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JAIL(8)                 FreeBSD System Manager's Manual                JAIL(8)

     jail - manage system jails

     jail [-dhilqv] [-J jid_file] [-u username] [-U username] [-cmr]
          param=value ... [command=command ...]
     jail [-dqv] [-f conf_file] [-p limit] [-cmr] [jail]
     jail [-qv] [-f conf_file] [-rR] [* | jail ...]
     jail [-dhilqv] [-J jid_file] [-u username] [-U username] [-n jailname]
          [-s securelevel] [path hostname [ip[,...]] command ...]

     The jail utility creates new jails, or modifies or removes existing
     jails.  A jail is specified via parameters on the command line, or in the
     jail.conf(5) file.

     At least one of the options -c, -m or -r must be specified.  These
     options are used alone or in combination describe the operation to

     -c      Create a new jail.  The jail jid and name parameters (if
             specified) on the command line, or any jails must not refer to an
             existing jail.

     -m      Modify an existing jail.  One of the jid or name parameters must
             exist and refer to an existing jail.  Some parameters may not be
             changed on a running jail.

     -r      Remove the jail specified by jid or name.  All jailed processes
             are killed, and all children of this jail are also removed.

     -rc     Restart an existing jail.  The jail is first removed and then re-
             created, as if ``jail -c'' and ``jail -r'' were run in

     -cm     Create a jail if it does not exist, or modify the jail if it does

     -mr     Modify an existing jail.  The jail may be restarted if necessary
             to modify parameters than could not otherwise be changed.

     -cmr    Create a jail if it doesn't exist, or modify (and possibly
             restart) the jail if it does exist.

     Other available options are:

     -d      Allow making changes to a dying jail, equivalent to the
             allow.dying parameter.

     -f conf_file
             Use configuration file conf_file instead of the default

     -h      Resolve the host.hostname parameter (or hostname) and add all IP
             addresses returned by the resolver to the list of addresses for
             this prison.  This is equivalent to the ip_hostname parameter.

     -i      Output (only) the jail identifier of the newly created jail(s).
             This implies the -q option.

     -J jid_file
             Write a jid_file file, containing parameters used to start the

     -l      Run commands in a clean environment.  This is deprecated and is
             equivalent to the exec.clean parameter.

     -n jailname
             Set the jail's name.  This is deprecated and is equivalent to the
             name parameter.

     -p limit
             Limit the number of commands from exec.* that can run

     -q      Suppress the message printed whenever a jail is created, modified
             or removed.  Only error messages will be printed.

     -R      A variation of the -r option that removes an existing jail
             without using the configuration file.  No removal-related
             parameters for this jail will be used - the jail will simply be

     -s securelevel
             Set the kern.securelevel MIB entry to the specified value inside
             the newly created jail.  This is deprecated and is equivalent to
             the securelevel parameter.

     -u username
             The user name from host environment as whom jailed commands
             should run.  This is deprecated and is equivalent to the
             exec.jail_user and exec.system_jail_user parameters.

     -U username
             The user name from jailed environment as whom jailed commands
             should run.  This is deprecated and is equivalent to the
             exec.jail_user parameter.

     -v      Print a message on every operation, such as running commands and
             mounting filesystems.

     If no arguments are given after the options, the operation (except
     remove) will be performed on all jails specified in the jail.conf(5)
     file.  A single argument of a jail name will operate only on the
     specified jail.  The -r and -R options can also remove running jails that
     aren't in the jail.conf(5) file, specified by name or jid.

     An argument of ``*'' is a wildcard that will operate on all jails,
     regardless of whether they appear in jail.conf(5); this is the surest way
     for -r to remove all jails.  If hierarchical jails exist, a partial-
     matching wildcard definition may be specified.  For example, an argument
     of ``foo.*'' would apply to jails with names like ``'' and

     A jail may be specified with parameters directly on the command line.  In
     this case, the jail.conf(5) file will not be used.  For backward
     compatibility, the command line may also have four fixed parameters,
     without names: path, hostname, ip, and command.  This mode will always
     create a new jail, and the -c and -m options don't apply (and must not

   Jail Parameters
     Parameters in the jail.conf(5) file, or on the command line, are
     generally in ``name=value'' form.  Some parameters are boolean, and do
     not have a value but are set by the name alone with or without a ``no''
     prefix, e.g.  persist or nopersist.  They can also be given the values
     ``true'' and ``false''.  Other parameters may have more than one value,
     specified as a comma-separated list or with ``+='' in the configuration
     file (see jail.conf(5) for details).

     The jail utility recognizes two classes of parameters.  There are the
     true jail parameters that are passed to the kernel when the jail is
     created, can be seen with jls(8), and can (usually) be changed with
     ``jail -m''.  Then there are pseudo-parameters that are only used by jail

     Jails have a set a core parameters, and kernel modules can add their own
     jail parameters.  The current set of available parameters can be
     retrieved via ``sysctl -d security.jail.param''.  Any parameters not set
     will be given default values, often based on the current environment.
     The core parameters are:

     jid     The jail identifier.  This will be assigned automatically to a
             new jail (or can be explicitly set), and can be used to identify
             the jail for later modification, or for such commands as jls(8)
             or jexec(8).

     name    The jail name.  This is an arbitrary string that identifies a
             jail (except it may not contain a `.').  Like the jid, it can be
             passed to later jail commands, or to jls(8) or jexec(8).  If no
             name is supplied, a default is assumed that is the same as the
             jid.  The name parameter is implied by the jail.conf(5) file
             format, and need not be explicitly set when using the
             configuration file.

     path    The directory which is to be the root of the prison.  Any
             commands run inside the prison, either by jail or from jexec(8),
             are run from this directory.

             A list of IPv4 addresses assigned to the prison.  If this is set,
             the jail is restricted to using only these addresses.  Any
             attempts to use other addresses fail, and attempts to use
             wildcard addresses silently use the jailed address instead.  For
             IPv4 the first address given will be kept used as the source
             address in case source address selection on unbound sockets
             cannot find a better match.  It is only possible to start
             multiple jails with the same IP address, if none of the jails has
             more than this single overlapping IP address assigned to itself.

             A boolean option to change the formerly mentioned behaviour and
             disable IPv4 source address selection for the prison in favour of
             the primary IPv4 address of the jail.  Source address selection
             is enabled by default for all jails and the ip4.nosaddrsel
             setting of a parent jail is not inherited for any child jails.

     ip4     Control the availability of IPv4 addresses.  Possible values are
             ``inherit'' to allow unrestricted access to all system addresses,
             ``new'' to restrict addresses via ip4.addr above, and ``disable''
             to stop the jail from using IPv4 entirely.  Setting the ip4.addr
             parameter implies a value of ``new''.

     ip6.addr, ip6.saddrsel, ip6
             A set of IPv6 options for the prison, the counterparts to
             ip4.addr, ip4.saddrsel and ip4 above.

     vnet    Create the prison with its own virtual network stack, with its
             own network interfaces, addresses, routing table, etc.  The
             kernel must have been compiled with the VIMAGE option for this to
             be available.  Possible values are ``inherit'' to use the system
             network stack, possibly with restricted IP addresses, and ``new''
             to create a new network stack.

             The hostname of the prison.  Other similar parameters are
             host.domainname, host.hostuuid and host.hostid.

     host    Set the origin of hostname and related information.  Possible
             values are ``inherit'' to use the system information and ``new''
             for the jail to use the information from the above fields.
             Setting any of the above fields implies a value of ``new''.

             The value of the jail's kern.securelevel sysctl.  A jail never
             has a lower securelevel than the default system, but by setting
             this parameter it may have a higher one.  If the system
             securelevel is changed, any jail securelevels will be at least as

             The number of the devfs ruleset that is enforced for mounting
             devfs in this jail.  A value of zero (default) means no ruleset
             is enforced.  Descendant jails inherit the parent jail's devfs
             ruleset enforcement.  Mounting devfs inside a jail is possible
             only if the allow.mount and allow.mount.devfs permissions are
             effective and enforce_statfs is set to a value lower than 2.
             Devfs rules and rulesets cannot be viewed or modified from inside
             a jail.

             NOTE: It is important that only appropriate device nodes in devfs
             be exposed to a jail; access to disk devices in the jail may
             permit processes in the jail to bypass the jail sandboxing by
             modifying files outside of the jail.  See devfs(8) for
             information on how to use devfs rules to limit access to entries
             in the per-jail devfs.  A simple devfs ruleset for jails is
             available as ruleset #4 in /etc/defaults/devfs.rules.

             The number of child jails allowed to be created by this jail (or
             by other jails under this jail).  This limit is zero by default,
             indicating the jail is not allowed to create child jails.  See
             the Hierarchical Jails section for more information.

             The number of descendents of this jail, including its own child
             jails and any jails created under them.

             This determines which information processes in a jail are able to
             get about mount points.  It affects the behaviour of the
             following syscalls: statfs(2), fstatfs(2), getfsstat(2) and
             fhstatfs(2) (as well as similar compatibility syscalls).  When
             set to 0, all mount points are available without any
             restrictions.  When set to 1, only mount points below the jail's
             chroot directory are visible.  In addition to that, the path to
             the jail's chroot directory is removed from the front of their
             pathnames.  When set to 2 (default), above syscalls can operate
             only on a mount-point where the jail's chroot directory is

             Setting this boolean parameter allows a jail to exist without any
             processes.  Normally, a command is run as part of jail creation,
             and then the jail is destroyed as its last process exits.  A new
             jail must have either the persist parameter or exec.start or
             command pseudo-parameter set.
             The ID of the cpuset associated with this jail (read-only).

     dying   This is true if the jail is in the process of shutting down

     parent  The jid of the parent of this jail, or zero if this is a top-
             level jail (read-only).

             Some restrictions of the jail environment may be set on a per-
             jail basis.  With the exception of allow.set_hostname, these
             boolean parameters are off by default.

                     The jail's hostname may be changed via hostname(1) or

                     A process within the jail has access to System V IPC
                     primitives.  In the current jail implementation, System V
                     primitives share a single namespace across the host and
                     jail environments, meaning that processes within a jail
                     would be able to communicate with (and potentially
                     interfere with) processes outside of the jail, and in
                     other jails.

                     The prison root is allowed to create raw sockets.
                     Setting this parameter allows utilities like ping(8) and
                     traceroute(8) to operate inside the prison.  If this is
                     set, the source IP addresses are enforced to comply with
                     the IP address bound to the jail, regardless of whether
                     or not the IP_HDRINCL flag has been set on the socket.
                     Since raw sockets can be used to configure and interact
                     with various network subsystems, extra caution should be
                     used where privileged access to jails is given out to
                     untrusted parties.

                     Normally, privileged users inside a jail are treated as
                     unprivileged by chflags(2).  When this parameter is set,
                     such users are treated as privileged, and may manipulate
                     system file flags subject to the usual constraints on

                     privileged users inside the jail will be able to mount
                     and unmount file system types marked as jail-friendly.
                     The lsvfs(1) command can be used to find file system
                     types available for mount from within a jail.  This
                     permission is effective only if enforce_statfs is set to
                     a value lower than 2.

                     privileged users inside the jail will be able to mount
                     and unmount the devfs file system.  This permission is
                     effective only together with allow.mount and if
                     enforce_statfs is set to a value lower than 2.  Please
                     consider restricting the devfs ruleset with the
                     devfs_ruleset option.

                     privileged users inside the jail will be able to mount
                     and unmount the nullfs file system.  This permission is
                     effective only together with allow.mount and if
                     enforce_statfs is set to a value lower than 2.

                     privileged users inside the jail will be able to mount
                     and unmount the procfs file system.  This permission is
                     effective only together with allow.mount and if
                     enforce_statfs is set to a value lower than 2.

                     privileged users inside the jail will be able to mount
                     and unmount the ZFS file system.  This permission is
                     effective only together with allow.mount and if
                     enforce_statfs is set to a value lower than 2.  See
                     zfs(8) for information on how to configure the ZFS
                     filesystem to operate from within a jail.

                     The prison root may administer quotas on the jail's
                     filesystem(s).  This includes filesystems that the jail
                     may share with other jails or with non-jailed parts of
                     the system.

                     Sockets within a jail are normally restricted to IPv4,
                     IPv6, local (UNIX), and route.  This allows access to
                     other protocol stacks that have not had jail
                     functionality added to them.

     There are pseudo-parameters that aren't passed to the kernel, but are
     used by jail to set up the prison environment, often by running specified
     commands when jails are created or removed.  The exec.* command
     parameters are sh(1) command lines that are run in either the system or
     prison environment.  They may be given multiple values, which run would
     the specified commands in sequence.  All commands must succeed (return a
     zero exit status), or the jail will not be created or removed.

     The pseudo-parameters are:

             Command(s) to run in the system environment before a prison is

             Command(s) to run in the prison environment when a jail is
             created.  A typical command to run is ``sh /etc/rc''.

             A synonym for exec.start for use when specifying a prison
             directly on the command line.  Unlike other parameters whose
             value is a single string, command uses the remainder of the jail
             command line as its own arguments.

             Command(s) to run in the system environment after a jail is
             created, and after any exec.start commands have completed.

             Command(s) to run in the system environment before a jail is

             Command(s) to run in the prison environment before a jail is
             removed, and after any exec.prestop commands have completed.  A
             typical command to run is ``sh /etc/rc.shutdown''.

             Command(s) to run in the system environment after a jail is

             Run commands in a clean environment.  The environment is
             discarded except for HOME, SHELL, TERM and USER.  HOME and SHELL
             are set to the target login's default values.  USER is set to the
             target login.  TERM is imported from the current environment.
             The environment variables from the login class capability
             database for the target login are also set.

             The user to run commands as, when running in the prison
             environment.  The default is to run the commands as the current

             This boolean option looks for the exec.jail_user in the system
             passwd(5) file, instead of in the prison's file.

             The user to run commands as, when running in the system
             environment.  The default is to run the commands as the current

             The maximum amount of time to wait for a command to complete.  If
             a command is still running after this many seconds have passed,
             the jail not be created or removed.

             A file to direct command output (stdout and stderr) to.

             The FIB (routing table) to set when running commands inside the

             The maximum amount of time to wait for a prison's processes to
             exit after sending them a SIGTERM signal (which happens after the
             exec.stop commands have completed).  After this many seconds have
             passed, the prison will be removed, which will kill any remaining
             processes.  If this is set to zero, no SIGTERM is sent and the
             prison is immediately removed.  The default is 10 seconds.

             A network interface to add the prison's IP addresses (ip4.addr
             and ip6.addr) to.  An alias for each address will be added to the
             interface before the prison is created, and will be removed from
             the interface after the prison is removed.

             In addition to the IP addresses that are passed to the kernel,
             and interface and/or a netmask may also be specified, in the form
             ``interface|ip-address/netmask''.  If an interface is given
             before the IP address, an alias for the address will be added to
             that interface, as it is with the interface parameter.  If a
             netmask in either dotted-quad or CIDR form is given after IP
             address, it will be used when adding the IP alias.

             In addition to the IP addresses that are passed to the kernel,
             and interface and/or a prefix may also be specified, in the form

             A network interface to give to a vnet-enabled jail after is it
             created.  The interface will automatically be returned when the
             jail is removed.

             Resolve the host.hostname parameter and add all IP addresses
             returned by the resolver to the list of addresses (ip4.addr or
             ip6.addr) for this prison.  This may affect default address
             selection for outgoing IPv4 connections of prisons.  The address
             first returned by the resolver for each address family will be
             used as primary address.

     mount   A filesystem to mount before creating the jail (and to unmount
             after removing it), given as a single fstab(5) line.

             An fstab(5) format file containing filesystems to mount before
             creating a jail.

             Mount a devfs filesystem on the chrooted /dev directory, and
             apply the ruleset in the devfs_ruleset parameter (or a default of
             ruleset 4: devfsrules_jail) to restrict the devices visible
             inside the prison.

             Allow making changes to a dying jail.

     depend  Specify a jail (or jails) that this jail depends on.  Any such
             jails must be fully created, up to the last exec.poststart
             command, before any action will taken to create this jail.  When
             jails are removed the opposite is true: this jail must be fully
             removed, up to the last exec.poststop command, before the jail(s)
             it depends on are stopped.

     Jails are typically set up using one of two philosophies: either to
     constrain a specific application (possibly running with privilege), or to
     create a ``virtual system image'' running a variety of daemons and
     services.  In both cases, a fairly complete file system install of
     FreeBSD is required, so as to provide the necessary command line tools,
     daemons, libraries, application configuration files, etc.  However, for a
     virtual server configuration, a fair amount of additional work is
     required so as to configure the ``boot'' process.  This manual page
     documents the configuration steps necessary to support either of these
     steps, although the configuration steps may be refined based on local

   Setting up a Jail Directory Tree
     To set up a jail directory tree containing an entire FreeBSD
     distribution, the following sh(1) command script can be used:

     cd /usr/src
     mkdir -p $D
     make world DESTDIR=$D
     make distribution DESTDIR=$D

     In many cases this example would put far more in the jail than needed.
     In the other extreme case a jail might contain only one file: the
     executable to be run in the jail.

     We recommend experimentation and caution that it is a lot easier to start
     with a ``fat'' jail and remove things until it stops working, than it is
     to start with a ``thin'' jail and add things until it works.

   Setting Up a Jail
     Do what was described in Setting Up a Jail Directory Tree to build the
     jail directory tree.  For the sake of this example, we will assume you
     built it in /data/jail/testjail, for a jail named ``testjail''.
     Substitute below as needed with your own directory, IP address, and

   Setting up the Host Environment
     First, you will want to set up your real system's environment to be
     ``jail-friendly''.  For consistency, we will refer to the parent box as
     the ``host environment'', and to the jailed virtual machine as the ``jail
     environment''.  Since jail is implemented using IP aliases, one of the
     first things to do is to disable IP services on the host system that
     listen on all local IP addresses for a service.  If a network service is
     present in the host environment that binds all available IP addresses
     rather than specific IP addresses, it may service requests sent to jail
     IP addresses if the jail did not bind the port.  This means changing
     inetd(8) to only listen on the appropriate IP address, and so forth.  Add
     the following to /etc/rc.conf in the host environment:

           inetd_flags="-wW -a"
           rpcbind_enable="NO" is the native IP address for the host system, in this example.
     Daemons that run out of inetd(8) can be easily set to use only the
     specified host IP address.  Other daemons will need to be manually
     configured--for some this is possible through the rc.conf(5) flags
     entries; for others it is necessary to modify per-application
     configuration files, or to recompile the applications.  The following
     frequently deployed services must have their individual configuration
     files modified to limit the application to listening to a specific IP

     To configure sshd(8), it is necessary to modify /etc/ssh/sshd_config.

     To configure sendmail(8), it is necessary to modify

     For named(8), it is necessary to modify /etc/namedb/named.conf.

     In addition, a number of services must be recompiled in order to run them
     in the host environment.  This includes most applications providing
     services using rpc(3), such as rpcbind(8), nfsd(8), and mountd(8).  In
     general, applications for which it is not possible to specify which IP
     address to bind should not be run in the host environment unless they
     should also service requests sent to jail IP addresses.  Attempting to
     serve NFS from the host environment may also cause confusion, and cannot
     be easily reconfigured to use only specific IPs, as some NFS services are
     hosted directly from the kernel.  Any third-party network software
     running in the host environment should also be checked and configured so
     that it does not bind all IP addresses, which would result in those
     services' also appearing to be offered by the jail environments.

     Once these daemons have been disabled or fixed in the host environment,
     it is best to reboot so that all daemons are in a known state, to reduce
     the potential for confusion later (such as finding that when you send
     mail to a jail, and its sendmail is down, the mail is delivered to the
     host, etc.).

   Configuring the Jail
     Start any jail for the first time without configuring the network
     interface so that you can clean it up a little and set up accounts.  As
     with any machine (virtual or not) you will need to set a root password,
     time zone, etc.  Some of these steps apply only if you intend to run a
     full virtual server inside the jail; others apply both for constraining a
     particular application or for running a virtual server.

     Start a shell in the jail:

           jail -c path=/data/jail/testjail mount.devfs host.hostname=testhostname \
                   ip4.addr= command=/bin/sh

     Assuming no errors, you will end up with a shell prompt within the jail.
     You can now run /usr/sbin/sysinstall and do the post-install
     configuration to set various configuration options, or perform these
     actions manually by editing /etc/rc.conf, etc.

           +o   Configure /etc/resolv.conf so that name resolution within the
               jail will work correctly
           +o   Run newaliases(1) to quell sendmail(8) warnings.
           +o   Set a root password, probably different from the real host
           +o   Set the timezone
           +o   Add accounts for users in the jail environment
           +o   Install any packages the environment requires

     You may also want to perform any package-specific configuration (web
     servers, SSH servers, etc), patch up /etc/syslog.conf so it logs as you
     would like, etc.  If you are not using a virtual server, you may wish to
     modify syslogd(8) in the host environment to listen on the syslog socket
     in the jail environment; in this example, the syslog socket would be
     stored in /data/jail/testjail/var/run/log.

     Exit from the shell, and the jail will be shut down.

   Starting the Jail
     You are now ready to restart the jail and bring up the environment with
     all of its daemons and other programs.  Create an entry for the jail in

           testjail {
                   path = /tmp/jail/testjail;
                   host.hostname = testhostname;
                   ip4.addr =;
                   interface = ed0;
                   exec.start = "/bin/sh /etc/rc";
                   exec.stop = "/bin/sh /etc/rc.shutdown";

     To start a virtual server environment, /etc/rc is run to launch various
     daemons and services, and /etc/rc.shutdown is run to shut them down when
     the jail is removed.  If you are running a single application in the
     jail, substitute the command used to start the application for ``/bin/sh
     /etc/rc''; there may be some script available to cleanly shut down the
     application, or it may be sufficient to go without a stop command, and
     have jail send SIGTERM to the application.

     Start the jail by running:

           jail -c testjail

     A few warnings may be produced; however, it should all work properly.
     You should be able to see inetd(8), syslogd(8), and other processes
     running within the jail using ps(1), with the `J' flag appearing beside
     jailed processes.  To see an active list of jails, use the jls(8)
     utility.  You should also be able to telnet(1) to the hostname or IP
     address of the jailed environment, and log in using the accounts you
     created previously.

     It is possible to have jails started at boot time.  Please refer to the
     ``jail_*'' variables in rc.conf(5) for more information.

   Managing the Jail
     Normal machine shutdown commands, such as halt(8), reboot(8), and
     shutdown(8), cannot be used successfully within the jail.  To kill all
     processes from within a jail, you may use one of the following commands,
     depending on what you want to accomplish:

           kill -TERM -1
           kill -KILL -1

     This will send the SIGTERM or SIGKILL signals to all processes in the
     jail - be careful not to run this from the host environment!  Once all of
     the jail's processes have died, unless the jail was created with the
     persist parameter, the jail will be removed.  Depending on the intended
     use of the jail, you may also want to run /etc/rc.shutdown from within
     the jail.

     To shut down the jail from the outside, simply remove it with jail -r,
     which will run any commands specified by exec.stop, and then send SIGTERM
     and eventually SIGKILL to any remaining jailed processes.

     The /proc/pid/status file contains, as its last field, the name of the
     jail in which the process runs, or ``-'' to indicate that the process is
     not running within a jail.  The ps(1) command also shows a `J' flag for
     processes in a jail.

     You can also list/kill processes based on their jail ID.  To show
     processes and their jail ID, use the following command:

           ps ax -o pid,jid,args

     To show and then kill processes in jail number 3 use the following

           pgrep -lfj 3
           pkill -j 3

           killall -j 3

   Jails and File Systems
     It is not possible to mount(8) or umount(8) any file system inside a jail
     unless the file system is marked jail-friendly, the jail's allow.mount
     parameter is set and the jail's enforce_statfs parameter is lower than 2.

     Multiple jails sharing the same file system can influence each other.
     For example a user in one jail can fill the file system also leaving no
     space for processes in the other jail.  Trying to use quota(1) to prevent
     this will not work either as the file system quotas are not aware of
     jails but only look at the user and group IDs.  This means the same user
     ID in two jails share the same file system quota.  One would need to use
     one file system per jail to make this work.

   Sysctl MIB Entries
     The read-only entry security.jail.jailed can be used to determine if a
     process is running inside a jail (value is one) or not (value is zero).

     The variable security.jail.max_af_ips determines how may address per
     address family a prison may have.  The default is 255.

     Some MIB variables have per-jail settings.  Changes to these variables by
     a jailed process do not effect the host environment, only the jail
     environment.  These variables are kern.securelevel, kern.hostname,
     kern.domainname, kern.hostid, and kern.hostuuid.

   Hierarchical Jails
     By setting a jail's children.max parameter, processes within a jail may
     be able to create jails of their own.  These child jails are kept in a
     hierarchy, with jails only able to see and/or modify the jails they
     created (or those jails' children).  Each jail has a read-only parent
     parameter, containing the jid of the jail that created it; a jid of 0
     indicates the jail is a child of the current jail (or is a top-level jail
     if the current process isn't jailed).

     Jailed processes are not allowed to confer greater permissions than they
     themselves are given, e.g. if a jail is created with allow.nomount, it is
     not able to create a jail with allow.mount set.  Similarly, such
     restrictions as ip4.addr and securelevel may not be bypassed in child

     A child jail may in turn create its own child jails if its own
     children.max parameter is set (remember it is zero by default).  These
     jails are visible to and can be modified by their parent and all

     Jail names reflect this hierarchy, with a full name being an MIB-type
     string separated by dots.  For example, if a base system process creates
     a jail ``foo'', and a process under that jail creates another jail
     ``bar'', then the second jail will be seen as ``'' in the base
     system (though it is only seen as ``bar'' to any processes inside jail
     ``foo'').  Jids on the other hand exist in a single space, and each jail
     must have a unique jid.

     Like the names, a child jail's path appears relative to its creator's own
     path.  This is by virtue of the child jail being created in the chrooted
     environment of the first jail.

     killall(1), lsvfs(1), newaliases(1), pgrep(1), pkill(1), ps(1), quota(1),
     jail_set(2), jail.conf(5), procfs(5), rc.conf(5), sysctl.conf(5),
     chroot(8), devfs(8), halt(8), inetd(8), jexec(8), jls(8), mount(8),
     named(8), reboot(8), rpcbind(8), sendmail(8), shutdown(8), sysctl(8),
     syslogd(8), umount(8)

     The jail utility appeared in FreeBSD 4.0.  Hierarchical/extensible jails
     were introduced in FreeBSD 8.0.  The configuration file was introduced in
     FreeBSD 9.1.

     The jail feature was written by Poul-Henning Kamp for R&D Associates who contributed it to FreeBSD.

     Robert Watson wrote the extended documentation, found a few bugs, added a
     few new features, and cleaned up the userland jail environment.

     Bjoern A. Zeeb added multi-IP jail support for IPv4 and IPv6 based on a
     patch originally done by Pawel Jakub Dawidek for IPv4.

     James Gritton added the extensible jail parameters, hierarchical jails,
     and the configuration file.

     It might be a good idea to add an address alias flag such that daemons
     listening on all IPs (INADDR_ANY) will not bind on that address, which
     would facilitate building a safe host environment such that host daemons
     do not impose on services offered from within jails.  Currently, the
     simplest answer is to minimize services offered on the host, possibly
     limiting it to services offered from inetd(8) which is easily

     Great care should be taken when managing directories visible within the
     jail.  For example, if a jailed process has its current working directory
     set to a directory that is moved out of the jail's chroot, then the
     process may gain access to the file space outside of the jail.  It is
     recommended that directories always be copied, rather than moved, out of
     a jail.

FreeBSD 11.0-PRERELEASE          May 23, 2012          FreeBSD 11.0-PRERELEASE


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