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.nullfs
584 privileged users inside the jail will be able to mount and unmount the
586 This permission is effective only together with
590 is set to a value lower than 2.
591 .It Va allow.mount.procfs
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.linprocfs
600 privileged users inside the jail will be able to mount and unmount the
601 linprocfs file system.
602 This permission is effective only together with
606 is set to a value lower than 2.
607 .It Va allow.mount.linsysfs
608 privileged users inside the jail will be able to mount and unmount the
609 linsysfs file system.
610 This permission is effective only together with
614 is set to a value lower than 2.
615 .It Va allow.mount.tmpfs
616 privileged users inside the jail will be able to mount and unmount the
618 This permission is effective only together with
622 is set to a value lower than 2.
623 .It Va allow.mount.zfs
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.
633 for information on how to configure the ZFS filesystem to operate from
636 Determine how a jail's Linux emulation environment appears.
639 will keep the same environment, and
641 will give the jail it's own environment (still originally inherited when
642 the jail is created).
643 .It Va linux.osname , linux.osrelease , linux.oss_version
644 The Linux OS name, OS release, and OSS version associated with this jail.
646 Allow access to SYSV IPC message primitives.
649 all IPC objects on the system are visible to this jail, whether they
650 were created by the jail itself, the base system, or other jails.
653 the jail will have its own key namespace, and can only see the objects
655 the system (or parent jail) has access to the jail's objects, but not to
659 the jail cannot perform any sysvmsg-related system calls.
660 .It Va sysvsem, sysvshm
661 Allow access to SYSV IPC semaphore and shared memory primitives, in the
666 There are pseudo-parameters that are not passed to the kernel, but are
669 to set up the jail environment, often by running specified commands
670 when jails are created or removed.
673 command parameters are
675 command lines that are run in either the system or jail environment.
676 They may be given multiple values, which would run the specified
677 commands in sequence.
678 All commands must succeed (return a zero exit status), or the jail will
679 not be created or removed, as appropriate.
681 The pseudo-parameters are:
682 .Bl -tag -width indent
684 Command(s) to run in the system environment before a jail is created.
686 Command(s) to run in the jail environment when a jail is created.
687 A typical command to run is
692 for use when specifying a jail directly on the command line.
693 Unlike other parameters whose value is a single string,
695 uses the remainder of the
697 command line as its own arguments.
698 .It Va exec.poststart
699 Command(s) to run in the system environment after a jail is created,
702 commands have completed.
704 Command(s) to run in the system environment before a jail is removed.
706 Command(s) to run in the jail environment before a jail is removed,
709 commands have completed.
710 A typical command to run is
711 .Dq sh /etc/rc.shutdown .
713 Command(s) to run in the system environment after a jail is removed.
715 Run commands in a clean environment.
716 The environment is discarded except for
717 .Ev HOME , SHELL , TERM
723 are set to the target login's default values.
725 is set to the target login.
727 is imported from the current environment.
728 The environment variables from the login class capability database for the
729 target login are also set.
730 .It Va exec.jail_user
731 The user to run commands as, when running in the jail environment.
732 The default is to run the commands as the current user.
733 .It Va exec.system_jail_user
734 This boolean option looks for the
738 file, instead of in the jail's file.
739 .It Va exec.system_user
740 The user to run commands as, when running in the system environment.
741 The default is to run the commands as the current user.
743 The maximum amount of time to wait for a command to complete, in
745 If a command is still running after this timeout has passed,
746 the jail will not be created or removed, as appropriate.
747 .It Va exec.consolelog
748 A file to direct command output (stdout and stderr) to.
750 The FIB (routing table) to set when running commands inside the jail.
752 The maximum amount of time to wait for a jail's processes to exit
755 signal (which happens after the
757 commands have completed).
758 After this many seconds have passed, the jail will be removed, which
759 will kill any remaining processes.
760 If this is set to zero, no
762 is sent and the jail is immediately removed.
763 The default is 10 seconds.
765 A network interface to add the jail's IP addresses
770 An alias for each address will be added to the interface before the
771 jail is created, and will be removed from the interface after the
774 In addition to the IP addresses that are passed to the kernel, an
775 interface, netmask and additional parameters (as supported by
777 may also be specified, in the form
778 .Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar netmask param ... .
779 If an interface is given before the IP address, an alias for the address
780 will be added to that interface, as it is with the
783 If a netmask in either dotted-quad or CIDR form is given
784 after an IP address, it will be used when adding the IP alias.
785 If additional parameters are specified then they will also be used when
788 In addition to the IP addresses that are passed to the kernel,
789 an interface, prefix and additional parameters (as supported by
791 may also be specified, in the form
792 .Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar prefix param ... .
793 .It Va vnet.interface
794 A network interface to give to a vnet-enabled jail after is it created.
795 The interface will automatically be released when the jail is removed.
799 parameter and add all IP addresses returned by the resolver
800 to the list of addresses
805 This may affect default address selection for outgoing IPv4 connections
807 The address first returned by the resolver for each address family
808 will be used as the primary address.
810 A filesystem to mount before creating the jail (and to unmount after
811 removing it), given as a single
817 format file containing filesystems to mount before creating a jail.
821 filesystem on the chrooted
823 directory, and apply the ruleset in the
825 parameter (or a default of ruleset 4: devfsrules_jail)
826 to restrict the devices visible inside the jail.
830 filesystem on the chrooted
836 filesystem on the chrooted
840 Allow making changes to a
844 Specify a jail (or jails) that this jail depends on.
845 When this jail is to be created, any jail(s) it depends on must already exist.
846 If not, they will be created automatically, up to the completion of the last
848 command, before any action will taken to create this jail.
849 When jails are removed the opposite is true:
850 this jail will be removed, up to the last
852 command, before any jail(s) it depends on are stopped.
855 Jails are typically set up using one of two philosophies: either to
856 constrain a specific application (possibly running with privilege), or
858 .Dq "virtual system image"
859 running a variety of daemons and services.
860 In both cases, a fairly complete file system install of
863 required, so as to provide the necessary command line tools, daemons,
864 libraries, application configuration files, etc.
865 However, for a virtual server configuration, a fair amount of
866 additional work is required so as to replace the
869 This manual page documents the configuration steps necessary to support
870 either of these steps, although the configuration steps may need to be
871 refined based on local requirements.
872 .Ss "Setting up a Jail Directory Tree"
873 To set up a jail directory tree containing an entire
875 distribution, the following
877 command script can be used:
882 make world DESTDIR=$D
883 make distribution DESTDIR=$D
886 In many cases this example would put far more in the jail than needed.
887 In the other extreme case a jail might contain only one file:
888 the executable to be run in the jail.
890 We recommend experimentation, and caution that it is a lot easier to
893 jail and remove things until it stops working,
894 than it is to start with a
896 jail and add things until it works.
897 .Ss "Setting Up a Jail"
898 Do what was described in
899 .Sx "Setting Up a Jail Directory Tree"
900 to build the jail directory tree.
901 For the sake of this example, we will
902 assume you built it in
903 .Pa /data/jail/testjail ,
906 Substitute below as needed with your
907 own directory, IP address, and hostname.
908 .Ss "Setting up the Host Environment"
909 First, set up the real system's environment to be
911 For consistency, we will refer to the parent box as the
912 .Dq "host environment" ,
913 and to the jailed virtual machine as the
914 .Dq "jail environment" .
915 Since jails are implemented using IP aliases, one of the first things to do
916 is to disable IP services on the host system that listen on all local
917 IP addresses for a service.
918 If a network service is present in the host environment that binds all
919 available IP addresses rather than specific IP addresses, it may service
920 requests sent to jail IP addresses if the jail did not bind the port.
923 to only listen on the
924 appropriate IP address, and so forth.
927 in the host environment:
928 .Bd -literal -offset indent
930 inetd_flags="-wW -a 192.0.2.23"
935 is the native IP address for the host system, in this example.
936 Daemons that run out of
938 can be easily configured to use only the specified host IP address.
940 will need to be manually configured \(em for some this is possible through
942 flags entries; for others it is necessary to modify per-application
943 configuration files, or to recompile the application.
944 The following frequently deployed services must have their individual
945 configuration files modified to limit the application to listening
946 to a specific IP address:
950 it is necessary to modify
951 .Pa /etc/ssh/sshd_config .
955 it is necessary to modify
956 .Pa /etc/mail/sendmail.cf .
960 it is necessary to modify
961 .Pa /etc/namedb/named.conf .
963 In addition, a number of services must be recompiled in order to run
964 them in the host environment.
965 This includes most applications providing services using
972 In general, applications for which it is not possible to specify which
973 IP address to bind should not be run in the host environment unless they
974 should also service requests sent to jail IP addresses.
976 NFS from the host environment may also cause confusion, and cannot be
977 easily reconfigured to use only specific IPs, as some NFS services are
978 hosted directly from the kernel.
979 Any third-party network software running
980 in the host environment should also be checked and configured so that it
981 does not bind all IP addresses, which would result in those services also
982 appearing to be offered by the jail environments.
985 these daemons have been disabled or fixed in the host environment, it is
986 best to reboot so that all daemons are in a known state, to reduce the
987 potential for confusion later (such as finding that when you send mail
988 to a jail, and its sendmail is down, the mail is delivered to the host,
990 .Ss "Configuring the Jail"
991 Start any jail for the first time without configuring the network
992 interface so that you can clean it up a little and set up accounts.
994 with any machine (virtual or not), you will need to set a root password, time
996 Some of these steps apply only if you intend to run a full virtual server
997 inside the jail; others apply both for constraining a particular application
998 or for running a virtual server.
1000 Start a shell in the jail:
1001 .Bd -literal -offset indent
1002 jail -c path=/data/jail/testjail mount.devfs \\
1003 host.hostname=testhostname ip4.addr=192.0.2.100 \\
1007 Assuming no errors, you will end up with a shell prompt within the jail.
1009 .Pa /usr/sbin/bsdinstall
1010 and do the post-install configuration to set various configuration options,
1011 or perform these actions manually by editing
1015 .Bl -bullet -offset indent -compact
1018 .Pa /etc/resolv.conf
1019 so that name resolution within the jail will work correctly.
1027 Set a root password, probably different from the real host system.
1031 Add accounts for users in the jail environment.
1033 Install any packages the environment requires.
1036 You may also want to perform any package-specific configuration (web servers,
1037 SSH servers, etc), patch up
1038 .Pa /etc/syslog.conf
1039 so it logs as you would like, etc.
1040 If you are not using a virtual server, you may wish to modify
1042 in the host environment to listen on the syslog socket in the jail
1043 environment; in this example, the syslog socket would be stored in
1044 .Pa /data/jail/testjail/var/run/log .
1046 Exit from the shell, and the jail will be shut down.
1047 .Ss "Starting the Jail"
1048 You are now ready to restart the jail and bring up the environment with
1049 all of its daemons and other programs.
1050 Create an entry for the jail in
1051 .Pa /etc/jail.conf :
1052 .Bd -literal -offset indent
1054 path = /tmp/jail/testjail;
1056 host.hostname = testhostname;
1057 ip4.addr = 192.0.2.100;
1059 exec.start = "/bin/sh /etc/rc";
1060 exec.stop = "/bin/sh /etc/rc.shutdown";
1064 To start a virtual server environment,
1066 is run to launch various daemons and services, and
1067 .Pa /etc/rc.shutdown
1068 is run to shut them down when the jail is removed.
1069 If you are running a single application in the jail,
1070 substitute the command used to start the application for
1071 .Dq /bin/sh /etc/rc ;
1072 there may be some script available to cleanly shut down the application,
1073 or it may be sufficient to go without a stop command, and have
1079 Start the jail by running:
1080 .Bd -literal -offset indent
1084 A few warnings may be produced; however, it should all work properly.
1085 You should be able to see
1088 and other processes running within the jail using
1092 flag appearing beside jailed processes.
1093 To see an active list of jails, use
1097 is enabled in the jail environment, you should be able to
1099 to the hostname or IP address of the jailed environment, and log
1100 in using the accounts you created previously.
1102 It is possible to have jails started at boot time.
1107 for more information.
1108 .Ss "Managing the Jail"
1109 Normal machine shutdown commands, such as
1114 cannot be used successfully within the jail.
1115 To kill all processes from within a jail, you may use one of the
1116 following commands, depending on what you want to accomplish:
1117 .Bd -literal -offset indent
1126 signals to all processes in the jail \(em be careful not to run this from
1127 the host environment!
1128 Once all of the jail's processes have died, unless the jail was created
1131 parameter, the jail will be removed.
1133 the intended use of the jail, you may also want to run
1134 .Pa /etc/rc.shutdown
1135 from within the jail.
1137 To shut down the jail from the outside, simply remove it with
1140 which will run any commands specified by
1146 to any remaining jailed processes.
1149 .Pa /proc/ Ns Ar pid Ns Pa /status
1150 file contains, as its last field, the name of the jail in which the
1153 to indicate that the process is not running within a jail.
1156 command also shows a
1158 flag for processes in a jail.
1160 You can also list/kill processes based on their jail ID.
1161 To show processes and their jail ID, use the following command:
1163 .Dl "ps ax -o pid,jid,args"
1165 To show and then kill processes in jail number 3 use the following commands:
1166 .Bd -literal -offset indent
1173 .Ss "Jails and File Systems"
1174 It is not possible to
1178 any file system inside a jail unless the file system is marked
1179 jail-friendly, the jail's
1181 parameter is set, and the jail's
1183 parameter is lower than 2.
1185 Multiple jails sharing the same file system can influence each other.
1186 For example, a user in one jail can fill the file system,
1187 leaving no space for processes in the other jail.
1190 to prevent this will not work either, as the file system quotas
1191 are not aware of jails but only look at the user and group IDs.
1192 This means the same user ID in two jails share a single file
1194 One would need to use one file system per jail to make this work.
1195 .Ss "Sysctl MIB Entries"
1197 .Va security.jail.jailed
1198 can be used to determine if a process is running inside a jail (value
1199 is one) or not (value is zero).
1202 .Va security.jail.max_af_ips
1203 determines how may address per address family a jail may have.
1206 Some MIB variables have per-jail settings.
1207 Changes to these variables by a jailed process do not affect the host
1208 environment, only the jail environment.
1210 .Va kern.securelevel ,
1212 .Va kern.domainname ,
1216 .Ss "Hierarchical Jails"
1219 parameter, processes within a jail may be able to create jails of their own.
1220 These child jails are kept in a hierarchy, with jails only able to see and/or
1221 modify the jails they created (or those jails' children).
1222 Each jail has a read-only
1224 parameter, containing the
1226 of the jail that created it; a
1228 of 0 indicates the jail is a child of the current jail (or is a top-level
1229 jail if the current process isn't jailed).
1231 Jailed processes are not allowed to confer greater permissions than they
1232 themselves are given, e.g., if a jail is created with
1234 it is not able to create a jail with
1237 Similarly, such restrictions as
1241 may not be bypassed in child jails.
1243 A child jail may in turn create its own child jails if its own
1245 parameter is set (remember it is zero by default).
1246 These jails are visible to and can be modified by their parent and all
1249 Jail names reflect this hierarchy, with a full name being an MIB-type string
1251 For example, if a base system process creates a jail
1253 and a process under that jail creates another jail
1255 then the second jail will be seen as
1257 in the base system (though it is only seen as
1259 to any processes inside jail
1261 Jids on the other hand exist in a single space, and each jail must have a
1264 Like the names, a child jail's
1266 appears relative to its creator's own
1268 This is by virtue of the child jail being created in the chrooted
1269 environment of the first jail.
1308 Hierarchical/extensible jails were introduced in
1310 The configuration file was introduced in
1314 The jail feature was written by
1315 .An Poul-Henning Kamp
1317 who contributed it to
1321 wrote the extended documentation, found a few bugs, added
1322 a few new features, and cleaned up the userland jail environment.
1325 added multi-IP jail support for IPv4 and IPv6 based on a patch
1327 .An Pawel Jakub Dawidek
1331 added the extensible jail parameters, hierarchical jails,
1332 and the configuration file.
1334 It might be a good idea to add an
1335 address alias flag such that daemons listening on all IPs
1337 will not bind on that address, which would facilitate building a safe
1338 host environment such that host daemons do not impose on services offered
1340 Currently, the simplest answer is to minimize services
1341 offered on the host, possibly limiting it to services offered from
1343 which is easily configurable.
1345 Great care should be taken when managing directories visible within the jail.
1346 For example, if a jailed process has its current working directory set to a
1347 directory that is moved out of the jail's chroot, then the process may gain
1348 access to the file space outside of the jail.
1349 It is recommended that directories always be copied, rather than moved, out
1352 In addition, there are several ways in which an unprivileged user
1353 outside the jail can cooperate with a privileged user inside the jail
1354 and thereby obtain elevated privileges in the host environment.
1355 Most of these attacks can be mitigated by ensuring that the jail root
1356 is not accessible to unprivileged users in the host environment.
1357 Regardless, as a general rule, untrusted users with privileged access
1358 to a jail should not be given access to the host environment.
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