|
|
| |
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
... |
jail |
[-f conf_file]
-e separator |
The jail utility creates new jails, or modifies or
removes existing jails. It can also print a list of configured jails and their
parameters. 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 ,
-e , -m or
-r must be specified. These options are used alone
or in combination to describe the operation to perform:
-c
- Create a new jail. The jail jid and
name parameters (if specified on the command line)
must not refer to an existing jail.
-e
separator
- Exhibit a list of all configured non-wildcard jails and their parameters.
No jail creation, modification or removal performed if this option is
used. The separator string is used to separate
parameters. Use
jls(8)
utility to list running jails.
-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 removed.
-rc
- Restart an existing jail. The jail is first removed and then re-created,
as if “
jail
-r ” and
“jail -c ”
were run in succession.
-cm
- Create a jail if it does not exist, or modify the jail if it does
exist.
-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 /etc/jail.conf.
-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 simultaneously.
-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
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 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 “foo.bar” and
“foo.bar.baz”.
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 do not
apply (and must not be present).
Parameters in the
jail.conf(5)
file, or on the command line, are generally 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”
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, 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 itself.
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 format, and need not be explicitly set when using the configuration
file.
- 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.
- ip4.addr
- 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 wildcard 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 overlapping
IP address assigned to itself.
- ip4.saddrsel
- 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 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, 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.
- host.hostname
- 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. Setting any of the above fields implies a value of
“new”.
- securelevel
- 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 secure.
- devfs_ruleset
- 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.
- children.max
- 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.
- children.cur
- The number of descendants of this jail, including its own child jails and
any jails created under them.
- enforce_statfs
- This determines what 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 located.
- persist
- 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.
- cpuset.id
- 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
(read-only).
- parent
- The jid of the parent of this jail, or zero if this
is a top-level jail (read-only).
- osrelease
- The string for the jail's kern.osrelease sysctl and
uname -r.
- osreldate
- The number for the jail's kern.osreldate and uname
-K.
- allow.*
- Some restrictions of the jail environment may be set on a per-jail basis.
With the exception of allow.set_hostname and
allow.reserved_ports, these boolean parameters are
off by default.
- allow.set_hostname
- The jail's hostname may be changed via
hostname(1)
or
sethostname(3).
- allow.sysvipc
- A process within the jail has access to System V IPC primitives. This
is deprecated in favor of the per-module parameters (see below). When
this parameter is set, it is equivalent to setting
sysvmsg, sysvsem, and
sysvshm all to “inherit”.
- allow.raw_sockets
- 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.
- allow.chflags
- 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
kern.securelevel.
- allow.mount
- 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.
- allow.mount.devfs
- 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.
- allow.quotas
- 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.
- allow.read_msgbuf
- Jailed users may read the kernel message buffer. If the
security.bsd.unprivileged_read_msgbuf MIB entry
is zero, this will be restricted to the root user.
- allow.socket_af
- 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.
- allow.mlock
- Locking or unlocking physical pages in memory are normally not
available within a jail. When this parameter is set, users may
mlock(2)
or
munlock(2)
memory subject to
security.bsd.unprivileged_mlock and resource
limits.
- allow.reserved_ports
- The jail root may bind to ports lower than 1024.
- allow.unprivileged_proc_debug
- Unprivileged processes in the jail may use debugging facilities.
- allow.suser
- The value of the jail's
security.bsd.suser_enabled sysctl. The
super-user will be disabled automatically if its parent system has it
disabled. The super-user is enabled by default.
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. Module-specific parameters include:
- allow.mount.fdescfs
- 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.
- allow.mount.fusefs
- privileged users inside the jail will be able to mount and unmount
fuse-based file systems. This permission is effective only together with
allow.mount and only when
enforce_statfs is set to a value lower than 2.
- allow.mount.nullfs
- 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.
- allow.mount.procfs
- 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.
- allow.mount.linprocfs
- 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.
- allow.mount.linsysfs
- 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.
- allow.mount.tmpfs
- 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.
- allow.mount.zfs
- 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.
- allow.vmm
- The jail may access
vmm(4).
This flag is only available when the
vmm(4)
kernel module is loaded.
- 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 its own environment (still
originally inherited 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.
- sysvmsg
- 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 system, or
other jails. If set to “new”, the jail will have its own key
namespace, and can only see the objects that it has created; 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 parameters 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:
- exec.prepare
- Command(s) to run in the system environment to prepare a jail for
creation. These commands are executed before assigning IP addresses and
mounting filesystems, so they may be used to create a new jail filesystem
if it does not already exist.
- exec.prestart
- Command(s) to run in the system environment before a jail is created.
- exec.created
- Command(s) to run in the system environment right after a jail has been
created, but before commands (or services) get executed in the jail.
- exec.start
- Command(s) to run in the jail environment when a jail is created. A
typical command to run is “sh /etc/rc”.
- command
- 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.
- exec.poststart
- Command(s) to run in the system environment after a jail is created, and
after any exec.start commands have completed.
- exec.prestop
- Command(s) to run in the system environment before a jail is removed.
- exec.stop
- 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 jail”.
- exec.poststop
- Command(s) to run in the system environment after a jail is removed.
- exec.release
- Command(s) to run in the system environment after all other actions are
done. These commands are executed after unmounting filesystems and
removing IP addresses, so they may be used to remove a jail filesystem if
it is no longer needed.
- exec.clean
- 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.
- exec.jail_user
- The user to run commands as, when running in the jail environment. The
default is to run the commands as the current user.
- exec.system_jail_user
- This boolean option looks for the exec.jail_user in
the system
passwd(5)
file, instead of in the jail's file.
- exec.system_user
- The user to run commands as, when running in the system environment. The
default is to run the commands as the current user.
- exec.timeout
- 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.
- exec.consolelog
- A file to direct command output (stdout and stderr) to.
- exec.fib
- The FIB (routing table) to set when running commands inside the jail.
- stop.timeout
- 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.
- interface
- 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.
- ip4.addr
- 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 additional parameters are specified then they
will also be used when adding the IP alias.
- ip6.addr
- 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 ...”.
- vnet.interface
- 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.
- ip_hostname
- 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 selection 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.
- mount.fstab
- An
fstab(5)
format file containing filesystems to mount before creating a jail.
- mount.devfs
- 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.fdescfs
- Mount a
fdescfs(5)
filesystem on the chrooted /dev/fd directory.
- mount.procfs
- Mount a
procfs(5)
filesystem on the chrooted /proc directory.
- allow.dying
- 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 opposite is true: this
jail will be removed, up to the last exec.poststop
command, before any 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 replace the “boot” process. This manual
page documents the configuration steps necessary to support either of these
steps, although the configuration steps may need to be refined based on local
requirements.
To set up a jail directory tree containing an entire
FreeBSD distribution, the following
sh(1) command
script can be used:
D=/here/is/the/jail
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.
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.
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:
sendmail_enable="NO"
inetd_flags="-wW -a 192.0.2.23"
rpcbind_enable="NO"
192.0.2.23 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 configured — 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 services 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 /etc/mail/sendmail.cf.
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.).
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=192.0.2.100 \
command=/bin/sh
Assuming no errors, you will end up with a shell prompt within the
jail. You can now run
bsdconfig(8)
and do the post-install configuration to set various configuration options,
or perform these actions manually by editing
/etc/rc.conf, etc.
- Configure /etc/resolv.conf so that name resolution
within the jail will work correctly.
- Run
newaliases(1)
to quell
sendmail(8)
warnings.
- Set a root password, probably different from the real host system.
- Set the timezone.
- Add accounts for users in the jail environment.
- 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.
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
/etc/jail.conf:
testjail {
path = /tmp/jail/testjail;
mount.devfs;
host.hostname = testhostname;
ip4.addr = 192.0.2.100;
interface = em0;
exec.start = "/bin/sh /etc/rc";
exec.stop = "/bin/sh /etc/rc.shutdown jail";
}
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:
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
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.
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
commands:
or:
killall -j 3
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, 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.
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 environment. These variables are
kern.securelevel,
security.bsd.suser_enabled,
kern.hostname, kern.domainname,
kern.hostid, and
kern.hostuuid.
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 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 ancestors.
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
“foo.bar” 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),
vmm(4),
devfs(5),
fdescfs(5),
jail.conf(5),
linprocfs(5),
linsysfs(5),
procfs(5),
rc.conf(5),
sysctl.conf(5),
bsdconfig(8),
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),
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 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.
Visit the GSP FreeBSD Man Page Interface. Output converted with ManDoc. |