xref: /freebsd/usr.sbin/jail/jail.8 (revision c7046f76c2c027b00c0e6ba57cfd28f1a78f5e23)
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2.\" Copyright (c) 2008-2012 James Gritton
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26.\" $FreeBSD$
27.\"
28.Dd July 18, 2022
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.Ar path hostname ip Ns Op Cm \&, Ns Ar ...
62.Ar command ...
63.Nm
64.Op Fl f Ar conf_file
65.Fl e
66.Ar separator
67.Sh DESCRIPTION
68The
69.Nm
70utility creates new jails, or modifies or removes existing jails.
71It can also print a list of configured jails and their parameters.
72A jail
73.Pq or Dq prison
74is specified via parameters on the command line, or in the
75.Xr jail.conf 5
76file.
77.Pp
78At least one of the options
79.Fl c ,
80.Fl e ,
81.Fl m
82or
83.Fl r
84must be specified.
85These options are used alone or in combination to describe the operation to
86perform:
87.Bl -tag -width indent
88.It Fl c
89Create a new jail.
90The jail
91.Va jid
92and
93.Va name
94parameters (if specified on the command line)
95must not refer to an existing jail.
96.It Fl e Ar separator
97Exhibit a list of all configured non-wildcard jails and their parameters.
98No jail creation, modification or removal performed if this option is used.
99The
100.Ar separator
101string is used to separate parameters.
102Use
103.Xr jls 8
104utility to list running jails.
105.It Fl m
106Modify an existing jail.
107One of the
108.Va jid
109or
110.Va name
111parameters must exist and refer to an existing jail.
112Some parameters may not be changed on a running jail.
113.It Fl r
114Remove the
115.Ar jail
116specified by jid or name.
117All jailed processes are killed, and all jails that are
118children of this jail are also
119removed.
120.It Fl rc
121Restart an existing jail.
122The jail is first removed and then re-created, as if
123.Dq Nm Fl r
124and
125.Dq Nm Fl c
126were run in succession.
127.It Fl cm
128Create a jail if it does not exist, or modify the jail if it does exist.
129.It Fl mr
130Modify an existing jail.
131The jail may be restarted if necessary to modify parameters than could
132not otherwise be changed.
133.It Fl cmr
134Create a jail if it doesn't exist, or modify (and possibly restart) the
135jail if it does exist.
136.El
137.Pp
138Other available options are:
139.Bl -tag -width indent
140.It Fl d
141Allow making changes to a dying jail, equivalent to the
142.Va allow.dying
143parameter.
144.It Fl f Ar conf_file
145Use configuration file
146.Ar conf_file
147instead of the default
148.Pa /etc/jail.conf .
149.It Fl h
150Resolve the
151.Va host.hostname
152parameter (or
153.Va hostname )
154and add all IP addresses returned by the resolver
155to the list of addresses for this jail.
156This is equivalent to the
157.Va ip_hostname
158parameter.
159.It Fl i
160Output (only) the jail identifier of the newly created jail(s).
161This implies the
162.Fl q
163option.
164.It Fl J Ar jid_file
165Write a
166.Ar jid_file
167file, containing the parameters used to start the jail.
168.It Fl l
169Run commands in a clean environment.
170This is deprecated and is equivalent to the exec.clean parameter.
171.It Fl n Ar jailname
172Set the jail's name.
173This is deprecated and is equivalent to the
174.Va name
175parameter.
176.It Fl p Ar limit
177Limit the number of commands from
178.Va  exec.*
179that can run simultaneously.
180.It Fl q
181Suppress the message printed whenever a jail is created, modified or removed.
182Only error messages will be printed.
183.It Fl R
184A variation of the
185.Fl r
186option that removes an existing jail without using the configuration file.
187No removal-related parameters for this jail will be used \(em the jail will
188simply be removed.
189.It Fl s Ar securelevel
190Set the
191.Va kern.securelevel
192MIB entry to the specified value inside the newly created jail.
193This is deprecated and is equivalent to the
194.Va securelevel
195parameter.
196.It Fl u Ar username
197The user name from host environment as whom jailed commands should run.
198This is deprecated and is equivalent to the
199.Va exec.jail_user
200and
201.Va exec.system_jail_user
202parameters.
203.It Fl U Ar username
204The user name from the jailed environment as whom jailed commands should run.
205This is deprecated and is equivalent to the
206.Va exec.jail_user
207parameter.
208.It Fl v
209Print a message on every operation, such as running commands and
210mounting filesystems.
211.El
212.Pp
213If no arguments are given after the options, the operation (except
214remove) will be performed on all jails specified in the
215.Xr jail.conf 5
216file.
217A single argument of a jail name will operate only on the specified jail.
218The
219.Fl r
220and
221.Fl R
222options can also remove running jails that aren't in the
223.Xr jail.conf 5
224file, specified by name or jid.
225.Pp
226An argument of
227.Dq *
228is a wildcard that will operate on all jails, regardless of whether
229they appear in
230.Xr jail.conf 5 ;
231this is the surest way for
232.Fl r
233to remove all jails.
234If hierarchical jails exist, a partial-matching wildcard definition may
235be specified.
236For example, an argument of
237.Dq foo.*
238would apply to jails with names like
239.Dq foo.bar
240and
241.Dq foo.bar.baz .
242.Pp
243A jail may be specified with parameters directly on the command line.
244In this case, the
245.Xr jail.conf 5
246file will not be used.
247For backward compatibility, the command line may also have four fixed
248parameters, without names:
249.Ar path ,
250.Ar hostname ,
251.Ar ip ,
252and
253.Ar command .
254This mode will always create a new jail, and the
255.Fl c
256and
257.Fl m
258options do not apply (and must not be present).
259.Ss Jail Parameters
260Parameters in the
261.Xr jail.conf 5
262file, or on the command line, are generally of the form
263.Dq name=value .
264Some parameters are boolean, and do not have a value but are set by the
265name alone with or without a
266.Dq no
267prefix, e.g.
268.Va persist
269or
270.Va nopersist .
271They can also be given the values
272.Dq true
273and
274.Dq false .
275Other parameters may have more than one value, specified as a
276comma-separated list or with
277.Dq +=
278in the configuration file (see
279.Xr jail.conf 5
280for details).
281.Pp
282The
283.Nm
284utility recognizes two classes of parameters.
285There are the true jail
286parameters that are passed to the kernel when the jail is created,
287which can be seen with
288.Xr jls 8 ,
289and can (usually) be changed with
290.Dq Nm Fl m .
291Then there are pseudo-parameters that are only used by
292.Nm
293itself.
294.Pp
295Jails have a set of core parameters, and kernel modules can add their own
296jail parameters.
297The current set of available parameters can be retrieved via
298.Dq Nm sysctl Fl d Va security.jail.param .
299Any parameters not set will be given default values, often based on the
300current environment.
301The core parameters are:
302.Bl -tag -width indent
303.It Va jid
304The jail identifier.
305This will be assigned automatically to a new jail (or can be explicitly
306set), and can be used to identify the jail for later modification, or
307for such commands as
308.Xr jls 8
309or
310.Xr jexec 8 .
311.It Va name
312The jail name.
313This is an arbitrary string that identifies a jail (except it may not
314contain a
315.Sq \&. ) .
316Like the
317.Va jid ,
318it can be passed to later
319.Nm
320commands, or to
321.Xr jls 8
322or
323.Xr jexec 8 .
324If no
325.Va name
326is supplied, a default is assumed that is the same as the
327.Va jid .
328The
329.Va name
330parameter is implied by the
331.Xr jail.conf 5
332file format, and need not be explicitly set when using the configuration
333file.
334.It Va path
335The directory which is to be the root of the jail.
336Any commands run inside the jail, either by
337.Nm
338or from
339.Xr jexec 8 ,
340are run from this directory.
341.It Va ip4.addr
342A list of IPv4 addresses assigned to the jail.
343If this is set, the jail is restricted to using only these addresses.
344Any attempts to use other addresses fail, and attempts to use wildcard
345addresses silently use the jailed address instead.
346For IPv4 the first address given will be used as the source address
347when source address selection on unbound sockets cannot find a better
348match.
349It is only possible to start multiple jails with the same IP address
350if none of the jails has more than this single overlapping IP address
351assigned to itself.
352.It Va ip4.saddrsel
353A boolean option to change the formerly mentioned behaviour and disable
354IPv4 source address selection for the jail in favour of the primary
355IPv4 address of the jail.
356Source address selection is enabled by default for all jails and the
357.Va ip4.nosaddrsel
358setting of a parent jail is not inherited for any child jails.
359.It Va ip4
360Control the availability of IPv4 addresses.
361Possible values are
362.Dq inherit
363to allow unrestricted access to all system addresses,
364.Dq new
365to restrict addresses via
366.Va ip4.addr ,
367and
368.Dq disable
369to stop the jail from using IPv4 entirely.
370Setting the
371.Va ip4.addr
372parameter implies a value of
373.Dq new .
374.It Va ip6.addr , Va ip6.saddrsel , Va ip6
375A set of IPv6 options for the jail, the counterparts to
376.Va ip4.addr ,
377.Va ip4.saddrsel
378and
379.Va ip4
380above.
381.It Va vnet
382Create the jail with its own virtual network stack,
383with its own network interfaces, addresses, routing table, etc.
384The kernel must have been compiled with the
385.Sy VIMAGE option
386for this to be available.
387Possible values are
388.Dq inherit
389to use the system network stack, possibly with restricted IP addresses,
390and
391.Dq new
392to create a new network stack.
393.It Va host.hostname
394The hostname of the jail.
395Other similar parameters are
396.Va host.domainname ,
397.Va host.hostuuid
398and
399.Va host.hostid .
400.It Va host
401Set the origin of hostname and related information.
402Possible values are
403.Dq inherit
404to use the system information and
405.Dq new
406for the jail to use the information from the above fields.
407Setting any of the above fields implies a value of
408.Dq new .
409.It Va securelevel
410The value of the jail's
411.Va kern.securelevel
412sysctl.
413A jail never has a lower securelevel than its parent system, but by
414setting this parameter it may have a higher one.
415If the system securelevel is changed, any jail securelevels will be at
416least as secure.
417.It Va devfs_ruleset
418The number of the devfs ruleset that is enforced for mounting devfs in
419this jail.
420A value of zero (default) means no ruleset is enforced.
421Descendant jails inherit the parent jail's devfs ruleset enforcement.
422Mounting devfs inside a jail is possible only if the
423.Va allow.mount
424and
425.Va allow.mount.devfs
426permissions are effective and
427.Va enforce_statfs
428is set to a value lower than 2.
429Devfs rules and rulesets cannot be viewed or modified from inside a jail.
430.Pp
431NOTE: It is important that only appropriate device nodes in devfs be
432exposed to a jail; access to disk devices in the jail may permit processes
433in the jail to bypass the jail sandboxing by modifying files outside of
434the jail.
435See
436.Xr devfs 8
437for information on how to use devfs rules to limit access to entries
438in the per-jail devfs.
439A simple devfs ruleset for jails is available as ruleset #4 in
440.Pa /etc/defaults/devfs.rules .
441.It Va children.max
442The number of child jails allowed to be created by this jail (or by
443other jails under this jail).
444This limit is zero by default, indicating the jail is not allowed to
445create child jails.
446See the
447.Sx "Hierarchical Jails"
448section for more information.
449.It Va children.cur
450The number of descendants of this jail, including its own child jails
451and any jails created under them.
452.It Va enforce_statfs
453This determines what information processes in a jail are able to get
454about mount points.
455It affects the behaviour of the following syscalls:
456.Xr statfs 2 ,
457.Xr fstatfs 2 ,
458.Xr getfsstat 2 ,
459and
460.Xr fhstatfs 2
461(as well as similar compatibility syscalls).
462When set to 0, all mount points are available without any restrictions.
463When set to 1, only mount points below the jail's chroot directory are
464visible.
465In addition to that, the path to the jail's chroot directory is removed
466from the front of their pathnames.
467When set to 2 (default), above syscalls can operate only on a mount-point
468where the jail's chroot directory is located.
469.It Va persist
470Setting this boolean parameter allows a jail to exist without any
471processes.
472Normally, a command is run as part of jail creation, and then the jail
473is destroyed as its last process exits.
474A new jail must have either the
475.Va persist
476parameter or
477.Va exec.start
478or
479.Va command
480pseudo-parameter set.
481.It Va cpuset.id
482The ID of the cpuset associated with this jail (read-only).
483.It Va dying
484This is true if the jail is in the process of shutting down (read-only).
485.It Va parent
486The
487.Va jid
488of the parent of this jail, or zero if this is a top-level jail
489(read-only).
490.It Va osrelease
491The string for the jail's
492.Va kern.osrelease
493sysctl and uname -r.
494.It Va osreldate
495The number for the jail's
496.Va kern.osreldate
497and uname -K.
498.It Va allow.*
499Some restrictions of the jail environment may be set on a per-jail
500basis.
501With the exception of
502.Va allow.set_hostname
503and
504.Va allow.reserved_ports ,
505these boolean parameters are off by default.
506.Bl -tag -width indent
507.It Va allow.set_hostname
508The jail's hostname may be changed via
509.Xr hostname 1
510or
511.Xr sethostname 3 .
512.It Va allow.sysvipc
513A process within the jail has access to System V IPC primitives.
514This is deprecated in favor of the per-module parameters (see below).
515When this parameter is set, it is equivalent to setting
516.Va sysvmsg ,
517.Va sysvsem ,
518and
519.Va sysvshm
520all to
521.Dq inherit .
522.It Va allow.raw_sockets
523The jail root is allowed to create raw sockets.
524Setting this parameter allows utilities like
525.Xr ping 8
526and
527.Xr traceroute 8
528to operate inside the jail.
529If this is set, the source IP addresses are enforced to comply
530with the IP address bound to the jail, regardless of whether or not
531the
532.Dv IP_HDRINCL
533flag has been set on the socket.
534Since raw sockets can be used to configure and interact with various
535network subsystems, extra caution should be used where privileged access
536to jails is given out to untrusted parties.
537.It Va allow.chflags
538Normally, privileged users inside a jail are treated as unprivileged by
539.Xr chflags 2 .
540When this parameter is set, such users are treated as privileged, and
541may manipulate system file flags subject to the usual constraints on
542.Va kern.securelevel .
543.It Va allow.mount
544privileged users inside the jail will be able to mount and unmount file
545system types marked as jail-friendly.
546The
547.Xr lsvfs 1
548command can be used to find file system types available for mount from
549within a jail.
550This permission is effective only if
551.Va enforce_statfs
552is set to a value lower than 2.
553.It Va allow.mount.devfs
554privileged users inside the jail will be able to mount and unmount the
555devfs file system.
556This permission is effective only together with
557.Va allow.mount
558and only when
559.Va enforce_statfs
560is set to a value lower than 2.
561The devfs ruleset should be restricted from the default by using the
562.Va devfs_ruleset
563option.
564.It Va allow.quotas
565The jail root may administer quotas on the jail's filesystem(s).
566This includes filesystems that the jail may share with other jails or
567with non-jailed parts of the system.
568.It Va allow.read_msgbuf
569Jailed users may read the kernel message buffer.
570If the
571.Va security.bsd.unprivileged_read_msgbuf
572MIB entry is zero, this will be restricted to the root user.
573.It Va allow.socket_af
574Sockets within a jail are normally restricted to IPv4, IPv6, local
575(UNIX), and route.  This allows access to other protocol stacks that
576have not had jail functionality added to them.
577.It Va allow.mlock
578Locking or unlocking physical pages in memory are normally not available
579within a jail.
580When this parameter is set, users may
581.Xr mlock 2
582or
583.Xr munlock 2
584memory subject to
585.Va security.bsd.unprivileged_mlock
586and resource limits.
587.It Va allow.reserved_ports
588The jail root may bind to ports lower than 1024.
589.It Va allow.unprivileged_proc_debug
590Unprivileged processes in the jail may use debugging facilities.
591.It Va allow.suser
592The value of the jail's
593.Va security.bsd.suser_enabled
594sysctl.
595The super-user will be disabled automatically if its parent system has it
596disabled.
597The super-user is enabled by default.
598.El
599.El
600.Pp
601Kernel modules may add their own parameters, which only exist when the
602module is loaded.
603These are typically headed under a parameter named after the module,
604with values of
605.Dq inherit
606to give the jail full use of the module,
607.Dq new
608to encapsulate the jail in some module-specific way,
609and
610.Dq disable
611to make the module unavailable to the jail.
612There also may be other parameters to define jail behavior within the module.
613Module-specific parameters include:
614.Bl -tag -width indent
615.It Va allow.mount.fdescfs
616privileged users inside the jail will be able to mount and unmount the
617fdescfs file system.
618This permission is effective only together with
619.Va allow.mount
620and only when
621.Va enforce_statfs
622is set to a value lower than 2.
623.It Va allow.mount.fusefs
624privileged users inside the jail will be able to mount and unmount
625fuse-based file systems.
626This permission is effective only together with
627.Va allow.mount
628and only when
629.Va enforce_statfs
630is set to a value lower than 2.
631.It Va allow.mount.nullfs
632privileged users inside the jail will be able to mount and unmount the
633nullfs file system.
634This permission is effective only together with
635.Va allow.mount
636and only when
637.Va enforce_statfs
638is set to a value lower than 2.
639.It Va allow.mount.procfs
640privileged users inside the jail will be able to mount and unmount the
641procfs file system.
642This permission is effective only together with
643.Va allow.mount
644and only when
645.Va enforce_statfs
646is set to a value lower than 2.
647.It Va allow.mount.linprocfs
648privileged users inside the jail will be able to mount and unmount the
649linprocfs file system.
650This permission is effective only together with
651.Va allow.mount
652and only when
653.Va enforce_statfs
654is set to a value lower than 2.
655.It Va allow.mount.linsysfs
656privileged users inside the jail will be able to mount and unmount the
657linsysfs file system.
658This permission is effective only together with
659.Va allow.mount
660and only when
661.Va enforce_statfs
662is set to a value lower than 2.
663.It Va allow.mount.tmpfs
664privileged users inside the jail will be able to mount and unmount the
665tmpfs file system.
666This permission is effective only together with
667.Va allow.mount
668and only when
669.Va enforce_statfs
670is set to a value lower than 2.
671.It Va allow.mount.zfs
672privileged users inside the jail will be able to mount and unmount the
673ZFS file system.
674This permission is effective only together with
675.Va allow.mount
676and only when
677.Va enforce_statfs
678is set to a value lower than 2.
679See
680.Xr zfs 8
681for information on how to configure the ZFS filesystem to operate from
682within a jail.
683.It Va allow.vmm
684The jail may access
685.Xr vmm 4 .
686This flag is only available when the
687.Xr vmm 4
688kernel module is loaded.
689.It Va linux
690Determine how a jail's Linux emulation environment appears.
691A value of
692.Dq inherit
693will keep the same environment, and
694.Dq new
695will give the jail its own environment (still originally inherited when
696the jail is created).
697.It Va linux.osname , linux.osrelease , linux.oss_version
698The Linux OS name, OS release, and OSS version associated with this jail.
699.It Va sysvmsg
700Allow access to SYSV IPC message primitives.
701If set to
702.Dq inherit ,
703all IPC objects on the system are visible to this jail, whether they
704were created by the jail itself, the base system, or other jails.
705If set to
706.Dq new ,
707the jail will have its own key namespace, and can only see the objects
708that it has created;
709the system (or parent jail) has access to the jail's objects, but not to
710its keys.
711If set to
712.Dq disable ,
713the jail cannot perform any sysvmsg-related system calls.
714.It Va sysvsem, sysvshm
715Allow access to SYSV IPC semaphore and shared memory primitives, in the
716same manner as
717.Va sysvmsg.
718.El
719.Pp
720There are pseudo-parameters that are not passed to the kernel, but are
721used by
722.Nm
723to set up the jail environment, often by running specified commands
724when jails are created or removed.
725The
726.Va exec.*
727command parameters are
728.Xr sh 1
729command lines that are run in either the system or jail environment.
730They may be given multiple values, which would run the specified
731commands in sequence.
732All commands must succeed (return a zero exit status), or the jail will
733not be created or removed, as appropriate.
734.Pp
735The pseudo-parameters are:
736.Bl -tag -width indent
737.It Va exec.prepare
738Command(s) to run in the system environment to prepare a jail for creation.
739These commands are executed before assigning IP addresses and mounting
740filesystems, so they may be used to create a new jail filesystem if it does
741not already exist.
742.It Va exec.prestart
743Command(s) to run in the system environment before a jail is created.
744.It Va exec.created
745Command(s) to run in the system environment right after a jail has been
746created, but before commands (or services) get executed in the jail.
747.It Va exec.start
748Command(s) to run in the jail environment when a jail is created.
749A typical command to run is
750.Dq sh /etc/rc .
751.It Va command
752A synonym for
753.Va exec.start
754for use when specifying a jail directly on the command line.
755Unlike other parameters whose value is a single string,
756.Va command
757uses the remainder of the
758.Nm
759command line as its own arguments.
760.It Va exec.poststart
761Command(s) to run in the system environment after a jail is created,
762and after any
763.Va exec.start
764commands have completed.
765.It Va exec.prestop
766Command(s) to run in the system environment before a jail is removed.
767.It Va exec.stop
768Command(s) to run in the jail environment before a jail is removed,
769and after any
770.Va exec.prestop
771commands have completed.
772A typical command to run is
773.Dq sh /etc/rc.shutdown jail .
774.It Va exec.poststop
775Command(s) to run in the system environment after a jail is removed.
776.It Va exec.release
777Command(s) to run in the system environment after all other actions are done.
778These commands are executed after unmounting filesystems and removing IP
779addresses, so they may be used to remove a jail filesystem if it is no longer
780needed.
781.It Va exec.clean
782Run commands in a clean environment.
783The environment is discarded except for
784.Ev HOME , SHELL , TERM
785and
786.Ev USER .
787.Ev HOME
788and
789.Ev SHELL
790are set to the target login's default values.
791.Ev USER
792is set to the target login.
793.Ev TERM
794is imported from the current environment.
795The environment variables from the login class capability database for the
796target login are also set.
797.It Va exec.jail_user
798The user to run commands as, when running in the jail environment.
799The default is to run the commands as the current user.
800.It Va exec.system_jail_user
801This boolean option looks for the
802.Va exec.jail_user
803in the system
804.Xr passwd 5
805file, instead of in the jail's file.
806.It Va exec.system_user
807The user to run commands as, when running in the system environment.
808The default is to run the commands as the current user.
809.It Va exec.timeout
810The maximum amount of time to wait for a command to complete, in
811seconds.
812If a command is still running after this timeout has passed,
813the jail will not be created or removed, as appropriate.
814.It Va exec.consolelog
815A file to direct command output (stdout and stderr) to.
816.It Va exec.fib
817The FIB (routing table) to set when running commands inside the jail.
818.It Va stop.timeout
819The maximum amount of time to wait for a jail's processes to exit
820after sending them a
821.Dv SIGTERM
822signal (which happens after the
823.Va exec.stop
824commands have completed).
825After this many seconds have passed, the jail will be removed, which
826will kill any remaining processes.
827If this is set to zero, no
828.Dv SIGTERM
829is sent and the jail is immediately removed.
830The default is 10 seconds.
831.It Va interface
832A network interface to add the jail's IP addresses
833.Va ( ip4.addr
834and
835.Va ip6.addr )
836to.
837An alias for each address will be added to the interface before the
838jail is created, and will be removed from the interface after the
839jail is removed.
840.It Va ip4.addr
841In addition to the IP addresses that are passed to the kernel, an
842interface, netmask and additional parameters (as supported by
843.Xr ifconfig 8 Ns )
844may also be specified, in the form
845.Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar netmask param ... .
846If an interface is given before the IP address, an alias for the address
847will be added to that interface, as it is with the
848.Va interface
849parameter.
850If a netmask in either dotted-quad or CIDR form is given
851after an IP address, it will be used when adding the IP alias.
852If additional parameters are specified then they will also be used when
853adding the IP alias.
854.It Va ip6.addr
855In addition to the IP addresses that are passed to the kernel,
856an interface, prefix and additional parameters (as supported by
857.Xr ifconfig 8 Ns )
858may also be specified, in the form
859.Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar prefix param ... .
860.It Va vnet.interface
861A network interface to give to a vnet-enabled jail after is it created.
862The interface will automatically be released when the jail is removed.
863.It Va ip_hostname
864Resolve the
865.Va host.hostname
866parameter and add all IP addresses returned by the resolver
867to the list of addresses
868.Po Va ip4.addr
869or
870.Va ip6.addr Pc
871for this jail.
872This may affect default address selection for outgoing IPv4 connections
873from jails.
874The address first returned by the resolver for each address family
875will be used as the primary address.
876.It Va mount
877A filesystem to mount before creating the jail (and to unmount after
878removing it), given as a single
879.Xr fstab 5
880line.
881.It Va mount.fstab
882An
883.Xr fstab 5
884format file containing filesystems to mount before creating a jail.
885.It Va mount.devfs
886Mount a
887.Xr devfs 5
888filesystem on the chrooted
889.Pa /dev
890directory, and apply the ruleset in the
891.Va devfs_ruleset
892parameter (or a default of ruleset 4: devfsrules_jail)
893to restrict the devices visible inside the jail.
894.It Va mount.fdescfs
895Mount a
896.Xr fdescfs 5
897filesystem on the chrooted
898.Pa /dev/fd
899directory.
900.It Va mount.procfs
901Mount a
902.Xr procfs 5
903filesystem on the chrooted
904.Pa /proc
905directory.
906.It Va allow.dying
907Allow making changes to a
908.Va dying
909jail.
910.It Va depend
911Specify a jail (or jails) that this jail depends on.
912When this jail is to be created, any jail(s) it depends on must already exist.
913If not, they will be created automatically, up to the completion of the last
914.Va exec.poststart
915command, before any action will taken to create this jail.
916When jails are removed the opposite is true:
917this jail will be removed, up to the last
918.Va exec.poststop
919command, before any jail(s) it depends on are stopped.
920.El
921.Sh EXAMPLES
922Jails are typically set up using one of two philosophies: either to
923constrain a specific application (possibly running with privilege), or
924to create a
925.Dq "virtual system image"
926running a variety of daemons and services.
927In both cases, a fairly complete file system install of
928.Fx
929is
930required, so as to provide the necessary command line tools, daemons,
931libraries, application configuration files, etc.
932However, for a virtual server configuration, a fair amount of
933additional work is required so as to replace the
934.Dq boot
935process.
936This manual page documents the configuration steps necessary to support
937either of these steps, although the configuration steps may need to be
938refined based on local requirements.
939.Ss "Setting up a Jail Directory Tree"
940To set up a jail directory tree containing an entire
941.Fx
942distribution, the following
943.Xr sh 1
944command script can be used:
945.Bd -literal -offset indent
946D=/here/is/the/jail
947cd /usr/src
948mkdir -p $D
949make world DESTDIR=$D
950make distribution DESTDIR=$D
951.Ed
952.Pp
953In many cases this example would put far more in the jail than needed.
954In the other extreme case a jail might contain only one file:
955the executable to be run in the jail.
956.Pp
957We recommend experimentation, and caution that it is a lot easier to
958start with a
959.Dq fat
960jail and remove things until it stops working,
961than it is to start with a
962.Dq thin
963jail and add things until it works.
964.Ss "Setting Up a Jail"
965Do what was described in
966.Sx "Setting Up a Jail Directory Tree"
967to build the jail directory tree.
968For the sake of this example, we will
969assume you built it in
970.Pa /data/jail/testjail ,
971for a jail named
972.Dq testjail .
973Substitute below as needed with your
974own directory, IP address, and hostname.
975.Ss "Setting up the Host Environment"
976First, set up the real system's environment to be
977.Dq jail-friendly .
978For consistency, we will refer to the parent box as the
979.Dq "host environment" ,
980and to the jailed virtual machine as the
981.Dq "jail environment" .
982Since jails are implemented using IP aliases, one of the first things to do
983is to disable IP services on the host system that listen on all local
984IP addresses for a service.
985If a network service is present in the host environment that binds all
986available IP addresses rather than specific IP addresses, it may service
987requests sent to jail IP addresses if the jail did not bind the port.
988This means changing
989.Xr inetd 8
990to only listen on the
991appropriate IP address, and so forth.
992Add the following to
993.Pa /etc/rc.conf
994in the host environment:
995.Bd -literal -offset indent
996sendmail_enable="NO"
997inetd_flags="-wW -a 192.0.2.23"
998rpcbind_enable="NO"
999.Ed
1000.Pp
1001.Li 192.0.2.23
1002is the native IP address for the host system, in this example.
1003Daemons that run out of
1004.Xr inetd 8
1005can be easily configured to use only the specified host IP address.
1006Other daemons
1007will need to be manually configured \(em for some this is possible through
1008.Xr rc.conf 5
1009flags entries; for others it is necessary to modify per-application
1010configuration files, or to recompile the application.
1011The following frequently deployed services must have their individual
1012configuration files modified to limit the application to listening
1013to a specific IP address:
1014.Pp
1015To configure
1016.Xr sshd 8 ,
1017it is necessary to modify
1018.Pa /etc/ssh/sshd_config .
1019.Pp
1020To configure
1021.Xr sendmail 8 ,
1022it is necessary to modify
1023.Pa /etc/mail/sendmail.cf .
1024.Pp
1025In addition, a number of services must be recompiled in order to run
1026them in the host environment.
1027This includes most applications providing services using
1028.Xr rpc 3 ,
1029such as
1030.Xr rpcbind 8 ,
1031.Xr nfsd 8 ,
1032and
1033.Xr mountd 8 .
1034In general, applications for which it is not possible to specify which
1035IP address to bind should not be run in the host environment unless they
1036should also service requests sent to jail IP addresses.
1037Attempting to serve
1038NFS from the host environment may also cause confusion, and cannot be
1039easily reconfigured to use only specific IPs, as some NFS services are
1040hosted directly from the kernel.
1041Any third-party network software running
1042in the host environment should also be checked and configured so that it
1043does not bind all IP addresses, which would result in those services also
1044appearing to be offered by the jail environments.
1045.Pp
1046Once
1047these daemons have been disabled or fixed in the host environment, it is
1048best to reboot so that all daemons are in a known state, to reduce the
1049potential for confusion later (such as finding that when you send mail
1050to a jail, and its sendmail is down, the mail is delivered to the host,
1051etc.).
1052.Ss "Configuring the Jail"
1053Start any jail for the first time without configuring the network
1054interface so that you can clean it up a little and set up accounts.
1055As
1056with any machine (virtual or not), you will need to set a root password, time
1057zone, etc.
1058Some of these steps apply only if you intend to run a full virtual server
1059inside the jail; others apply both for constraining a particular application
1060or for running a virtual server.
1061.Pp
1062Start a shell in the jail:
1063.Bd -literal -offset indent
1064jail -c path=/data/jail/testjail mount.devfs \\
1065	host.hostname=testhostname ip4.addr=192.0.2.100 \\
1066	command=/bin/sh
1067.Ed
1068.Pp
1069Assuming no errors, you will end up with a shell prompt within the jail.
1070You can now run
1071.Xr bsdconfig 8
1072and do the post-install configuration to set various configuration options,
1073or perform these actions manually by editing
1074.Pa /etc/rc.conf ,
1075etc.
1076.Pp
1077.Bl -bullet -offset indent -compact
1078.It
1079Configure
1080.Pa /etc/resolv.conf
1081so that name resolution within the jail will work correctly.
1082.It
1083Run
1084.Xr newaliases 1
1085to quell
1086.Xr sendmail 8
1087warnings.
1088.It
1089Set a root password, probably different from the real host system.
1090.It
1091Set the timezone.
1092.It
1093Add accounts for users in the jail environment.
1094.It
1095Install any packages the environment requires.
1096.El
1097.Pp
1098You may also want to perform any package-specific configuration (web servers,
1099SSH servers, etc), patch up
1100.Pa /etc/syslog.conf
1101so it logs as you would like, etc.
1102If you are not using a virtual server, you may wish to modify
1103.Xr syslogd 8
1104in the host environment to listen on the syslog socket in the jail
1105environment; in this example, the syslog socket would be stored in
1106.Pa /data/jail/testjail/var/run/log .
1107.Pp
1108Exit from the shell, and the jail will be shut down.
1109.Ss "Starting the Jail"
1110You are now ready to restart the jail and bring up the environment with
1111all of its daemons and other programs.
1112Create an entry for the jail in
1113.Pa /etc/jail.conf :
1114.Bd -literal -offset indent
1115testjail {
1116	path = /tmp/jail/testjail;
1117	mount.devfs;
1118	host.hostname = testhostname;
1119	ip4.addr = 192.0.2.100;
1120	interface = em0;
1121	exec.start = "/bin/sh /etc/rc";
1122	exec.stop = "/bin/sh /etc/rc.shutdown jail";
1123}
1124.Ed
1125.Pp
1126To start a virtual server environment,
1127.Pa /etc/rc
1128is run to launch various daemons and services, and
1129.Pa /etc/rc.shutdown
1130is run to shut them down when the jail is removed.
1131If you are running a single application in the jail,
1132substitute the command used to start the application for
1133.Dq /bin/sh /etc/rc ;
1134there may be some script available to cleanly shut down the application,
1135or it may be sufficient to go without a stop command, and have
1136.Nm
1137send
1138.Dv SIGTERM
1139to the application.
1140.Pp
1141Start the jail by running:
1142.Bd -literal -offset indent
1143jail -c testjail
1144.Ed
1145.Pp
1146A few warnings may be produced; however, it should all work properly.
1147You should be able to see
1148.Xr inetd 8 ,
1149.Xr syslogd 8 ,
1150and other processes running within the jail using
1151.Xr ps 1 ,
1152with the
1153.Ql J
1154flag appearing beside jailed processes.
1155To see an active list of jails, use
1156.Xr jls 8 .
1157If
1158.Xr sshd 8
1159is enabled in the jail environment, you should be able to
1160.Xr ssh 1
1161to the hostname or IP address of the jailed environment, and log
1162in using the accounts you created previously.
1163.Pp
1164It is possible to have jails started at boot time.
1165Please refer to the
1166.Dq jail_*
1167variables in
1168.Xr rc.conf 5
1169for more information.
1170.Ss "Managing the Jail"
1171Normal machine shutdown commands, such as
1172.Xr halt 8 ,
1173.Xr reboot 8 ,
1174and
1175.Xr shutdown 8 ,
1176cannot be used successfully within the jail.
1177To kill all processes from within a jail, you may use one of the
1178following commands, depending on what you want to accomplish:
1179.Bd -literal -offset indent
1180kill -TERM -1
1181kill -KILL -1
1182.Ed
1183.Pp
1184This will send the
1185.Dv SIGTERM
1186or
1187.Dv SIGKILL
1188signals to all processes in the jail \(em be careful not to run this from
1189the host environment!
1190Once all of the jail's processes have died, unless the jail was created
1191with the
1192.Va persist
1193parameter, the jail will be removed.
1194Depending on
1195the intended use of the jail, you may also want to run
1196.Pa /etc/rc.shutdown
1197from within the jail.
1198.Pp
1199To shut down the jail from the outside, simply remove it with:
1200.Bd -literal -offset indent
1201jail -r
1202.Ed
1203.Pp
1204which will run any commands specified by
1205.Va exec.stop ,
1206and then send
1207.Dv SIGTERM
1208and eventually
1209.Dv SIGKILL
1210to any remaining jailed processes.
1211.Pp
1212The
1213.Pa /proc/ Ns Ar pid Ns Pa /status
1214file contains, as its last field, the name of the jail in which the
1215process runs, or
1216.Dq Li -
1217to indicate that the process is not running within a jail.
1218The
1219.Xr ps 1
1220command also shows a
1221.Ql J
1222flag for processes in a jail.
1223.Pp
1224You can also list/kill processes based on their jail ID.
1225To show processes and their jail ID, use the following command:
1226.Pp
1227.Dl "ps ax -o pid,jid,args"
1228.Pp
1229To show and then kill processes in jail number 3 use the following commands:
1230.Bd -literal -offset indent
1231pgrep -lfj 3
1232pkill -j 3
1233.Ed
1234or:
1235.Pp
1236.Dl "killall -j 3"
1237.Ss "Jails and File Systems"
1238It is not possible to
1239.Xr mount 8
1240or
1241.Xr umount 8
1242any file system inside a jail unless the file system is marked
1243jail-friendly, the jail's
1244.Va allow.mount
1245parameter is set, and the jail's
1246.Va enforce_statfs
1247parameter is lower than 2.
1248.Pp
1249Multiple jails sharing the same file system can influence each other.
1250For example, a user in one jail can fill the file system,
1251leaving no space for processes in the other jail.
1252Trying to use
1253.Xr quota 1
1254to prevent this will not work either, as the file system quotas
1255are not aware of jails but only look at the user and group IDs.
1256This means the same user ID in two jails share a single file
1257system quota.
1258One would need to use one file system per jail to make this work.
1259.Ss "Sysctl MIB Entries"
1260The read-only entry
1261.Va security.jail.jailed
1262can be used to determine if a process is running inside a jail (value
1263is one) or not (value is zero).
1264.Pp
1265The variable
1266.Va security.jail.max_af_ips
1267determines how may address per address family a jail may have.
1268The default is 255.
1269.Pp
1270Some MIB variables have per-jail settings.
1271Changes to these variables by a jailed process do not affect the host
1272environment, only the jail environment.
1273These variables are
1274.Va kern.securelevel ,
1275.Va security.bsd.suser_enabled ,
1276.Va kern.hostname ,
1277.Va kern.domainname ,
1278.Va kern.hostid ,
1279and
1280.Va kern.hostuuid .
1281.Ss "Hierarchical Jails"
1282By setting a jail's
1283.Va children.max
1284parameter, processes within a jail may be able to create jails of their own.
1285These child jails are kept in a hierarchy, with jails only able to see and/or
1286modify the jails they created (or those jails' children).
1287Each jail has a read-only
1288.Va parent
1289parameter, containing the
1290.Va jid
1291of the jail that created it; a
1292.Va jid
1293of 0 indicates the jail is a child of the current jail (or is a top-level
1294jail if the current process isn't jailed).
1295.Pp
1296Jailed processes are not allowed to confer greater permissions than they
1297themselves are given, e.g., if a jail is created with
1298.Va allow.nomount ,
1299it is not able to create a jail with
1300.Va allow.mount
1301set.
1302Similarly, such restrictions as
1303.Va ip4.addr
1304and
1305.Va securelevel
1306may not be bypassed in child jails.
1307.Pp
1308A child jail may in turn create its own child jails if its own
1309.Va children.max
1310parameter is set (remember it is zero by default).
1311These jails are visible to and can be modified by their parent and all
1312ancestors.
1313.Pp
1314Jail names reflect this hierarchy, with a full name being an MIB-type string
1315separated by dots.
1316For example, if a base system process creates a jail
1317.Dq foo ,
1318and a process under that jail creates another jail
1319.Dq bar ,
1320then the second jail will be seen as
1321.Dq foo.bar
1322in the base system (though it is only seen as
1323.Dq bar
1324to any processes inside jail
1325.Dq foo ) .
1326Jids on the other hand exist in a single space, and each jail must have a
1327unique jid.
1328.Pp
1329Like the names, a child jail's
1330.Va path
1331appears relative to its creator's own
1332.Va path .
1333This is by virtue of the child jail being created in the chrooted
1334environment of the first jail.
1335.Sh SEE ALSO
1336.Xr killall 1 ,
1337.Xr lsvfs 1 ,
1338.Xr newaliases 1 ,
1339.Xr pgrep 1 ,
1340.Xr pkill 1 ,
1341.Xr ps 1 ,
1342.Xr quota 1 ,
1343.Xr jail_set 2 ,
1344.Xr vmm 4 ,
1345.Xr devfs 5 ,
1346.Xr fdescfs 5 ,
1347.Xr jail.conf 5 ,
1348.Xr linprocfs 5 ,
1349.Xr linsysfs 5 ,
1350.Xr procfs 5 ,
1351.Xr rc.conf 5 ,
1352.Xr sysctl.conf 5 ,
1353.Xr bsdconfig 8 ,
1354.Xr chroot 8 ,
1355.Xr devfs 8 ,
1356.Xr halt 8 ,
1357.Xr ifconfig 8 ,
1358.Xr inetd 8 ,
1359.Xr jexec 8 ,
1360.Xr jls 8 ,
1361.Xr mount 8 ,
1362.Xr reboot 8 ,
1363.Xr rpcbind 8 ,
1364.Xr sendmail 8 ,
1365.Xr shutdown 8 ,
1366.Xr sysctl 8 ,
1367.Xr syslogd 8 ,
1368.Xr umount 8
1369.Sh HISTORY
1370The
1371.Nm
1372utility appeared in
1373.Fx 4.0 .
1374Hierarchical/extensible jails were introduced in
1375.Fx 8.0 .
1376The configuration file was introduced in
1377.Fx 9.1 .
1378.Sh AUTHORS
1379.An -nosplit
1380The jail feature was written by
1381.An Poul-Henning Kamp
1382for R&D Associates
1383who contributed it to
1384.Fx .
1385.Pp
1386.An Robert Watson
1387wrote the extended documentation, found a few bugs, added
1388a few new features, and cleaned up the userland jail environment.
1389.Pp
1390.An Bjoern A. Zeeb
1391added multi-IP jail support for IPv4 and IPv6 based on a patch
1392originally done by
1393.An Pawel Jakub Dawidek
1394for IPv4.
1395.Pp
1396.An James Gritton
1397added the extensible jail parameters, hierarchical jails,
1398and the configuration file.
1399.Sh BUGS
1400It might be a good idea to add an
1401address alias flag such that daemons listening on all IPs
1402.Pq Dv INADDR_ANY
1403will not bind on that address, which would facilitate building a safe
1404host environment such that host daemons do not impose on services offered
1405from within jails.
1406Currently, the simplest answer is to minimize services
1407offered on the host, possibly limiting it to services offered from
1408.Xr inetd 8
1409which is easily configurable.
1410.Sh NOTES
1411Great care should be taken when managing directories visible within the jail.
1412For example, if a jailed process has its current working directory set to a
1413directory that is moved out of the jail's chroot, then the process may gain
1414access to the file space outside of the jail.
1415It is recommended that directories always be copied, rather than moved, out
1416of a jail.
1417.Pp
1418In addition, there are several ways in which an unprivileged user
1419outside the jail can cooperate with a privileged user inside the jail
1420and thereby obtain elevated privileges in the host environment.
1421Most of these attacks can be mitigated by ensuring that the jail root
1422is not accessible to unprivileged users in the host environment.
1423Regardless, as a general rule, untrusted users with privileged access
1424to a jail should not be given access to the host environment.
1425