path: root/doc/lxc.conf.sgml.in

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lxc: linux Container library

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Authors:
Daniel Lezcano <dlezcano at fr.ibm.com>

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<refentry>

  <docinfo><date>@LXC_GENERATE_DATE@</date></docinfo>

  <refmeta>
    <refentrytitle>lxc.conf</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>lxc.conf</refname>

    <refpurpose>
      linux container configuration file
    </refpurpose>
  </refnamediv>

  <refsect1>
    <title>Description</title>

    <para>
      The linux containers (<command>lxc</command>) are always created
      before being used. This creation defines a set of system
      resources to be virtualized / isolated when a process is using
      the container. By default, the pids, sysv ipc and mount points
      are virtualized and isolated. The other system resources are
      shared across containers, until they are explicitly defined in
      the configuration file. For example, if there is no network
      configuration, the network will be shared between the creator of
      the container and the container itself, but if the network is
      specified, a new network stack is created for the container and
      the container can no longer use the network of its ancestor.
    </para>

    <para>
      The configuration file defines the different system resources to
      be assigned for the container. At present, the utsname, the
      network, the mount points, the root file system and the control
      groups are supported.
    </para>

    <para>
      Each option in the configuration file has the form <command>key
      = value</command> fitting in one line. The '#' character means
      the line is a comment.
    </para>

    <refsect2>
      <title>Architecture</title>
      <para>
	Allows to set the architecture for the container. For example,
	set a 32bits architecture for a container running 32bits
	binaries on a 64bits host. That fix the container scripts
	which rely on the architecture to do some work like
	downloading the packages.
      </para>

      <variablelist>
	<varlistentry>
	  <term>
	    <option>lxc.arch</option>
	  </term>
	  <listitem>
	    <para>
	      Specify the architecture for the container.
	    </para>
	    <para>
	      Valid options are
	      <option>x86</option>,
	      <option>i686</option>,
	      <option>x86_64</option>,
	      <option>amd64</option>
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>

    </refsect2>

    <refsect2>
      <title>Hostname</title>
      <para>
	The utsname section defines the hostname to be set for the
	container. That means the container can set its own hostname
	without changing the one from the system. That makes the
	hostname private for the container.
      </para>
      <variablelist>
	<varlistentry>
	  <term>
	    <option>lxc.utsname</option>
	  </term>
	  <listitem>
	    <para>
	      specify the hostname for the container
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </refsect2>

    <refsect2>
      <title>Network</title>
      <para>
	The network section defines how the network is virtualized in
	the container. The network virtualization acts at layer
	two. In order to use the network virtualization, parameters
	must be specified to define the network interfaces of the
	container. Several virtual interfaces can be assigned and used
	in a container even if the system has only one physical
	network interface.
      </para>
      <variablelist>
	<varlistentry>
	  <term>
	    <option>lxc.network.type</option>
	  </term>
	  <listitem>
	    <para>
	      specify what kind of network virtualization to be used
	      for the container. Each time
	      a <option>lxc.network.type</option> field is found a new
	      round of network configuration begins. In this way,
	      several network virtualization types can be specified
	      for the same container, as well as assigning several
	      network interfaces for one container. The different
	      virtualization types can be:
	    </para>

	    <para>
	      <option>empty:</option> will create only the loopback
	      interface.
	    </para>

	    <para>
	      <option>veth:</option> a peer network device is created
	      with one side assigned to the container and the other
	      side is attached to a bridge specified by
	      the <option>lxc.network.link</option>. If the bridge is
	      not specified, then the veth pair device will be created
	      but not attached to any bridge. Otherwise, the bridge
	      has to be setup before on the
	      system, <command>lxc</command> won't handle any
	      configuration outside of the container.  By
	      default <command>lxc</command> choose a name for the
	      network device belonging to the outside of the
	      container, this name is handled
	      by <command>lxc</command>, but if you wish to handle
	      this name yourself, you can tell <command>lxc</command>
	      to set a specific name with
	      the <option>lxc.network.veth.pair</option> option.
	    </para>

	    <para>
	      <option>vlan:</option> a vlan interface is linked with
	      the interface specified by
	      the <option>lxc.network.link</option> and assigned to
	      the container. The vlan identifier is specified with the
	      option <option>lxc.network.vlan.id</option>.
	    </para>

	    <para>
	      <option>macvlan:</option> a macvlan interface is linked
	      with the interface specified by
	      the <option>lxc.network.link</option> and assigned to
	      the container.
	      <option>lxc.network.macvlan.mode</option> specifies the
	      mode the macvlan will use to communicate between
	      different macvlan on the same upper device. The accepted
	      modes are <option>private</option>, the device never
	      communicates with any other device on the same upper_dev (default),
	      <option>vepa</option>, the new Virtual Ethernet Port
	      Aggregator (VEPA) mode, it assumes that the adjacent
	      bridge returns all frames where both source and
	      destination are local to the macvlan port, i.e. the
	      bridge is set up as a reflective relay.  Broadcast
	      frames coming in from the upper_dev get flooded to all
	      macvlan interfaces in VEPA mode, local frames are not
	      delivered locallay, or <option>bridge</option>, it
	      provides the behavior of a simple bridge between
	      different macvlan interfaces on the same port. Frames
	      from one interface to another one get delivered directly
	      and are not sent out externally. Broadcast frames get
	      flooded to all other bridge ports and to the external
	      interface, but when they come back from a reflective
	      relay, we don't deliver them again.  Since we know all
	      the MAC addresses, the macvlan bridge mode does not
	      require learning or STP like the bridge module does.
	    </para>

	    <para>
	      <option>phys:</option> an already existing interface
	      specified by the <option>lxc.network.link</option> is
	      assigned to the container.
	    </para>
	  </listitem>
	  </varlistentry>

	<varlistentry>
	  <term>
	    <option>lxc.network.flags</option>
	  </term>
	  <listitem>
	    <para>
	      specify an action to do for the
	      network.
	    </para>
	    
	    <para><option>up:</option> activates the interface.
	    </para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>
	    <option>lxc.network.link</option>
	  </term>
	  <listitem>
	    <para>
	      specify the interface to be used for real network
	      traffic.
	    </para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>
	    <option>lxc.network.name</option>
	  </term>
	  <listitem>
	    <para>
	      the interface name is dynamically allocated, but if
	      another name is needed because the configuration files
	      being used by the container use a generic name,
	      eg. eth0, this option will rename the interface in the
	      container.
	    </para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>
	    <option>lxc.network.hwaddr</option>
	  </term>
	  <listitem>
	    <para>
	      the interface mac address is dynamically allocated by
	      default to the virtual interface, but in some cases,
	      this is needed to resolve a mac address conflict or to
	      always have the same link-local ipv6 address
	    </para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>
	    <option>lxc.network.ipv4</option>
	  </term>
	  <listitem>
	    <para>
	      specify the ipv4 address to assign to the virtualized
	      interface. Several lines specify several ipv4 addresses.
	      The address is in format x.y.z.t/m,
	      eg. 192.168.1.123/24.
	    </para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>
	    <option>lxc.network.ipv6</option>
	  </term>
	  <listitem>
	    <para>
	      specify the ipv6 address to assign to the virtualized
	      interface. Several lines specify several ipv6 addresses.
	      The address is in format x::y/m,
	      eg. 2003:db8:1:0:214:1234:fe0b:3596/64
	    </para>
	  </listitem>
	</varlistentry>

      </variablelist>

    </refsect2>

    <refsect2>
      <title>New pseudo tty instance (devpts)</title>
      <para>
	For stricter isolation the container can have its own private
	instance of the pseudo tty.
      </para>
      <variablelist>
	<varlistentry>
	  <term>
	    <option>lxc.pts</option>
	  </term>
	  <listitem>
	    <para>
	      If set, the container will have a new pseudo tty
	      instance, making this private to it. The value specifies
              the maximum number of pseudo ttys allowed for a pts
              instance (this limitation is not implemented yet).
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </refsect2>

    <refsect2>
      <title>Container system console</title>
      <para>
	If the container is configured with a root filesystem and the
	inittab file is setup to use the console, you may want to specify
	where goes the output of this console.
      </para>
      <variablelist>
	<varlistentry>
	  <term>
	    <option>lxc.console</option>
	  </term>
	  <listitem>
	    <para>
	      Specify a path to a file where the console output will
	      be written.
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </refsect2>

    <refsect2>
      <title>Console through the ttys</title>
      <para>
	If the container is configured with a root filesystem and the
	inittab file is setup to launch a getty on the ttys. This
	option will specify the number of ttys to be available for the
	container. The number of getty in the inittab file of the
	container should not be greater than the number of ttys
	specified in this configuration file, otherwise the excess
	getty sessions will die and respawn indefinitly giving
	annoying messages on the console.
      </para>
      <variablelist>
	<varlistentry>
	  <term>
	    <option>lxc.tty</option>
	  </term>
	  <listitem>
	    <para>
	      Specify the number of tty to make available to the
	      container.
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </refsect2>

    <refsect2>
      <title>Mount points</title>
      <para>
	The mount points section specifies the different places to be
	mounted. These mount points will be private to the container
	and won't be visible by the processes running outside of the
	container. This is useful to mount /etc, /var or /home for
	examples.
      </para>
      <variablelist>
	<varlistentry>
	  <term>
	    <option>lxc.mount</option>
	  </term>
	  <listitem>
	    <para>
	      specify a file location in
	      the <filename>fstab</filename> format, containing the
	      mount informations. If the rootfs is an image file or a
	      device block and the fstab is used to mount a point
	      somewhere in this rootfs, the path of the rootfs mount
	      point should be prefixed with the
	      <filename>@LXCROOTFSMOUNT@</filename> default path or
	      the value of <option>lxc.rootfs.mount</option> if
	      specified.
	    </para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>
	    <option>lxc.mount.entry</option>
	  </term>
	  <listitem>
	    <para>
	      specify a mount point corresponding to a line in the
	      fstab format.
	    </para>
	  </listitem>
	</varlistentry>

      </variablelist>
    </refsect2>

    <refsect2>
      <title>Root file system</title>
      <para>
	The root file system of the container can be different than that
	of the host system.
      </para>
      <variablelist>
	<varlistentry>
	  <term>
	    <option>lxc.rootfs</option>
	  </term>
	  <listitem>
	    <para>
	      specify the root file system for the container. It can
	      be an image file, a directory or a block device. If not
	      specified, the container shares its root file system
	      with the host.
	    </para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>
	    <option>lxc.rootfs.mount</option>
	  </term>
	  <listitem>
	    <para>
	      where to recursively bind <option>lxc.rootfs</option>
	      before pivoting.  This is to ensure success of the
	      <citerefentry>
		<refentrytitle><command>pivot_root</command></refentrytitle>
		<manvolnum>8</manvolnum>
	      </citerefentry>
	      syscall.  Any directory suffices, the default should
	      generally work.
	    </para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>
	    <option>lxc.pivotdir</option>
	  </term>
	  <listitem>
	    <para>
	      where to pivot the original root file system under
	      <option>lxc.rootfs</option>, specified relatively to
	      that.  The default is <filename>mnt</filename>.
	      It is created if necessary, and also removed after
	      unmounting everything from it during container setup.
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </refsect2>

    <refsect2>
      <title>Control group</title>
      <para>
	The control group section contains the configuration for the
	different subsystem. <command>lxc</command> does not check the
	correctness of the subsystem name. This has the disadvantage
	of not detecting configuration errors until the container is
	started, but has the advantage of permitting any future
	subsystem.
      </para>
      <variablelist>
	<varlistentry>
	  <term>
	    <option>lxc.cgroup.[subsystem name]</option>
	  </term>
	  <listitem>
	    <para>
	      specify the control group value to be set.  The
	      subsystem name is the literal name of the control group
	      subsystem.  The permitted names and the syntax of their
	      values is not dictated by LXC, instead it depends on the
	      features of the Linux kernel running at the time the
	      container is started,
	      eg. <option>lxc.cgroup.cpuset.cpus</option>
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </refsect2>

    <refsect2>
      <title>Capabilities</title>
      <para>
	The capabilities can be dropped in the container if this one
	is run as root.
      </para>
      <variablelist>
	<varlistentry>
	  <term>
	    <option>lxc.cap.drop</option>
	  </term>
	  <listitem>
	    <para>
	      Specify the capability to be dropped in the container. A
	      single line defining several capabilities with a space
	      separation is allowed. The format is the lower case of
	      the capability definition without the "CAP_" prefix,
	      eg. CAP_SYS_MODULE should be specified as
	      sys_module. See
	      <citerefentry>
		<refentrytitle><command>capabilities</command></refentrytitle>
		<manvolnum>7</manvolnum>
	      </citerefentry>,
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </refsect2>

  </refsect1>

  <refsect1>
    <title>Examples</title>
      <para>
	In addition to the few examples given below, you will find
	some other examples of configuration file in @DOCDIR@/examples
      </para>
    <refsect2>
      <title>Network</title>
      <para>This configuration sets up a container to use a veth pair
	device with one side plugged to a bridge br0 (which has been
	configured before on the system by the administrator). The
	virtual network device visible in the container is renamed to
	eth0.</para>
      <programlisting>
	lxc.utsname = myhostname
	lxc.network.type = veth
	lxc.network.flags = up
	lxc.network.link = br0
	lxc.network.name = eth0
	lxc.network.hwaddr = 4a:49:43:49:79:bf
	lxc.network.ipv4 = 1.2.3.5/24
	lxc.network.ipv6 = 2003:db8:1:0:214:1234:fe0b:3597
      </programlisting>
    </refsect2>

    <refsect2>
      <title>Control group</title>
      <para>This configuration will setup several control groups for
      the application, cpuset.cpus restricts usage of the defined cpu,
      cpus.share prioritize the control group, devices.allow makes
      usable the specified devices.</para>
      <programlisting>
	lxc.cgroup.cpuset.cpus = 0,1
	lxc.cgroup.cpu.shares = 1234
	lxc.cgroup.devices.deny = a
	lxc.cgroup.devices.allow = c 1:3 rw
	lxc.cgroup.devices.allow = b 8:0 rw
      </programlisting>
    </refsect2>

    <refsect2>
      <title>Complex configuration</title>
      <para>This example show a complex configuration making a complex
      network stack, using the control groups, setting a new hostname,
      mounting some locations and a changing root file system.</para>
      <programlisting>
	lxc.utsname = complex
	lxc.network.type = veth
	lxc.network.flags = up
	lxc.network.link = br0
	lxc.network.hwaddr = 4a:49:43:49:79:bf
	lxc.network.ipv4 = 1.2.3.5/24
	lxc.network.ipv6 = 2003:db8:1:0:214:1234:fe0b:3597
	lxc.network.ipv6 = 2003:db8:1:0:214:5432:feab:3588
	lxc.network.type = macvlan
	lxc.network.flags = up
	lxc.network.link = eth0
	lxc.network.hwaddr = 4a:49:43:49:79:bd
	lxc.network.ipv4 = 1.2.3.4/24
	lxc.network.ipv4 = 192.168.10.125/24
	lxc.network.ipv6 = 2003:db8:1:0:214:1234:fe0b:3596
	lxc.network.type = phys
	lxc.network.flags = up
	lxc.network.link = dummy0
	lxc.network.hwaddr = 4a:49:43:49:79:ff
	lxc.network.ipv4 = 1.2.3.6/24
	lxc.network.ipv6 = 2003:db8:1:0:214:1234:fe0b:3297
	lxc.cgroup.cpuset.cpus = 0,1
	lxc.cgroup.cpu.shares = 1234
	lxc.cgroup.devices.deny = a
	lxc.cgroup.devices.allow = c 1:3 rw
	lxc.cgroup.devices.allow = b 8:0 rw
	lxc.mount = /etc/fstab.complex
	lxc.mount.entry = /lib /root/myrootfs/lib none ro,bind 0 0
	lxc.rootfs = /mnt/rootfs.complex
	lxc.cap.drop = sys_module mknod setuid net_raw
	lxc.cap.drop = mac_override
      </programlisting>
    </refsect2>

  </refsect1>

  <refsect1>
    <title>See Also</title>
    <simpara>    
      <citerefentry>
	<refentrytitle><command>chroot</command></refentrytitle>
	<manvolnum>1</manvolnum>
      </citerefentry>,

      <citerefentry>
	<refentrytitle><command>pivot_root</command></refentrytitle>
	<manvolnum>8</manvolnum>
      </citerefentry>,

      <citerefentry>
	<refentrytitle><filename>fstab</filename></refentrytitle>
	<manvolnum>5</manvolnum>
      </citerefentry>

    </simpara>
  </refsect1>
  
  &seealso;

  <refsect1>
    <title>Author</title>
    <para>Daniel Lezcano <email>daniel.lezcano@free.fr</email></para>
  </refsect1>
  
</refentry>

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