mirror of https://gitee.com/openkylin/libvirt.git
473 lines
15 KiB
XML
473 lines
15 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
|
|
<html xmlns="http://www.w3.org/1999/xhtml">
|
|
<body>
|
|
<h1>LXC container driver</h1>
|
|
|
|
<ul id="toc"></ul>
|
|
|
|
<p>
|
|
The libvirt LXC driver manages "Linux Containers". At their simplest, containers
|
|
can just be thought of as a collection of processes, separated from the main
|
|
host processes via a set of resource namespaces and constrained via control
|
|
groups resource tunables. The libvirt LXC driver has no dependency on the LXC
|
|
userspace tools hosted on sourceforge.net. It directly utilizes the relevant
|
|
kernel features to build the container environment. This allows for sharing
|
|
of many libvirt technologies across both the QEMU/KVM and LXC drivers. In
|
|
particular sVirt for mandatory access control, auditing of operations,
|
|
integration with control groups and many other features.
|
|
</p>
|
|
|
|
<h2><a name="cgroups">Control groups Requirements</a></h2>
|
|
|
|
<p>
|
|
In order to control the resource usage of processes inside containers, the
|
|
libvirt LXC driver requires that certain cgroups controllers are mounted on
|
|
the host OS. The minimum required controllers are 'cpuacct', 'memory' and
|
|
'devices', while recommended extra controllers are 'cpu', 'freezer' and
|
|
'blkio'. Libvirt will not mount the cgroups filesystem itself, leaving
|
|
this up to the init system to take care of. Systemd will do the right thing
|
|
in this respect, while for other init systems the <code>cgconfig</code>
|
|
init service will be required. For further information, consult the general
|
|
libvirt <a href="cgroups.html">cgroups documentation</a>.
|
|
</p>
|
|
|
|
<h2><a name="namespaces">Namespace requirements</a></h2>
|
|
|
|
<p>
|
|
In order to separate processes inside a container from those in the
|
|
primary "host" OS environment, the libvirt LXC driver requires that
|
|
certain kernel namespaces are compiled in. Libvirt currently requires
|
|
the 'mount', 'ipc', 'pid', and 'uts' namespaces to be available. If
|
|
separate network interfaces are desired, then the 'net' namespace is
|
|
required. In the near future, the 'user' namespace will optionally be
|
|
supported.
|
|
</p>
|
|
|
|
<p>
|
|
<strong>NOTE: In the absence of support for the 'user' namespace,
|
|
processes inside containers cannot be securely isolated from host
|
|
process without the use of a mandatory access control technology
|
|
such as SELinux or AppArmor.</strong>
|
|
</p>
|
|
|
|
<h2><a name="init">Default container setup</a></h2>
|
|
|
|
<h3><a name="cliargs">Command line arguments</a></h3>
|
|
|
|
<p>
|
|
When the container "init" process is started, it will typically
|
|
not be given any command line arguments (eg the equivalent of
|
|
the bootloader args visible in <code>/proc/cmdline</code>). If
|
|
any arguments are desired, then must be explicitly set in the
|
|
container XML configuration via one or more <code>initarg</code>
|
|
elements. For example, to run <code>systemd --unit emergency.service</code>
|
|
would use the following XML
|
|
</p>
|
|
|
|
<pre>
|
|
<os>
|
|
<type arch='x86_64'>exe</type>
|
|
<init>/bin/systemd</init>
|
|
<initarg>--unit</initarg>
|
|
<initarg>emergency.service</initarg>
|
|
</os>
|
|
</pre>
|
|
|
|
<h3><a name="envvars">Environment variables</a></h3>
|
|
|
|
<p>
|
|
When the container "init" process is started, it will be given several useful
|
|
environment variables. The following standard environment variables are mandated
|
|
by <a href="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">systemd container interface</a>
|
|
to be provided by all container technologies on Linux.
|
|
</p>
|
|
|
|
<dl>
|
|
<dt>container</dt>
|
|
<dd>The fixed string <code>libvirt-lxc</code> to identify libvirt as the creator</dd>
|
|
<dt>container_uuid</dt>
|
|
<dd>The UUID assigned to the container by libvirt</dd>
|
|
<dt>PATH</dt>
|
|
<dd>The fixed string <code>/bin:/usr/bin</code></dd>
|
|
<dt>TERM</dt>
|
|
<dd>The fixed string <code>linux</code></dd>
|
|
</dl>
|
|
|
|
<p>
|
|
In addition to the standard variables, the following libvirt specific
|
|
environment variables are also provided
|
|
</p>
|
|
|
|
<dl>
|
|
<dt>LIBVIRT_LXC_NAME</dt>
|
|
<dd>The name assigned to the container by libvirt</dd>
|
|
<dt>LIBVIRT_LXC_UUID</dt>
|
|
<dd>The UUID assigned to the container by libvirt</dd>
|
|
<dt>LIBVIRT_LXC_CMDLINE</dt>
|
|
<dd>The unparsed command line arguments specified in the container configuration.
|
|
Use of this is discouraged, in favour of passing arguments directly to the
|
|
container init process via the <code>initarg</code> config element.</dd>
|
|
</dl>
|
|
|
|
<h3><a name="fsmounts">Filesystem mounts</a></h3>
|
|
|
|
<p>
|
|
In the absence of any explicit configuration, the container will
|
|
inherit the host OS filesystem mounts. A number of mount points will
|
|
be made read only, or re-mounted with new instances to provide
|
|
container specific data. The following special mounts are setup
|
|
by libvirt
|
|
</p>
|
|
|
|
<ul>
|
|
<li><code>/dev</code> a new "tmpfs" pre-populated with authorized device nodes</li>
|
|
<li><code>/dev/pts</code> a new private "devpts" instance for console devices</li>
|
|
<li><code>/sys</code> the host "sysfs" instance remounted read-only</li>
|
|
<li><code>/proc</code> a new instance of the "proc" filesystem</li>
|
|
<li><code>/proc/sys</code> the host "/proc/sys" bind-mounted read-only</li>
|
|
<li><code>/sys/fs/selinux</code> the host "selinux" instance remounted read-only</li>
|
|
<li><code>/sys/fs/cgroup/NNNN</code> the host cgroups controllers bind-mounted to
|
|
only expose the sub-tree associated with the container</li>
|
|
<li><code>/proc/meminfo</code> a FUSE backed file reflecting memory limits of the container</li>
|
|
</ul>
|
|
|
|
|
|
<h3><a name="devnodes">Device nodes</a></h3>
|
|
|
|
<p>
|
|
The container init process will be started with <code>CAP_MKNOD</code>
|
|
capability removed and blocked from re-acquiring it. As such it will
|
|
not be able to create any device nodes in <code>/dev</code> or anywhere
|
|
else in its filesystems. Libvirt itself will take care of pre-populating
|
|
the <code>/dev</code> filesystem with any devices that the container
|
|
is authorized to use. The current devices that will be made available
|
|
to all containers are
|
|
</p>
|
|
|
|
<ul>
|
|
<li><code>/dev/zero</code></li>
|
|
<li><code>/dev/null</code></li>
|
|
<li><code>/dev/full</code></li>
|
|
<li><code>/dev/random</code></li>
|
|
<li><code>/dev/urandom</code></li>
|
|
<li><code>/dev/stdin</code> symlinked to <code>/proc/self/fd/0</code></li>
|
|
<li><code>/dev/stdout</code> symlinked to <code>/proc/self/fd/1</code></li>
|
|
<li><code>/dev/stderr</code> symlinked to <code>/proc/self/fd/2</code></li>
|
|
<li><code>/dev/fd</code> symlinked to <code>/proc/self/fd</code></li>
|
|
<li><code>/dev/ptmx</code> symlinked to <code>/dev/pts/ptmx</code></li>
|
|
<li><code>/dev/console</code> symlinked to <code>/dev/pts/0</code></li>
|
|
</ul>
|
|
|
|
<p>
|
|
In addition, for every console defined in the guest configuration,
|
|
a symlink will be created from <code>/dev/ttyN</code> symlinked to
|
|
the corresponding <code>/dev/pts/M</code> pseudo TTY device. The
|
|
first console will be <code>/dev/tty1</code>, with further consoles
|
|
numbered incrementally from there.
|
|
</p>
|
|
|
|
<p>
|
|
Further block or character devices will be made available to containers
|
|
depending on their configuration.
|
|
</p>
|
|
|
|
<!--
|
|
<h2>Container configuration</h2>
|
|
|
|
<h3>Init process</h3>
|
|
|
|
<h3>Console devices</h3>
|
|
|
|
<h3>Filesystem devices</h3>
|
|
|
|
<h3>Disk devices</h3>
|
|
|
|
<h3>Block devices</h3>
|
|
|
|
<h3>USB devices</h3>
|
|
|
|
<h3>Character devices</h3>
|
|
|
|
<h3>Network devices</h3>
|
|
-->
|
|
|
|
<h2>Container security</h2>
|
|
|
|
<h3>sVirt SELinux</h3>
|
|
|
|
<p>
|
|
In the absence of the "user" namespace being used, containers cannot
|
|
be considered secure against exploits of the host OS. The sVirt SELinux
|
|
driver provides a way to secure containers even when the "user" namespace
|
|
is not used. The cost is that writing a policy to allow execution of
|
|
arbitrary OS is not practical. The SELinux sVirt policy is typically
|
|
tailored to work with an simpler application confinement use case,
|
|
as provided by the "libvirt-sandbox" project.
|
|
</p>
|
|
|
|
<h3>Auditing</h3>
|
|
|
|
<p>
|
|
The LXC driver is integrated with libvirt's auditing subsystem, which
|
|
causes audit messages to be logged whenever there is an operation
|
|
performed against a container which has impact on host resources.
|
|
So for example, start/stop, device hotplug will all log audit messages
|
|
providing details about what action occurred and any resources
|
|
associated with it. There are the following 3 types of audit messages
|
|
</p>
|
|
|
|
<ul>
|
|
<li><code>VIRT_MACHINE_ID</code> - details of the SELinux process and
|
|
image security labels assigned to the container.</li>
|
|
<li><code>VIRT_CONTROL</code> - details of an action / operation
|
|
performed against a container. There are the following types of
|
|
operation
|
|
<ul>
|
|
<li><code>op=start</code> - a container has been started. Provides
|
|
the machine name, uuid and PID of the <code>libvirt_lxc</code>
|
|
controller process</li>
|
|
<li><code>op=init</code> - the init PID of the container has been
|
|
started. Provides the machine name, uuid and PID of the
|
|
<code>libvirt_lxc</code> controller process and PID of the
|
|
init process (in the host PID namespace)</li>
|
|
<li><code>op=stop</code> - a container has been stopped. Provides
|
|
the machine name, uuid</li>
|
|
</ul>
|
|
</li>
|
|
<li><code>VIRT_RESOURCE</code> - details of a host resource
|
|
associated with a container action.</li>
|
|
</ul>
|
|
|
|
<h3>Device access</h3>
|
|
|
|
<p>
|
|
All containers are launched with the CAP_MKNOD capability cleared
|
|
and removed from the bounding set. Libvirt will ensure that the
|
|
/dev filesystem is pre-populated with all devices that a container
|
|
is allowed to use. In addition, the cgroup "device" controller is
|
|
configured to block read/write/mknod from all devices except those
|
|
that a container is authorized to use.
|
|
</p>
|
|
|
|
<h2><a name="exconfig">Example configurations</a></h2>
|
|
|
|
<h3>Example config version 1</h3>
|
|
<p></p>
|
|
<pre>
|
|
<domain type='lxc'>
|
|
<name>vm1</name>
|
|
<memory>500000</memory>
|
|
<os>
|
|
<type>exe</type>
|
|
<init>/bin/sh</init>
|
|
</os>
|
|
<vcpu>1</vcpu>
|
|
<clock offset='utc'/>
|
|
<on_poweroff>destroy</on_poweroff>
|
|
<on_reboot>restart</on_reboot>
|
|
<on_crash>destroy</on_crash>
|
|
<devices>
|
|
<emulator>/usr/libexec/libvirt_lxc</emulator>
|
|
<interface type='network'>
|
|
<source network='default'/>
|
|
</interface>
|
|
<console type='pty' />
|
|
</devices>
|
|
</domain>
|
|
</pre>
|
|
|
|
<p>
|
|
In the <emulator> element, be sure you specify the correct path
|
|
to libvirt_lxc, if it does not live in /usr/libexec on your system.
|
|
</p>
|
|
|
|
<p>
|
|
The next example assumes there is a private root filesystem
|
|
(perhaps hand-crafted using busybox, or installed from media,
|
|
debootstrap, whatever) under /opt/vm-1-root:
|
|
</p>
|
|
<p></p>
|
|
<pre>
|
|
<domain type='lxc'>
|
|
<name>vm1</name>
|
|
<memory>32768</memory>
|
|
<os>
|
|
<type>exe</type>
|
|
<init>/init</init>
|
|
</os>
|
|
<vcpu>1</vcpu>
|
|
<clock offset='utc'/>
|
|
<on_poweroff>destroy</on_poweroff>
|
|
<on_reboot>restart</on_reboot>
|
|
<on_crash>destroy</on_crash>
|
|
<devices>
|
|
<emulator>/usr/libexec/libvirt_lxc</emulator>
|
|
<filesystem type='mount'>
|
|
<source dir='/opt/vm-1-root'/>
|
|
<target dir='/'/>
|
|
</filesystem>
|
|
<interface type='network'>
|
|
<source network='default'/>
|
|
</interface>
|
|
<console type='pty' />
|
|
</devices>
|
|
</domain>
|
|
</pre>
|
|
|
|
|
|
<h2><a name="usage">Container usage / management</a></h2>
|
|
|
|
<p>
|
|
As with any libvirt virtualization driver, LXC containers can be
|
|
managed via a wide variety of libvirt based tools. At the lowest
|
|
level the <code>virsh</code> command can be used to perform many
|
|
tasks, by passing the <code>-c lxc:///</code> argument. As an
|
|
alternative to repeating the URI with every command, the <code>LIBVIRT_DEFAULT_URI</code>
|
|
environment variable can be set to <code>lxc:///</code>. The
|
|
examples that follow outline some common operations with virsh
|
|
and LXC. For further details about usage of virsh consult its
|
|
manual page.
|
|
</p>
|
|
|
|
<h3><a name="usageSave">Defining (saving) container configuration></a></h3>
|
|
|
|
<p>
|
|
The <code>virsh define</code> command takes an XML configuration
|
|
document and loads it into libvirt, saving the configuration on disk
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// define myguest.xml
|
|
</pre>
|
|
|
|
<h3><a name="usageView">Viewing container configuration</a></h3>
|
|
|
|
<p>
|
|
The <code>virsh dumpxml</code> command can be used to view the
|
|
current XML configuration of a container. By default the XML
|
|
output reflects the current state of the container. If the
|
|
container is running, it is possible to explicitly request the
|
|
persistent configuration, instead of the current live configuration
|
|
using the <code>--inactive</code> flag
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// dumpxml myguest
|
|
</pre>
|
|
|
|
<h3><a name="usageStart">Starting containers</a></h3>
|
|
|
|
<p>
|
|
The <code>virsh start</code> command can be used to start a
|
|
container from a previously defined persistent configuration
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// start myguest
|
|
</pre>
|
|
|
|
<p>
|
|
It is also possible to start so called "transient" containers,
|
|
which do not require a persistent configuration to be saved
|
|
by libvirt, using the <code>virsh create</code> command.
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// create myguest.xml
|
|
</pre>
|
|
|
|
|
|
<h3><a name="usageStop">Stopping containers</a></h3>
|
|
|
|
<p>
|
|
The <code>virsh shutdown</code> command can be used
|
|
to request a graceful shutdown of the container. By default
|
|
this command will first attempt to send a message to the
|
|
init process via the <code>/dev/initctl</code> device node.
|
|
If no such device node exists, then it will send SIGTERM
|
|
to PID 1 inside the container.
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// shutdown myguest
|
|
</pre>
|
|
|
|
<p>
|
|
If the container does not respond to the graceful shutdown
|
|
request, it can be forceably stopped using the <code>virsh destroy</code>
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// destroy myguest
|
|
</pre>
|
|
|
|
|
|
<h3><a name="usageReboot">Rebooting a container</a></h3>
|
|
|
|
<p>
|
|
The <code>virsh reboot</code> command can be used
|
|
to request a graceful shutdown of the container. By default
|
|
this command will first attempt to send a message to the
|
|
init process via the <code>/dev/initctl</code> device node.
|
|
If no such device node exists, then it will send SIGHUP
|
|
to PID 1 inside the container.
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// reboot myguest
|
|
</pre>
|
|
|
|
<h3><a name="usageDelete">Undefining (deleting) a container configuration</a></h3>
|
|
|
|
<p>
|
|
The <code>virsh undefine</code> command can be used to delete the
|
|
persistent configuration of a container. If the guest is currently
|
|
running, this will turn it into a "transient" guest.
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// undefine myguest
|
|
</pre>
|
|
|
|
<h3><a name="usageConnect">Connecting to a container console</a></h3>
|
|
|
|
<p>
|
|
The <code>virsh console</code> command can be used to connect
|
|
to the text console associated with a container. If the container
|
|
has been configured with multiple console devices, then the
|
|
<code>--devname</code> argument can be used to choose the
|
|
console to connect to
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// console myguest
|
|
</pre>
|
|
|
|
<h3><a name="usageEnter">Running commands in a container</a></h3>
|
|
|
|
<p>
|
|
The <code>virsh lxc-enter-namespace</code> command can be used
|
|
to enter the namespaces and security context of a container
|
|
and then execute an arbitrary command.
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// lxc-enter-namespace myguest -- /bin/ls -al /dev
|
|
</pre>
|
|
|
|
<h3><a name="usageTop">Monitoring container utilization</a></h3>
|
|
|
|
<p>
|
|
The <code>virt-top</code> command can be used to monitor the
|
|
activity and resource utilization of all containers on a
|
|
host
|
|
</p>
|
|
|
|
<pre>
|
|
# virt-top -c lxc:///
|
|
</pre>
|
|
|
|
</body>
|
|
</html>
|