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 ...
54 .Op Cm * | Ar jail ...
61 .Op Fl s Ar securelevel
62 .Op Ar path hostname [ Ar ip Ns [ Ns Ar ,... Ns ]] Ar command ...
66 utility creates new jails, or modifies or removes existing jails.
67 It can also print a list of configured jails and their parameters.
70 is specified via parameters on the command line, or in the
74 At least one of the options
81 These options are used alone or in combination to describe the operation to
83 .Bl -tag -width indent
90 parameters (if specified on the command line)
91 must not refer to an existing jail.
93 Exhibit a list of all configured non-wildcard jails and their parameters.
94 No jail creation, modification or removal performed if this option is used.
97 string is used to separate parameters.
100 utility to list running jails.
102 Modify an existing jail.
107 parameters must exist and refer to an existing jail.
108 Some parameters may not be changed on a running jail.
112 specified by jid or name.
113 All jailed processes are killed, and all jails that are
114 children of this jail are also
117 Restart an existing jail.
118 The jail is first removed and then re-created, as if
122 were run in succession.
124 Create a jail if it does not exist, or modify the jail if it does exist.
126 Modify an existing jail.
127 The jail may be restarted if necessary to modify parameters than could
128 not otherwise be changed.
130 Create a jail if it doesn't exist, or modify (and possibly restart) the
131 jail if it does exist.
134 Other available options are:
135 .Bl -tag -width indent
137 Allow making changes to a dying jail, equivalent to the
140 .It Fl f Ar conf_file
141 Use configuration file
143 instead of the default
150 and add all IP addresses returned by the resolver
151 to the list of addresses for this jail.
152 This is equivalent to the
156 Output (only) the jail identifier of the newly created jail(s).
163 file, containing the parameters used to start the jail.
165 Run commands in a clean environment.
166 This is deprecated and is equivalent to the exec.clean parameter.
169 This is deprecated and is equivalent to the
173 Limit the number of commands from
175 that can run simultaneously.
177 Suppress the message printed whenever a jail is created, modified or removed.
178 Only error messages will be printed.
182 option that removes an existing jail without using the configuration file.
183 No removal-related parameters for this jail will be used \(em the jail will
185 .It Fl s Ar securelevel
188 MIB entry to the specified value inside the newly created jail.
189 This is deprecated and is equivalent to the
193 The user name from host environment as whom jailed commands should run.
194 This is deprecated and is equivalent to the
197 .Va exec.system_jail_user
200 The user name from the jailed environment as whom jailed commands should run.
201 This is deprecated and is equivalent to the
205 Print a message on every operation, such as running commands and
206 mounting filesystems.
209 If no arguments are given after the options, the operation (except
210 remove) will be performed on all jails specified in the
213 A single argument of a jail name will operate only on the specified jail.
218 options can also remove running jails that aren't in the
220 file, specified by name or jid.
224 is a wildcard that will operate on all jails, regardless of whether
227 this is the surest way for
230 If hierarchical jails exist, a partial-matching wildcard definition may
232 For example, an argument of
234 would apply to jails with names like
239 A jail may be specified with parameters directly on the command line.
242 file will not be used.
243 For backward compatibility, the command line may also have four fixed
244 parameters, without names:
250 This mode will always create a new jail, and the
254 options do not apply (and must not be present).
258 file, or on the command line, are generally of the form
260 Some parameters are boolean, and do not have a value but are set by the
261 name alone with or without a
267 They can also be given the values
271 Other parameters may have more than one value, specified as a
272 comma-separated list or with
274 in the configuration file (see
280 utility recognizes two classes of parameters.
281 There are the true jail
282 parameters that are passed to the kernel when the jail is created,
283 which can be seen with
285 and can (usually) be changed with
287 Then there are pseudo-parameters that are only used by
291 Jails have a set of core parameters, and kernel modules can add their own
293 The current set of available parameters can be retrieved via
294 .Dq Nm sysctl Fl d Va security.jail.param .
295 Any parameters not set will be given default values, often based on the
297 The core parameters are:
298 .Bl -tag -width indent
301 This will be assigned automatically to a new jail (or can be explicitly
302 set), and can be used to identify the jail for later modification, or
309 This is an arbitrary string that identifies a jail (except it may not
314 it can be passed to later
322 is supplied, a default is assumed that is the same as the
326 parameter is implied by the
328 file format, and need not be explicitly set when using the configuration
331 The directory which is to be the root of the jail.
332 Any commands run inside the jail, either by
336 are run from this directory.
338 A list of IPv4 addresses assigned to the jail.
339 If this is set, the jail is restricted to using only these addresses.
340 Any attempts to use other addresses fail, and attempts to use wildcard
341 addresses silently use the jailed address instead.
342 For IPv4 the first address given will be used as the source address
343 when source address selection on unbound sockets cannot find a better
345 It is only possible to start multiple jails with the same IP address
346 if none of the jails has more than this single overlapping IP address
349 A boolean option to change the formerly mentioned behaviour and disable
350 IPv4 source address selection for the jail in favour of the primary
351 IPv4 address of the jail.
352 Source address selection is enabled by default for all jails and the
354 setting of a parent jail is not inherited for any child jails.
356 Control the availability of IPv4 addresses.
359 to allow unrestricted access to all system addresses,
361 to restrict addresses via
365 to stop the jail from using IPv4 entirely.
368 parameter implies a value of
370 .It Va ip6.addr , Va ip6.saddrsel , Va ip6
371 A set of IPv6 options for the jail, the counterparts to
378 Create the jail with its own virtual network stack,
379 with its own network interfaces, addresses, routing table, etc.
380 The kernel must have been compiled with the
382 for this to be available.
385 to use the system network stack, possibly with restricted IP addresses,
388 to create a new network stack.
390 The hostname of the jail.
391 Other similar parameters are
392 .Va host.domainname ,
397 Set the origin of hostname and related information.
400 to use the system information and
402 for the jail to use the information from the above fields.
403 Setting any of the above fields implies a value of
406 The value of the jail's
409 A jail never has a lower securelevel than its parent system, but by
410 setting this parameter it may have a higher one.
411 If the system securelevel is changed, any jail securelevels will be at
414 The number of the devfs ruleset that is enforced for mounting devfs in
416 A value of zero (default) means no ruleset is enforced.
417 Descendant jails inherit the parent jail's devfs ruleset enforcement.
418 Mounting devfs inside a jail is possible only if the
421 .Va allow.mount.devfs
422 permissions are effective and
424 is set to a value lower than 2.
425 Devfs rules and rulesets cannot be viewed or modified from inside a jail.
427 NOTE: It is important that only appropriate device nodes in devfs be
428 exposed to a jail; access to disk devices in the jail may permit processes
429 in the jail to bypass the jail sandboxing by modifying files outside of
433 for information on how to use devfs rules to limit access to entries
434 in the per-jail devfs.
435 A simple devfs ruleset for jails is available as ruleset #4 in
436 .Pa /etc/defaults/devfs.rules .
438 The number of child jails allowed to be created by this jail (or by
439 other jails under this jail).
440 This limit is zero by default, indicating the jail is not allowed to
443 .Sx "Hierarchical Jails"
444 section for more information.
446 The number of descendants of this jail, including its own child jails
447 and any jails created under them.
448 .It Va enforce_statfs
449 This determines what information processes in a jail are able to get
451 It affects the behaviour of the following syscalls:
457 (as well as similar compatibility syscalls).
458 When set to 0, all mount points are available without any restrictions.
459 When set to 1, only mount points below the jail's chroot directory are
461 In addition to that, the path to the jail's chroot directory is removed
462 from the front of their pathnames.
463 When set to 2 (default), above syscalls can operate only on a mount-point
464 where the jail's chroot directory is located.
466 Setting this boolean parameter allows a jail to exist without any
468 Normally, a command is run as part of jail creation, and then the jail
469 is destroyed as its last process exits.
470 A new jail must have either the
476 pseudo-parameter set.
478 The ID of the cpuset associated with this jail (read-only).
480 This is true if the jail is in the process of shutting down (read-only).
484 of the parent of this jail, or zero if this is a top-level jail
487 The string for the jail's
491 The number for the jail's
495 Some restrictions of the jail environment may be set on a per-jail
497 With the exception of
498 .Va allow.set_hostname
500 .Va allow.reserved_ports ,
501 these boolean parameters are off by default.
502 .Bl -tag -width indent
503 .It Va allow.set_hostname
504 The jail's hostname may be changed via
509 A process within the jail has access to System V IPC primitives.
510 This is deprecated in favor of the per-module parameters (see below).
511 When this parameter is set, it is equivalent to setting
518 .It Va allow.raw_sockets
519 The jail root is allowed to create raw sockets.
520 Setting this parameter allows utilities like
524 to operate inside the jail.
525 If this is set, the source IP addresses are enforced to comply
526 with the IP address bound to the jail, regardless of whether or not
529 flag has been set on the socket.
530 Since raw sockets can be used to configure and interact with various
531 network subsystems, extra caution should be used where privileged access
532 to jails is given out to untrusted parties.
534 Normally, privileged users inside a jail are treated as unprivileged by
536 When this parameter is set, such users are treated as privileged, and
537 may manipulate system file flags subject to the usual constraints on
538 .Va kern.securelevel .
540 privileged users inside the jail will be able to mount and unmount file
541 system types marked as jail-friendly.
544 command can be used to find file system types available for mount from
546 This permission is effective only if
548 is set to a value lower than 2.
549 .It Va allow.mount.devfs
550 privileged users inside the jail will be able to mount and unmount the
552 This permission is effective only together with
556 is set to a value lower than 2.
557 The devfs ruleset should be restricted from the default by using the
561 The jail root may administer quotas on the jail's filesystem(s).
562 This includes filesystems that the jail may share with other jails or
563 with non-jailed parts of the system.
564 .It Va allow.read_msgbuf
565 Jailed users may read the kernel message buffer.
567 .Va security.bsd.unprivileged_read_msgbuf
568 MIB entry is zero, this will be restricted to the root user.
569 .It Va allow.socket_af
570 Sockets within a jail are normally restricted to IPv4, IPv6, local
571 (UNIX), and route. This allows access to other protocol stacks that
572 have not had jail functionality added to them.
574 Locking or unlocking physical pages in memory are normally not available
576 When this parameter is set, users may
581 .Va security.bsd.unprivileged_mlock
583 .It Va allow.reserved_ports
584 The jail root may bind to ports lower than 1024.
588 Kernel modules may add their own parameters, which only exist when the
590 These are typically headed under a parameter named after the module,
593 to give the jail full use of the module,
595 to encapsulate the jail in some module-specific way,
598 to make the module unavailable to the jail.
599 There also may be other parameters to define jail behavior within the module.
600 Module-specific parameters include:
601 .Bl -tag -width indent
602 .It Va allow.mount.fdescfs
603 privileged users inside the jail will be able to mount and unmount the
605 This permission is effective only together with
609 is set to a value lower than 2.
610 .It Va allow.mount.fusefs
611 privileged users inside the jail will be able to mount and unmount
612 fuse-based file systems.
613 This permission is effective only together with
617 is set to a value lower than 2.
618 .It Va allow.mount.nullfs
619 privileged users inside the jail will be able to mount and unmount the
621 This permission is effective only together with
625 is set to a value lower than 2.
626 .It Va allow.mount.procfs
627 privileged users inside the jail will be able to mount and unmount the
629 This permission is effective only together with
633 is set to a value lower than 2.
634 .It Va allow.mount.linprocfs
635 privileged users inside the jail will be able to mount and unmount the
636 linprocfs file system.
637 This permission is effective only together with
641 is set to a value lower than 2.
642 .It Va allow.mount.linsysfs
643 privileged users inside the jail will be able to mount and unmount the
644 linsysfs file system.
645 This permission is effective only together with
649 is set to a value lower than 2.
650 .It Va allow.mount.tmpfs
651 privileged users inside the jail will be able to mount and unmount the
653 This permission is effective only together with
657 is set to a value lower than 2.
658 .It Va allow.mount.zfs
659 privileged users inside the jail will be able to mount and unmount the
661 This permission is effective only together with
665 is set to a value lower than 2.
668 for information on how to configure the ZFS filesystem to operate from
673 This flag is only available when the
675 kernel module is loaded.
677 Determine how a jail's Linux emulation environment appears.
680 will keep the same environment, and
682 will give the jail it's own environment (still originally inherited when
683 the jail is created).
684 .It Va linux.osname , linux.osrelease , linux.oss_version
685 The Linux OS name, OS release, and OSS version associated with this jail.
687 Allow access to SYSV IPC message primitives.
690 all IPC objects on the system are visible to this jail, whether they
691 were created by the jail itself, the base system, or other jails.
694 the jail will have its own key namespace, and can only see the objects
696 the system (or parent jail) has access to the jail's objects, but not to
700 the jail cannot perform any sysvmsg-related system calls.
701 .It Va sysvsem, sysvshm
702 Allow access to SYSV IPC semaphore and shared memory primitives, in the
707 There are pseudo-parameters that are not passed to the kernel, but are
710 to set up the jail environment, often by running specified commands
711 when jails are created or removed.
714 command parameters are
716 command lines that are run in either the system or jail environment.
717 They may be given multiple values, which would run the specified
718 commands in sequence.
719 All commands must succeed (return a zero exit status), or the jail will
720 not be created or removed, as appropriate.
722 The pseudo-parameters are:
723 .Bl -tag -width indent
725 Command(s) to run in the system environment before a jail is created.
727 Command(s) to run in the system environment right after a jail has been
728 created, but before commands (or services) get executed in the jail.
730 Command(s) to run in the jail environment when a jail is created.
731 A typical command to run is
736 for use when specifying a jail directly on the command line.
737 Unlike other parameters whose value is a single string,
739 uses the remainder of the
741 command line as its own arguments.
742 .It Va exec.poststart
743 Command(s) to run in the system environment after a jail is created,
746 commands have completed.
748 Command(s) to run in the system environment before a jail is removed.
750 Command(s) to run in the jail environment before a jail is removed,
753 commands have completed.
754 A typical command to run is
755 .Dq sh /etc/rc.shutdown .
757 Command(s) to run in the system environment after a jail is removed.
759 Run commands in a clean environment.
760 The environment is discarded except for
761 .Ev HOME , SHELL , TERM
767 are set to the target login's default values.
769 is set to the target login.
771 is imported from the current environment.
772 The environment variables from the login class capability database for the
773 target login are also set.
774 .It Va exec.jail_user
775 The user to run commands as, when running in the jail environment.
776 The default is to run the commands as the current user.
777 .It Va exec.system_jail_user
778 This boolean option looks for the
782 file, instead of in the jail's file.
783 .It Va exec.system_user
784 The user to run commands as, when running in the system environment.
785 The default is to run the commands as the current user.
787 The maximum amount of time to wait for a command to complete, in
789 If a command is still running after this timeout has passed,
790 the jail will not be created or removed, as appropriate.
791 .It Va exec.consolelog
792 A file to direct command output (stdout and stderr) to.
794 The FIB (routing table) to set when running commands inside the jail.
796 The maximum amount of time to wait for a jail's processes to exit
799 signal (which happens after the
801 commands have completed).
802 After this many seconds have passed, the jail will be removed, which
803 will kill any remaining processes.
804 If this is set to zero, no
806 is sent and the jail is immediately removed.
807 The default is 10 seconds.
809 A network interface to add the jail's IP addresses
814 An alias for each address will be added to the interface before the
815 jail is created, and will be removed from the interface after the
818 In addition to the IP addresses that are passed to the kernel, an
819 interface, netmask and additional parameters (as supported by
821 may also be specified, in the form
822 .Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar netmask param ... .
823 If an interface is given before the IP address, an alias for the address
824 will be added to that interface, as it is with the
827 If a netmask in either dotted-quad or CIDR form is given
828 after an IP address, it will be used when adding the IP alias.
829 If additional parameters are specified then they will also be used when
832 In addition to the IP addresses that are passed to the kernel,
833 an interface, prefix and additional parameters (as supported by
835 may also be specified, in the form
836 .Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar prefix param ... .
837 .It Va vnet.interface
838 A network interface to give to a vnet-enabled jail after is it created.
839 The interface will automatically be released when the jail is removed.
843 parameter and add all IP addresses returned by the resolver
844 to the list of addresses
849 This may affect default address selection for outgoing IPv4 connections
851 The address first returned by the resolver for each address family
852 will be used as the primary address.
854 A filesystem to mount before creating the jail (and to unmount after
855 removing it), given as a single
861 format file containing filesystems to mount before creating a jail.
865 filesystem on the chrooted
867 directory, and apply the ruleset in the
869 parameter (or a default of ruleset 4: devfsrules_jail)
870 to restrict the devices visible inside the jail.
874 filesystem on the chrooted
880 filesystem on the chrooted
884 Allow making changes to a
888 Specify a jail (or jails) that this jail depends on.
889 When this jail is to be created, any jail(s) it depends on must already exist.
890 If not, they will be created automatically, up to the completion of the last
892 command, before any action will taken to create this jail.
893 When jails are removed the opposite is true:
894 this jail will be removed, up to the last
896 command, before any jail(s) it depends on are stopped.
899 Jails are typically set up using one of two philosophies: either to
900 constrain a specific application (possibly running with privilege), or
902 .Dq "virtual system image"
903 running a variety of daemons and services.
904 In both cases, a fairly complete file system install of
907 required, so as to provide the necessary command line tools, daemons,
908 libraries, application configuration files, etc.
909 However, for a virtual server configuration, a fair amount of
910 additional work is required so as to replace the
913 This manual page documents the configuration steps necessary to support
914 either of these steps, although the configuration steps may need to be
915 refined based on local requirements.
916 .Ss "Setting up a Jail Directory Tree"
917 To set up a jail directory tree containing an entire
919 distribution, the following
921 command script can be used:
926 make world DESTDIR=$D
927 make distribution DESTDIR=$D
930 In many cases this example would put far more in the jail than needed.
931 In the other extreme case a jail might contain only one file:
932 the executable to be run in the jail.
934 We recommend experimentation, and caution that it is a lot easier to
937 jail and remove things until it stops working,
938 than it is to start with a
940 jail and add things until it works.
941 .Ss "Setting Up a Jail"
942 Do what was described in
943 .Sx "Setting Up a Jail Directory Tree"
944 to build the jail directory tree.
945 For the sake of this example, we will
946 assume you built it in
947 .Pa /data/jail/testjail ,
950 Substitute below as needed with your
951 own directory, IP address, and hostname.
952 .Ss "Setting up the Host Environment"
953 First, set up the real system's environment to be
955 For consistency, we will refer to the parent box as the
956 .Dq "host environment" ,
957 and to the jailed virtual machine as the
958 .Dq "jail environment" .
959 Since jails are implemented using IP aliases, one of the first things to do
960 is to disable IP services on the host system that listen on all local
961 IP addresses for a service.
962 If a network service is present in the host environment that binds all
963 available IP addresses rather than specific IP addresses, it may service
964 requests sent to jail IP addresses if the jail did not bind the port.
967 to only listen on the
968 appropriate IP address, and so forth.
971 in the host environment:
972 .Bd -literal -offset indent
974 inetd_flags="-wW -a 192.0.2.23"
979 is the native IP address for the host system, in this example.
980 Daemons that run out of
982 can be easily configured to use only the specified host IP address.
984 will need to be manually configured \(em for some this is possible through
986 flags entries; for others it is necessary to modify per-application
987 configuration files, or to recompile the application.
988 The following frequently deployed services must have their individual
989 configuration files modified to limit the application to listening
990 to a specific IP address:
994 it is necessary to modify
995 .Pa /etc/ssh/sshd_config .
999 it is necessary to modify
1000 .Pa /etc/mail/sendmail.cf .
1004 it is necessary to modify
1005 .Pa /etc/namedb/named.conf .
1007 In addition, a number of services must be recompiled in order to run
1008 them in the host environment.
1009 This includes most applications providing services using
1016 In general, applications for which it is not possible to specify which
1017 IP address to bind should not be run in the host environment unless they
1018 should also service requests sent to jail IP addresses.
1020 NFS from the host environment may also cause confusion, and cannot be
1021 easily reconfigured to use only specific IPs, as some NFS services are
1022 hosted directly from the kernel.
1023 Any third-party network software running
1024 in the host environment should also be checked and configured so that it
1025 does not bind all IP addresses, which would result in those services also
1026 appearing to be offered by the jail environments.
1029 these daemons have been disabled or fixed in the host environment, it is
1030 best to reboot so that all daemons are in a known state, to reduce the
1031 potential for confusion later (such as finding that when you send mail
1032 to a jail, and its sendmail is down, the mail is delivered to the host,
1034 .Ss "Configuring the Jail"
1035 Start any jail for the first time without configuring the network
1036 interface so that you can clean it up a little and set up accounts.
1038 with any machine (virtual or not), you will need to set a root password, time
1040 Some of these steps apply only if you intend to run a full virtual server
1041 inside the jail; others apply both for constraining a particular application
1042 or for running a virtual server.
1044 Start a shell in the jail:
1045 .Bd -literal -offset indent
1046 jail -c path=/data/jail/testjail mount.devfs \\
1047 host.hostname=testhostname ip4.addr=192.0.2.100 \\
1051 Assuming no errors, you will end up with a shell prompt within the jail.
1054 and do the post-install configuration to set various configuration options,
1055 or perform these actions manually by editing
1059 .Bl -bullet -offset indent -compact
1062 .Pa /etc/resolv.conf
1063 so that name resolution within the jail will work correctly.
1071 Set a root password, probably different from the real host system.
1075 Add accounts for users in the jail environment.
1077 Install any packages the environment requires.
1080 You may also want to perform any package-specific configuration (web servers,
1081 SSH servers, etc), patch up
1082 .Pa /etc/syslog.conf
1083 so it logs as you would like, etc.
1084 If you are not using a virtual server, you may wish to modify
1086 in the host environment to listen on the syslog socket in the jail
1087 environment; in this example, the syslog socket would be stored in
1088 .Pa /data/jail/testjail/var/run/log .
1090 Exit from the shell, and the jail will be shut down.
1091 .Ss "Starting the Jail"
1092 You are now ready to restart the jail and bring up the environment with
1093 all of its daemons and other programs.
1094 Create an entry for the jail in
1095 .Pa /etc/jail.conf :
1096 .Bd -literal -offset indent
1098 path = /tmp/jail/testjail;
1100 host.hostname = testhostname;
1101 ip4.addr = 192.0.2.100;
1103 exec.start = "/bin/sh /etc/rc";
1104 exec.stop = "/bin/sh /etc/rc.shutdown";
1108 To start a virtual server environment,
1110 is run to launch various daemons and services, and
1111 .Pa /etc/rc.shutdown
1112 is run to shut them down when the jail is removed.
1113 If you are running a single application in the jail,
1114 substitute the command used to start the application for
1115 .Dq /bin/sh /etc/rc ;
1116 there may be some script available to cleanly shut down the application,
1117 or it may be sufficient to go without a stop command, and have
1123 Start the jail by running:
1124 .Bd -literal -offset indent
1128 A few warnings may be produced; however, it should all work properly.
1129 You should be able to see
1132 and other processes running within the jail using
1136 flag appearing beside jailed processes.
1137 To see an active list of jails, use
1141 is enabled in the jail environment, you should be able to
1143 to the hostname or IP address of the jailed environment, and log
1144 in using the accounts you created previously.
1146 It is possible to have jails started at boot time.
1151 for more information.
1152 .Ss "Managing the Jail"
1153 Normal machine shutdown commands, such as
1158 cannot be used successfully within the jail.
1159 To kill all processes from within a jail, you may use one of the
1160 following commands, depending on what you want to accomplish:
1161 .Bd -literal -offset indent
1170 signals to all processes in the jail \(em be careful not to run this from
1171 the host environment!
1172 Once all of the jail's processes have died, unless the jail was created
1175 parameter, the jail will be removed.
1177 the intended use of the jail, you may also want to run
1178 .Pa /etc/rc.shutdown
1179 from within the jail.
1181 To shut down the jail from the outside, simply remove it with
1184 which will run any commands specified by
1190 to any remaining jailed processes.
1193 .Pa /proc/ Ns Ar pid Ns Pa /status
1194 file contains, as its last field, the name of the jail in which the
1197 to indicate that the process is not running within a jail.
1200 command also shows a
1202 flag for processes in a jail.
1204 You can also list/kill processes based on their jail ID.
1205 To show processes and their jail ID, use the following command:
1207 .Dl "ps ax -o pid,jid,args"
1209 To show and then kill processes in jail number 3 use the following commands:
1210 .Bd -literal -offset indent
1217 .Ss "Jails and File Systems"
1218 It is not possible to
1222 any file system inside a jail unless the file system is marked
1223 jail-friendly, the jail's
1225 parameter is set, and the jail's
1227 parameter is lower than 2.
1229 Multiple jails sharing the same file system can influence each other.
1230 For example, a user in one jail can fill the file system,
1231 leaving no space for processes in the other jail.
1234 to prevent this will not work either, as the file system quotas
1235 are not aware of jails but only look at the user and group IDs.
1236 This means the same user ID in two jails share a single file
1238 One would need to use one file system per jail to make this work.
1239 .Ss "Sysctl MIB Entries"
1241 .Va security.jail.jailed
1242 can be used to determine if a process is running inside a jail (value
1243 is one) or not (value is zero).
1246 .Va security.jail.max_af_ips
1247 determines how may address per address family a jail may have.
1250 Some MIB variables have per-jail settings.
1251 Changes to these variables by a jailed process do not affect the host
1252 environment, only the jail environment.
1254 .Va kern.securelevel ,
1256 .Va kern.domainname ,
1260 .Ss "Hierarchical Jails"
1263 parameter, processes within a jail may be able to create jails of their own.
1264 These child jails are kept in a hierarchy, with jails only able to see and/or
1265 modify the jails they created (or those jails' children).
1266 Each jail has a read-only
1268 parameter, containing the
1270 of the jail that created it; a
1272 of 0 indicates the jail is a child of the current jail (or is a top-level
1273 jail if the current process isn't jailed).
1275 Jailed processes are not allowed to confer greater permissions than they
1276 themselves are given, e.g., if a jail is created with
1278 it is not able to create a jail with
1281 Similarly, such restrictions as
1285 may not be bypassed in child jails.
1287 A child jail may in turn create its own child jails if its own
1289 parameter is set (remember it is zero by default).
1290 These jails are visible to and can be modified by their parent and all
1293 Jail names reflect this hierarchy, with a full name being an MIB-type string
1295 For example, if a base system process creates a jail
1297 and a process under that jail creates another jail
1299 then the second jail will be seen as
1301 in the base system (though it is only seen as
1303 to any processes inside jail
1305 Jids on the other hand exist in a single space, and each jail must have a
1308 Like the names, a child jail's
1310 appears relative to its creator's own
1312 This is by virtue of the child jail being created in the chrooted
1313 environment of the first jail.
1354 Hierarchical/extensible jails were introduced in
1356 The configuration file was introduced in
1360 The jail feature was written by
1361 .An Poul-Henning Kamp
1363 who contributed it to
1367 wrote the extended documentation, found a few bugs, added
1368 a few new features, and cleaned up the userland jail environment.
1371 added multi-IP jail support for IPv4 and IPv6 based on a patch
1373 .An Pawel Jakub Dawidek
1377 added the extensible jail parameters, hierarchical jails,
1378 and the configuration file.
1380 It might be a good idea to add an
1381 address alias flag such that daemons listening on all IPs
1383 will not bind on that address, which would facilitate building a safe
1384 host environment such that host daemons do not impose on services offered
1386 Currently, the simplest answer is to minimize services
1387 offered on the host, possibly limiting it to services offered from
1389 which is easily configurable.
1391 Great care should be taken when managing directories visible within the jail.
1392 For example, if a jailed process has its current working directory set to a
1393 directory that is moved out of the jail's chroot, then the process may gain
1394 access to the file space outside of the jail.
1395 It is recommended that directories always be copied, rather than moved, out
1398 In addition, there are several ways in which an unprivileged user
1399 outside the jail can cooperate with a privileged user inside the jail
1400 and thereby obtain elevated privileges in the host environment.
1401 Most of these attacks can be mitigated by ensuring that the jail root
1402 is not accessible to unprivileged users in the host environment.
1403 Regardless, as a general rule, untrusted users with privileged access
1404 to a jail should not be given access to the host environment.