Linux容器技术-lxc创建虚拟机的执行过程分析

1. lxc介绍 容器是一种轻量级的虚拟化技术，与qemu/kvm、VMware、Xen等完全的虚拟化方案相比，LXC更像是加强的“chroot”，因为LXC不但没有没有对硬件设备进行仿真，而且可以与主机共享一模一样的操作系统，所以LXC与solaris的zones和BSD的jails相比，更具优势。目前，有两个比较方便的管理容器的用户空间的工具：libvirt和lxc。libvirt通过"lxc:///"像管理其他虚拟机驱动一样管理lxc虚拟机。另一个是与libvirt完全独立的LXC，它定义了一些列的命令，可以更灵活的管理和使用lxc。下面，将以LXC为例来介绍lxc的使用。2 LXC的安装和使用（1）LXC的安装

sudo apt-get install lxc

该命令将自动安装LXC依赖的其他软件：cgroup-lite, lvm2, and debootstrap。如果想使用libvirt来实现lxc的管理，还需要安装 libvirt-bin和libvirt-lxc。（2）LXC主机端的配置文件介绍在使用LXC之前，首先对其配置文件进行简单的介绍，以便使大家能更好的理解LXC的工作原理。 a. /etc/lxc/lxc.conf 容器默认的配置文件，如果在创建lxc容器的时候不指定配置文件，将默认使用这个配置文件。主要针对网络以及命名空间的配置。还有一些其他的配置例子可以在/usr/share/doc/lxc/examples/目录下找到。 b. /usr/lib/lxc/templates/ 该目录下保存了当前LXC支持的各种发行版的linux的模板配置文件，目前主要有: lxc-Ubuntu, lxc-Fedora,lxc-openSUSE,lxc-debian,lxc-busybox,lxc-sshd,lxc-cloud-ubuntu等。 c. /var/lib/lxc 每个容器的实例存放在这个目录下。 d. /var/cache/lxc 容器实例的cache，当用户创建一种类型的实例后，将会在此目录下cache，再次创建时将不需要从网上下载，直接采用cache的版本，加速了容器实例的创建过程。
下面来分析下lxc-ubuntu的创建过程（详见最下面的注释说明）：

#！/bin/bash
#
# template script for generating ubuntu container for LXC
#
# This script consolidates and extends the existing lxc ubuntu scripts
#
# Author: Wilhelm Meier <wilhelm.meier@fh-kl.de>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2, as
# published by the Free Software Foundation.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
#
set -e ##如果命令带非零值返回,立即退出
if [ -r /etc/default/lxc ]; then
. /etc/default/lxc #导入一些环境变量
fi
configure_ubuntu（）
{
rootfs=$1
hostname=$2
release=$3
# configure the network using the dhcp
cat <<EOF > $rootfs/etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces（5）.
# The loopback network interface
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp
EOF
# set the hostname
cat <<EOF > $rootfs/etc/hostname
$hostname
EOF
# set minimal hosts
cat <<EOF > $rootfs/etc/hosts
127.0.0.1 localhost
127.0.1.1 $hostname
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
EOF
if [ ！ -f $rootfs/etc/init/container-detect.conf ]; then
# suppress log level output for udev
sed -i "s/="err"/=0/" $rootfs/etc/udev/udev.conf
# remove jobs for consoles 5 and 6 since we only create 4 consoles in
# this template
rm -f $rootfs/etc/init/tty{5,6}.conf
fi
if [ -z "$bindhome" ]; then
chroot $rootfs useradd --create-home -s /bin/bash ubuntu
echo "ubuntu:ubuntu" | chroot $rootfs chpasswd
fi
return 0
}
# finish setting up the user in the container by injecting ssh key and
# adding sudo group membership.
# passed-in user is either "ubuntu" or the user to bind in from host.
finalize_user（）
{
user=$1
sudo_version=$（chroot $rootfs dpkg-query -W -f="${Version}" sudo）
if chroot $rootfs dpkg --compare-versions $sudo_version gt "1.8.3p1-1"; then
groups="sudo"
else
groups="sudo admin"
fi
for group in $groups; do
chroot $rootfs groupadd --system $group >/dev/null 2>&1 || true
chroot $rootfs adduser ${user} $group >/dev/null 2>&1 || true
done
if [ -n "$auth_key" -a -f "$auth_key" ]; then
u_path="/home/${user}/.ssh"
root_u_path="$rootfs/$u_path"
mkdir -p $root_u_path
cp $auth_key "$root_u_path/authorized_keys"
chroot $rootfs chown -R ${user}: "$u_path"
echo "Inserted SSH public key from $auth_key into /home/${user}/.ssh/authorized_keys"
fi
return 0
}
write_sourceslist（）
{
# $1 => path to the rootfs
# $2 => architecture we want to add
# $3 => whether to use the multi-arch syntax or not
case $2 in
amd64|i386）
MIRROR=${MIRROR:-http://archive.ubuntu.com/ubuntu}
SECURITY_MIRROR=${SECURITY_MIRROR:-http://security.ubuntu.com/ubuntu}
;;
*）
MIRROR=${MIRROR:-http://ports.ubuntu.com/ubuntu-ports}
SECURITY_MIRROR=${SECURITY_MIRROR:-http://ports.ubuntu.com/ubuntu-ports}
;;
esac
if [ -n "$3" ]; then
cat >> "$1/etc/apt/sources.list" << EOF
deb [arch=$2] $MIRROR ${release} main restricted universe multiverse
deb [arch=$2] $MIRROR ${release}-updates main restricted universe multiverse
deb [arch=$2] $SECURITY_MIRROR ${release}-security main restricted universe multiverse
EOF
else
cat >> "$1/etc/apt/sources.list" << EOF
deb $MIRROR ${release} main restricted universe multiverse
deb $MIRROR ${release}-updates main restricted universe multiverse
deb $SECURITY_MIRROR ${release}-security main restricted universe multiverse
EOF
fi
}
download_ubuntu（）
{
cache=$1
arch=$2
release=$3
packages=vim,ssh
echo "installing packages: $packages"
# check the mini ubuntu was not already downloaded
mkdir -p "$cache/partial-$arch"
if [ $？ -ne 0 ]; then
echo "Failed to create "$cache/partial-$arch" directory"
return 1
fi
# download a mini ubuntu into a cache
echo "Downloading ubuntu $release minimal ..."
if [ -n "$（which qemu-debootstrap）" ]; then
qemu-debootstrap --verbose --components=main,universe --arch=$arch --include=$packages $release $cache/partial-$arch $MIRROR
else
debootstrap --verbose --components=main,universe --arch=$arch --include=$packages $release $cache/partial-$arch $MIRROR ##在这里下载制定的linux发行版
fi
if [ $？ -ne 0 ]; then
echo "Failed to download the rootfs, aborting."
return 1
fi
# Serge isn"t sure whether we should avoid doing this when
# $release == `distro-info -d`
echo "Installing updates"
> $cache/partial-$arch/etc/apt/sources.list
write_sourceslist $cache/partial-$arch/ $arch ##下载完成后，修改source.lst文件，升级和安装软件做准备
##改变系统的根目录，执行update，因为，要用新的source.lst

chroot "$1/partial-${arch}" apt-get update
if [ $？ -ne 0 ]; then
echo "Failed to update the apt cache"
return 1
fi
cat > "$1/partial-${arch}"/usr/sbin/policy-rc.d << EOF
#！/bin/sh
exit 101
EOF
chmod +x "$1/partial-${arch}"/usr/sbin/policy-rc.d
lxc-unshare -s MOUNT -- chroot "$1/partial-${arch}" apt-get dist-upgrade -y
ret=$？
rm -f "$1/partial-${arch}"/usr/sbin/policy-rc.d
if [ $ret -ne 0 ]; then
echo "Failed to upgrade the cache"
return 1
fi
mv "$1/partial-$arch" "$1/rootfs-$arch"
echo "Download complete"
return 0
}
copy_ubuntu（）
{
cache=$1
arch=$2
rootfs=$3
# make a local copy of the miniubuntu
echo "Copying rootfs to $rootfs ..."
mkdir -p $rootfs
#使用rsync进行镜像的备份，实际相当于镜像的拷贝
rsync -a $cache/rootfs-$arch/ $rootfs/ || return 1
return 0
}
install_ubuntu（）
{
rootfs=$1
release=$2
flushcache=$3