image Modify for kvm , openstack

mindong

　　4. Modifying images
　　guestfish.......................................................................................................................11
　　guestmount...................................................................................................................12
　　virt-*tools.....................................................................................................................13
　　Loopdevices, kpartx, network block devices.................................................................. 14
　　Onceyou have obtained a virtual machine image, you may want to make some changes
　　toit before uploading it to the OpenStack Image service. Here we describe severaltools
　　availablethat allow you to modify images.
　　Warning
　　Donot attempt to use these tools to modify an image that is attached to a
　　runningvirtual machine. These tools are designed to only modify images that
　　arenot currently running.
　　guestfish
　　Theguestfish program is a tool from the libguestfs project that allows you to modify the
　　filesinside of a virtual machine image.
　　Notethat guestfish doesn't mount the image directly into the local filesystem.Instead, it
　　providesyou with a shell interface that allows you to view, edit, and delete files.Many of
　　theguestfish commands (e.g., touch, chmod, rm) are similar totraditional bash commands.
　　Example guestfish session
　　Weoften need to modify a virtual machine image to remove any traces of the MAC
　　addressthat was assigned to the virtual network interface card when the image was
　　firstcreated, since the MAC address will be different when it boots the next time.In this
　　example,we show how we can use guestfish to remove references to the old MAC address
　　bydeleting the /etc/udev/rules.d/70-persistent-net.rules file and removing
　　theHWADDR line from the /etc/sysconfig/network-scripts/ifcfg-eth0 file.
　　Assumewe have a CentOS qcow2 image called centos63_desktop.img. We would
　　mountthe image in read-write mode by doing, as root:
　　#guestfish --rw -a centos63_desktop.img
　　Welcometo guestfish, the libguestfs filesystem interactive shell for
　　editingvirtual machine filesystems.
　　Type:'help' for help on commands
　　'man'to read the manual
　　'quit'to quit the shell
　　><fs>
　　Thisstarts a guestfish session. Note that the guestfish prompt looks like a fish: ><fs>.
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　　Wemust first use the run command at the guestfish prompt before we can doanything
　　else.This will launch a virtual machine, which will be used to perform all of thefile
　　manipulations.
　　><fs>run
　　Wecan now view the filesystems in the image using the list-filesystems command:
　　><fs>list-filesystems
　　/dev/vda1:ext4
　　/dev/vg_centosbase/lv_root:ext4
　　/dev/vg_centosbase/lv_swap:swap
　　Weneed to mount the logical volume that contains the root partition:
　　><fs>mount /dev/vg_centosbase/lv_root /
　　Next,we want to delete a file. We can use the rm guestfish command, whichworks the
　　sameway it does in a traditional shell.
　　><fs>rm /etc/udev/rules.d/70-persistent-net.rules
　　Wewant to edit the ifcfg-eth0 file to remove the HWADDR line. The edit commandwill
　　copythe file to the host, invoke your editor, and then copy the file back.
　　><fs>edit /etc/sysconfig/network-scripts/ifcfg-eth0
　　Le'ssay we want to modify this image to load the 8021q kernel at boot time. We'llneed to
　　createan executable script in the /etc/sysconfig/modules/ directory. We can use the
　　touchguestfish command to create an empty file,use the edit command to edit it, and use
　　thechmod command to make it executable.
　　><fs>touch /etc/sysconfig/modules/8021q.modules
　　><fs>edit /etc/sysconfig/modules/8021q.modules
　　Weadd the following line to the file and save it
　　modprobe8021q
　　Thenwe set to executable:
　　><fs>chmod 0755 /etc/sysconfig/modules/8021q.modules
　　We'redone, so we can exit using the exit command:
　　><fs>exit
　　Going further with guestfish
　　Thereis an enormous amount of functionality in guestfish and a full treatment isbeyond
　　thescope of this document. Instead, we recommend that you read the guestfs-recipes
　　documentationpage for a sense of what is possible with these tools.
　　guestmount
　　Forsome types of changes, you may find it easier to mount the image's filesystemdirectly
　　inthe guest. The guestmount program, also from the libguestfs project,allows you to do
　　so.
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　　Forexample, to mount the root partition from our centos63_desktop.qcow2 image to
　　/mnt,we can do:
　　#guestmount -a centos63_desktop.qcow2 -m /dev/vg_centosbase/lv_root --rw /mnt
　　Ifwe didn't know in advance what the mountpoint is in the guest, we could use the-
　　i(inspect)flag to tell guestmount to automatically determine what mount point to use:
　　#guestmount -a centos63_desktop.qcow2 -i --rw /mnt
　　Oncemounted, we could do things like list the installed packages using rpm:
　　#rpm -qa --dbpath /mnt/var/lib/rpm
　　Oncedone, we unmount:
　　#umount /mnt
　　virt-* tools
　　Thelibguestfs project has a number of other useful tools,including:
　　 virt-df for displaying free space inside of an image.
　　 virt-resize for resizing an image.
　　 virt-sysprep for preparing an image for distribution(e.g., delete SSH host keys, remove
　　MACaddress info, remove user accounts).
　　 virt-sparsify for making an image sparse
　　 virt-p2v for converting a physical machine to an imagethat runs on KVM
　　 virt-v2v for converting Xen and VMWare images to KVMimages
　　Resize an image
　　Here'sa simple of example of how to use virt-resize to resize an image. Assumewe have a
　　16GBWindows image in qcow2 format that we want to resize to 50GB. First, we use virtfilesystems
　　toidentify the partitions:
　　#virt-filesystems --long --parts --blkdevs -h -a /data/images/win2012.qcow2
　　NameType MBR Size Parent
　　/dev/sda1partition 07 350M /dev/sda
　　/dev/sda2partition 07 16G /dev/sda
　　/dev/sdadevice - 16G -
　　Inthis case, it's the /dev/sda2 partition that we want to resize. We create a newqcow2
　　imageand use the virt-resize command to write a resized copy of the originalinto the new
　　image
　　#qemu-img create -f qcow2 /data/images/win2012-50gb.qcw2 50G
　　#virt-resize --expand /dev/sda2 /data/images/win2012.qcow2 /data/images/
　　win2012-50gb.qcow2
　　Examining/data/images/win2012.qcow2 ...
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　　**********
　　Summaryof changes:
　　/dev/sda1:This partition will be left alone.
　　/dev/sda2:This partition will be resized from 15.7G to 49.7G. The
　　filesystemntfs on /dev/sda2 will be expanded using the
　　'ntfsresize'method.
　　**********
　　Settingup initial partition table on /data/images/win2012-50gb.qcow2 ...
　　Copying/dev/sda1 ...
　　100%###################################################################
　　00:00
　　Copying/dev/sda2 ...
　　100%###################################################################
　　00:00
　　Expanding/dev/sda2 using the 'ntfsresize' method ...
　　Resizeoperation completed with no errors. Before deleting the old
　　disk,carefully check that the resized disk boots and works correctly.
　　Loop devices, kpartx, network block devices
　　Ifyou don't have access to libguestfs, you can mount image file systems directlyin the host
　　usingloop devices, kpartx, and network block devices.
　　Warning
　　Mountinguntrusted guest images using the tools described in this section is a
　　securityrisk, always use libguestfs tools such as guestfish and guestmount if you
　　haveaccess to them. See Areminder why you should never mount guest disk
　　imageson the host OS byDaniel Berrangé for more details.
　　Mounting a raw image (without LVM)
　　Ifyou have a raw virtual machine image that is not using LVM to manage itspartitions.
　　First,use the losetup command to find an unused loop device.
　　#losetup -f
　　/dev/loop0
　　Inthis example, /dev/loop0 is free. Associate a loop device with the raw image:
　　#losetup /dev/loop0 fedora17.img
　　Ifthe image only has a single partition, you can mount the loop device directly:
　　#mount /dev/loop0 /mnt
　　Ifthe image has multiple partitions, use kpartx to expose the partitionsas separate devices
　　(e.g.,/dev/mapper/loop0p1), then mount the partition that corresponds to the rootfile
　　system:
　　#kpartx -av /dev/loop0
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　　Ifthe image has, say three partitions (/boot, /, /swap), there should be one newdevice
　　createdper partition:
　　$ls -l /dev/mapper/loop0p*
　　brw-rw----1 root disk 43, 49 2012-03-05 15:32 /dev/mapper/loop0p1
　　brw-rw----1 root disk 43, 50 2012-03-05 15:32 /dev/mapper/loop0p2
　　brw-rw----1 root disk 43, 51 2012-03-05 15:32 /dev/mapper/loop0p3
　　Tomount the second partition, as root:
　　#mkdir /mnt/image
　　#mount /dev/mapper/loop0p2 /mnt
　　Onceyou're done, to clean up:
　　#umount /mnt
　　#kpartx -d /dev/loop0
　　#losetup -d /dev/loop0
　　Mounting a raw image (with LVM)
　　Ifyour partitions are managed with LVM, use losetup and kpartx as in the previous
　　exampleto expose the partitions to the host:
　　#losetup -f
　　/dev/loop0
　　#losetup /dev/loop0 rhel62.img
　　#kpartx -av /dev/loop0
　　Next,you need to use the vgscan command to identify the LVM volume groups andthen
　　vgchangeto expose the volumes as devices:
　　#vgscan
　　Readingall physical volumes. This may take a while...
　　Foundvolume group "vg_rhel62x8664" using metadata type lvm2
　　#vgchange -ay
　　2logical volume(s) in volume group "vg_rhel62x8664" now active
　　#mount /dev/vg_rhel62x8664/lv_root /mnt
　　Cleanup when you're done:
　　#umount /mnt
　　#vgchange -an vg_rhel62x8664
　　#kpartx -d /dev/loop0
　　#losetup -d /dev/loop0
　　Mounting a qcow2 image (without LVM)
　　Youneed the nbd (network block device) kernel module loaded to mount qcow2 images.
　　Thiswill load it with support for 16 block devices, which is fine for our purposes.As root:
　　#modprobe nbd max_part=16
　　Assumingthe first block device (/dev/nbd0) is not currently in use, we can expose thedisk
　　partitionsusing the qemu-nbd and partprobe commands. As root:
　　#qemu-nbd -c /dev/nbd0 image.qcow2
　　#partprobe /dev/nbd0
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　　Ifthe image has, say three partitions (/boot, /, /swap), there should be one newdevice
　　createdper partition:
　　$ls -l /dev/nbd3*
　　brw-rw----1 root disk 43, 48 2012-03-05 15:32 /dev/nbd0
　　brw-rw----1 root disk 43, 49 2012-03-05 15:32 /dev/nbd0p1
　　brw-rw----1 root disk 43, 50 2012-03-05 15:32 /dev/nbd0p2
　　brw-rw----1 root disk 43, 51 2012-03-05 15:32 /dev/nbd0p3
　　Note
　　Ifthe network block device you selected was already in use, the initial qemunbd
　　commandwill fail silently, and the /dev/nbd3p{1,2,3} device files will
　　notbe created.
　　Ifthe image partitions are not managed with LVM, they can be mounted directly:
　　#mkdir /mnt/image
　　#mount /dev/nbd3p2 /mnt
　　Whenyou're done, clean up:
　　#umount /mnt
　　#qemu-nbd -d /dev/g nbd0
　　Mounting a qcow2 image (with LVM)
　　Ifthe image partitions are managed with LVM, after you use qemu-nbd and partprobe,
　　youmust use vgscan and vgchange -ay in order to expose the LVMpartitions as devices
　　thatcan be mounted:
　　#modprobe nbd max_part=16
　　#qemu-nbd -c /dev/nbd0 image.qcow2
　　#partprobe /dev/nbd0# vgscan
　　Readingall physical volumes. This may take a while...
　　Foundvolume group "vg_rhel62x8664" using metadata type lvm2
　　#vgchange -ay
　　2logical volume(s) in volume group "vg_rhel62x8664" now active
　　#mount /dev/vg_rhel62x8664/lv_root /mnt
　　Whenyou're done, clean up:
　　#umount /mnt
　　#vgchange -an vg_rhel62x8664
　　#qemu-nbd -d /dev/nbd0
　　

　　

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