988 lines
39 KiB
XML
988 lines
39 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!--
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The FreeBSD Documentation Project
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$FreeBSD$
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-->
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<chapter id="jails">
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<chapterinfo>
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<authorgroup>
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<author>
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<firstname>Matteo</firstname>
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<surname>Riondato</surname>
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<contrib>Contributed by </contrib>
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</author>
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</authorgroup>
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</chapterinfo>
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<title>Jails</title>
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<indexterm><primary>jails</primary></indexterm>
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<sect1 id="jails-synopsis">
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<title>Synopsis</title>
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<para>This chapter will provide an explanation of what &os; jails
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are and how to use them. Jails, sometimes referred to as an
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enhanced replacement of <emphasis>chroot environments</emphasis>,
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are a very powerful tool for system administrators, but their basic
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usage can also be useful for advanced users.</para>
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<important>
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<para>Jails are a powerful tool, but they are not a security
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panacea. It is particularly important to note that while it
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is not possible for a jailed process to break out on its own,
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there are several ways in which an unprivileged user outside
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the jail can cooperate with a privileged user inside the jail
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and thereby obtain elevated privileges in the host
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environment.</para>
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<para>Most of these attacks can be mitigated by ensuring that
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the jail root is not accessible to unprivileged users in the
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host environment. Regardless, as a general rule, untrusted
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users with privileged access to a jail should not be given
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access to the host environment.</para>
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</important>
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<para>After reading this chapter, you will know:</para>
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<itemizedlist>
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<listitem>
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<para>What a jail is, and what purpose it may serve in &os;
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installations.</para>
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</listitem>
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<listitem>
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<para>How to build, start, and stop a jail.</para>
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</listitem>
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<listitem>
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<para>The basics of jail administration, both from inside
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and outside the jail.</para>
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</listitem>
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</itemizedlist>
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<para>Other sources of useful information about jails are:</para>
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<itemizedlist>
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<listitem>
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<para>The &man.jail.8; manual page. This is the full reference
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of the <command>jail</command> utility — the
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administrative tool which can be used in &os; to start, stop,
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and control &os; jails.</para>
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</listitem>
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<listitem>
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<para>The mailing lists and their archives. The archives of the
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&a.questions; and other mailing lists hosted by the
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&a.mailman.lists; already contain a wealth of material for
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jails. It should always be engaging to search the archives,
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or post a new question to the &a.questions.name; mailing
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list.</para>
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</listitem>
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</itemizedlist>
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</sect1>
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<sect1 id="jails-terms">
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<title>Terms Related to Jails</title>
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<para>To facilitate better understanding of parts of the &os; system
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related to jails, their internals and the way they interact with
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the rest of &os;, the following terms are used further in this
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chapter:</para>
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<variablelist>
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<varlistentry>
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<term>&man.chroot.8; (command)</term>
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<listitem>
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<para>Utility, which uses &man.chroot.2; &os; system call to change
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the root directory of a process and all its descendants.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>&man.chroot.2; (environment)</term>
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<listitem>
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<para>The environment of processes running in
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a <quote>chroot</quote>. This includes resources such as the part
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of the file system which is visible, user and group IDs which are
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available, network interfaces and other IPC mechanisms,
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etc.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>&man.jail.8; (command)</term>
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<listitem>
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<para>The system administration utility which allows launching of
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processes within a jail environment.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>host (system, process, user, etc.)</term>
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<listitem>
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<para>The controlling system of a jail environment. The host system
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has access to all the hardware resources available, and can
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control processes both outside of and inside a jail environment.
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One of the important differences of the host system from a jail is
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that the limitations which apply to superuser processes inside a
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jail are not enforced for processes of the host system.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>hosted (system, process, user, etc.)</term>
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<listitem>
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<para>A process, user or other entity, whose access to resources is
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restricted by a &os; jail.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</sect1>
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<sect1 id="jails-intro">
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<title>Introduction</title>
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<para>Since system administration is a difficult and perplexing
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task, many powerful tools were developed to make life easier for
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the administrator. These tools mostly provide enhancements of some sort
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to the way systems are installed, configured and maintained.
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Part of the tasks which an administrator is
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expected to do is to properly configure the security of a system,
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so that it can continue serving its real purpose, without allowing
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security violations.</para>
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<para>One of the tools which can be used to enhance the security of
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a &os; system are <emphasis>jails</emphasis>. Jails were
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introduced in &os; 4.X by &a.phk;, but were greatly improved in
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&os; 5.X to make them a powerful and flexible subsystem. Their
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development still goes on, enhancing their usefulness, performance, reliability,
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and security.</para>
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<sect2 id="jails-what">
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<title>What is a Jail</title>
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<para>BSD-like operating systems have had &man.chroot.2; since the
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time of 4.2BSD. The &man.chroot.8; utility can be used to
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change the root directory
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of a set of processes, creating a safe environment, separate
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from the rest of the system. Processes created in the chrooted
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environment can not access files or resources outside of it.
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For that reason, compromising a service running in a chrooted
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environment should not allow the attacker to compromise the
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entire system. The &man.chroot.8; utility is good for easy
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tasks, which do not require a lot of flexibility or complex and
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advanced features. Since the inception of the
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chroot concept, however, many ways have been found to escape from a
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chrooted environment and, although they have been fixed in
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modern versions of the &os; kernel, it was clear that
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&man.chroot.2; was not the ideal solution for securing services.
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A new subsystem had to be implemented.</para>
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<para>This is one of the main reasons why
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<emphasis>jails</emphasis> were developed.</para>
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<para>Jails improve on the concept of the traditional
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&man.chroot.2; environment, in several ways. In a traditional
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&man.chroot.2; environment, processes are only limited in the
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part of the file system they can access. The rest of the system
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resources (like the set of system users, the running processes,
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or the networking subsystem) are shared by the chrooted
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processes and the processes of the host system. Jails expand
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this model by virtualizing not only access to the file system,
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but also the set of users, the networking subsystem of the &os;
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kernel and a few other things. A more complete set of
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fine-grained controls available for tuning the access of a
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jailed environment is described in <xref
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linkend="jails-tuning"/>.</para>
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<para>A jail is characterized by four elements:</para>
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<itemizedlist>
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<listitem>
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<para>A directory subtree — the starting point from
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which a jail is entered. Once inside the jail, a process
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is not permitted to escape outside of this subtree.
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Traditional security issues which plagued the original
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&man.chroot.2; design will not affect &os; jails.</para>
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</listitem>
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<listitem>
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<para>A hostname — the hostname which will be used
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within the jail. Jails are mainly used for hosting network
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services, therefore having a descriptive hostname for each
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jail can really help the system administrator.</para>
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</listitem>
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<listitem>
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<para>An <acronym>IP</acronym> address — this will be
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assigned to the jail and cannot be changed in any way during
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the jail's life span. The IP address of a jail is usually an alias address
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for an existing network interface, but this is not strictly necessary.</para>
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</listitem>
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<listitem>
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<para>A command — the path name of an executable to run
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inside the jail. This is relative to the root directory of
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the jail environment, and may vary a lot, depending on the
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type of the specific jail environment.</para>
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</listitem>
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</itemizedlist>
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<para>Apart from these, jails can have their own set of users and
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their own <username>root</username> user. Naturally, the powers
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of the <username>root</username> user are limited within the
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jail environment and, from the point of view of the host system,
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the jail <username>root</username> user is not an omnipotent user.
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In addition, the <username>root</username> user of a jail is not
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allowed to perform critical operations to the system outside of
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the associated &man.jail.8; environment. More information
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about capabilities and restrictions of the
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<username>root</username> user will be discussed in <xref
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linkend="jails-tuning"/> below.</para>
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</sect2>
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</sect1>
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<sect1 id="jails-build">
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<title>Creating and Controlling Jails</title>
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<para>Some administrators divide jails into the following two types:
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<quote>complete</quote> jails, which resemble a real &os; system,
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and <quote>service</quote> jails, dedicated to one application or
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service, possibly running with privileges. This is only a
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conceptual division and the process of building a jail is not
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affected by it. The &man.jail.8; manual page is quite clear about
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the procedure for building a jail:</para>
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<screen>&prompt.root; <userinput>setenv D <replaceable>/here/is/the/jail</replaceable></userinput>
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&prompt.root; <userinput>mkdir -p $D</userinput> <co id="jailpath"/>
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&prompt.root; <userinput>cd /usr/src</userinput>
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&prompt.root; <userinput>make buildworld</userinput> <co id="jailbuildworld"/>
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&prompt.root; <userinput>make installworld DESTDIR=$D</userinput> <co id="jailinstallworld"/>
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&prompt.root; <userinput>make distribution DESTDIR=$D</userinput> <co id="jaildistrib"/>
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&prompt.root; <userinput>mount -t devfs devfs $D/dev</userinput> <co id="jaildevfs"/></screen>
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<calloutlist>
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<callout arearefs="jailpath">
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<para>Selecting a location for a jail is the best starting point.
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This is where the jail will physically reside within the file system of the jail's host.
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A good choice can be <filename
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class="directory">/usr/jail/<replaceable>jailname</replaceable></filename>,
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where <replaceable>jailname</replaceable> is the hostname
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identifying the jail. The <filename
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class="directory">/usr/</filename> file system usually has
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enough space for the jail file system, which for <quote>complete</quote> jails is, essentially,
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a replication of every file present in a default installation
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of the &os; base system.</para>
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</callout>
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<callout arearefs="jailbuildworld">
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<para>If you have already rebuilt your userland using
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<command>make world</command> or <command>make buildworld</command>,
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you can skip this step and install your existing userland into the
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new jail.</para>
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</callout>
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<callout arearefs="jailinstallworld">
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<para>This command will populate the directory subtree chosen
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as jail's physical location on the file system with the
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necessary binaries, libraries, manual pages and so on.</para>
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</callout>
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<callout arearefs="jaildistrib">
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<para>The <maketarget>distribution</maketarget> target for
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<application>make</application> installs every needed
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configuration file. In simple words, it installs every installable file of
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<filename class="directory">/usr/src/etc/</filename> to the
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<filename class="directory">/etc</filename> directory of the jail
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environment:
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<filename class="directory">$D/etc/</filename>.</para>
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</callout>
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<callout arearefs="jaildevfs">
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<para>Mounting the &man.devfs.8; file system inside a jail is
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not required. On the other hand, any, or almost any
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application requires access to at least one device, depending
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on the purpose of the given application. It is very important
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to control access to devices from inside a jail, as improper
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settings could permit an attacker to do nasty things in the
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jail. Control over &man.devfs.8; is managed through rulesets
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which are described in the &man.devfs.8; and
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&man.devfs.conf.5; manual pages.</para>
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</callout>
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</calloutlist>
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<para>Once a jail is installed, it can be started by using the
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&man.jail.8; utility. The &man.jail.8; utility takes four
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mandatory arguments which are described in the <xref
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linkend="jails-what"/>. Other arguments may be
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specified too, e.g., to run the jailed process with the credentials of a specific
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user. The <option><replaceable>command</replaceable></option> argument depends on
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the type of the jail; for a <emphasis>virtual system</emphasis>,
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<filename>/etc/rc</filename> is a good choice, since it will
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replicate the startup sequence of a real &os; system. For a
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<emphasis>service</emphasis> jail, it depends on the service or
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application that will run within the jail.</para>
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<para>Jails are often started at boot time and the &os;
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<filename>rc</filename> mechanism provides an easy way to do
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this.</para>
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<procedure>
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<step>
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<para>A list of the jails which are enabled to start at boot
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time should be added to the &man.rc.conf.5; file:</para>
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<programlisting>jail_enable="YES" # Set to NO to disable starting of any jails
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jail_list="<replaceable>www</replaceable>" # Space separated list of names of jails</programlisting>
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<note>
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<para>Jail names in <varname>jail_list</varname> should
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contain alphanumeric characters only.</para>
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</note>
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</step>
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<step>
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<para>For each jail listed in <varname>jail_list</varname>, a
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group of &man.rc.conf.5; settings, which describe the
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particular jail, should be added:</para>
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<programlisting>jail_<replaceable>www</replaceable>_rootdir="/usr/jail/www" # jail's root directory
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jail_<replaceable>www</replaceable>_hostname="<replaceable>www</replaceable>.example.org" # jail's hostname
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jail_<replaceable>www</replaceable>_ip="192.168.0.10" # jail's IP address
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jail_<replaceable>www</replaceable>_devfs_enable="YES" # mount devfs in the jail
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jail_<replaceable>www</replaceable>_devfs_ruleset="<replaceable>www_ruleset</replaceable>" # devfs ruleset to apply to jail</programlisting>
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<para>The default startup of jails configured in
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&man.rc.conf.5;, will run the <filename>/etc/rc</filename>
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script of the jail, which assumes the jail is a complete
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virtual system. For service jails, the default startup
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command of the jail should be changed, by setting the
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<varname>jail_<replaceable>jailname</replaceable>_exec_start</varname>
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option appropriately.</para>
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<note>
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<para>For a full list of available options, please see the
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&man.rc.conf.5; manual page.</para>
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</note>
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</step>
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</procedure>
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<para>&man.service.8; can be used to
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start or stop a jail by hand, if an entry for it exists in
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<filename>rc.conf</filename>:</para>
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<screen>&prompt.root; <userinput>service jail start <replaceable>www</replaceable></userinput>
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&prompt.root; <userinput>service jail stop <replaceable>www</replaceable></userinput></screen>
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<para>A clean way to shut down a &man.jail.8; is not available at
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the moment. This is because commands normally used to accomplish
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a clean system shutdown cannot be used inside a jail. The best
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way to shut down a jail is to run the following command from
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within the jail itself or using the &man.jexec.8; utility from
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outside the jail:</para>
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<screen>&prompt.root; <userinput>sh /etc/rc.shutdown</userinput></screen>
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<para>More information about this can be found in the &man.jail.8;
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manual page.</para>
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</sect1>
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<sect1 id="jails-tuning">
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<title>Fine Tuning and Administration</title>
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<para>There are several options which can be set for any jail, and
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various ways of combining a host &os; system with jails, to produce
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higher level applications. This section presents:</para>
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<itemizedlist>
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<listitem>
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<para>Some of the options available for tuning the behavior and
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security restrictions implemented by a jail
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installation.</para>
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</listitem>
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<listitem>
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<para>Some of the high-level applications for jail management,
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which are available through the &os; Ports Collection, and can
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be used to implement overall jail-based solutions.</para>
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</listitem>
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</itemizedlist>
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<sect2 id="jails-tuning-utilities">
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<title>System Tools for Jail Tuning in &os;</title>
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<para>Fine tuning of a jail's configuration is mostly done by
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setting &man.sysctl.8; variables. A special subtree of sysctl
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exists as a basis for organizing all the relevant options: the
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<varname>security.jail.*</varname> hierarchy of &os; kernel
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options. Here is a list of the main jail-related sysctls,
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complete with their default value. Names should be
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self-explanatory, but for more information about them, please
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refer to the &man.jail.8; and &man.sysctl.8; manual
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pages.</para>
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<itemizedlist>
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<listitem>
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<para><varname>security.jail.set_hostname_allowed:
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1</varname></para>
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</listitem>
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<listitem>
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<para><varname>security.jail.socket_unixiproute_only:
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1</varname></para>
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</listitem>
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<listitem>
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<para><varname>security.jail.sysvipc_allowed:
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0</varname></para>
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</listitem>
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<listitem>
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<para><varname>security.jail.enforce_statfs:
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2</varname></para>
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</listitem>
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<listitem>
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<para><varname>security.jail.allow_raw_sockets:
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0</varname></para>
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</listitem>
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<listitem>
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<para><varname>security.jail.chflags_allowed:
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0</varname></para>
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</listitem>
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<listitem>
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<para><varname>security.jail.jailed: 0</varname></para>
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</listitem>
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</itemizedlist>
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<para>These variables can be used by the system administrator of
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the <emphasis>host system</emphasis> to add or remove some of
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the limitations imposed by default on the
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<username>root</username> user. Note that there are some
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limitations which cannot be removed. The
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<username>root</username> user is not allowed to mount or
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unmount file systems from within a &man.jail.8;. The
|
|
<username>root</username> inside a jail may not load or unload
|
|
&man.devfs.8; rulesets, set firewall rules, or do many other
|
|
administrative tasks which require modifications of in-kernel
|
|
data, such as setting the <varname>securelevel</varname> of the
|
|
kernel.</para>
|
|
|
|
<para>The base system of &os; contains a basic set of tools for
|
|
viewing information about the active jails, and attaching to a
|
|
jail to run administrative commands. The &man.jls.8; and
|
|
&man.jexec.8; commands are part of the base &os; system, and can be used
|
|
to perform the following simple tasks:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Print a list of active jails and their corresponding
|
|
jail identifier (<acronym>JID</acronym>),
|
|
<acronym>IP</acronym> address, hostname and path.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Attach to a running jail, from its host system, and run
|
|
a command inside the jail or perform administrative tasks inside the
|
|
jail itself. This is especially useful when the
|
|
<username>root</username> user wants to cleanly shut down a
|
|
jail. The &man.jexec.8; utility can also be used to start a
|
|
shell in a jail to do administration in it; for
|
|
example:</para>
|
|
|
|
<screen>&prompt.root; <userinput>jexec <replaceable>1</replaceable> tcsh</userinput></screen>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect2>
|
|
|
|
<sect2 id="jails-tuning-admintools">
|
|
<title>High-Level Administrative Tools in the &os; Ports
|
|
Collection</title>
|
|
|
|
<para>Among the many third-party utilities for jail administration,
|
|
one of the most complete and useful is <filename
|
|
role="package">sysutils/jailutils</filename>. It is a set of
|
|
small applications that contribute to &man.jail.8; management.
|
|
Please refer to its web page for more information.</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1 id="jails-application">
|
|
<title>Application of Jails</title>
|
|
|
|
<sect2 id="jails-service-jails">
|
|
<sect2info>
|
|
<authorgroup>
|
|
<author>
|
|
<firstname>Daniel</firstname>
|
|
<surname>Gerzo</surname>
|
|
<contrib>Contributed by </contrib>
|
|
<!-- 15. May 2007 -->
|
|
</author>
|
|
</authorgroup>
|
|
</sect2info>
|
|
|
|
<title>Service Jails</title>
|
|
|
|
<para>This section is based upon an idea originally presented by
|
|
&a.simon; at <ulink
|
|
url="http://simon.nitro.dk/service-jails.html"></ulink>, and an
|
|
updated article written by Ken Tom
|
|
<email>locals@gmail.com</email>. This section illustrates how
|
|
to set up a &os; system that adds an additional layer of
|
|
security, using the &man.jail.8; feature. It is also assumed
|
|
that the given system is at least running RELENG_6_0 and the
|
|
information provided earlier in this chapter has been well
|
|
understood.</para>
|
|
|
|
<sect3 id="jails-service-jails-design">
|
|
<title>Design</title>
|
|
|
|
<para>One of the major problems with jails is the management of
|
|
their upgrade process. This tends to be a problem because
|
|
every jail has to be rebuilt from scratch whenever it is
|
|
updated. This is usually not a problem for a single jail,
|
|
since the update process is fairly simple, but can be quite
|
|
time consuming and tedious if a lot of jails are
|
|
created.</para>
|
|
|
|
<warning>
|
|
<para>This setup requires advanced experience with &os; and
|
|
usage of its features. If the presented steps below look
|
|
too complicated, it is advised to take a look at a simpler
|
|
system such as <filename
|
|
role="package">sysutils/ezjail</filename>, which provides
|
|
an easier method of administering &os; jails and is not as
|
|
sophisticated as this setup.</para>
|
|
</warning>
|
|
|
|
<para>This idea has been presented to resolve such issues by
|
|
sharing as much as is possible between jails, in a safe way
|
|
— using read-only &man.mount.nullfs.8; mounts, so that
|
|
updating will be simpler, and putting single services into
|
|
individual jails will become more attractive. Additionally,
|
|
it provides a simple way to add or remove jails as well as a
|
|
way to upgrade them.</para>
|
|
|
|
<note>
|
|
<para>Examples of services in this context are: an
|
|
<acronym>HTTP</acronym> server, a <acronym>DNS</acronym>
|
|
server, a <acronym>SMTP</acronym> server, and so forth.</para>
|
|
</note>
|
|
|
|
<para>The goals of the setup described in this section
|
|
are:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Create a simple and easy to understand jail structure.
|
|
This implies <emphasis>not</emphasis> having to run a full
|
|
installworld on each and every jail.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>Make it easy to add new jails or remove existing
|
|
ones.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>Make it easy to update or upgrade existing
|
|
jails.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>Make it possible to run a customized &os;
|
|
branch.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>Be paranoid about security, reducing as much as
|
|
possible the possibility of compromise.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>Save space and inodes, as much as possible.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>As it has been already mentioned, this design relies
|
|
heavily on having a single master template which is read-only
|
|
(known as <application>nullfs</application>) mounted into each
|
|
jail and one read-write device per jail. A device can be a
|
|
separate physical disc, a partition, or a vnode backed
|
|
&man.md.4; device. In this example, we will use read-write
|
|
<application>nullfs</application> mounts.</para>
|
|
|
|
<para>The file system layout is described in the following
|
|
list:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Each jail will be mounted under the <filename
|
|
class="directory">/home/j</filename> directory.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para><filename class="directory">/home/j/mroot</filename> is
|
|
the template for each jail and the read-only partition for
|
|
all of the jails.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>A blank directory will be created for each jail under
|
|
the <filename class="directory">/home/j</filename>
|
|
directory.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>Each jail will have a <filename
|
|
class="directory">/s</filename> directory, that will be
|
|
linked to the read-write portion of the system.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>Each jail shall have its own read-write system that is
|
|
based upon <filename
|
|
class="directory">/home/j/skel</filename>.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>Each jailspace (read-write portion of each jail) shall
|
|
be created in <filename
|
|
class="directory">/home/js</filename>.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<note>
|
|
<para>This assumes that the jails are based under the
|
|
<filename class="directory">/home</filename> partition. This
|
|
can, of course, be changed to anything else, but this change
|
|
will have to be reflected in each of the examples
|
|
below.</para>
|
|
</note>
|
|
<!-- Insert an image or drawing here to illustrate the example. -->
|
|
</sect3>
|
|
|
|
<sect3 id="jails-service-jails-template">
|
|
<title>Creating the Template</title>
|
|
|
|
<para>This section will describe the steps needed to create the
|
|
master template that will be the read-only portion for the
|
|
jails to use.</para>
|
|
|
|
<para>It is always a good idea to update the &os; system to the
|
|
latest -RELEASE branch. Check the corresponding Handbook
|
|
<ulink url="&url.books.handbook;/makeworld.html">Chapter</ulink>
|
|
to accomplish this task. In the case the update is not
|
|
feasible, the buildworld will be required in order to be able
|
|
to proceed. Additionally, the <filename
|
|
role="package">sysutils/cpdup</filename> package will be
|
|
required. We will use the &man.portsnap.8; utility to
|
|
download the &os; Ports Collection. The Handbook <ulink
|
|
url="&url.books.handbook;/portsnap.html">Portsnap Chapter</ulink>
|
|
is always good reading for newcomers.</para>
|
|
|
|
<procedure>
|
|
<step>
|
|
<para>First, create a directory structure for the read-only
|
|
file system which will contain the &os; binaries for our
|
|
jails, then change directory to the &os; source tree and
|
|
install the read-only file system to the jail
|
|
template:</para>
|
|
|
|
<screen>&prompt.root; <userinput>mkdir /home/j /home/j/mroot</userinput>
|
|
&prompt.root; <userinput>cd /usr/src</userinput>
|
|
&prompt.root; <userinput>make installworld DESTDIR=/home/j/mroot</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>Next, prepare a &os; Ports Collection for the jails as
|
|
well as a &os; source tree, which is required for
|
|
<application>mergemaster</application>:</para>
|
|
|
|
<screen>&prompt.root; <userinput>cd /home/j/mroot</userinput>
|
|
&prompt.root; <userinput>mkdir usr/ports</userinput>
|
|
&prompt.root; <userinput>portsnap -p /home/j/mroot/usr/ports fetch extract</userinput>
|
|
&prompt.root; <userinput>cpdup /usr/src /home/j/mroot/usr/src</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>Create a skeleton for the read-write portion of the
|
|
system:</para>
|
|
|
|
<screen>&prompt.root; <userinput>mkdir /home/j/skel /home/j/skel/home /home/j/skel/usr-X11R6 /home/j/skel/distfiles</userinput>
|
|
&prompt.root; <userinput>mv etc /home/j/skel</userinput>
|
|
&prompt.root; <userinput>mv usr/local /home/j/skel/usr-local</userinput>
|
|
&prompt.root; <userinput>mv tmp /home/j/skel</userinput>
|
|
&prompt.root; <userinput>mv var /home/j/skel</userinput>
|
|
&prompt.root; <userinput>mv root /home/j/skel</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>Use <application>mergemaster</application> to install
|
|
missing configuration files. Then get rid of the extra
|
|
directories that <application>mergemaster</application>
|
|
creates:</para>
|
|
|
|
<screen>&prompt.root; <userinput>mergemaster -t /home/j/skel/var/tmp/temproot -D /home/j/skel -i</userinput>
|
|
&prompt.root; <userinput>cd /home/j/skel</userinput>
|
|
&prompt.root; <userinput>rm -R bin boot lib libexec mnt proc rescue sbin sys usr dev</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>Now, symlink the read-write file system to the
|
|
read-only file system. Please make sure that the symlinks
|
|
are created in the correct <filename
|
|
class="directory">s/</filename> locations. Real
|
|
directories or the creation of directories in the wrong
|
|
locations will cause the installation to fail.</para>
|
|
|
|
<screen>&prompt.root; <userinput>cd /home/j/mroot</userinput>
|
|
&prompt.root; <userinput>mkdir s</userinput>
|
|
&prompt.root; <userinput>ln -s s/etc etc</userinput>
|
|
&prompt.root; <userinput>ln -s s/home home</userinput>
|
|
&prompt.root; <userinput>ln -s s/root root</userinput>
|
|
&prompt.root; <userinput>ln -s ../s/usr-local usr/local</userinput>
|
|
&prompt.root; <userinput>ln -s ../s/usr-X11R6 usr/X11R6</userinput>
|
|
&prompt.root; <userinput>ln -s ../../s/distfiles usr/ports/distfiles</userinput>
|
|
&prompt.root; <userinput>ln -s s/tmp tmp</userinput>
|
|
&prompt.root; <userinput>ln -s s/var var</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>As a last step, create a generic
|
|
<filename>/home/j/skel/etc/make.conf</filename> with its
|
|
contents as shown below:</para>
|
|
|
|
<programlisting>WRKDIRPREFIX?= /s/portbuild</programlisting>
|
|
|
|
|
|
<para>Having <literal>WRKDIRPREFIX</literal> set up this
|
|
way will make it possible to compile &os; ports inside
|
|
each jail. Remember that the ports directory is part of
|
|
the read-only system. The custom path for
|
|
<literal>WRKDIRPREFIX</literal> allows builds to be done
|
|
in the read-write portion of every jail.</para>
|
|
</step>
|
|
</procedure>
|
|
</sect3>
|
|
|
|
<sect3 id="jails-service-jails-creating">
|
|
<title>Creating Jails</title>
|
|
|
|
<para>Now that we have a complete &os; jail template, we can
|
|
setup and configure the jails in
|
|
<filename>/etc/rc.conf</filename>. This example demonstrates
|
|
the creation of 3 jails: <quote>NS</quote>,
|
|
<quote>MAIL</quote> and <quote>WWW</quote>.</para>
|
|
|
|
<procedure>
|
|
<step>
|
|
<para>Put the following lines into the
|
|
<filename>/etc/fstab</filename> file, so that the
|
|
read-only template for the jails and the read-write space
|
|
will be available in the respective jails:</para>
|
|
|
|
<programlisting>/home/j/mroot /home/j/ns nullfs ro 0 0
|
|
/home/j/mroot /home/j/mail nullfs ro 0 0
|
|
/home/j/mroot /home/j/www nullfs ro 0 0
|
|
/home/js/ns /home/j/ns/s nullfs rw 0 0
|
|
/home/js/mail /home/j/mail/s nullfs rw 0 0
|
|
/home/js/www /home/j/www/s nullfs rw 0 0</programlisting>
|
|
|
|
<note>
|
|
<para>Partitions marked with a 0 pass number are not
|
|
checked by &man.fsck.8; during boot, and partitions
|
|
marked with a 0 dump number are not backed up by
|
|
&man.dump.8;. We do not want
|
|
<application>fsck</application> to check
|
|
<application>nullfs</application> mounts or
|
|
<application>dump</application> to back up the read-only
|
|
nullfs mounts of the jails. This is why they are marked
|
|
with <quote>0 0</quote> in the last two columns of
|
|
each <filename>fstab</filename> entry above.</para>
|
|
</note>
|
|
</step>
|
|
<step>
|
|
<para>Configure the jails in
|
|
<filename>/etc/rc.conf</filename>:</para>
|
|
|
|
<programlisting>jail_enable="YES"
|
|
jail_set_hostname_allow="NO"
|
|
jail_list="ns mail www"
|
|
jail_ns_hostname="ns.example.org"
|
|
jail_ns_ip="192.168.3.17"
|
|
jail_ns_rootdir="/usr/home/j/ns"
|
|
jail_ns_devfs_enable="YES"
|
|
jail_mail_hostname="mail.example.org"
|
|
jail_mail_ip="192.168.3.18"
|
|
jail_mail_rootdir="/usr/home/j/mail"
|
|
jail_mail_devfs_enable="YES"
|
|
jail_www_hostname="www.example.org"
|
|
jail_www_ip="62.123.43.14"
|
|
jail_www_rootdir="/usr/home/j/www"
|
|
jail_www_devfs_enable="YES"</programlisting>
|
|
|
|
<warning>
|
|
<para>The reason why the
|
|
<varname>jail_<replaceable>name</replaceable>_rootdir</varname>
|
|
variable is set to <filename
|
|
class="directory">/usr/home</filename> instead of
|
|
<filename class="directory">/home</filename> is that the
|
|
physical path of the <filename
|
|
class="directory">/home</filename> directory on a
|
|
default &os; installation is <filename
|
|
class="directory">/usr/home</filename>. The
|
|
<varname>jail_<replaceable>name</replaceable>_rootdir</varname>
|
|
variable must <emphasis>not</emphasis> be set to a path
|
|
which includes a symbolic link, otherwise the jails will
|
|
refuse to start. Use the &man.realpath.1; utility to
|
|
determine a value which should be set to this variable.
|
|
Please see the &os;-SA-07:01.jail Security Advisory for
|
|
more information.</para>
|
|
</warning>
|
|
</step>
|
|
<step>
|
|
<para>Create the required mount points for the read-only
|
|
file system of each jail:</para>
|
|
|
|
<screen>&prompt.root; <userinput>mkdir /home/j/ns /home/j/mail /home/j/www</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>Install the read-write template into each jail. Note
|
|
the use of <filename
|
|
role="package">sysutils/cpdup</filename>, which helps to
|
|
ensure that a correct copy is done of each
|
|
directory:</para>
|
|
<!-- keramida: Why is cpdup required here? Doesn't cpio(1)
|
|
already include adequate functionality for performing this
|
|
job *and* have the advantage of being part of the base
|
|
system of FreeBSD? -->
|
|
|
|
<screen>&prompt.root; <userinput>mkdir /home/js</userinput>
|
|
&prompt.root; <userinput>cpdup /home/j/skel /home/js/ns</userinput>
|
|
&prompt.root; <userinput>cpdup /home/j/skel /home/js/mail</userinput>
|
|
&prompt.root; <userinput>cpdup /home/j/skel /home/js/www</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>In this phase, the jails are built and prepared to
|
|
run. First, mount the required file systems for each
|
|
jail, and then start them using the jail rc
|
|
script.</para>
|
|
|
|
<screen>&prompt.root; <userinput>mount -a</userinput>
|
|
&prompt.root; <userinput>service jail start</userinput></screen>
|
|
</step>
|
|
</procedure>
|
|
|
|
<para>The jails should be running now. To check if they have
|
|
started correctly, use the &man.jls.8; command. Its output
|
|
should be similar to the following:</para>
|
|
|
|
<screen>&prompt.root; <userinput>jls</userinput>
|
|
JID IP Address Hostname Path
|
|
3 192.168.3.17 ns.example.org /home/j/ns
|
|
2 192.168.3.18 mail.example.org /home/j/mail
|
|
1 62.123.43.14 www.example.org /home/j/www</screen>
|
|
|
|
<para>At this point, it should be possible to log onto each
|
|
jail, add new users or configure daemons. The
|
|
<literal>JID</literal> column indicates the jail
|
|
identification number of each running jail. Use the
|
|
following command in order to perform administrative tasks in
|
|
the jail whose <literal>JID</literal> is 3:</para>
|
|
|
|
<screen>&prompt.root; <userinput>jexec 3 tcsh</userinput></screen>
|
|
</sect3>
|
|
|
|
<sect3 id="jails-service-jails-upgrading">
|
|
<title>Upgrading</title>
|
|
|
|
<para>In time, there will be a need to upgrade the system to a
|
|
newer version of &os;, either because of a security issue, or
|
|
because new features have been implemented which are useful
|
|
for the existing jails. The design of this setup provides an
|
|
easy way to upgrade existing jails. Additionally, it
|
|
minimizes their downtime, as the jails will be brought down
|
|
only in the very last minute. Also, it provides a way to roll
|
|
back to the older versions should any problems occur.</para>
|
|
|
|
<procedure>
|
|
<step>
|
|
<para>The first step is to upgrade the host system in the
|
|
usual manner. Then create a new temporary read-only
|
|
template in <filename
|
|
class="directory">/home/j/mroot2</filename>.</para>
|
|
|
|
<screen>&prompt.root; <userinput>mkdir /home/j/mroot2</userinput>
|
|
&prompt.root; <userinput>cd /usr/src</userinput>
|
|
&prompt.root; <userinput>make installworld DESTDIR=/home/j/mroot2</userinput>
|
|
&prompt.root; <userinput>cd /home/j/mroot2</userinput>
|
|
&prompt.root; <userinput>cpdup /usr/src usr/src</userinput>
|
|
&prompt.root; <userinput>mkdir s</userinput></screen>
|
|
|
|
<para>The <maketarget>installworld</maketarget> run creates
|
|
a few unnecessary directories, which should be
|
|
removed:</para>
|
|
|
|
<screen>&prompt.root; <userinput>chflags -R 0 var</userinput>
|
|
&prompt.root; <userinput>rm -R etc var root usr/local tmp</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>Recreate the read-write symlinks for the master file
|
|
system:</para>
|
|
|
|
<screen>&prompt.root; <userinput>ln -s s/etc etc</userinput>
|
|
&prompt.root; <userinput>ln -s s/root root</userinput>
|
|
&prompt.root; <userinput>ln -s s/home home</userinput>
|
|
&prompt.root; <userinput>ln -s ../s/usr-local usr/local</userinput>
|
|
&prompt.root; <userinput>ln -s ../s/usr-X11R6 usr/X11R6</userinput>
|
|
&prompt.root; <userinput>ln -s s/tmp tmp</userinput>
|
|
&prompt.root; <userinput>ln -s s/var var</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>The right time to stop the jails is now:</para>
|
|
|
|
<screen>&prompt.root; <userinput>service jail stop</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>Unmount the original file systems:</para>
|
|
<!-- keramida: Shouldn't we suggest a short script-based
|
|
loop here, instead of tediously copying the same commands
|
|
multiple times? -->
|
|
|
|
<screen>&prompt.root; <userinput>umount /home/j/ns/s</userinput>
|
|
&prompt.root; <userinput>umount /home/j/ns</userinput>
|
|
&prompt.root; <userinput>umount /home/j/mail/s</userinput>
|
|
&prompt.root; <userinput>umount /home/j/mail</userinput>
|
|
&prompt.root; <userinput>umount /home/j/www/s</userinput>
|
|
&prompt.root; <userinput>umount /home/j/www</userinput></screen>
|
|
|
|
<note>
|
|
<para>The read-write systems are attached to the read-only
|
|
system (<filename class="directory">/s</filename>) and
|
|
must be unmounted first.</para>
|
|
</note>
|
|
</step>
|
|
<step>
|
|
<para>Move the old read-only file system and replace it with
|
|
the new one. This will serve as a backup and archive of the
|
|
old read-only file system should something go wrong. The
|
|
naming convention used here corresponds to when a new
|
|
read-only file system has been created. Move the original
|
|
&os; Ports Collection over to the new file system to save
|
|
some space and inodes:</para>
|
|
|
|
<screen>&prompt.root; <userinput>cd /home/j</userinput>
|
|
&prompt.root; <userinput>mv mroot mroot.20060601</userinput>
|
|
&prompt.root; <userinput>mv mroot2 mroot</userinput>
|
|
&prompt.root; <userinput>mv mroot.20060601/usr/ports mroot/usr</userinput></screen>
|
|
</step>
|
|
<step>
|
|
<para>At this point the new read-only template is ready, so
|
|
the only remaining task is to remount the file systems and
|
|
start the jails:</para>
|
|
|
|
<screen>&prompt.root; <userinput>mount -a</userinput>
|
|
&prompt.root; <userinput>service jail start</userinput></screen>
|
|
</step>
|
|
</procedure>
|
|
|
|
<para>Use &man.jls.8; to check if the jails started correctly.
|
|
Do not forget to run mergemaster in each jail. The
|
|
configuration files will need to be updated as well as the
|
|
rc.d scripts.</para>
|
|
</sect3>
|
|
</sect2>
|
|
</sect1>
|
|
</chapter>
|