1 .\" Copyright (c) 2000, 2003 Robert N. M. Watson
2 .\" Copyright (c) 2008-2012 James Gritton
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33 .Nd "manage system jails"
41 .Ar param Ns = Ns Ar value ...
42 .Op Cm command Ns = Ns Ar command ...
53 .Op Cm * | Ar jail ...
60 .Op Fl s Ar securelevel
61 .Op Ar path hostname [ Ar ip Ns [ Ns Ar ,... Ns ]] Ar command ...
65 utility creates new jails, or modifies or removes existing jails.
68 is specified via parameters on the command line, or in the
72 At least one of the options
78 These options are used alone or in combination to describe the operation to
80 .Bl -tag -width indent
87 parameters (if specified on the command line)
88 must not refer to an existing jail.
90 Modify an existing jail.
95 parameters must exist and refer to an existing jail.
96 Some parameters may not be changed on a running jail.
100 specified by jid or name.
101 All jailed processes are killed, and all jails that are
102 children of this jail are also
105 Restart an existing jail.
106 The jail is first removed and then re-created, as if
110 were run in succession.
112 Create a jail if it does not exist, or modify the jail if it does exist.
114 Modify an existing jail.
115 The jail may be restarted if necessary to modify parameters than could
116 not otherwise be changed.
118 Create a jail if it doesn't exist, or modify (and possibly restart) the
119 jail if it does exist.
122 Other available options are:
123 .Bl -tag -width indent
125 Allow making changes to a dying jail, equivalent to the
128 .It Fl f Ar conf_file
129 Use configuration file
131 instead of the default
138 and add all IP addresses returned by the resolver
139 to the list of addresses for this jail.
140 This is equivalent to the
144 Output (only) the jail identifier of the newly created jail(s).
151 file, containing the parameters used to start the jail.
153 Run commands in a clean environment.
154 This is deprecated and is equivalent to the exec.clean parameter.
157 This is deprecated and is equivalent to the
161 Limit the number of commands from
163 that can run simultaneously.
165 Suppress the message printed whenever a jail is created, modified or removed.
166 Only error messages will be printed.
170 option that removes an existing jail without using the configuration file.
171 No removal-related parameters for this jail will be used \(em the jail will
173 .It Fl s Ar securelevel
176 MIB entry to the specified value inside the newly created jail.
177 This is deprecated and is equivalent to the
181 The user name from host environment as whom jailed commands should run.
182 This is deprecated and is equivalent to the
185 .Va exec.system_jail_user
188 The user name from the jailed environment as whom jailed commands should run.
189 This is deprecated and is equivalent to the
193 Print a message on every operation, such as running commands and
194 mounting filesystems.
197 If no arguments are given after the options, the operation (except
198 remove) will be performed on all jails specified in the
201 A single argument of a jail name will operate only on the specified jail.
206 options can also remove running jails that aren't in the
208 file, specified by name or jid.
212 is a wildcard that will operate on all jails, regardless of whether
215 this is the surest way for
218 If hierarchical jails exist, a partial-matching wildcard definition may
220 For example, an argument of
222 would apply to jails with names like
227 A jail may be specified with parameters directly on the command line.
230 file will not be used.
231 For backward compatibility, the command line may also have four fixed
232 parameters, without names:
238 This mode will always create a new jail, and the
242 options do not apply (and must not be present).
246 file, or on the command line, are generally of the form
248 Some parameters are boolean, and do not have a value but are set by the
249 name alone with or without a
255 They can also be given the values
259 Other parameters may have more than one value, specified as a
260 comma-separated list or with
262 in the configuration file (see
268 utility recognizes two classes of parameters.
269 There are the true jail
270 parameters that are passed to the kernel when the jail is created,
271 which can be seen with
273 and can (usually) be changed with
275 Then there are pseudo-parameters that are only used by
279 Jails have a set of core parameters, and kernel modules can add their own
281 The current set of available parameters can be retrieved via
282 .Dq Nm sysctl Fl d Va security.jail.param .
283 Any parameters not set will be given default values, often based on the
285 The core parameters are:
286 .Bl -tag -width indent
289 This will be assigned automatically to a new jail (or can be explicitly
290 set), and can be used to identify the jail for later modification, or
297 This is an arbitrary string that identifies a jail (except it may not
302 it can be passed to later
310 is supplied, a default is assumed that is the same as the
314 parameter is implied by the
316 file format, and need not be explicitly set when using the configuration
319 The directory which is to be the root of the jail.
320 Any commands run inside the jail, either by
324 are run from this directory.
326 A list of IPv4 addresses assigned to the jail.
327 If this is set, the jail is restricted to using only these addresses.
328 Any attempts to use other addresses fail, and attempts to use wildcard
329 addresses silently use the jailed address instead.
330 For IPv4 the first address given will be used as the source address
331 when source address selection on unbound sockets cannot find a better
333 It is only possible to start multiple jails with the same IP address
334 if none of the jails has more than this single overlapping IP address
337 A boolean option to change the formerly mentioned behaviour and disable
338 IPv4 source address selection for the jail in favour of the primary
339 IPv4 address of the jail.
340 Source address selection is enabled by default for all jails and the
342 setting of a parent jail is not inherited for any child jails.
344 Control the availability of IPv4 addresses.
347 to allow unrestricted access to all system addresses,
349 to restrict addresses via
353 to stop the jail from using IPv4 entirely.
356 parameter implies a value of
358 .It Va ip6.addr , Va ip6.saddrsel , Va ip6
359 A set of IPv6 options for the jail, the counterparts to
366 Create the jail with its own virtual network stack,
367 with its own network interfaces, addresses, routing table, etc.
368 The kernel must have been compiled with the
370 for this to be available.
373 to use the system network stack, possibly with restricted IP addresses,
376 to create a new network stack.
378 The hostname of the jail.
379 Other similar parameters are
380 .Va host.domainname ,
385 Set the origin of hostname and related information.
388 to use the system information and
390 for the jail to use the information from the above fields.
391 Setting any of the above fields implies a value of
394 The value of the jail's
397 A jail never has a lower securelevel than its parent system, but by
398 setting this parameter it may have a higher one.
399 If the system securelevel is changed, any jail securelevels will be at
402 The number of the devfs ruleset that is enforced for mounting devfs in
404 A value of zero (default) means no ruleset is enforced.
405 Descendant jails inherit the parent jail's devfs ruleset enforcement.
406 Mounting devfs inside a jail is possible only if the
409 .Va allow.mount.devfs
410 permissions are effective and
412 is set to a value lower than 2.
413 Devfs rules and rulesets cannot be viewed or modified from inside a jail.
415 NOTE: It is important that only appropriate device nodes in devfs be
416 exposed to a jail; access to disk devices in the jail may permit processes
417 in the jail to bypass the jail sandboxing by modifying files outside of
421 for information on how to use devfs rules to limit access to entries
422 in the per-jail devfs.
423 A simple devfs ruleset for jails is available as ruleset #4 in
424 .Pa /etc/defaults/devfs.rules .
426 The number of child jails allowed to be created by this jail (or by
427 other jails under this jail).
428 This limit is zero by default, indicating the jail is not allowed to
431 .Sx "Hierarchical Jails"
432 section for more information.
434 The number of descendants of this jail, including its own child jails
435 and any jails created under them.
436 .It Va enforce_statfs
437 This determines what information processes in a jail are able to get
439 It affects the behaviour of the following syscalls:
445 (as well as similar compatibility syscalls).
446 When set to 0, all mount points are available without any restrictions.
447 When set to 1, only mount points below the jail's chroot directory are
449 In addition to that, the path to the jail's chroot directory is removed
450 from the front of their pathnames.
451 When set to 2 (default), above syscalls can operate only on a mount-point
452 where the jail's chroot directory is located.
454 Setting this boolean parameter allows a jail to exist without any
456 Normally, a command is run as part of jail creation, and then the jail
457 is destroyed as its last process exits.
458 A new jail must have either the
464 pseudo-parameter set.
466 The ID of the cpuset associated with this jail (read-only).
468 This is true if the jail is in the process of shutting down (read-only).
472 of the parent of this jail, or zero if this is a top-level jail
475 The string for the jail's
479 The number for the jail's
483 Some restrictions of the jail environment may be set on a per-jail
485 With the exception of
486 .Va allow.set_hostname
488 .Va allow.reserved_ports ,
489 these boolean parameters are off by default.
490 .Bl -tag -width indent
491 .It Va allow.set_hostname
492 The jail's hostname may be changed via
497 A process within the jail has access to System V IPC primitives.
498 This is deprecated in favor of the per-module parameters (see below).
499 When this parameter is set, it is equivalent to setting
506 .It Va allow.raw_sockets
507 The jail root is allowed to create raw sockets.
508 Setting this parameter allows utilities like
512 to operate inside the jail.
513 If this is set, the source IP addresses are enforced to comply
514 with the IP address bound to the jail, regardless of whether or not
517 flag has been set on the socket.
518 Since raw sockets can be used to configure and interact with various
519 network subsystems, extra caution should be used where privileged access
520 to jails is given out to untrusted parties.
522 Normally, privileged users inside a jail are treated as unprivileged by
524 When this parameter is set, such users are treated as privileged, and
525 may manipulate system file flags subject to the usual constraints on
526 .Va kern.securelevel .
528 privileged users inside the jail will be able to mount and unmount file
529 system types marked as jail-friendly.
532 command can be used to find file system types available for mount from
534 This permission is effective only if
536 is set to a value lower than 2.
537 .It Va allow.mount.devfs
538 privileged users inside the jail will be able to mount and unmount the
540 This permission is effective only together with
544 is set to a value lower than 2.
545 The devfs ruleset should be restricted from the default by using the
549 The jail root may administer quotas on the jail's filesystem(s).
550 This includes filesystems that the jail may share with other jails or
551 with non-jailed parts of the system.
552 .It Va allow.socket_af
553 Sockets within a jail are normally restricted to IPv4, IPv6, local
554 (UNIX), and route. This allows access to other protocol stacks that
555 have not had jail functionality added to them.
556 .It Va allow.reserved_ports
557 The jail root may bind to ports lower than 1024.
561 Kernel modules may add their own parameters, which only exist when the
563 These are typically headed under a parameter named after the module,
566 to give the jail full use of the module,
568 to encapsulate the jail in some module-specific way,
571 to make the module unavailable to the jail.
572 There also may be other parameters to define jail behavior within the module.
573 Module-specific parameters include:
574 .Bl -tag -width indent
575 .It Va allow.mount.fdescfs
576 privileged users inside the jail will be able to mount and unmount the
578 This permission is effective only together with
582 is set to a value lower than 2.
583 .It Va allow.mount.fusefs
584 privileged users inside the jail will be able to mount and unmount
585 fuse-based file systems.
586 This permission is effective only together with
590 is set to a value lower than 2.
591 .It Va allow.mount.nullfs
592 privileged users inside the jail will be able to mount and unmount the
594 This permission is effective only together with
598 is set to a value lower than 2.
599 .It Va allow.mount.procfs
600 privileged users inside the jail will be able to mount and unmount the
602 This permission is effective only together with
606 is set to a value lower than 2.
607 .It Va allow.mount.linprocfs
608 privileged users inside the jail will be able to mount and unmount the
609 linprocfs file system.
610 This permission is effective only together with
614 is set to a value lower than 2.
615 .It Va allow.mount.linsysfs
616 privileged users inside the jail will be able to mount and unmount the
617 linsysfs file system.
618 This permission is effective only together with
622 is set to a value lower than 2.
623 .It Va allow.mount.tmpfs
624 privileged users inside the jail will be able to mount and unmount the
626 This permission is effective only together with
630 is set to a value lower than 2.
631 .It Va allow.mount.zfs
632 privileged users inside the jail will be able to mount and unmount the
634 This permission is effective only together with
638 is set to a value lower than 2.
641 for information on how to configure the ZFS filesystem to operate from
644 Determine how a jail's Linux emulation environment appears.
647 will keep the same environment, and
649 will give the jail it's own environment (still originally inherited when
650 the jail is created).
651 .It Va linux.osname , linux.osrelease , linux.oss_version
652 The Linux OS name, OS release, and OSS version associated with this jail.
654 Allow access to SYSV IPC message primitives.
657 all IPC objects on the system are visible to this jail, whether they
658 were created by the jail itself, the base system, or other jails.
661 the jail will have its own key namespace, and can only see the objects
663 the system (or parent jail) has access to the jail's objects, but not to
667 the jail cannot perform any sysvmsg-related system calls.
668 .It Va sysvsem, sysvshm
669 Allow access to SYSV IPC semaphore and shared memory primitives, in the
674 There are pseudo-parameters that are not passed to the kernel, but are
677 to set up the jail environment, often by running specified commands
678 when jails are created or removed.
681 command parameters are
683 command lines that are run in either the system or jail environment.
684 They may be given multiple values, which would run the specified
685 commands in sequence.
686 All commands must succeed (return a zero exit status), or the jail will
687 not be created or removed, as appropriate.
689 The pseudo-parameters are:
690 .Bl -tag -width indent
692 Command(s) to run in the system environment before a jail is created.
694 Command(s) to run in the jail environment when a jail is created.
695 A typical command to run is
700 for use when specifying a jail directly on the command line.
701 Unlike other parameters whose value is a single string,
703 uses the remainder of the
705 command line as its own arguments.
706 .It Va exec.poststart
707 Command(s) to run in the system environment after a jail is created,
710 commands have completed.
712 Command(s) to run in the system environment before a jail is removed.
714 Command(s) to run in the jail environment before a jail is removed,
717 commands have completed.
718 A typical command to run is
719 .Dq sh /etc/rc.shutdown .
721 Command(s) to run in the system environment after a jail is removed.
723 Run commands in a clean environment.
724 The environment is discarded except for
725 .Ev HOME , SHELL , TERM
731 are set to the target login's default values.
733 is set to the target login.
735 is imported from the current environment.
736 The environment variables from the login class capability database for the
737 target login are also set.
738 .It Va exec.jail_user
739 The user to run commands as, when running in the jail environment.
740 The default is to run the commands as the current user.
741 .It Va exec.system_jail_user
742 This boolean option looks for the
746 file, instead of in the jail's file.
747 .It Va exec.system_user
748 The user to run commands as, when running in the system environment.
749 The default is to run the commands as the current user.
751 The maximum amount of time to wait for a command to complete, in
753 If a command is still running after this timeout has passed,
754 the jail will not be created or removed, as appropriate.
755 .It Va exec.consolelog
756 A file to direct command output (stdout and stderr) to.
758 The FIB (routing table) to set when running commands inside the jail.
760 The maximum amount of time to wait for a jail's processes to exit
763 signal (which happens after the
765 commands have completed).
766 After this many seconds have passed, the jail will be removed, which
767 will kill any remaining processes.
768 If this is set to zero, no
770 is sent and the jail is immediately removed.
771 The default is 10 seconds.
773 A network interface to add the jail's IP addresses
778 An alias for each address will be added to the interface before the
779 jail is created, and will be removed from the interface after the
782 In addition to the IP addresses that are passed to the kernel, an
783 interface, netmask and additional parameters (as supported by
785 may also be specified, in the form
786 .Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar netmask param ... .
787 If an interface is given before the IP address, an alias for the address
788 will be added to that interface, as it is with the
791 If a netmask in either dotted-quad or CIDR form is given
792 after an IP address, it will be used when adding the IP alias.
793 If additional parameters are specified then they will also be used when
796 In addition to the IP addresses that are passed to the kernel,
797 an interface, prefix and additional parameters (as supported by
799 may also be specified, in the form
800 .Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar prefix param ... .
801 .It Va vnet.interface
802 A network interface to give to a vnet-enabled jail after is it created.
803 The interface will automatically be released when the jail is removed.
807 parameter and add all IP addresses returned by the resolver
808 to the list of addresses
813 This may affect default address selection for outgoing IPv4 connections
815 The address first returned by the resolver for each address family
816 will be used as the primary address.
818 A filesystem to mount before creating the jail (and to unmount after
819 removing it), given as a single
825 format file containing filesystems to mount before creating a jail.
829 filesystem on the chrooted
831 directory, and apply the ruleset in the
833 parameter (or a default of ruleset 4: devfsrules_jail)
834 to restrict the devices visible inside the jail.
838 filesystem on the chrooted
844 filesystem on the chrooted
848 Allow making changes to a
852 Specify a jail (or jails) that this jail depends on.
853 When this jail is to be created, any jail(s) it depends on must already exist.
854 If not, they will be created automatically, up to the completion of the last
856 command, before any action will taken to create this jail.
857 When jails are removed the opposite is true:
858 this jail will be removed, up to the last
860 command, before any jail(s) it depends on are stopped.
863 Jails are typically set up using one of two philosophies: either to
864 constrain a specific application (possibly running with privilege), or
866 .Dq "virtual system image"
867 running a variety of daemons and services.
868 In both cases, a fairly complete file system install of
871 required, so as to provide the necessary command line tools, daemons,
872 libraries, application configuration files, etc.
873 However, for a virtual server configuration, a fair amount of
874 additional work is required so as to replace the
877 This manual page documents the configuration steps necessary to support
878 either of these steps, although the configuration steps may need to be
879 refined based on local requirements.
880 .Ss "Setting up a Jail Directory Tree"
881 To set up a jail directory tree containing an entire
883 distribution, the following
885 command script can be used:
890 make world DESTDIR=$D
891 make distribution DESTDIR=$D
894 In many cases this example would put far more in the jail than needed.
895 In the other extreme case a jail might contain only one file:
896 the executable to be run in the jail.
898 We recommend experimentation, and caution that it is a lot easier to
901 jail and remove things until it stops working,
902 than it is to start with a
904 jail and add things until it works.
905 .Ss "Setting Up a Jail"
906 Do what was described in
907 .Sx "Setting Up a Jail Directory Tree"
908 to build the jail directory tree.
909 For the sake of this example, we will
910 assume you built it in
911 .Pa /data/jail/testjail ,
914 Substitute below as needed with your
915 own directory, IP address, and hostname.
916 .Ss "Setting up the Host Environment"
917 First, set up the real system's environment to be
919 For consistency, we will refer to the parent box as the
920 .Dq "host environment" ,
921 and to the jailed virtual machine as the
922 .Dq "jail environment" .
923 Since jails are implemented using IP aliases, one of the first things to do
924 is to disable IP services on the host system that listen on all local
925 IP addresses for a service.
926 If a network service is present in the host environment that binds all
927 available IP addresses rather than specific IP addresses, it may service
928 requests sent to jail IP addresses if the jail did not bind the port.
931 to only listen on the
932 appropriate IP address, and so forth.
935 in the host environment:
936 .Bd -literal -offset indent
938 inetd_flags="-wW -a 192.0.2.23"
943 is the native IP address for the host system, in this example.
944 Daemons that run out of
946 can be easily configured to use only the specified host IP address.
948 will need to be manually configured \(em for some this is possible through
950 flags entries; for others it is necessary to modify per-application
951 configuration files, or to recompile the application.
952 The following frequently deployed services must have their individual
953 configuration files modified to limit the application to listening
954 to a specific IP address:
958 it is necessary to modify
959 .Pa /etc/ssh/sshd_config .
963 it is necessary to modify
964 .Pa /etc/mail/sendmail.cf .
968 it is necessary to modify
969 .Pa /etc/namedb/named.conf .
971 In addition, a number of services must be recompiled in order to run
972 them in the host environment.
973 This includes most applications providing services using
980 In general, applications for which it is not possible to specify which
981 IP address to bind should not be run in the host environment unless they
982 should also service requests sent to jail IP addresses.
984 NFS from the host environment may also cause confusion, and cannot be
985 easily reconfigured to use only specific IPs, as some NFS services are
986 hosted directly from the kernel.
987 Any third-party network software running
988 in the host environment should also be checked and configured so that it
989 does not bind all IP addresses, which would result in those services also
990 appearing to be offered by the jail environments.
993 these daemons have been disabled or fixed in the host environment, it is
994 best to reboot so that all daemons are in a known state, to reduce the
995 potential for confusion later (such as finding that when you send mail
996 to a jail, and its sendmail is down, the mail is delivered to the host,
998 .Ss "Configuring the Jail"
999 Start any jail for the first time without configuring the network
1000 interface so that you can clean it up a little and set up accounts.
1002 with any machine (virtual or not), you will need to set a root password, time
1004 Some of these steps apply only if you intend to run a full virtual server
1005 inside the jail; others apply both for constraining a particular application
1006 or for running a virtual server.
1008 Start a shell in the jail:
1009 .Bd -literal -offset indent
1010 jail -c path=/data/jail/testjail mount.devfs \\
1011 host.hostname=testhostname ip4.addr=192.0.2.100 \\
1015 Assuming no errors, you will end up with a shell prompt within the jail.
1017 .Pa /usr/sbin/bsdinstall
1018 and do the post-install configuration to set various configuration options,
1019 or perform these actions manually by editing
1023 .Bl -bullet -offset indent -compact
1026 .Pa /etc/resolv.conf
1027 so that name resolution within the jail will work correctly.
1035 Set a root password, probably different from the real host system.
1039 Add accounts for users in the jail environment.
1041 Install any packages the environment requires.
1044 You may also want to perform any package-specific configuration (web servers,
1045 SSH servers, etc), patch up
1046 .Pa /etc/syslog.conf
1047 so it logs as you would like, etc.
1048 If you are not using a virtual server, you may wish to modify
1050 in the host environment to listen on the syslog socket in the jail
1051 environment; in this example, the syslog socket would be stored in
1052 .Pa /data/jail/testjail/var/run/log .
1054 Exit from the shell, and the jail will be shut down.
1055 .Ss "Starting the Jail"
1056 You are now ready to restart the jail and bring up the environment with
1057 all of its daemons and other programs.
1058 Create an entry for the jail in
1059 .Pa /etc/jail.conf :
1060 .Bd -literal -offset indent
1062 path = /tmp/jail/testjail;
1064 host.hostname = testhostname;
1065 ip4.addr = 192.0.2.100;
1067 exec.start = "/bin/sh /etc/rc";
1068 exec.stop = "/bin/sh /etc/rc.shutdown";
1072 To start a virtual server environment,
1074 is run to launch various daemons and services, and
1075 .Pa /etc/rc.shutdown
1076 is run to shut them down when the jail is removed.
1077 If you are running a single application in the jail,
1078 substitute the command used to start the application for
1079 .Dq /bin/sh /etc/rc ;
1080 there may be some script available to cleanly shut down the application,
1081 or it may be sufficient to go without a stop command, and have
1087 Start the jail by running:
1088 .Bd -literal -offset indent
1092 A few warnings may be produced; however, it should all work properly.
1093 You should be able to see
1096 and other processes running within the jail using
1100 flag appearing beside jailed processes.
1101 To see an active list of jails, use
1105 is enabled in the jail environment, you should be able to
1107 to the hostname or IP address of the jailed environment, and log
1108 in using the accounts you created previously.
1110 It is possible to have jails started at boot time.
1115 for more information.
1116 .Ss "Managing the Jail"
1117 Normal machine shutdown commands, such as
1122 cannot be used successfully within the jail.
1123 To kill all processes from within a jail, you may use one of the
1124 following commands, depending on what you want to accomplish:
1125 .Bd -literal -offset indent
1134 signals to all processes in the jail \(em be careful not to run this from
1135 the host environment!
1136 Once all of the jail's processes have died, unless the jail was created
1139 parameter, the jail will be removed.
1141 the intended use of the jail, you may also want to run
1142 .Pa /etc/rc.shutdown
1143 from within the jail.
1145 To shut down the jail from the outside, simply remove it with
1148 which will run any commands specified by
1154 to any remaining jailed processes.
1157 .Pa /proc/ Ns Ar pid Ns Pa /status
1158 file contains, as its last field, the name of the jail in which the
1161 to indicate that the process is not running within a jail.
1164 command also shows a
1166 flag for processes in a jail.
1168 You can also list/kill processes based on their jail ID.
1169 To show processes and their jail ID, use the following command:
1171 .Dl "ps ax -o pid,jid,args"
1173 To show and then kill processes in jail number 3 use the following commands:
1174 .Bd -literal -offset indent
1181 .Ss "Jails and File Systems"
1182 It is not possible to
1186 any file system inside a jail unless the file system is marked
1187 jail-friendly, the jail's
1189 parameter is set, and the jail's
1191 parameter is lower than 2.
1193 Multiple jails sharing the same file system can influence each other.
1194 For example, a user in one jail can fill the file system,
1195 leaving no space for processes in the other jail.
1198 to prevent this will not work either, as the file system quotas
1199 are not aware of jails but only look at the user and group IDs.
1200 This means the same user ID in two jails share a single file
1202 One would need to use one file system per jail to make this work.
1203 .Ss "Sysctl MIB Entries"
1205 .Va security.jail.jailed
1206 can be used to determine if a process is running inside a jail (value
1207 is one) or not (value is zero).
1210 .Va security.jail.max_af_ips
1211 determines how may address per address family a jail may have.
1214 Some MIB variables have per-jail settings.
1215 Changes to these variables by a jailed process do not affect the host
1216 environment, only the jail environment.
1218 .Va kern.securelevel ,
1220 .Va kern.domainname ,
1224 .Ss "Hierarchical Jails"
1227 parameter, processes within a jail may be able to create jails of their own.
1228 These child jails are kept in a hierarchy, with jails only able to see and/or
1229 modify the jails they created (or those jails' children).
1230 Each jail has a read-only
1232 parameter, containing the
1234 of the jail that created it; a
1236 of 0 indicates the jail is a child of the current jail (or is a top-level
1237 jail if the current process isn't jailed).
1239 Jailed processes are not allowed to confer greater permissions than they
1240 themselves are given, e.g., if a jail is created with
1242 it is not able to create a jail with
1245 Similarly, such restrictions as
1249 may not be bypassed in child jails.
1251 A child jail may in turn create its own child jails if its own
1253 parameter is set (remember it is zero by default).
1254 These jails are visible to and can be modified by their parent and all
1257 Jail names reflect this hierarchy, with a full name being an MIB-type string
1259 For example, if a base system process creates a jail
1261 and a process under that jail creates another jail
1263 then the second jail will be seen as
1265 in the base system (though it is only seen as
1267 to any processes inside jail
1269 Jids on the other hand exist in a single space, and each jail must have a
1272 Like the names, a child jail's
1274 appears relative to its creator's own
1276 This is by virtue of the child jail being created in the chrooted
1277 environment of the first jail.
1316 Hierarchical/extensible jails were introduced in
1318 The configuration file was introduced in
1322 The jail feature was written by
1323 .An Poul-Henning Kamp
1325 who contributed it to
1329 wrote the extended documentation, found a few bugs, added
1330 a few new features, and cleaned up the userland jail environment.
1333 added multi-IP jail support for IPv4 and IPv6 based on a patch
1335 .An Pawel Jakub Dawidek
1339 added the extensible jail parameters, hierarchical jails,
1340 and the configuration file.
1342 It might be a good idea to add an
1343 address alias flag such that daemons listening on all IPs
1345 will not bind on that address, which would facilitate building a safe
1346 host environment such that host daemons do not impose on services offered
1348 Currently, the simplest answer is to minimize services
1349 offered on the host, possibly limiting it to services offered from
1351 which is easily configurable.
1353 Great care should be taken when managing directories visible within the jail.
1354 For example, if a jailed process has its current working directory set to a
1355 directory that is moved out of the jail's chroot, then the process may gain
1356 access to the file space outside of the jail.
1357 It is recommended that directories always be copied, rather than moved, out
1360 In addition, there are several ways in which an unprivileged user
1361 outside the jail can cooperate with a privileged user inside the jail
1362 and thereby obtain elevated privileges in the host environment.
1363 Most of these attacks can be mitigated by ensuring that the jail root
1364 is not accessible to unprivileged users in the host environment.
1365 Regardless, as a general rule, untrusted users with privileged access
1366 to a jail should not be given access to the host environment.