, possibly limiting it to services offered from
1241.Xr inetd 8
1242which is easily configurable.
1243.Sh NOTES
1244Great care should be taken when managing directories visible within the jail.
1245For example, if a jailed process has its current working directory set to a
1246directory that is moved out of the jail's chroot, then the process may gain
1247access to the file space outside of the jail.
1248It is recommended that directories always be copied, rather than moved, out
1249of a jail.
1250.Pp
1251In addition, there are several ways in which an unprivileged user
1252outside the jail can cooperate with a privileged user inside the jail
1253and thereby obtain elevated privileges in the host environment.
1254Most of these attacks can be mitigated by ensuring that the jail root
1255is not accessible to unprivileged users in the host environment.
1256Regardless, as a general rule, untrusted users with privileged access
1257to a jail should not be given access to the host environment.
1258