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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 (or	``prison'') 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 to describe the operation	to

     -c	     Create a new jail.	 The jail jid and name parameters (if speci-
	     fied on the command line) 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 jails that are	children of this jail are also

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

     -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 jail.	 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 the parameters used to start
	     the jail.

     -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	the 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 speci-
     fied 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 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 do not	apply (and must	not be

   Jail	Parameters
     Parameters	in the jail.conf(5) file, or on	the command line, are gener-
     ally of the form ``name=value''.  Some parameters are boolean, and	do not
     have a value but are set by the name alone	with or	without	a ``no'' pre-
     fix, 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, which 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 of 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 for-
	     mat, and need not be explicitly set when using the	configuration

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

	     A list of IPv4 addresses assigned to the jail.  If	this is	set,
	     the jail is restricted to using only these	addresses.  Any
	     attempts to use other addresses fail, and attempts	to use wild-
	     card addresses silently use the jailed address instead.  For IPv4
	     the first address given will be used as the source	address	when
	     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 over-
	     lapping IP	address	assigned to itself.

	     A boolean option to change	the formerly mentioned behaviour and
	     disable IPv4 source address selection for the jail	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, 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 jail, the counterparts to ip4.addr,
	     ip4.saddrsel and ip4 above.

     vnet    Create the	jail 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 jail.	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.	 Set-
	     ting 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 its parent 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 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 descendants of this jail, including its own child
	     jails and any jails created under them.

	     This determines what 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 restric-
	     tions.  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	path-
	     names.  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).

	     The string	for the	jail's kern.osrelease sysctl and uname -r.

	     The number	for the	jail's kern.osreldate and uname	-K.

	     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.  This is deprecated in	favor of the per-mod-
		     ule parameters (see below).  When this parameter is set,
		     it	is equivalent to setting sysvmsg, sysvsem, and sysvshm
		     all to ``inherit''.

		     The jail root is allowed to create	raw sockets.  Setting
		     this parameter allows utilities like ping(8) and
		     traceroute(8) to operate inside the jail.	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 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 only when
		     enforce_statfs is set to a	value lower than 2.  The devfs
		     ruleset should be restricted from the default by using
		     the devfs_ruleset option.

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

		     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 only when
		     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 only when
		     enforce_statfs is set to a	value lower than 2.

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

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

		     privileged	users inside the jail will be able to mount
		     and unmount the tmpfs file	system.	 This permission is
		     effective only together with allow.mount and only when
		     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 only when
		     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 jail 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.

     Kernel modules may	add their own parameters, which	only exist when	the
     module is loaded.	These are typically headed under a parameter named
     after the module, with values of ``inherit'' to give the jail full	use of
     the module, ``new'' to encapsulate	the jail in some module-specific way,
     and ``disable'' to	make the module	unavailable to the jail.  There	also
     may be other parameters to	define jail behavior within the	module.	 Mod-
     ule-specific parameters include:

     linux   Determine how a jail's Linux emulation environment	appears.  A
	     value of ``inherit'' will keep the	same environment, and ``new''
	     will give the jail	it's own environment (still originally inher-
	     ited when the jail	is created).

     linux.osname, linux.osrelease, linux.oss_version
	     The Linux OS name,	OS release, and	OSS version associated with
	     this jail.

	     Allow access to SYSV IPC message primitives.  If set to
	     ``inherit'', all IPC objects on the system	are visible to this
	     jail, whether they	were created by	the jail itself, the base sys-
	     tem, or other jails.  If set to ``new'', the jail will have its
	     own key namespace,	and can	only see the objects that it has cre-
	     ated; the system (or parent jail) has access to the jail's
	     objects, but not to its keys.  If set to ``disable'', the jail
	     cannot perform any	sysvmsg-related	system calls.

     sysvsem, sysvshm
	     Allow access to SYSV IPC semaphore	and shared memory primitives,
	     in	the same manner	as sysvmsg.

     There are pseudo-parameters that are not passed to	the kernel, but	are
     used by jail to set up the	jail 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 jail
     environment.  They	may be given multiple values, which would run the
     specified commands	in sequence.  All commands must	succeed	(return	a zero
     exit status), or the jail will not	be created or removed, as appropriate.

     The pseudo-parameters are:

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

	     Command(s)	to run in the jail 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	jail 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 cre-
	     ated, 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 jail 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 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 jail 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 jail'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, in
	     seconds.  If a command is still running after this	timeout	has
	     passed, the jail will not be created or removed, as appropriate.

	     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 jail'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 jail will be removed, which will kill any remaining
	     processes.	 If this is set	to zero, no SIGTERM is sent and	the
	     jail is immediately removed.  The default is 10 seconds.

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

	     In	addition to the	IP addresses that are passed to	the kernel, an
	     interface,	netmask	and additional parameters (as supported	by
	     ifconfig(8)) may also be specified, in the	form
	     ``interface|ip-address/netmask param ...''.  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 an
	     IP	address, it will be used when adding the IP alias.  If addi-
	     tional parameters are specified then they will also be used when
	     adding the	IP alias.

	     In	addition to the	IP addresses that are passed to	the kernel, an
	     interface,	prefix and additional parameters (as supported by
	     ifconfig(8)) may also be specified, in the	form
	     ``interface|ip-address/prefix param ...''.

	     A network interface to give to a vnet-enabled jail	after is it
	     created.  The interface will automatically	be released 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	jail.  This may	affect default address selec-
	     tion for outgoing IPv4 connections	from jails.  The address first
	     returned by the resolver for each address family will be used as
	     the 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(5) 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	jail.

	     Mount a fdescfs(5)	filesystem on the chrooted /dev/fd directory.

	     Mount a procfs(5) filesystem on the chrooted /proc	directory.

	     Allow making changes to a dying jail.

     depend  Specify a jail (or	jails) that this jail depends on.  When	this
	     jail is to	be created, any	jail(s)	it depends on must already
	     exist.  If	not, they will be created automatically, up to the
	     completion	of the last exec.poststart command, before any action
	     will taken	to create this jail.  When jails are removed the oppo-
	     site is true: this	jail will be removed, up to the	last
	     exec.poststop command, before any jail(s) it depends on are

     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	replace	the ``boot'' process.  This manual page	documents the configu-
     ration steps necessary to support either of these steps, although the
     configuration steps may need to 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''.  Substi-
     tute below	as needed with your own	directory, IP address, and hostname.

   Setting up the Host Environment
     First, set	up the 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
     jails are 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 configured to use only the
     specified host IP address.	 Other daemons will need to be manually	con-
     figured --	for some this is possible through rc.conf(5) flags entries;
     for others	it is necessary	to modify per-application configuration	files,
     or	to recompile the application.  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
     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	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= \

     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
     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 run-
     ning within the jail using	ps(1), with the	`J' flag appearing beside
     jailed processes.	To see an active list of jails,	use jls(8).  If
     sshd(8) is	enabled	in the jail environment, you should be able to ssh(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 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

     Multiple jails sharing the	same file system can influence each other.
     For example, a user in one	jail can fill the file system, 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 a single 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 jail may have.  The default is 255.

     Some MIB variables	have per-jail settings.	 Changes to these variables by
     a jailed process do not affect 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
     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 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	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), devfs(5), fdescfs(5),	jail.conf(5), linprocfs(5),
     linsysfs(5), procfs(5), rc.conf(5), sysctl.conf(5), chroot(8), devfs(8),
     halt(8), ifconfig(8), inetd(8), jexec(8), jls(8), mount(8), named(8),
     reboot(8),	rpcbind(8), sendmail(8), shutdown(8), sysctl(8), syslogd(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.

     In	addition, there	are several ways in which an unprivileged user outside
     the jail can cooperate with a privileged user inside the jail and thereby
     obtain elevated privileges	in the host environment.  Most of these
     attacks can be mitigated by ensuring that the jail	root is	not accessible
     to	unprivileged users in the host environment.  Regardless, as a general
     rule, untrusted users with	privileged access to a jail should not be
     given access to the host environment.

FreeBSD	11.0			April 30, 2016			  FreeBSD 11.0


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