379 lines
13 KiB
Groff
379 lines
13 KiB
Groff
.\"
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.\"Copyright (c) 2000 Robert N. M. Watson
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.\"All rights reserved.
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.\"
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.\"Redistribution and use in source and binary forms, with or without
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.\"modification, are permitted provided that the following conditions
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.\"are met:
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.\"1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\"2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\"THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\"ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\"IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\"ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\"FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\"DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\"OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\"HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\"LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\"OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\"SUCH DAMAGE.
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.\"
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.\"
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.\"----------------------------------------------------------------------------
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.\""THE BEER-WARE LICENSE" (Revision 42):
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.\"<phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
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.\"can do whatever you want with this stuff. If we meet some day, and you think
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.\"this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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.\"----------------------------------------------------------------------------
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.\"
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.\"$FreeBSD$
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.\"
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.Dd April 28, 1999
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.Dt JAIL 8
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.Os FreeBSD
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.Sh NAME
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.Nm jail
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.Nd imprison process and its descendants
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.Sh SYNOPSIS
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.Nm
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.Ar path
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.Ar hostname
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.Ar ip-number
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.Ar command
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.Ar ...
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.Sh DESCRIPTION
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The
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.Nm
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command imprisons a process and all future descendants.
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.Pp
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Please see the
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.Xr jail 2
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man page for further details.
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.Sh EXAMPLES
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.Ss Setting up a Jail Directory Tree
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This shows how to setup a jail directory tree:
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.Bd -literal
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D=/here/is/the/jail
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cd /usr/src
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make hierarchy DESTDIR=$D
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make obj
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make depend
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make all
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make install DESTDIR=$D
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cd etc
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make distribution DESTDIR=$D NO_MAKEDEV=yes
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cd $D/dev
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sh MAKEDEV jail
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cd $D
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ln -sf dev/null kernel
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.Ed
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.Ss Setting Up a Jail
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Do what was described in
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.Sx Setting Up a Jail Directory Tree
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to build the jail directory tree. For the sake of this example, we will
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assume you built it in
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.Pa /data/jail/192.168.11.100 ,
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named for the jailed IP address. Substitute below as needed with your
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own directory, IP address, and hostname.
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.Pp
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First, you will want to set up your real system's environment to be
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.Dq jail-friendly.
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For consistency, we will refer to the parent box as the
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.Dq host environment,
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and to the jailed virtual machine as the
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.Dq jail environment.
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Because jail is implemented using IP aliases, one of the first things to do
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is to disable IP services on the host system that listen on all local
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IP addresses for a service. This means changing
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.Xr inetd 8
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to only listen on the
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appropriate IP address, and so forth. Add the following to
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.Pa /etc/rc.conf
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in the host environment:
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.Bd -literal -offset indent
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sendmail_enable="NO"
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inetd_flags="-wW -a 192.168.11.23"
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portmap_enable="NO"
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syslogd_flags="-ss"
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.Ed
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.Pp
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.Li 192.169.11.23
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is the native IP address for the host system, in this example. Daemons that
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run out of
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.Xr inetd 8
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can be easily set to use only the specified host IP address. Other daemons
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will need to be manually configured--for some this is possible through
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the
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.Xr rc.conf 5
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flags entries, for others it is not possible without munging
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the per-application configuration files, or even recompiling. For those
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applications that cannot specify the IP they run on, it is better to disable
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them, if possible.
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.Pp
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A number of daemons ship with the base system that may have problems when
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run from outside of a jail in a jail-centric environment. This includes
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.Xr syslogd 8 ,
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.Xr sendmail 8 ,
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.Xr named 8 ,
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and
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.Xr portmap 8 .
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While sendmail and named can be configured to listen only on a specific
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IP using their configuration files, in most cases it is easier to simply
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run the daemons in jails only, and not in the host environment. Syslogd
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cannot be configured to bind only a single IP, but can be configured to
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not bind a network port, using the ``-ss'' argument. Attempting to serve
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NFS from the host environment may also cause confusion, and cannot be
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easily reconfigured to use only specific IPs, as some NFS services are
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hosted directly from the kernel. Any third party network software running
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in the host environment should also be checked and configured so that it
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does not bind all IP addresses, which would result in those services also
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appearing to be offered by the jail environments.
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.Pp
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Once
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these daemons have been disabled or fixed in the host environment, it is
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best to reboot so that all daemons are in a known state, to reduce the
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potential for confusion later (such as finding that when you send mail
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to a jail, and its sendmail is down, the mail is delivered to the host,
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etc.)
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.Pp
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Start any jails for the first time without configuring the network
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interface so that you can clean it up a little and set up accounts. As
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with any machine (virtual or not) you will need to set a root password, time
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zone, etc. Before beginning, you may want to copy
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.Xr sysinstall 8
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into the tree so that you can use it to set things up easily. Do this using:
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.Bd -literal -offset indent
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# mkdir /data/jail/192.168.11.100/stand
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# cp /stand/sysinstall /data/jail/192.168.11.100/stand
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.Ed
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.Pp
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Now start the jail:
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.Bd -literal -offset indent
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# jail /data/jail/192.168.11.100 testhostname 192.168.11.100 /bin/sh
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.Ed
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.Pp
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You will end up with a shell prompt, assuming no errors, within the jail. You
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can now run
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.Pa /stand/sysinstall
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and do the post-install configuration to set various configuration options,
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or perform these actions manually by editing rc.conf, etc.
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.Pp
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.Bl -bullet -offset indent -compact
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.It
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Create an empty /etc/fstab to quell startup warnings about missing fstab
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.It
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Disable the port mapper (rc.conf: portmap_enable="NO")
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.It
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Run
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.Xr newaliases 1
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to quell sendmail warnings.
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.It
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Disable interface configuration to quell startup warnings about ifconfig
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(network_interfaces="")
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.It
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Configure /etc/resolv.conf
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so that name resolution within the jail will work correctly
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.It
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Set a root password, probably different from the real host system
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.It
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Set the timezone
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.It
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Add accounts for users in the jail environment
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.It
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Install any packages that you think the environment requires
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.El
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.Pp
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You may also want to perform any package-specific configuration (web servers,
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SSH servers, etc), patch up /etc/syslog.conf so it logs as you'd like, etc.
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.Pp
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Exit from the shell, and the jail will be shut down.
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.Ss Starting the Jail
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You are now ready to restart the jail and bring up the environment with
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all of its daemons and other programs. To do this, first bring up the
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virtual host interface, and then start the jail's
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.Pa /etc/rc
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script from within the jail.
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.Pp
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NOTE: If you plan to allow untrusted users to have root access inside the
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jail, you may wish to consider setting the jail.set_hostname_allowed to
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0. Please see the management reasons why this is a good idea. If you
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do decide to set this variable, it must be set before starting any jails,
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and once each boot.
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.Bd -literal -offset indent
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# ifconfig ed0 inet alias 192.168.11.100 netmask 255.255.255.255
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# mount -t procfs proc /data/jail/192.168.11.100/proc
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# jail /data/jail/192.168.11.100 testhostname 192.168.11.100 \\
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/bin/sh /etc/rc
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.Ed
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.Pp
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A few warnings will be produced, because most
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.Xr sysctl 8
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configuration variables cannot be set from within the jail, as they are
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global across all jails and the host environment.
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However, it should all
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work properly.
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You should be able to see
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.Xr inetd 8 ,
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.Xr syslogd 8 ,
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and other processes running within the jail using
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.Xr ps 1 ,
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with the
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.Dq J
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flag appearing beside jailed processes. You should also be able to
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telnet to the hostname or IP address of the jailed environment, and log
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in using the accounts you created previously.
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.Ss Managing the jail
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Normal machine shutdown commands, such as
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.Xr halt 8 ,
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.Xr reboot 8 ,
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and
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.Xr shutdown 8 ,
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cannot be used successfully within the jail. To kill all processes in a
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jail, you may log into the jail and, as root, use one of the following
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commands, depending on what you want to accomplish:
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.Pp
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.Bl -bullet -offset indent -compact
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.It
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.Li kill -TERM -1
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.It
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.Li kill -KILL -1
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.El
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.Pp
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This will send the
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.Dq TERM
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or
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.Dq KILL
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signals to all processes in the jail from within the jail. Depending on
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the intended use of the jail, you may also want to run
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.Pa /etc/rc.shutdown
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from within the jail. Currently there is no way to insert new processes
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into a jail, so you must first log into the jail before performing these
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actions.
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.Pp
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To kill processes from outside the jail, you must individually identify the
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PID of each process to be killed. The
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.Pa /proc/ Ns Va pid Ns Pa /status
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file contains, as its last field, the hostname of the jail in which the
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process runs, or
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.Dq -
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to indicate that the process is not running within a jail. The
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.Xr ps 1
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command also shows a
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.Dq J
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flag for processes in a jail. However, the hostname for a jail may be, by
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default, modified from within the jail, so the
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.Pa /proc
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status entry is unreliable by default. To disable the setting of the hostname
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from within a jail, set the
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.Dq Va jail.set_hostname_allowed
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sysctl variable in the host environment to 0, which will affect all jails.
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You can have this sysctl set each boot using
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.Xr sysctl.conf 5 .
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Just add the following line to sysctl.conf:
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.Bd -literal -offset indent
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jail.set_hostname_allowed=0
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.Ed
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.Pp
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In a future version of
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.Fx ,
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the mechanisms for managing jails will be
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more refined.
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.Ss Sysctl MIB Entries
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Certain aspects of the jail containments environment may be modified from
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the host environment using
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.Xr sysctl 8
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MIB variables.
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Currently, these variables affect all jails on the system, although in
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the future this functionality may be finer grained.
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.Bl -tag -width XXX
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.It jail.set_hostname_allowed
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This MIB entry determines whether or not processes within a jail are
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allowed to change their hostname via
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.Xr hostname 1
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or
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.Xr sethostname 3 .
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In the current jail implementation, the ability to set the hostname from
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within the jail can impact management tools relying on the accuracy of jail
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information in
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.Pa /proc .
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As such, this should be disabled in environments where privileged access to
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jails is given out to untrusted parties.
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.It jail.socket_unixiproute_only
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The jail functionality binds an IPv4 address to each jail, and limits
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access to other network addresses in the IPv4 space that may be available
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in the host environment.
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However, jail is not currently able to limit access to other network
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protocol stacks that have not had jail functionality added to them.
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As such, by default, processes within jails may only access protocols
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in the following domains:
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.Dv PF_LOCAL ,
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.Dv PF_INET ,
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and
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.Dv PF_ROUTE ,
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permitting them access to UNIX domain sockets,
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IPv4 addresses, and routing sockets.
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To enable access to other domains, this MIB variable may be set to
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0.
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.It jail.sysvipc_allowed
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This MIB entry determines whether or not processes within a jail have access
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to System V IPC primitives.
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In the current jail implementation, System V primitives share a single
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namespace across the host and jail environments, meaning that processes
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within a jail would be able to communicate with (and potentially interfere
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with) processes outside of the jail, and in other jails.
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As such, this functionality is disabled by default, but can be enabled
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by setting this MIB entry to 1.
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.El
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.Sh SEE ALSO
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.Xr newaliases 1 ,
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.Xr ps 1 ,
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.Xr chroot 2 ,
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.Xr jail 2 ,
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.Xr procfs 5 ,
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.Xr rc.conf 5 ,
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.Xr sysctl.conf 5 ,
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.Xr halt 8 ,
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.Xr inetd 8 ,
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.Xr named 8 ,
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.Xr portmap 8 ,
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.Xr reboot 8 ,
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.Xr sendmail 8 ,
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.Xr shutdown 8 ,
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.Xr sysctl 8 ,
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.Xr syslogd 8
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.Sh HISTORY
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The
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.Fn jail
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function call appeared in
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.Fx 4.0 .
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.Sh AUTHORS
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The jail feature was written by
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.An Poul-Henning Kamp
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for R&D Associates
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.Dq Li http://www.rndassociates.com/
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who contributed it to
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.Fx .
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.Pp
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Robert Watson wrote the extended documentation, found a few bugs, added
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a few new features, and cleaned up the userland jail environment.
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.Sh BUGS
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Jail currently lacks strong management functionality, such as the ability
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to deliver signals to all processes in a jail, and to allow access to
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specific jail information via
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.Xr ps 1
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as opposed to
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.Xr procfs 5 .
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Similarly, it might be a good idea to add an
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address alias flag such that daemons listening on all IPs (INADDR_ANY)
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will not bind on that address, which would facilitate building a safe
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host environment such that host daemons do not impose on services offered
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from within jails. Currently, the simplist answer is to minimize services
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offered on the host, possibly limiting it to services offered from
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.Xr inetd 8
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which is easily configurable.
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