Qmeu-img create VM

Document directory

•  
• Qemu-IMG basic commands
• Increase or decrease the image size
• Snapshots

Qmeu-img create virtual machine (create virtual machine, virtual machine snapshot) Use Qmeu-img Manage Virtual Machine Disk Images (create virtual machines and Virtual Machine snapshots)

The core of a virtual machine is a disk image, which can be understood as the disk of a virtual machine, which contains important files such as the operating system and driver of the virtual machine. This document describes how to create a VM.

Create a virtual machine image

 

Two steps are required to run a VM on a host:

Step 1: create a virtual machine image

qemu-img create -f raw /images/vm1.raw 8G

The image created by qmeu-img is a sparse file. That is to say, the newly created file does not have 8 GB, And it will gradually increase with the increase of data until 8 GB.

 

Step 2: Start the VM

kvm /imges/vm1.raw

Running result: the system prompts that the bootable device cannot be found because the image does not contain any content.

 

Use qemu-img to manage Images Qemu-img basic commands

 

The previous section describes how to use qemu-img to create an image. This section describes the powerful features of qemu-img in image management.

Qemu-img has many commands, including the following commonly used commands. Of course, you know qemu-img-h.

info

View image information

create

Create an image

check

Check image

convert

Format of the converted image, (raw, qcow ......)

snapshot

Manage image snapshots

rebase

Create a new image based on an existing image

resize

Increase or decrease the image size

  Create an image

 

qemu-img create -f <fmt> -o <options> <fname> <size>

Example:

qemu-img create -f raw -o size=4G /images/vm2.raw

 

Hzgatt @ hzgatt :~ /Images $LlTotal 0-rw-r -- r -- 1 hzgatt 4.0g June 29 14:11 vm2.rawhzgatt @ hzgatt :~ /Images $Ll-STotal 00-RW-r -- 1 hzgatt 4.0g June 29 14:11 vm2.raw

 

hzgatt@hzgatt:~/images$ qemu-img info vm2.raw image: vm2.rawfile format: rawvirtual size: 4.0G (4294967296 bytes)disk size: 0

 

Although the file size in LS is 4 GB, the disk size is actually 0. This is a sparse file.

 

 

Conversion

Convert an image file to another format. The formats supported by qemu-IMG can be viewed in the last line of qemu-IMG-H.

Supported formats: vvfat vpc vmdk vdi sheepdog rbd raw host_cdrom host_floppy host_device file qed qcow2 qcow parallels nbd dmg tftp ftps ftp https http cow cloop bochs blkverify blkdebug

 

Conversion command:

qemu-img convert -c -f fmt -O out_fmt -o options fname out_fname

 

-C: compression is adopted. Only qcow and qcow2 are supported.

-F: the format of the source image, which is automatically detected and therefore omitted.

-O Target Image Format

-O other options

Fname: source file

Out_fname: converted file

Example:

hzgatt@hzgatt:~/images$ qemu-img convert -c -O qcow2 vm2.raw vm2.qcow2

 

Hzgatt @ hzgatt :~ /Images $Ll-STotal 136 K 0-RW-r -- 1 hzgatt 5.0g June 29 13:55 vm1.raw136k-RW-r -- 1 hzgatt 193 K June 29 14:22 vm2.qcow2 0-RW-r -- r -- 1 hzgatt 4.0g June 29 14:11 vm2.raw

hzgatt@hzgatt:~/images$ qemu-img info vm2.qcow2 image: vm2.qcow2file format: qcow2virtual size: 4.0G (4294967296 bytes)disk size: 136Kcluster_size: 65536

 

If you want to see which-o options are supported by the format to be converted, you can add-o at the end of the command?

hzgatt@hzgatt:~/images$ qemu-img convert -c -O qcow2 vm2.raw vm2.qcow2 -o ?Supported options:size             Virtual disk sizebacking_file     File name of a base imagebacking_fmt      Image format of the base imageencryption       Encrypt the imagecluster_size     qcow2 cluster sizepreallocation    Preallocation mode (allowed values: off, metadata)

 

Increase or decrease the image size

Note: Only raw images can be changed.

hzgatt@hzgatt:~/images$ qemu-img resize vm2.raw +2GB

Hzgatt @ hzgatt :~ /Images $Ll-stotal 136 K 0-rw-r -- 1 hzgatt 5.0G June 29 13:55 vm1.raw136K-rw-r -- 1 hzgatt 193 K June 29 14:22 vm2.qcow2 0-rw- r -- 1 hzgatt 6.0G June 29 14:28 vm2.rawhzgatt @ hzgatt: ~ /Images $ qemu-img info vm2.raw image: vm2.rawfile format: rawvirtual size: 6.0G (6442450944 bytes) disk size: 0

 

Snapshots

View snapshots

qemu-img snapshot -l /images/vm2.qcow2

Note: Only qcow2 supports snapshots.

Snapshot taking

qemu-img snapshot -c booting vm2.qcow2

 

Example:

hzgatt@hzgatt:~/images$ qemu-img snapshot -c booting vm2.qcow2 hzgatt@hzgatt:~/images$ qemu-img snapshot -l vm2.qcow2 Snapshot list:ID        TAG                 VM SIZE                DATE       VM CLOCK1         booting                   0 2012-06-29 14:35:04   00:00:00.000

 

Restore from snapshot:

qemu-img snapshot -a 1 /images/vm2.qcow2

Then, start the VM from kvm and you will find that the VM is in another State when a snapshot is taken.

 

Delete a snapshot:

qemu-img snapshot -d 2 /images/vm2.qcow

 

 

Use a derived image (qcow2)

When more and more virtual machines are created, and you find that many virtual machines are the same operating system, the difference is that the software installed is not the same, then you will certainly want to extract their public parts, only save things that are different from the public part, so the size of the image goes down, the space increases, and the management is convenient. A derived image is used to do this!

First, check an original image.

hzgatt@hzgatt:~/images$ qemu-img info vm3_base.raw image: vm3_base.rawfile format: rawvirtual size: 2.0G (2147483648 bytes)disk size: 2.0G

Now we create an image, but it is derived from

hzgatt@hzgatt:~/images$ qemu-img create -f qcow2 vm3_5.qcow2 -o backing_file=vm3_base.raw 5GFormatting 'vm3_5.qcow2', fmt=qcow2 size=5368709120 backing_file='vm3_base.raw' encryption=off cluster_size=65536

 

Hzgatt @ hzgatt :~ /Images $Ll-RW-r -- 1 hzgatt 193 K June 29 15:00 vm3_5.qcow2-rw-r -- r -- 1 hzgatt 2.0g June 29 14:51 vm3_base.raw

 

hzgatt@hzgatt:~/images$ qemu-img info vm3_5.qcow2 image: vm3_5.qcow2file format: qcow2virtual size: 5.0G (5368709120 bytes)disk size: 136Kcluster_size: 65536backing file: vm3_base.raw (actual path: vm3_base.raw)

 

^ _ ^, This image is only 136 K, enough to save. Dry is always the truth!

Now we have installed a lot of security patches on vm3_5.qcow2 and found that I want to create a new virtual machine on vm3_5.qcow2. What should I do next?

hzgatt@hzgatt:~/images$ qemu-img convert -O raw vm3_5.qcow2 vm3_base2.raw

 

hzgatt@hzgatt:~/images$ qemu-img info vm3_base2.raw image: vm3_base2.rawfile format: rawvirtual size: 5.0G (5368709120 bytes)disk size: 592M

 

This conversion will merge vm3_5 and base to generate a new vm3_base2.raw, and then you can continue the endless derivation journey!

Original