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 ...
69 utility creates new jails, or modifies or removes existing jails.
70 It can also print a list of configured jails and their parameters.
73 is specified via parameters on the command line, or in the
77 At least one of the options
84 These options are used alone or in combination to describe the operation to
86 .Bl -tag -width indent
93 parameters (if specified on the command line)
94 must not refer to an existing jail.
96 Exhibit a list of all configured non-wildcard jails and their parameters.
97 No jail creation, modification or removal performed if this option is used.
100 string is used to separate parameters.
103 utility to list running jails.
105 Modify an existing jail.
110 parameters must exist and refer to an existing jail.
111 Some parameters may not be changed on a running jail.
115 specified by jid or name.
116 All jailed processes are killed, and all jails that are
117 children of this jail are also
120 Restart an existing jail.
121 The jail is first removed and then re-created, as if
125 were run in succession.
127 Create a jail if it does not exist, or modify the jail if it does exist.
129 Modify an existing jail.
130 The jail may be restarted if necessary to modify parameters than could
131 not otherwise be changed.
133 Create a jail if it doesn't exist, or modify (and possibly restart) the
134 jail if it does exist.
137 Other available options are:
138 .Bl -tag -width indent
140 Allow making changes to a dying jail, equivalent to the
143 .It Fl f Ar conf_file
144 Use configuration file
146 instead of the default
153 and add all IP addresses returned by the resolver
154 to the list of addresses for this jail.
155 This is equivalent to the
159 Output (only) the jail identifier of the newly created jail(s).
166 file, containing the parameters used to start the jail.
168 Run commands in a clean environment.
169 This is deprecated and is equivalent to the exec.clean parameter.
172 This is deprecated and is equivalent to the
176 Limit the number of commands from
178 that can run simultaneously.
180 Suppress the message printed whenever a jail is created, modified or removed.
181 Only error messages will be printed.
185 option that removes an existing jail without using the configuration file.
186 No removal-related parameters for this jail will be used \(em the jail will
188 .It Fl s Ar securelevel
191 MIB entry to the specified value inside the newly created jail.
192 This is deprecated and is equivalent to the
196 The user name from host environment as whom jailed commands should run.
197 This is deprecated and is equivalent to the
200 .Va exec.system_jail_user
203 The user name from the jailed environment as whom jailed commands should run.
204 This is deprecated and is equivalent to the
208 Print a message on every operation, such as running commands and
209 mounting filesystems.
212 If no arguments are given after the options, the operation (except
213 remove) will be performed on all jails specified in the
216 A single argument of a jail name will operate only on the specified jail.
221 options can also remove running jails that aren't in the
223 file, specified by name or jid.
227 is a wildcard that will operate on all jails, regardless of whether
230 this is the surest way for
233 If hierarchical jails exist, a partial-matching wildcard definition may
235 For example, an argument of
237 would apply to jails with names like
242 A jail may be specified with parameters directly on the command line.
245 file will not be used.
246 For backward compatibility, the command line may also have four fixed
247 parameters, without names:
253 This mode will always create a new jail, and the
257 options do not apply (and must not be present).
261 file, or on the command line, are generally of the form
263 Some parameters are boolean, and do not have a value but are set by the
264 name alone with or without a
270 They can also be given the values
274 Other parameters may have more than one value, specified as a
275 comma-separated list or with
277 in the configuration file (see
283 utility recognizes two classes of parameters.
284 There are the true jail
285 parameters that are passed to the kernel when the jail is created,
286 which can be seen with
288 and can (usually) be changed with
290 Then there are pseudo-parameters that are only used by
294 Jails have a set of core parameters, and kernel modules can add their own
296 The current set of available parameters can be retrieved via
297 .Dq Nm sysctl Fl d Va security.jail.param .
298 Any parameters not set will be given default values, often based on the
300 The core parameters are:
301 .Bl -tag -width indent
304 This will be assigned automatically to a new jail (or can be explicitly
305 set), and can be used to identify the jail for later modification, or
312 This is an arbitrary string that identifies a jail (except it may not
317 it can be passed to later
325 is supplied, a default is assumed that is the same as the
329 parameter is implied by the
331 file format, and need not be explicitly set when using the configuration
334 The directory which is to be the root of the jail.
335 Any commands run inside the jail, either by
339 are run from this directory.
341 A list of IPv4 addresses assigned to the jail.
342 If this is set, the jail is restricted to using only these addresses.
343 Any attempts to use other addresses fail, and attempts to use wildcard
344 addresses silently use the jailed address instead.
345 For IPv4 the first address given will be used as the source address
346 when source address selection on unbound sockets cannot find a better
348 It is only possible to start multiple jails with the same IP address
349 if none of the jails has more than this single overlapping IP address
352 A boolean option to change the formerly mentioned behaviour and disable
353 IPv4 source address selection for the jail in favour of the primary
354 IPv4 address of the jail.
355 Source address selection is enabled by default for all jails and the
357 setting of a parent jail is not inherited for any child jails.
359 Control the availability of IPv4 addresses.
362 to allow unrestricted access to all system addresses,
364 to restrict addresses via
368 to stop the jail from using IPv4 entirely.
371 parameter implies a value of
373 .It Va ip6.addr , Va ip6.saddrsel , Va ip6
374 A set of IPv6 options for the jail, the counterparts to
381 Create the jail with its own virtual network stack,
382 with its own network interfaces, addresses, routing table, etc.
383 The kernel must have been compiled with the
385 for this to be available.
388 to use the system network stack, possibly with restricted IP addresses,
391 to create a new network stack.
393 The hostname of the jail.
394 Other similar parameters are
395 .Va host.domainname ,
400 Set the origin of hostname and related information.
403 to use the system information and
405 for the jail to use the information from the above fields.
406 Setting any of the above fields implies a value of
409 The value of the jail's
412 A jail never has a lower securelevel than its parent system, but by
413 setting this parameter it may have a higher one.
414 If the system securelevel is changed, any jail securelevels will be at
417 The number of the devfs ruleset that is enforced for mounting devfs in
419 A value of zero (default) means no ruleset is enforced.
420 Descendant jails inherit the parent jail's devfs ruleset enforcement.
421 Mounting devfs inside a jail is possible only if the
424 .Va allow.mount.devfs
425 permissions are effective and
427 is set to a value lower than 2.
428 Devfs rules and rulesets cannot be viewed or modified from inside a jail.
430 NOTE: It is important that only appropriate device nodes in devfs be
431 exposed to a jail; access to disk devices in the jail may permit processes
432 in the jail to bypass the jail sandboxing by modifying files outside of
436 for information on how to use devfs rules to limit access to entries
437 in the per-jail devfs.
438 A simple devfs ruleset for jails is available as ruleset #4 in
439 .Pa /etc/defaults/devfs.rules .
441 The number of child jails allowed to be created by this jail (or by
442 other jails under this jail).
443 This limit is zero by default, indicating the jail is not allowed to
446 .Sx "Hierarchical Jails"
447 section for more information.
449 The number of descendants of this jail, including its own child jails
450 and any jails created under them.
451 .It Va enforce_statfs
452 This determines what information processes in a jail are able to get
454 It affects the behaviour of the following syscalls:
460 (as well as similar compatibility syscalls).
461 When set to 0, all mount points are available without any restrictions.
462 When set to 1, only mount points below the jail's chroot directory are
464 In addition to that, the path to the jail's chroot directory is removed
465 from the front of their pathnames.
466 When set to 2 (default), above syscalls can operate only on a mount-point
467 where the jail's chroot directory is located.
469 Setting this boolean parameter allows a jail to exist without any
471 Normally, a command is run as part of jail creation, and then the jail
472 is destroyed as its last process exits.
473 A new jail must have either the
479 pseudo-parameter set.
481 The ID of the cpuset associated with this jail (read-only).
483 This is true if the jail is in the process of shutting down (read-only).
487 of the parent of this jail, or zero if this is a top-level jail
490 The string for the jail's
494 The number for the jail's
498 Some restrictions of the jail environment may be set on a per-jail
500 With the exception of
501 .Va allow.set_hostname
503 .Va allow.reserved_ports ,
504 these boolean parameters are off by default.
505 .Bl -tag -width indent
506 .It Va allow.set_hostname
507 The jail's hostname may be changed via
512 A process within the jail has access to System V IPC primitives.
513 This is deprecated in favor of the per-module parameters (see below).
514 When this parameter is set, it is equivalent to setting
521 .It Va allow.raw_sockets
522 The jail root is allowed to create raw sockets.
523 Setting this parameter allows utilities like
527 to operate inside the jail.
528 If this is set, the source IP addresses are enforced to comply
529 with the IP address bound to the jail, regardless of whether or not
532 flag has been set on the socket.
533 Since raw sockets can be used to configure and interact with various
534 network subsystems, extra caution should be used where privileged access
535 to jails is given out to untrusted parties.
537 Normally, privileged users inside a jail are treated as unprivileged by
539 When this parameter is set, such users are treated as privileged, and
540 may manipulate system file flags subject to the usual constraints on
541 .Va kern.securelevel .
543 privileged users inside the jail will be able to mount and unmount file
544 system types marked as jail-friendly.
547 command can be used to find file system types available for mount from
549 This permission is effective only if
551 is set to a value lower than 2.
552 .It Va allow.mount.devfs
553 privileged users inside the jail will be able to mount and unmount the
555 This permission is effective only together with
559 is set to a value lower than 2.
560 The devfs ruleset should be restricted from the default by using the
564 The jail root may administer quotas on the jail's filesystem(s).
565 This includes filesystems that the jail may share with other jails or
566 with non-jailed parts of the system.
567 .It Va allow.read_msgbuf
568 Jailed users may read the kernel message buffer.
570 .Va security.bsd.unprivileged_read_msgbuf
571 MIB entry is zero, this will be restricted to the root user.
572 .It Va allow.socket_af
573 Sockets within a jail are normally restricted to IPv4, IPv6, local
574 (UNIX), and route. This allows access to other protocol stacks that
575 have not had jail functionality added to them.
577 Locking or unlocking physical pages in memory are normally not available
579 When this parameter is set, users may
584 .Va security.bsd.unprivileged_mlock
586 .It Va allow.reserved_ports
587 The jail root may bind to ports lower than 1024.
588 .It Va allow.unprivileged_proc_debug
589 Unprivileged processes in the jail may use debugging facilities.
593 Kernel modules may add their own parameters, which only exist when the
595 These are typically headed under a parameter named after the module,
598 to give the jail full use of the module,
600 to encapsulate the jail in some module-specific way,
603 to make the module unavailable to the jail.
604 There also may be other parameters to define jail behavior within the module.
605 Module-specific parameters include:
606 .Bl -tag -width indent
607 .It Va allow.mount.fdescfs
608 privileged users inside the jail will be able to mount and unmount the
610 This permission is effective only together with
614 is set to a value lower than 2.
615 .It Va allow.mount.fusefs
616 privileged users inside the jail will be able to mount and unmount
617 fuse-based file systems.
618 This permission is effective only together with
622 is set to a value lower than 2.
623 .It Va allow.mount.nullfs
624 privileged users inside the jail will be able to mount and unmount the
626 This permission is effective only together with
630 is set to a value lower than 2.
631 .It Va allow.mount.procfs
632 privileged users inside the jail will be able to mount and unmount the
634 This permission is effective only together with
638 is set to a value lower than 2.
639 .It Va allow.mount.linprocfs
640 privileged users inside the jail will be able to mount and unmount the
641 linprocfs file system.
642 This permission is effective only together with
646 is set to a value lower than 2.
647 .It Va allow.mount.linsysfs
648 privileged users inside the jail will be able to mount and unmount the
649 linsysfs file system.
650 This permission is effective only together with
654 is set to a value lower than 2.
655 .It Va allow.mount.tmpfs
656 privileged users inside the jail will be able to mount and unmount the
658 This permission is effective only together with
662 is set to a value lower than 2.
663 .It Va allow.mount.zfs
664 privileged users inside the jail will be able to mount and unmount the
666 This permission is effective only together with
670 is set to a value lower than 2.
673 for information on how to configure the ZFS filesystem to operate from
678 This flag is only available when the
680 kernel module is loaded.
682 Determine how a jail's Linux emulation environment appears.
685 will keep the same environment, and
687 will give the jail its own environment (still originally inherited when
688 the jail is created).
689 .It Va linux.osname , linux.osrelease , linux.oss_version
690 The Linux OS name, OS release, and OSS version associated with this jail.
692 Allow access to SYSV IPC message primitives.
695 all IPC objects on the system are visible to this jail, whether they
696 were created by the jail itself, the base system, or other jails.
699 the jail will have its own key namespace, and can only see the objects
701 the system (or parent jail) has access to the jail's objects, but not to
705 the jail cannot perform any sysvmsg-related system calls.
706 .It Va sysvsem, sysvshm
707 Allow access to SYSV IPC semaphore and shared memory primitives, in the
712 There are pseudo-parameters that are not passed to the kernel, but are
715 to set up the jail environment, often by running specified commands
716 when jails are created or removed.
719 command parameters are
721 command lines that are run in either the system or jail environment.
722 They may be given multiple values, which would run the specified
723 commands in sequence.
724 All commands must succeed (return a zero exit status), or the jail will
725 not be created or removed, as appropriate.
727 The pseudo-parameters are:
728 .Bl -tag -width indent
730 Command(s) to run in the system environment before a jail is created.
732 Command(s) to run in the system environment right after a jail has been
733 created, but before commands (or services) get executed in the jail.
735 Command(s) to run in the jail environment when a jail is created.
736 A typical command to run is
741 for use when specifying a jail directly on the command line.
742 Unlike other parameters whose value is a single string,
744 uses the remainder of the
746 command line as its own arguments.
747 .It Va exec.poststart
748 Command(s) to run in the system environment after a jail is created,
751 commands have completed.
753 Command(s) to run in the system environment before a jail is removed.
755 Command(s) to run in the jail environment before a jail is removed,
758 commands have completed.
759 A typical command to run is
760 .Dq sh /etc/rc.shutdown jail .
762 Command(s) to run in the system environment after a jail is removed.
764 Run commands in a clean environment.
765 The environment is discarded except for
766 .Ev HOME , SHELL , TERM
772 are set to the target login's default values.
774 is set to the target login.
776 is imported from the current environment.
777 The environment variables from the login class capability database for the
778 target login are also set.
779 .It Va exec.jail_user
780 The user to run commands as, when running in the jail environment.
781 The default is to run the commands as the current user.
782 .It Va exec.system_jail_user
783 This boolean option looks for the
787 file, instead of in the jail's file.
788 .It Va exec.system_user
789 The user to run commands as, when running in the system environment.
790 The default is to run the commands as the current user.
792 The maximum amount of time to wait for a command to complete, in
794 If a command is still running after this timeout has passed,
795 the jail will not be created or removed, as appropriate.
796 .It Va exec.consolelog
797 A file to direct command output (stdout and stderr) to.
799 The FIB (routing table) to set when running commands inside the jail.
801 The maximum amount of time to wait for a jail's processes to exit
804 signal (which happens after the
806 commands have completed).
807 After this many seconds have passed, the jail will be removed, which
808 will kill any remaining processes.
809 If this is set to zero, no
811 is sent and the jail is immediately removed.
812 The default is 10 seconds.
814 A network interface to add the jail's IP addresses
819 An alias for each address will be added to the interface before the
820 jail is created, and will be removed from the interface after the
823 In addition to the IP addresses that are passed to the kernel, an
824 interface, netmask and additional parameters (as supported by
826 may also be specified, in the form
827 .Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar netmask param ... .
828 If an interface is given before the IP address, an alias for the address
829 will be added to that interface, as it is with the
832 If a netmask in either dotted-quad or CIDR form is given
833 after an IP address, it will be used when adding the IP alias.
834 If additional parameters are specified then they will also be used when
837 In addition to the IP addresses that are passed to the kernel,
838 an interface, prefix and additional parameters (as supported by
840 may also be specified, in the form
841 .Dq Ar interface Ns | Ns Ar ip-address Ns / Ns Ar prefix param ... .
842 .It Va vnet.interface
843 A network interface to give to a vnet-enabled jail after is it created.
844 The interface will automatically be released when the jail is removed.
848 parameter and add all IP addresses returned by the resolver
849 to the list of addresses
854 This may affect default address selection for outgoing IPv4 connections
856 The address first returned by the resolver for each address family
857 will be used as the primary address.
859 A filesystem to mount before creating the jail (and to unmount after
860 removing it), given as a single
866 format file containing filesystems to mount before creating a jail.
870 filesystem on the chrooted
872 directory, and apply the ruleset in the
874 parameter (or a default of ruleset 4: devfsrules_jail)
875 to restrict the devices visible inside the jail.
879 filesystem on the chrooted
885 filesystem on the chrooted
889 Allow making changes to a
893 Specify a jail (or jails) that this jail depends on.
894 When this jail is to be created, any jail(s) it depends on must already exist.
895 If not, they will be created automatically, up to the completion of the last
897 command, before any action will taken to create this jail.
898 When jails are removed the opposite is true:
899 this jail will be removed, up to the last
901 command, before any jail(s) it depends on are stopped.
904 Jails are typically set up using one of two philosophies: either to
905 constrain a specific application (possibly running with privilege), or
907 .Dq "virtual system image"
908 running a variety of daemons and services.
909 In both cases, a fairly complete file system install of
912 required, so as to provide the necessary command line tools, daemons,
913 libraries, application configuration files, etc.
914 However, for a virtual server configuration, a fair amount of
915 additional work is required so as to replace the
918 This manual page documents the configuration steps necessary to support
919 either of these steps, although the configuration steps may need to be
920 refined based on local requirements.
921 .Ss "Setting up a Jail Directory Tree"
922 To set up a jail directory tree containing an entire
924 distribution, the following
926 command script can be used:
931 make world DESTDIR=$D
932 make distribution DESTDIR=$D
935 In many cases this example would put far more in the jail than needed.
936 In the other extreme case a jail might contain only one file:
937 the executable to be run in the jail.
939 We recommend experimentation, and caution that it is a lot easier to
942 jail and remove things until it stops working,
943 than it is to start with a
945 jail and add things until it works.
946 .Ss "Setting Up a Jail"
947 Do what was described in
948 .Sx "Setting Up a Jail Directory Tree"
949 to build the jail directory tree.
950 For the sake of this example, we will
951 assume you built it in
952 .Pa /data/jail/testjail ,
955 Substitute below as needed with your
956 own directory, IP address, and hostname.
957 .Ss "Setting up the Host Environment"
958 First, set up the real system's environment to be
960 For consistency, we will refer to the parent box as the
961 .Dq "host environment" ,
962 and to the jailed virtual machine as the
963 .Dq "jail environment" .
964 Since jails are implemented using IP aliases, one of the first things to do
965 is to disable IP services on the host system that listen on all local
966 IP addresses for a service.
967 If a network service is present in the host environment that binds all
968 available IP addresses rather than specific IP addresses, it may service
969 requests sent to jail IP addresses if the jail did not bind the port.
972 to only listen on the
973 appropriate IP address, and so forth.
976 in the host environment:
977 .Bd -literal -offset indent
979 inetd_flags="-wW -a 192.0.2.23"
984 is the native IP address for the host system, in this example.
985 Daemons that run out of
987 can be easily configured to use only the specified host IP address.
989 will need to be manually configured \(em for some this is possible through
991 flags entries; for others it is necessary to modify per-application
992 configuration files, or to recompile the application.
993 The following frequently deployed services must have their individual
994 configuration files modified to limit the application to listening
995 to a specific IP address:
999 it is necessary to modify
1000 .Pa /etc/ssh/sshd_config .
1004 it is necessary to modify
1005 .Pa /etc/mail/sendmail.cf .
1009 it is necessary to modify
1010 .Pa /etc/namedb/named.conf .
1012 In addition, a number of services must be recompiled in order to run
1013 them in the host environment.
1014 This includes most applications providing services using
1021 In general, applications for which it is not possible to specify which
1022 IP address to bind should not be run in the host environment unless they
1023 should also service requests sent to jail IP addresses.
1025 NFS from the host environment may also cause confusion, and cannot be
1026 easily reconfigured to use only specific IPs, as some NFS services are
1027 hosted directly from the kernel.
1028 Any third-party network software running
1029 in the host environment should also be checked and configured so that it
1030 does not bind all IP addresses, which would result in those services also
1031 appearing to be offered by the jail environments.
1034 these daemons have been disabled or fixed in the host environment, it is
1035 best to reboot so that all daemons are in a known state, to reduce the
1036 potential for confusion later (such as finding that when you send mail
1037 to a jail, and its sendmail is down, the mail is delivered to the host,
1039 .Ss "Configuring the Jail"
1040 Start any jail for the first time without configuring the network
1041 interface so that you can clean it up a little and set up accounts.
1043 with any machine (virtual or not), you will need to set a root password, time
1045 Some of these steps apply only if you intend to run a full virtual server
1046 inside the jail; others apply both for constraining a particular application
1047 or for running a virtual server.
1049 Start a shell in the jail:
1050 .Bd -literal -offset indent
1051 jail -c path=/data/jail/testjail mount.devfs \\
1052 host.hostname=testhostname ip4.addr=192.0.2.100 \\
1056 Assuming no errors, you will end up with a shell prompt within the jail.
1059 and do the post-install configuration to set various configuration options,
1060 or perform these actions manually by editing
1064 .Bl -bullet -offset indent -compact
1067 .Pa /etc/resolv.conf
1068 so that name resolution within the jail will work correctly.
1076 Set a root password, probably different from the real host system.
1080 Add accounts for users in the jail environment.
1082 Install any packages the environment requires.
1085 You may also want to perform any package-specific configuration (web servers,
1086 SSH servers, etc), patch up
1087 .Pa /etc/syslog.conf
1088 so it logs as you would like, etc.
1089 If you are not using a virtual server, you may wish to modify
1091 in the host environment to listen on the syslog socket in the jail
1092 environment; in this example, the syslog socket would be stored in
1093 .Pa /data/jail/testjail/var/run/log .
1095 Exit from the shell, and the jail will be shut down.
1096 .Ss "Starting the Jail"
1097 You are now ready to restart the jail and bring up the environment with
1098 all of its daemons and other programs.
1099 Create an entry for the jail in
1100 .Pa /etc/jail.conf :
1101 .Bd -literal -offset indent
1103 path = /tmp/jail/testjail;
1105 host.hostname = testhostname;
1106 ip4.addr = 192.0.2.100;
1108 exec.start = "/bin/sh /etc/rc";
1109 exec.stop = "/bin/sh /etc/rc.shutdown jail";
1113 To start a virtual server environment,
1115 is run to launch various daemons and services, and
1116 .Pa /etc/rc.shutdown
1117 is run to shut them down when the jail is removed.
1118 If you are running a single application in the jail,
1119 substitute the command used to start the application for
1120 .Dq /bin/sh /etc/rc ;
1121 there may be some script available to cleanly shut down the application,
1122 or it may be sufficient to go without a stop command, and have
1128 Start the jail by running:
1129 .Bd -literal -offset indent
1133 A few warnings may be produced; however, it should all work properly.
1134 You should be able to see
1137 and other processes running within the jail using
1141 flag appearing beside jailed processes.
1142 To see an active list of jails, use
1146 is enabled in the jail environment, you should be able to
1148 to the hostname or IP address of the jailed environment, and log
1149 in using the accounts you created previously.
1151 It is possible to have jails started at boot time.
1156 for more information.
1157 .Ss "Managing the Jail"
1158 Normal machine shutdown commands, such as
1163 cannot be used successfully within the jail.
1164 To kill all processes from within a jail, you may use one of the
1165 following commands, depending on what you want to accomplish:
1166 .Bd -literal -offset indent
1175 signals to all processes in the jail \(em be careful not to run this from
1176 the host environment!
1177 Once all of the jail's processes have died, unless the jail was created
1180 parameter, the jail will be removed.
1182 the intended use of the jail, you may also want to run
1183 .Pa /etc/rc.shutdown
1184 from within the jail.
1186 To shut down the jail from the outside, simply remove it with
1189 which will run any commands specified by
1195 to any remaining jailed processes.
1198 .Pa /proc/ Ns Ar pid Ns Pa /status
1199 file contains, as its last field, the name of the jail in which the
1202 to indicate that the process is not running within a jail.
1205 command also shows a
1207 flag for processes in a jail.
1209 You can also list/kill processes based on their jail ID.
1210 To show processes and their jail ID, use the following command:
1212 .Dl "ps ax -o pid,jid,args"
1214 To show and then kill processes in jail number 3 use the following commands:
1215 .Bd -literal -offset indent
1222 .Ss "Jails and File Systems"
1223 It is not possible to
1227 any file system inside a jail unless the file system is marked
1228 jail-friendly, the jail's
1230 parameter is set, and the jail's
1232 parameter is lower than 2.
1234 Multiple jails sharing the same file system can influence each other.
1235 For example, a user in one jail can fill the file system,
1236 leaving no space for processes in the other jail.
1239 to prevent this will not work either, as the file system quotas
1240 are not aware of jails but only look at the user and group IDs.
1241 This means the same user ID in two jails share a single file
1243 One would need to use one file system per jail to make this work.
1244 .Ss "Sysctl MIB Entries"
1246 .Va security.jail.jailed
1247 can be used to determine if a process is running inside a jail (value
1248 is one) or not (value is zero).
1251 .Va security.jail.max_af_ips
1252 determines how may address per address family a jail may have.
1255 Some MIB variables have per-jail settings.
1256 Changes to these variables by a jailed process do not affect the host
1257 environment, only the jail environment.
1259 .Va kern.securelevel ,
1261 .Va kern.domainname ,
1265 .Ss "Hierarchical Jails"
1268 parameter, processes within a jail may be able to create jails of their own.
1269 These child jails are kept in a hierarchy, with jails only able to see and/or
1270 modify the jails they created (or those jails' children).
1271 Each jail has a read-only
1273 parameter, containing the
1275 of the jail that created it; a
1277 of 0 indicates the jail is a child of the current jail (or is a top-level
1278 jail if the current process isn't jailed).
1280 Jailed processes are not allowed to confer greater permissions than they
1281 themselves are given, e.g., if a jail is created with
1283 it is not able to create a jail with
1286 Similarly, such restrictions as
1290 may not be bypassed in child jails.
1292 A child jail may in turn create its own child jails if its own
1294 parameter is set (remember it is zero by default).
1295 These jails are visible to and can be modified by their parent and all
1298 Jail names reflect this hierarchy, with a full name being an MIB-type string
1300 For example, if a base system process creates a jail
1302 and a process under that jail creates another jail
1304 then the second jail will be seen as
1306 in the base system (though it is only seen as
1308 to any processes inside jail
1310 Jids on the other hand exist in a single space, and each jail must have a
1313 Like the names, a child jail's
1315 appears relative to its creator's own
1317 This is by virtue of the child jail being created in the chrooted
1318 environment of the first jail.
1359 Hierarchical/extensible jails were introduced in
1361 The configuration file was introduced in
1365 The jail feature was written by
1366 .An Poul-Henning Kamp
1368 who contributed it to
1372 wrote the extended documentation, found a few bugs, added
1373 a few new features, and cleaned up the userland jail environment.
1376 added multi-IP jail support for IPv4 and IPv6 based on a patch
1378 .An Pawel Jakub Dawidek
1382 added the extensible jail parameters, hierarchical jails,
1383 and the configuration file.
1385 It might be a good idea to add an
1386 address alias flag such that daemons listening on all IPs
1388 will not bind on that address, which would facilitate building a safe
1389 host environment such that host daemons do not impose on services offered
1391 Currently, the simplest answer is to minimize services
1392 offered on the host, possibly limiting it to services offered from
1394 which is easily configurable.
1396 Great care should be taken when managing directories visible within the jail.
1397 For example, if a jailed process has its current working directory set to a
1398 directory that is moved out of the jail's chroot, then the process may gain
1399 access to the file space outside of the jail.
1400 It is recommended that directories always be copied, rather than moved, out
1403 In addition, there are several ways in which an unprivileged user
1404 outside the jail can cooperate with a privileged user inside the jail
1405 and thereby obtain elevated privileges in the host environment.
1406 Most of these attacks can be mitigated by ensuring that the jail root
1407 is not accessible to unprivileged users in the host environment.
1408 Regardless, as a general rule, untrusted users with privileged access
1409 to a jail should not be given access to the host environment.