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.read_msgbuf
553 Jailed users may read the kernel message buffer.
555 .Va security.bsd.unprivileged_read_msgbuf
556 MIB entry is zero, this will be restricted to the root user.
557 .It Va allow.socket_af
558 Sockets within a jail are normally restricted to IPv4, IPv6, local
559 (UNIX), and route. This allows access to other protocol stacks that
560 have not had jail functionality added to them.
562 Locking or unlocking physical pages in memory are normally not available
564 When this parameter is set, users may
569 .Va security.bsd.unprivileged_mlock
571 .It Va allow.reserved_ports
572 The jail root may bind to ports lower than 1024.
576 Kernel modules may add their own parameters, which only exist when the
578 These are typically headed under a parameter named after the module,
581 to give the jail full use of the module,
583 to encapsulate the jail in some module-specific way,
586 to make the module unavailable to the jail.
587 There also may be other parameters to define jail behavior within the module.
588 Module-specific parameters include:
589 .Bl -tag -width indent
590 .It Va allow.mount.fdescfs
591 privileged users inside the jail will be able to mount and unmount the
593 This permission is effective only together with
597 is set to a value lower than 2.
598 .It Va allow.mount.fusefs
599 privileged users inside the jail will be able to mount and unmount
600 fuse-based file systems.
601 This permission is effective only together with
605 is set to a value lower than 2.
606 .It Va allow.mount.nullfs
607 privileged users inside the jail will be able to mount and unmount the
609 This permission is effective only together with
613 is set to a value lower than 2.
614 .It Va allow.mount.procfs
615 privileged users inside the jail will be able to mount and unmount the
617 This permission is effective only together with
621 is set to a value lower than 2.
622 .It Va allow.mount.linprocfs
623 privileged users inside the jail will be able to mount and unmount the
624 linprocfs file system.
625 This permission is effective only together with
629 is set to a value lower than 2.
630 .It Va allow.mount.linsysfs
631 privileged users inside the jail will be able to mount and unmount the
632 linsysfs file system.
633 This permission is effective only together with
637 is set to a value lower than 2.
638 .It Va allow.mount.tmpfs
639 privileged users inside the jail will be able to mount and unmount the
641 This permission is effective only together with
645 is set to a value lower than 2.
646 .It Va allow.mount.zfs
647 privileged users inside the jail will be able to mount and unmount the
649 This permission is effective only together with
653 is set to a value lower than 2.
656 for information on how to configure the ZFS filesystem to operate from
661 This flag is only available when the
663 kernel module is loaded.
665 Determine how a jail's Linux emulation environment appears.
668 will keep the same environment, and
670 will give the jail it's own environment (still originally inherited when
671 the jail is created).
672 .It Va linux.osname , linux.osrelease , linux.oss_version
673 The Linux OS name, OS release, and OSS version associated with this jail.
675 Allow access to SYSV IPC message primitives.
678 all IPC objects on the system are visible to this jail, whether they
679 were created by the jail itself, the base system, or other jails.
682 the jail will have its own key namespace, and can only see the objects
684 the system (or parent jail) has access to the jail's objects, but not to
688 the jail cannot perform any sysvmsg-related system calls.
689 .It Va sysvsem, sysvshm
690 Allow access to SYSV IPC semaphore and shared memory primitives, in the
695 There are pseudo-parameters that are not passed to the kernel, but are
698 to set up the jail environment, often by running specified commands
699 when jails are created or removed.
702 command parameters are
704 command lines that are run in either the system or jail environment.
705 They may be given multiple values, which would run the specified
706 commands in sequence.
707 All commands must succeed (return a zero exit status), or the jail will
708 not be created or removed, as appropriate.
710 The pseudo-parameters are:
711 .Bl -tag -width indent
713 Command(s) to run in the system environment before a jail is created.
715 Command(s) to run in the system environment right after a jail has been
716 created, but before commands (or services) get executed in the jail.
718 Command(s) to run in the jail environment when a jail is created.
719 A typical command to run is
724 for use when specifying a jail directly on the command line.
725 Unlike other parameters whose value is a single string,
727 uses the remainder of the
729 command line as its own arguments.
730 .It Va exec.poststart
731 Command(s) to run in the system environment after a jail is created,
734 commands have completed.
736 Command(s) to run in the system environment before a jail is removed.
738 Command(s) to run in the jail environment before a jail is removed,
741 commands have completed.
742 A typical command to run is
743 .Dq sh /etc/rc.shutdown .
745 Command(s) to run in the system environment after a jail is removed.
747 Run commands in a clean environment.
748 The environment is discarded except for
749 .Ev HOME , SHELL , TERM
755 are set to the target login's default values.
757 is set to the target login.
759 is imported from the current environment.
760 The environment variables from the login class capability database for the
761 target login are also set.
762 .It Va exec.jail_user
763 The user to run commands as, when running in the jail environment.
764 The default is to run the commands as the current user.
765 .It Va exec.system_jail_user
766 This boolean option looks for the
770 file, instead of in the jail's file.
771 .It Va exec.system_user
772 The user to run commands as, when running in the system environment.
773 The default is to run the commands as the current user.
775 The maximum amount of time to wait for a command to complete, in
777 If a command is still running after this timeout has passed,
778 the jail will not be created or removed, as appropriate.
779 .It Va exec.consolelog
780 A file to direct command output (stdout and stderr) to.
782 The FIB (routing table) to set when running commands inside the jail.
784 The maximum amount of time to wait for a jail's processes to exit
787 signal (which happens after the
789 commands have completed).
790 After this many seconds have passed, the jail will be removed, which
791 will kill any remaining processes.
792 If this is set to zero, no
794 is sent and the jail is immediately removed.
795 The default is 10 seconds.
797 A network interface to add the jail's IP addresses
802 An alias for each address will be added to the interface before the
803 jail is created, and will be removed from the interface after the
806 In addition to the IP addresses that are passed to the kernel, an
807 interface, netmask and additional parameters (as supported by
809 may also be specified, in the form
810 .Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar netmask param ... .
811 If an interface is given before the IP address, an alias for the address
812 will be added to that interface, as it is with the
815 If a netmask in either dotted-quad or CIDR form is given
816 after an IP address, it will be used when adding the IP alias.
817 If additional parameters are specified then they will also be used when
820 In addition to the IP addresses that are passed to the kernel,
821 an interface, prefix and additional parameters (as supported by
823 may also be specified, in the form
824 .Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar prefix param ... .
825 .It Va vnet.interface
826 A network interface to give to a vnet-enabled jail after is it created.
827 The interface will automatically be released when the jail is removed.
831 parameter and add all IP addresses returned by the resolver
832 to the list of addresses
837 This may affect default address selection for outgoing IPv4 connections
839 The address first returned by the resolver for each address family
840 will be used as the primary address.
842 A filesystem to mount before creating the jail (and to unmount after
843 removing it), given as a single
849 format file containing filesystems to mount before creating a jail.
853 filesystem on the chrooted
855 directory, and apply the ruleset in the
857 parameter (or a default of ruleset 4: devfsrules_jail)
858 to restrict the devices visible inside the jail.
862 filesystem on the chrooted
868 filesystem on the chrooted
872 Allow making changes to a
876 Specify a jail (or jails) that this jail depends on.
877 When this jail is to be created, any jail(s) it depends on must already exist.
878 If not, they will be created automatically, up to the completion of the last
880 command, before any action will taken to create this jail.
881 When jails are removed the opposite is true:
882 this jail will be removed, up to the last
884 command, before any jail(s) it depends on are stopped.
887 Jails are typically set up using one of two philosophies: either to
888 constrain a specific application (possibly running with privilege), or
890 .Dq "virtual system image"
891 running a variety of daemons and services.
892 In both cases, a fairly complete file system install of
895 required, so as to provide the necessary command line tools, daemons,
896 libraries, application configuration files, etc.
897 However, for a virtual server configuration, a fair amount of
898 additional work is required so as to replace the
901 This manual page documents the configuration steps necessary to support
902 either of these steps, although the configuration steps may need to be
903 refined based on local requirements.
904 .Ss "Setting up a Jail Directory Tree"
905 To set up a jail directory tree containing an entire
907 distribution, the following
909 command script can be used:
914 make world DESTDIR=$D
915 make distribution DESTDIR=$D
918 In many cases this example would put far more in the jail than needed.
919 In the other extreme case a jail might contain only one file:
920 the executable to be run in the jail.
922 We recommend experimentation, and caution that it is a lot easier to
925 jail and remove things until it stops working,
926 than it is to start with a
928 jail and add things until it works.
929 .Ss "Setting Up a Jail"
930 Do what was described in
931 .Sx "Setting Up a Jail Directory Tree"
932 to build the jail directory tree.
933 For the sake of this example, we will
934 assume you built it in
935 .Pa /data/jail/testjail ,
938 Substitute below as needed with your
939 own directory, IP address, and hostname.
940 .Ss "Setting up the Host Environment"
941 First, set up the real system's environment to be
943 For consistency, we will refer to the parent box as the
944 .Dq "host environment" ,
945 and to the jailed virtual machine as the
946 .Dq "jail environment" .
947 Since jails are implemented using IP aliases, one of the first things to do
948 is to disable IP services on the host system that listen on all local
949 IP addresses for a service.
950 If a network service is present in the host environment that binds all
951 available IP addresses rather than specific IP addresses, it may service
952 requests sent to jail IP addresses if the jail did not bind the port.
955 to only listen on the
956 appropriate IP address, and so forth.
959 in the host environment:
960 .Bd -literal -offset indent
962 inetd_flags="-wW -a 192.0.2.23"
967 is the native IP address for the host system, in this example.
968 Daemons that run out of
970 can be easily configured to use only the specified host IP address.
972 will need to be manually configured \(em for some this is possible through
974 flags entries; for others it is necessary to modify per-application
975 configuration files, or to recompile the application.
976 The following frequently deployed services must have their individual
977 configuration files modified to limit the application to listening
978 to a specific IP address:
982 it is necessary to modify
983 .Pa /etc/ssh/sshd_config .
987 it is necessary to modify
988 .Pa /etc/mail/sendmail.cf .
992 it is necessary to modify
993 .Pa /etc/namedb/named.conf .
995 In addition, a number of services must be recompiled in order to run
996 them in the host environment.
997 This includes most applications providing services using
1004 In general, applications for which it is not possible to specify which
1005 IP address to bind should not be run in the host environment unless they
1006 should also service requests sent to jail IP addresses.
1008 NFS from the host environment may also cause confusion, and cannot be
1009 easily reconfigured to use only specific IPs, as some NFS services are
1010 hosted directly from the kernel.
1011 Any third-party network software running
1012 in the host environment should also be checked and configured so that it
1013 does not bind all IP addresses, which would result in those services also
1014 appearing to be offered by the jail environments.
1017 these daemons have been disabled or fixed in the host environment, it is
1018 best to reboot so that all daemons are in a known state, to reduce the
1019 potential for confusion later (such as finding that when you send mail
1020 to a jail, and its sendmail is down, the mail is delivered to the host,
1022 .Ss "Configuring the Jail"
1023 Start any jail for the first time without configuring the network
1024 interface so that you can clean it up a little and set up accounts.
1026 with any machine (virtual or not), you will need to set a root password, time
1028 Some of these steps apply only if you intend to run a full virtual server
1029 inside the jail; others apply both for constraining a particular application
1030 or for running a virtual server.
1032 Start a shell in the jail:
1033 .Bd -literal -offset indent
1034 jail -c path=/data/jail/testjail mount.devfs \\
1035 host.hostname=testhostname ip4.addr=192.0.2.100 \\
1039 Assuming no errors, you will end up with a shell prompt within the jail.
1042 and do the post-install configuration to set various configuration options,
1043 or perform these actions manually by editing
1047 .Bl -bullet -offset indent -compact
1050 .Pa /etc/resolv.conf
1051 so that name resolution within the jail will work correctly.
1059 Set a root password, probably different from the real host system.
1063 Add accounts for users in the jail environment.
1065 Install any packages the environment requires.
1068 You may also want to perform any package-specific configuration (web servers,
1069 SSH servers, etc), patch up
1070 .Pa /etc/syslog.conf
1071 so it logs as you would like, etc.
1072 If you are not using a virtual server, you may wish to modify
1074 in the host environment to listen on the syslog socket in the jail
1075 environment; in this example, the syslog socket would be stored in
1076 .Pa /data/jail/testjail/var/run/log .
1078 Exit from the shell, and the jail will be shut down.
1079 .Ss "Starting the Jail"
1080 You are now ready to restart the jail and bring up the environment with
1081 all of its daemons and other programs.
1082 Create an entry for the jail in
1083 .Pa /etc/jail.conf :
1084 .Bd -literal -offset indent
1086 path = /tmp/jail/testjail;
1088 host.hostname = testhostname;
1089 ip4.addr = 192.0.2.100;
1091 exec.start = "/bin/sh /etc/rc";
1092 exec.stop = "/bin/sh /etc/rc.shutdown";
1096 To start a virtual server environment,
1098 is run to launch various daemons and services, and
1099 .Pa /etc/rc.shutdown
1100 is run to shut them down when the jail is removed.
1101 If you are running a single application in the jail,
1102 substitute the command used to start the application for
1103 .Dq /bin/sh /etc/rc ;
1104 there may be some script available to cleanly shut down the application,
1105 or it may be sufficient to go without a stop command, and have
1111 Start the jail by running:
1112 .Bd -literal -offset indent
1116 A few warnings may be produced; however, it should all work properly.
1117 You should be able to see
1120 and other processes running within the jail using
1124 flag appearing beside jailed processes.
1125 To see an active list of jails, use
1129 is enabled in the jail environment, you should be able to
1131 to the hostname or IP address of the jailed environment, and log
1132 in using the accounts you created previously.
1134 It is possible to have jails started at boot time.
1139 for more information.
1140 .Ss "Managing the Jail"
1141 Normal machine shutdown commands, such as
1146 cannot be used successfully within the jail.
1147 To kill all processes from within a jail, you may use one of the
1148 following commands, depending on what you want to accomplish:
1149 .Bd -literal -offset indent
1158 signals to all processes in the jail \(em be careful not to run this from
1159 the host environment!
1160 Once all of the jail's processes have died, unless the jail was created
1163 parameter, the jail will be removed.
1165 the intended use of the jail, you may also want to run
1166 .Pa /etc/rc.shutdown
1167 from within the jail.
1169 To shut down the jail from the outside, simply remove it with
1172 which will run any commands specified by
1178 to any remaining jailed processes.
1181 .Pa /proc/ Ns Ar pid Ns Pa /status
1182 file contains, as its last field, the name of the jail in which the
1185 to indicate that the process is not running within a jail.
1188 command also shows a
1190 flag for processes in a jail.
1192 You can also list/kill processes based on their jail ID.
1193 To show processes and their jail ID, use the following command:
1195 .Dl "ps ax -o pid,jid,args"
1197 To show and then kill processes in jail number 3 use the following commands:
1198 .Bd -literal -offset indent
1205 .Ss "Jails and File Systems"
1206 It is not possible to
1210 any file system inside a jail unless the file system is marked
1211 jail-friendly, the jail's
1213 parameter is set, and the jail's
1215 parameter is lower than 2.
1217 Multiple jails sharing the same file system can influence each other.
1218 For example, a user in one jail can fill the file system,
1219 leaving no space for processes in the other jail.
1222 to prevent this will not work either, as the file system quotas
1223 are not aware of jails but only look at the user and group IDs.
1224 This means the same user ID in two jails share a single file
1226 One would need to use one file system per jail to make this work.
1227 .Ss "Sysctl MIB Entries"
1229 .Va security.jail.jailed
1230 can be used to determine if a process is running inside a jail (value
1231 is one) or not (value is zero).
1234 .Va security.jail.max_af_ips
1235 determines how may address per address family a jail may have.
1238 Some MIB variables have per-jail settings.
1239 Changes to these variables by a jailed process do not affect the host
1240 environment, only the jail environment.
1242 .Va kern.securelevel ,
1244 .Va kern.domainname ,
1248 .Ss "Hierarchical Jails"
1251 parameter, processes within a jail may be able to create jails of their own.
1252 These child jails are kept in a hierarchy, with jails only able to see and/or
1253 modify the jails they created (or those jails' children).
1254 Each jail has a read-only
1256 parameter, containing the
1258 of the jail that created it; a
1260 of 0 indicates the jail is a child of the current jail (or is a top-level
1261 jail if the current process isn't jailed).
1263 Jailed processes are not allowed to confer greater permissions than they
1264 themselves are given, e.g., if a jail is created with
1266 it is not able to create a jail with
1269 Similarly, such restrictions as
1273 may not be bypassed in child jails.
1275 A child jail may in turn create its own child jails if its own
1277 parameter is set (remember it is zero by default).
1278 These jails are visible to and can be modified by their parent and all
1281 Jail names reflect this hierarchy, with a full name being an MIB-type string
1283 For example, if a base system process creates a jail
1285 and a process under that jail creates another jail
1287 then the second jail will be seen as
1289 in the base system (though it is only seen as
1291 to any processes inside jail
1293 Jids on the other hand exist in a single space, and each jail must have a
1296 Like the names, a child jail's
1298 appears relative to its creator's own
1300 This is by virtue of the child jail being created in the chrooted
1301 environment of the first jail.
1342 Hierarchical/extensible jails were introduced in
1344 The configuration file was introduced in
1348 The jail feature was written by
1349 .An Poul-Henning Kamp
1351 who contributed it to
1355 wrote the extended documentation, found a few bugs, added
1356 a few new features, and cleaned up the userland jail environment.
1359 added multi-IP jail support for IPv4 and IPv6 based on a patch
1361 .An Pawel Jakub Dawidek
1365 added the extensible jail parameters, hierarchical jails,
1366 and the configuration file.
1368 It might be a good idea to add an
1369 address alias flag such that daemons listening on all IPs
1371 will not bind on that address, which would facilitate building a safe
1372 host environment such that host daemons do not impose on services offered
1374 Currently, the simplest answer is to minimize services
1375 offered on the host, possibly limiting it to services offered from
1377 which is easily configurable.
1379 Great care should be taken when managing directories visible within the jail.
1380 For example, if a jailed process has its current working directory set to a
1381 directory that is moved out of the jail's chroot, then the process may gain
1382 access to the file space outside of the jail.
1383 It is recommended that directories always be copied, rather than moved, out
1386 In addition, there are several ways in which an unprivileged user
1387 outside the jail can cooperate with a privileged user inside the jail
1388 and thereby obtain elevated privileges in the host environment.
1389 Most of these attacks can be mitigated by ensuring that the jail root
1390 is not accessible to unprivileged users in the host environment.
1391 Regardless, as a general rule, untrusted users with privileged access
1392 to a jail should not be given access to the host environment.
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