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JAIL(8)			  BSD 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	op-
     tions are used alone or in	combination describe the operation to perform:

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

     -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 simultane-

     -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	with-
	     out using the configuration file.	No removal-related parameters
	     for this jail will	be used	- the jail will	simply be removed.

     -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	re-
     move) 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, regard-
     less 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 compati-
     bility, 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 exist).

   Jail	Parameters
     Parameters	in the jail.conf(5) file, or on	the command line, are gener-
     ally 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 cre-
     ated, 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 itself.

     Jails have	a set a	core parameters, and kernel modules can	add their own
     jail parameters.  The current set of available parameters can be re-
     trieved 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 for-
	     mat, and need not be explicitly set when using the	configuration

     path    The directory which is to be the root of the prison.  Any com-
	     mands 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	at-
	     tempts 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 sin-
	     gle 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	set-
	     ting 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 pa-
	     rameter 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 ker-
	     nel must have been	compiled with the VIMAGE option	for this to be
	     available.	 Possible values are "inherit" to use the system net-
	     work 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 se-
	     curelevel is changed, any jail securelevels will be at least as

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

	     NOTE: It is important that	only appropriate device	nodes in devfs
	     be	exposed	to a jail; access to disk devices in the jail may per-
	     mit processes in the jail to bypass the jail sandboxing by	modi-
	     fying 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 follow-
	     ing 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	visi-
	     ble.  In addition to that,	the path to the	jail's chroot direc-
	     tory 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 located.

	     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	inter-
		     fere with)	processes outside of the jail, and in other

		     The prison	root is	allowed	to create raw sockets.	Set-
		     ting 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 un-
		     trusted 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 per-
		     mission 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 ef-
		     fective 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 functional-
		     ity 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 parame-
     ters 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	cre-
	     ated.  A typical command to run is	"sh /etc/rc".

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

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

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

	     Command(s)	to run in the prison environment before	a jail is re-
	     moved, 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 re-

	     Run commands in a clean environment.  The environment is dis-
	     carded 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 data-
	     base for the target login are also	set.

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

	     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 environ-
	     ment.  The	default	is to run the commands as the current user.

	     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 re-
	     turned by the resolver to the list	of addresses (ip4.addr or
	     ip6.addr) for this	prison.	 This may affect default address se-
	     lection 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 ap-
	     ply the ruleset in	the devfs_ruleset parameter (or	a default of
	     ruleset 4:	devfsrules_jail) to restrict the devices visible in-
	     side 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	com-
	     mand, 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 con-
     strain a specific application (possibly running with privilege), or to
     create a "virtual system image" running a variety of daemons and ser-
     vices.  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 configu-
     ration steps necessary to support either of these steps, although the
     configuration steps may be	refined	based on local requirements.

   Setting up a	Jail Directory Tree
     To	set up a jail directory	tree containing	an entire FreeBSD distribu-
     tion, 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 exe-
     cutable 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 hostname.

   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 lis-
     ten 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	speci-
     fied host IP address.  Other daemons will need to be manually config-
     ured--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 ser-
     vices must	have their individual configuration files modified to limit
     the application to	listening to a specific	IP address:

     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 ser-
     vices using rpc(3), such as rpcbind(8), nfsd(8), and mountd(8).  In gen-
     eral, applications	for which it is	not possible to	specify	which IP ad-
     dress 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	run-
     ning in the host environment should also be checked and configured	so
     that it does not bind all IP addresses, which would result	in those ser-
     vices' 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 inter-
     face 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 par-
     ticular 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 configura-
     tion to set various configuration options,	or perform these actions manu-
     ally 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 sys-
	   +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 ap-
     plication,	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 run-
     ning 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) util-
     ity.  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 pre-

     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 pro-
     cesses 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	com-

	   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 ad-
     dress 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	envi-
     ronment.  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 cre-
     ated (or those jails' children).  Each jail has a read-only parent	param-
     eter, containing the jid of the jail that created it; a jid of 0 indi-
     cates 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 restric-
     tions as ip4.addr and securelevel may not be bypassed in child jails.

     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 ances-

     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

     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 sim-
     plest answer is to	minimize services offered on the host, possibly	limit-
     ing it to services	offered	from inetd(8) which is easily configurable.

     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.

BSD				 May 23, 2012				   BSD


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