mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2024-12-29 09:05:25 +00:00
788 lines
27 KiB
XML
788 lines
27 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. If the guest configuration declares a
|
|
<a href="formatdomain.html#elementsOSContainer">UID or GID mapping</a>,
|
|
the 'user' namespace will be enabled to apply these. <strong>A suitably
|
|
configured UID/GID mapping is a pre-requisite to making containers
|
|
secure, in the absence of sVirt confinement.</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>
|
|
<dt>HOME</dt>
|
|
<dd>The fixed string <code>/</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>
|
|
Since /dev/ttyN and /dev/console are linked to the pts devices. The
|
|
tty device of login program is pts device. The pam module securetty
|
|
may prevent root user from logging in container. If you want root
|
|
user to log in container successfully, add the pts device to the file
|
|
/etc/securetty of container.
|
|
</p>
|
|
|
|
<p>
|
|
Further block or character devices will be made available to containers
|
|
depending on their configuration.
|
|
</p>
|
|
|
|
<h2><a name="security">Security considerations</a></h2>
|
|
|
|
<p>
|
|
The libvirt LXC driver is fairly flexible in how it can be configured,
|
|
and as such does not enforce a requirement for strict security
|
|
separation between a container and the host. This allows it to be used
|
|
in scenarios where only resource control capabilities are important,
|
|
and resource sharing is desired. Applications wishing to ensure secure
|
|
isolation between a container and the host must ensure that they are
|
|
writing a suitable configuration.
|
|
</p>
|
|
|
|
<h3><a name="securenetworking">Network isolation</a></h3>
|
|
|
|
<p>
|
|
If the guest configuration does not list any network interfaces,
|
|
the <code>network</code> namespace will not be activated, and thus
|
|
the container will see all the host's network interfaces. This will
|
|
allow apps in the container to bind to/connect from TCP/UDP addresses
|
|
and ports from the host OS. It also allows applications to access
|
|
UNIX domain sockets associated with the host OS, which are in the
|
|
abstract namespace. If access to UNIX domains sockets in the abstract
|
|
namespace is not wanted, then applications should set the
|
|
<code><privnet/></code> flag in the
|
|
<code><features>....</features></code> element.
|
|
</p>
|
|
|
|
<h3><a name="securefs">Filesystem isolation</a></h3>
|
|
|
|
<p>
|
|
If the guest configuration does not list any filesystems, then
|
|
the container will be set up with a root filesystem that matches
|
|
the host's root filesystem. As noted earlier, only a few locations
|
|
such as <code>/dev</code>, <code>/proc</code> and <code>/sys</code>
|
|
will be altered. This means that, in the absence of restrictions
|
|
from sVirt, a process running as user/group N:M inside the container
|
|
will be able to access almost exactly the same files as a process
|
|
running as user/group N:M in the host.
|
|
</p>
|
|
|
|
<p>
|
|
There are multiple options for restricting this. It is possible to
|
|
simply map the existing root filesystem through to the container in
|
|
read-only mode. Alternatively a completely separate root filesystem
|
|
can be configured for the guest. In both cases, further sub-mounts
|
|
can be applied to customize the content that is made visible. Note
|
|
that in the absence of sVirt controls, it is still possible for the
|
|
root user in a container to unmount any sub-mounts applied. The user
|
|
namespace feature can also be used to restrict access to files based
|
|
on the UID/GID mappings.
|
|
</p>
|
|
|
|
<p>
|
|
Sharing the host filesystem tree, also allows applications to access
|
|
UNIX domains sockets associated with the host OS, which are in the
|
|
filesystem namespaces. It should be noted that a number of init
|
|
systems including at least <code>systemd</code> and <code>upstart</code>
|
|
have UNIX domain socket which are used to control their operation.
|
|
Thus, if the directory/filesystem holding their UNIX domain socket is
|
|
exposed to the container, it will be possible for a user in the container
|
|
to invoke operations on the init service in the same way it could if
|
|
outside the container. This also applies to other applications in the
|
|
host which use UNIX domain sockets in the filesystem, such as DBus,
|
|
Libvirtd, and many more. If this is not desired, then applications
|
|
should either specify the UID/GID mapping in the configuration to
|
|
enable user namespaces and thus block access to the UNIX domain socket
|
|
based on permissions, or should ensure the relevant directories have
|
|
a bind mount to hide them. This is particularly important for the
|
|
<code>/run</code> or <code>/var/run</code> directories.
|
|
</p>
|
|
|
|
|
|
<h3><a name="secureusers">User and group isolation</a></h3>
|
|
|
|
<p>
|
|
If the guest configuration does not list any ID mapping, then the
|
|
user and group IDs used inside the container will match those used
|
|
outside the container. In addition, the capabilities associated with
|
|
a process in the container will infer the same privileges they would
|
|
for a process in the host. This has obvious implications for security,
|
|
since a root user inside the container will be able to access any
|
|
file owned by root that is visible to the container, and perform more
|
|
or less any privileged kernel operation. In the absence of additional
|
|
protection from sVirt, this means that the root user inside a container
|
|
is effectively as powerful as the root user in the host. There is no
|
|
security isolation of the root user.
|
|
</p>
|
|
|
|
<p>
|
|
The ID mapping facility was introduced to allow for stricter control
|
|
over the privileges of users inside the container. It allows apps to
|
|
define rules such as "user ID 0 in the container maps to user ID 1000
|
|
in the host". In addition the privileges associated with capabilities
|
|
are somewhat reduced so that they cannot be used to escape from the
|
|
container environment. A full description of user namespaces is outside
|
|
the scope of this document, however LWN has
|
|
<a href="https://lwn.net/Articles/532593/">a good write-up on the topic</a>.
|
|
From the libvirt point of view, the key thing to remember is that defining
|
|
an ID mapping for users and groups in the container XML configuration
|
|
causes libvirt to activate the user namespace feature.
|
|
</p>
|
|
|
|
|
|
<h2><a name="activation">Systemd Socket Activation Integration</a></h2>
|
|
|
|
<p>
|
|
The libvirt LXC driver provides the ability to pass across pre-opened file
|
|
descriptors when starting LXC guests. This allows for libvirt LXC to support
|
|
systemd's <a href="http://0pointer.de/blog/projects/socket-activated-containers.html">socket
|
|
activation capability</a>, where an incoming client connection
|
|
in the host OS will trigger the startup of a container, which runs another
|
|
copy of systemd which gets passed the server socket, and then activates the
|
|
actual service handler in the container.
|
|
</p>
|
|
|
|
<p>
|
|
Let us assume that you already have a LXC guest created, running
|
|
a systemd instance as PID 1 inside the container, which has an
|
|
SSHD service configured. The goal is to automatically activate
|
|
the container when the first SSH connection is made. The first
|
|
step is to create a couple of unit files for the host OS systemd
|
|
instance. The <code>/etc/systemd/system/mycontainer.service</code>
|
|
unit file specifies how systemd will start the libvirt LXC container
|
|
</p>
|
|
|
|
<pre>
|
|
[Unit]
|
|
Description=My little container
|
|
|
|
[Service]
|
|
ExecStart=/usr/bin/virsh -c lxc:/// start --pass-fds 3 mycontainer
|
|
ExecStop=/usr/bin/virsh -c lxc:/// destroy mycontainer
|
|
Type=oneshot
|
|
RemainAfterExit=yes
|
|
KillMode=none
|
|
</pre>
|
|
|
|
<p>
|
|
The <code>--pass-fds 3</code> argument specifies that the file
|
|
descriptor number 3 that <code>virsh</code> inherits from systemd,
|
|
is to be passed into the container. Since <code>virsh</code> will
|
|
exit immediately after starting the container, the <code>RemainAfterExit</code>
|
|
and <code>KillMode</code> settings must be altered from their defaults.
|
|
</p>
|
|
|
|
<p>
|
|
Next, the <code>/etc/systemd/system/mycontainer.socket</code> unit
|
|
file is created to get the host systemd to listen on port 23 for
|
|
TCP connections. When this unit file is activated by the first
|
|
incoming connection, it will cause the <code>mycontainer.service</code>
|
|
unit to be activated with the FD corresponding to the listening TCP
|
|
socket passed in as FD 3.
|
|
</p>
|
|
|
|
<pre>
|
|
[Unit]
|
|
Description=The SSH socket of my little container
|
|
|
|
[Socket]
|
|
ListenStream=23
|
|
</pre>
|
|
|
|
<p>
|
|
Port 23 was picked here so that the container doesn't conflict
|
|
with the host's SSH which is on the normal port 22. That's it
|
|
in terms of host side configuration.
|
|
</p>
|
|
|
|
<p>
|
|
Inside the container, the <code>/etc/systemd/system/sshd.socket</code>
|
|
unit file must be created
|
|
</p>
|
|
|
|
<pre>
|
|
[Unit]
|
|
Description=SSH Socket for Per-Connection Servers
|
|
|
|
[Socket]
|
|
ListenStream=23
|
|
Accept=yes
|
|
</pre>
|
|
|
|
<p>
|
|
The <code>ListenStream</code> value listed in this unit file, must
|
|
match the value used in the host file. When systemd in the container
|
|
receives the pre-opened FD from libvirt during container startup, it
|
|
looks at the <code>ListenStream</code> values to figure out which
|
|
FD to give to which service. The actual service to start is defined
|
|
by a correspondingly named <code>/etc/systemd/system/sshd@.service</code>
|
|
</p>
|
|
|
|
<pre>
|
|
[Unit]
|
|
Description=SSH Per-Connection Server for %I
|
|
|
|
[Service]
|
|
ExecStart=-/usr/sbin/sshd -i
|
|
StandardInput=socket
|
|
</pre>
|
|
|
|
<p>
|
|
Finally, make sure this SSH service is set to start on boot of the container,
|
|
by running the following command inside the container:
|
|
</p>
|
|
|
|
<pre>
|
|
# mkdir -p /etc/systemd/system/sockets.target.wants/
|
|
# ln -s /etc/systemd/system/sshd.socket /etc/systemd/system/sockets.target.wants/
|
|
</pre>
|
|
|
|
<p>
|
|
This example shows how to activate the container based on an incoming
|
|
SSH connection. If the container was also configured to have an httpd
|
|
service, it may be desirable to activate it upon either an httpd or a
|
|
sshd connection attempt. In this case, the <code>mycontainer.socket</code>
|
|
file in the host would simply list multiple socket ports. Inside the
|
|
container a separate <code>xxxxx.socket</code> file would need to be
|
|
created for each service, with a corresponding <code>ListenStream</code>
|
|
value set.
|
|
</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="capabilities">Altering the available capabilities</a></h2>
|
|
|
|
<p>
|
|
By default the libvirt LXC driver drops some capabilities among which CAP_MKNOD.
|
|
However <span class="since">since 1.2.6</span> libvirt can be told to keep or
|
|
drop some capabilities using a domain configuration like the following:
|
|
</p>
|
|
<pre>
|
|
...
|
|
<features>
|
|
<capabilities policy='default'>
|
|
<mknod state='on'/>
|
|
<sys_chroot state='off'/>
|
|
</capabilities>
|
|
</features>
|
|
...
|
|
</pre>
|
|
<p>
|
|
The capabilities children elements are named after the capabilities as defined in
|
|
<code>man 7 capabilities</code>. An <code>off</code> state tells libvirt to drop the
|
|
capability, while an <code>on</code> state will force to keep the capability even though
|
|
this one is dropped by default.
|
|
</p>
|
|
<p>
|
|
The <code>policy</code> attribute can be one of <code>default</code>, <code>allow</code>
|
|
or <code>deny</code>. It defines the default rules for capabilities: either keep the
|
|
default behavior that is dropping a few selected capabilities, or keep all capabilities
|
|
or drop all capabilities. The interest of <code>allow</code> and <code>deny</code> is that
|
|
they guarantee that all capabilities will be kept (or removed) even if new ones are added
|
|
later.
|
|
</p>
|
|
<p>
|
|
The following example, drops all capabilities but CAP_MKNOD:
|
|
</p>
|
|
<pre>
|
|
...
|
|
<features>
|
|
<capabilities policy='deny'>
|
|
<mknod state='on'/>
|
|
</capabilities>
|
|
</features>
|
|
...
|
|
</pre>
|
|
<p>
|
|
Note that allowing capabilities that are normally dropped by default can seriously
|
|
affect the security of the container and the host.
|
|
</p>
|
|
|
|
<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 forcibly 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.
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// console myguest
|
|
</pre>
|
|
|
|
<p>
|
|
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.
|
|
In LXC, multiple consoles will be named
|
|
as 'console0', 'console1', 'console2', etc.
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// console myguest --devname console1
|
|
</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>
|
|
|
|
<h3><a name="usageConvert">Converting LXC container configuration</a></h3>
|
|
|
|
<p>
|
|
The <code>virsh domxml-from-native</code> command can be used to convert
|
|
most of the LXC container configuration into a domain XML fragment
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh -c lxc:/// domxml-from-native lxc-tools /var/lib/lxc/myguest/config
|
|
</pre>
|
|
|
|
<p>
|
|
This conversion has some limitations due to the fact that the
|
|
domxml-from-native command output has to be independent of the host. Here
|
|
are a few things to take care of before converting:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
Replace the fstab file referenced by <tt>lxc.mount</tt> by the corresponding
|
|
lxc.mount.entry lines.
|
|
</li>
|
|
<li>
|
|
Replace all relative sizes of tmpfs mount entries to absolute sizes. Also
|
|
make sure that tmpfs entries all have a size option (default is 50%).
|
|
</li>
|
|
<li>
|
|
Define <tt>lxc.cgroup.memory.limit_in_bytes</tt> to properly limit the memory
|
|
available to the container. The conversion will use 64MiB as the default.
|
|
</li>
|
|
</ul>
|
|
|
|
</body>
|
|
</html>
|