Virtualization

nói về máy ảo

621 28 Virtualization Copyright © 2009 by The McGraw-Hill Companies. Click here for terms of use. 622 Linux Administration: A Beginner’s Guide V irtualization technologies have been around in various forms for a long time. This technology has been especially pervasive and more commonplace in recent years. This recent pervasiveness has been due to many factors: necessity, reduction in cost, new innovations, simpler implementations, etc. Simply put, virtualization is making something look like something else. Technically speaking, virtualization refers to the abstraction of computer resources. This abstraction can be achieved in various ways: via software, hardware, or a mix of both. In this chapter we discuss some abstraction concepts and techniques that are com- mon in Linux platforms today. WHY VIRTUALIZE? As mentioned in the beginning of this chapter, virtualization has become quite common- place in recent times. And one of the reasons for this has been the necessity for it. The necessity for virtualization has been borne out of different reasons, such as firms and individuals being more environmentally conscious/sensitive (ten virtual machines running on one server have a smaller carbon footprint than ten physical machines serv- ing the same purpose), the need to save costs on hardware (ten virtual machines are, or should be, cheaper than ten physical machines), the need to increase return on invest- ment on existing hardware or increased server utilization, improved server and applica- tion availability and reduced server downtimes (achieved by virtualization platforms that support live host migration), better cross-platform support (for example, virtualiza- tion makes it possible to run a Microsoft Windows operating system within Linux or a Linux-based operating system within Microsoft Windows), etc. Virtualization provides a great environment for testing and debugging new applica- tions and/or operating systems, since virtual machines can be wiped clean quickly or restored to a known state. In the same vein, virtual machines can be used to test and run legacy or old software. Another reason why virtualization has become so commonplace is due to the ease with which it can be implemented today. If “ceteris” is “paribus” (if other things are equal), it is possible for a typical Linux system administrator to set up an environment for machine virtualization in less than ten minutes. Virtualization Concepts In this section we try to lay the groundwork for common virtualization concepts and terminologies that appear in the rest of this chapter and that are used in everyday discus- sions about virtualization: ▼ Guest OS (VM) This is also known as a virtual machine (VM). It is the operat- ing system that is being virtualized. ■ Host OS This is the system or host on which the guest operating systems (VM) run. 623 Chapter 28: Virtualization ■ Hypervisor (VMM) A hypervisor is also referred to as the virtual machine monitor (VMM). A hypervisor provides a CPU-like interface to virtual machines or applications. The hypervisor is at the heart of the entire virtualization concept. It can be implemented with support built natively into the hardware, purely in software, or a combination of both. ■ Hardware emulation This is when software is used to emulate the instruc- tion set of different CPU architectures. The resulting VMs that run in this type of environment typically run slowly, due to the sheer amount of processing required for the emulation. An example virtualization solution that provides hardware emulation is Bochs (http://bochs.sourceforge.net). ■ Full virtualization This is also known as bare-metal or native virtualization. The host CPU(s) has extended instructions that allow the VMs to directly inter- act with it. Guest operating systems that can use this type of virtualization do not need any modification. As a matter of fact, the VMs do not know—and need not know—that they are running in a virtual platform. Hardware virtual machine (HVM) is a vendor-neutral term used to describe hypervisors that sup- port full virtualization. In full virtualization, the virtual hardware seen by the guest OS is functionally similar to the hardware the host OS is running on. Examples of vendor CPUs and platforms that support the required extended CPU instructions are Intel Virtualization Technology (Intel VT), AMD Secure Virtual Machine (SVM/AMD-V), and IBM System z series. Examples of virtualization platforms that support full virtualization are kernel- based virtual machines (KVM), Xen, IBM’s z/VM, VMware, Virtualbox, and Microsoft’s Hyper-V. ▲ Paravirtualization This is a virtualization technique. Essentially, this class of virtualization is done via software. Guest operating systems that use this type of virtualization typically need to be modified. To be precise, the kernel of the guest OS (VM) needs to be modified to run in this environment. This required modification is the one big disadvantage of paravirtualization. This type of vir- tualization is currently relatively faster than its full virtualization counterparts. Examples of virtualization platforms that support full virtualization are Xen and UML (User Mode Linux). VIRTUALIZATION IMPLEMENTATIONS There are many virtualization implementations that run on Linux-based systems (and Windows-based systems). Some are more mature than others. Some are easier to set up and manage than others, but the objective remains pretty much the same across the board. We’ll briefly look at some of the more popular virtualization implementations in this section. 624 Linux Administration: A Beginner’s Guide QEMU QEMU falls into the class of virtualization called machine emulators. It can emulate a completely different machine architecture from the one on which it is running (e.g., emulating an ARM architecture on an x86 platform). The code for QEMU is mature and well tested, and as such, it is relied upon by many other virtualization platforms and projects. Xen This is a popular virtualization implementation, with a large community following. The code base is quite mature and well tested. It supports both the full and paravirtualization methods of virtualization. Xen is considered a high-performing virtualization platform. It is commercially backed by Citrix Systems, and the Xen open source interest is main- tained at www.xen.org. User-Mode Linux (UML) This is one of the earliest virtualization implementations for Linux. As the name implies, virtualization is implemented entirely in user space. This singular attribute gives it the advantage of being quite secure, since its components run in the context of a regular user. Running entirely in user space also gives this implementation the disadvantage of not being very fast. More information about UML can be found at http://user-mode-linux .sourceforge.net. Kernel-based Virtual Machines (KVM) This is the first official Linux virtualization implementation to be implemented in the kernel. It currently supports only full virtualization. KVM is discussed in more detail later on in this chapter. VMware This is one of the earliest and most well-known mainstream commercial virtualization implementations. It offers great cross-platform support, excellent user and management interface, and great performance. There are several VMware products families designed to cater to various needs (from desktop needs all the way to enterprise needs). Some ver- sions of VMware are free (e.g., VMware Server), and some are purely commercial (e.g., VMware ESX Server, VMware Workstation, etc.). Virtualbox This is a popular virtualization platform. It is well known for its ease of use and nice user interface. It has great cross-platform support. It supports both full and paravirtualization 625 Chapter 28: Virtualization virtualization techniques. There are two versions of Virtualbox: a purely commercial ver- sion and an open source edition, which is free for personal and educational use. Hyper-V This is Microsoft’s virtualization implementation. It currently can only be used on hard- ware that supports full virtualization (i.e., Intel VT and AMD-V processors). It has a great management interface and is well integrated into the Windows Server 2008 operat- ing system. KERNEL-BASED VIRTUAL MACHINES (KVM) Kernel-based Virtual Machines (aka KVM) is the official Linux answer and contribu- tion to the virtualization space. KVM works by turning the Linux kernel into a hyper- visor. Current stable implementations of KVM are supported on the x86 platforms that support virtualization CPU extensions (like the ones provided in Intel-VT and AMD-V lines). Because KVM is implemented right in the Linux kernel, it has great support across a wide variety of Linux distros. The main difference across the different distros is prob- ably the virtual machine management tools and user space tools that have been built around the specific implementation. However, if one chooses to go with a bare-bones KVM setup, it is possible to use the same set of instructions on any Linux distro. The /proc/cpuinfo pseudo file system entry provides details about the running CPU on a Linux system. Among other things, the entry shows the flags/extensions that the running CPU supports. On an Intel platform, the flag that shows support for full hardware-based virtualiza- tion is the vmx flag. To check if an Intel processor has support for vmx, we could grep for the desired flag in /proc/cpuinfo, like so: [root@intel-serverA ~]# grep -i "vmx" /proc/cpuinfo flags : fpu pae mce cx8 apic <OUTPUT TRUNCATED> vmx The presence of vmx in the previous sample output shows that necessary CPU exten- sions are in place on the Intel processor. On an AMD platform, the flag that shows support for full hardware-based virtualiza- tion is the Secure Virtual Machine (svm) flag. To check if an Intel processor has support for svm, we could grep for the desired flag in /proc/cpuinfo, like so: [root@amd-serverA ~]# grep color -i svm /proc/cpuinfo flags : fpu vme de pse 3dnowext <OUTPUT TRUNCATED> svm The presence of svm in the previous sample output shows that necessary CPU exten- sions are in place on the AMD processor. 626 Linux Administration: A Beginner’s Guide KVM Example As mentioned earlier, KVM has great cross-platform/distro support. In this following section, we will look at a sample KVM implementation on the Fedora distribution of Linux. We will be using a set of tools that are based on the Libvirt C library. In particu- lar, we will be using the “Virtual Machine Manager” (virt-manager) application tool kit. virt-manager is a desktop user interface for managing virtual machines. It com- prises both full-blown graphical user interface (GUI) front-ends and command-line utilities. In this example, we will use the “Virt Install” tool (virt-install). virt-install is a command-line tool that provides an easy way to provision virtual machines. It also provides an application programming interface (API) to the virt-manager application for its graphical VM creation wizard. The specifications on our sample host system are ▼ Hardware supports full virtualization (specifically, AMD-V) ■ 4 gigabytes (GB) of RAM ■ Sufficiently free space on the host OS ▲ Host OS is running Fedora flavor of Linux For our sample virtualization environment, our objectives are ▼ Use the built-in KVM virtualization platform. ■ Set up a guest OS (VM) running a Fedora distribution of Linux. We will install Fedora using the install media in the DVD drive (/dev/sr0) of the host system. ■ Allocate a total of 10GB of disk space to the VM. ▲ Allocate 1GB RAM to the VM. We will use the following steps to achieve our objectives: 1. Use Yum to install the “Virtualization” package group. This package group com- prises the python-virtinst, kvm, qemu, virt-manager, and virt-viewer packages. Type [root@serverA ~]# yum groupinstall 'Virtualization' 2. Start the libvirtd service. Type [root@serverA ~]# service libvirtd start Starting libvirtd daemon: [ OK ] 627 Chapter 28: Virtualization 3. Use the chkconfig utility to make sure that the libvirtd service starts up automatically during the next system boot. Type [root@serverA ~]# chkconfig libvirtd on 4. Use the virsh utility to make sure that virtualization is enabled and running properly on the system. Type [root@serverA ~]# virsh -c qemu:///system list Id Name State As long as the previous output does not return any errors, we are fine. 5. On our sample server, we will store all the files pertaining to each VM under their own folder, using the virtual machine name as the parent folder name. So, for our sample VM with the name fedora-VM, we will begin by creating the directory structure that will house the VM. Type [root@serverA ~]# mkdir -p /home/vms/fedora-VM/ 6. We will use the virt-install utility that comes with the python-virtinst package to set up the virtual machine. The virt-install utility will run you through a quick setup wizard by asking a series of questions at the console. Launch virt-install by running [root@serverA ~]# virt-install hvm 7. We will set the name of our virtual machine (VM) to fedora-VM. What is the name of your virtual machine? fedora-VM 8. We will allocate 1GB, or 1000 megabytes (MB), of RAM to the VM. How much RAM should be allocated (in megabytes)? 1000 9. We will store the disk image under the /home/vms/fedora-VM/ directory and name the virtual disk fedora-VM-disk. What would you like to use as the disk (file path)? \ /home/vms/fedora-VM/fedora-VM-disk.img 10. Specify the virtual disk size to be 10GB when prompted. How large would you like the disk (/home/vms/fedora-VM/fedora-VM-disk) to be (in gigabytes)? 10 11. We will enable graphics support for the VM. Would you like to enable graphics support? (yes or no) yes 628 Linux Administration: A Beginner’s Guide 12. The physical optical drive device on our sample server is at /dev/sr0. We will specify this as the virtual CD device. What is the virtual CD image, CD device or install location? \ /dev/sr0 13. The newly configured VM should start up immediately in the “Virt Viewer” window. The VM will attempt to boot from the install media in the optical drive referenced by /dev/sr0. A window similar to the one shown here will open. 14. From here on, you can continue the installation as if you were installing on a regular machine. That’s it! Setting Up KVM in Ubuntu/Debian We had mentioned early on that one main difference between the virtualization implementations on the various Linux distros is in the management tools built around the virtualization solution. 629 Chapter 28: Virtualization The KVM virtualization that was set up earlier was done using the manage- ment tools (virt-manager, ZENworks Virtual Machine Management, etc.) that were designed to work seamlessly on Fedora, Red Hat Enterprise Linux (RHEL), and Centos platforms. Here, we will run through a quick and dirty setup of KVM vir- tualization that should work with little modification on any Linux distro. NOTE Libvirt and virt-manager have been ported for use on the newest versions of the Ubuntu Linux distro. Virt-manager can be easily installed with yyang@ubuntu-serverA:~$ sudo apt-get install virt-manager. Specifically, we will look at how to set up KVM in a Debian-based distro, like Ubuntu. The processor on our sample Ubuntu server supports the neces- sary CPU extensions. We will be installing on a computer with an Intel-VT–based processor. The target virtual machine will be a desktop version of Ubuntu and will be installed using the ISO image downloaded from http://releases.ubuntu.com/ releases/8.04/ubuntu-8.04-desktop-i386.iso. 1. Install the KVM and QEMU packages. On the Ubuntu server, type yyang@ubuntu-server:~$ sudo apt-get -y install kvm qemu 2. Manually load the kvm-intel module. Type yyang@ubuntu-server:~$ sudo modprobe kvm-intel NOTE Loading the kvm-intel module will also automatically load the required kvm module. On an AMD-based system, the required module is instead called kvm-amd. 3. We are going to run KVM as a regular user, so we need to add our sample user (yyang) to the kvm system group. Type yyang@ubuntu-server:~$ sudo adduser yyang kvm 4. Log out of the system and log back in as the user yyang so that the new group membership can take effect. 5. Create a folder in the user’s home directory to store the virtual machine, and change into that directory. Type yyang@ubuntu-server:~$ mkdir -p /home/yyang/vms/ubuntu-VM yyang@ubuntu-server:~$ cd /home/yyang/vms/ubuntu-VM 630 Linux Administration: A Beginner’s Guide 6. We will use the qemu-img utility to create a disk image for the virtual machine. The image will be 10GB in size. The file that will hold the virtual disk will be named “disk.img.” Type yyang@ubuntu-server:~/vms/ubuntu-VM$ qemu-img create disk.img -f qcow2 10G TIP The -f option specified with the qemu-img command is used to specify the disk image format. Here we use the -qcow2 format. This format offers space-saving options by not allocating the entire disk space specified up front. Instead, a small file is created, which grows as data is written to the virtual disk image. Another interesting virtual image disk format is the -vmdk option, which allows the creation of virtual disks that are compatible with VMware virtual machines. 7. Once the virtual disk image is created, we can fire up the installer for the VM by passing the necessary options to the kvm directly. The command to do this is yyang@ubuntu-server:~/vms/ubuntu-VM$ kvm -m 1024 \ -cdrom ubuntu-8.04-desktop-i386.iso \ -boot d disk.img NOTE The options that were passed to the kvm command are -m Specifies the amount of memory to allocate to the VM. In this case, we specified 1024MB, or 1GB. -cdrom Specifies the virtual CD-ROM device. In this case, we point to the ISO image that was downloaded earlier and saved under the current working directory. -boot d Specifies the boot device. In this case, “d” means CD-ROM. Other options are floppy (a), hard disk (c), and network (n). disk.img Specifies the raw hard disk image. This is the virtual disk that was created earlier using qemu-img. TIP Due to some issues with the graphical boot screen found on some installers, you may have to add the -no-kvm switch to the kvm command used to start the installation of the operating system into the VM. 8. The newly configured VM should start up immediately in the QEMU win- dow. The VM will attempt to boot from the ISO image specified by the -cdrom option. A window similar to the one shown here will open. [...]... Numerous virtualization technologies and implementations exist today Some of them have been around much longer than others, but the ideas and needs remain almost the same Virtualization is obviously not a panacea for every information technology problem, but its use and value is also too great to be ignored 631 632 Linux Administration: A Beginner’s Guide We had a high-level walkthrough of virtualization. .. problem, but its use and value is also too great to be ignored 631 632 Linux Administration: A Beginner’s Guide We had a high-level walkthrough of virtualization and common virtualization concepts in this chapter We looked at common virtualization offerings in the Linux world We paid particular attention to the KVM platform because of its native and complete integration into the Linux kernel Finally,...Chapter 28: 9 Virtualization From here on, you can continue the installation as if you were installing on a regular machine 10 Once the operating system has been installed into the VM, you can boot the virtual machine... KVM The first example used the “Virtual Machine Manager” toolset, which is based on the Libvirt library The second example demonstrated setting up and using KVM in other Linux distros that don’t use the Virtualization Manager toolset