Play with VM snapshots and linked-clones with ESXi command line tools
In this article, we will see how to create, commit, revert-to virtual machine snapshots from ESXi command line. We will also talk about the very useful “linked clones” that are related to the snapshot feature.
- Linked clone
You only need to have a running VM on the ESXi and to know its Vmid:
Here is the VMware definition of VM snapshot feature (source):
The snapshot feature is most useful when you want to preserve the state of the virtual machine so you can return to the same state repeatedly.
You can take a snapshot of a virtual machine at any time and revert to that snapshot at any time.
You can take a snapshot while a virtual machine is powered on, powered off or suspended. A snapshot preserves the virtual machine just as it was when you took the snapshot - the state of the data on all the virtual machine’s disks and whether the virtual machine was powered on, powered off or suspended.
To create a snapshot, you can use the ‘vim-cmd’ command:
$ vim-cmd vmsvc/snapshot.create 3 snap01 'snap01 description'
Command usage is:
Usage: snapshot.create vmid [snapshotName] [snapshotDescription] [includeMemory] [quiesced]
So you can make a snapshot with VM memory and quiesced:
vim-cmd vmsvc/snapshot.create 3 "SnapName" "Snap Description" 1 1
Get snapshot(s) list
You may need to get the list of VM snapshots:
$ vim-cmd vmsvc/snapshot.get 3 Get Snapshot: |-ROOT --Snapshot Name : snap01 --Snapshot Id : 1 --Snapshot Desciption : snap01 description --Snapshot Created On : 2/23/2015 18:12:50 --Snapshot State : powered on --|-CHILD ----Snapshot Name : snap02 ----Snapshot Id : 2 ----Snapshot Desciption : snap02 description ----Snapshot Created On : 2/23/2015 18:13:15 ----Snapshot State : powered off ----|-CHILD ------Snapshot Name : snap03 ------Snapshot Id : 3 ------Snapshot Desciption : snap03 description ------Snapshot Created On : 2/23/2015 18:13:32 ------Snapshot State : powered off ------|-CHILD --------Snapshot Name : snap04 --------Snapshot Id : 4 --------Snapshot Desciption : snap04 description --------Snapshot Created On : 2/23/2015 18:13:59 --------Snapshot State : powered off
The list is displayed as a tree according to the parents or children of a snapshot.
Remove/Commit a snapshot
As you can create and list snapshot(s) for a VM, you can remove them. Deletion operation is also called the “commit” as all recent changes made from the moment the snapshot is taken, are committed to the based disk or the parent snapshot disk file.
To remove or commit a snapshot for a VM:
Usage: snapshot.remove vmid snapId
$ vim-cmd vmsvc/snapshot.remove 3 4 Remove Snapshot: |-ROOT --Snapshot Name : snap01 --Snapshot Id : 1 --Snapshot Desciption : snap01 description --Snapshot Created On : 2/23/2015 18:12:50 --Snapshot State : powered off --|-CHILD ----Snapshot Name : snap02 ----Snapshot Id : 2 ----Snapshot Desciption : snap02 description ----Snapshot Created On : 2/23/2015 18:13:15 ----Snapshot State : powered off ----|-CHILD ------Snapshot Name : snap03 ------Snapshot Id : 3 ------Snapshot Desciption : snap03 description ------Snapshot Created On : 2/23/2015 18:13:32 ------Snapshot State : powered off
There is also a
snapshot.removeall argument to remove… all snapshots on a VM. \o/
Revert to a snapshot
Goal of VM snapshot is not to only create, list or remove snapshots… It’s to be able to revert the VM state to the moment you take the snapshot. To do so, you can use the
Usage: snapshot.revert vmid snapshotId suppressPowerOff
So to revert to the first snapshot of the VM with Vmid 3:
$ vim-cmd vmsvc/snapshot.revert 3 1 0 Revert Snapshot: |-ROOT --Snapshot Name : snap01 --Snapshot Id : 1 --Snapshot Desciption : snap01 description --Snapshot Created On : 2/23/2015 18:12:50 --Snapshot State : powered on ...
This will restore VM, powered-on (!), at the state where you take the first snapshot. Last option is to revert to snapshot with or without memory content:
suppressPowerOff = 0 |-> With RAM content |-> Virtual machine is restored with power-on state suppressPowerOff = 1 |-> Without RAM content |-> Virtual machine is restored with power-off state
Linked-clone definition (source):
A linked clone is a copy of a virtual machine that shares virtual disks with the parent virtual machine in an ongoing manner.
Because a linked clone is made from a snapshot of the parent, disk space is conserved and multiple virtual machines can use the same software installation. All files available on the parent at the moment you take the snapshot continue to remain available to the linked clone.
Ongoing changes to the virtual disk of the parent do not affect the linked clone, and changes to the disk of the linked clone do not affect the parent. A linked clone must have access to the parent. Without access to the parent, you cannot use a linked clone.
Create a linked clone
Create a reference snapshot on a source VM. This will be our base for clones.
$ vim-cmd vmsvc/snapshot.create 3 "ReferenceSnapshot" "Used for linked clones of Centos VM" Create Snapshot: $ vim-cmd vmsvc/snapshot.get 3 Get Snapshot: |-ROOT --Snapshot Name : ReferenceSnapshot --Snapshot Id : 7 --Snapshot Desciption : Used for linked clones of Centos VM --Snapshot Created On : 2/24/2015 21:22:25 --Snapshot State : powered off
To have more understandable command lines, we set in variable the reference and destination path:
First step for a linked clone from command line, is to create a destination folder :
Then we copy reference VM’s
.vmx file and the
.vmdk (including the
-delta file) corresponding to our reference snapshot:
$ cat $src/CentosTest.vmx | grep fileName ide1:0.fileName = "cdrom0" scsi0:0.fileName = "CentosTest-000001.vmdk" **cp $src/CentosTest-000001*.vmdk $dst/ $ cp $src/CentosTest.vmx $dst/ $ ls $dst CentosTest-000001-delta.vmdk CentosTest-000001.vmdk CentosTest.vmx
Then we rename files:
$ mv $dst/*-delta.vmdk $dst/LinkedClone1-000001-delta.vmdk mv $dst/*000001.vmdk $dst/LinkedClone1-000001.vmdk mv $dst/*.vmx $dst/LinkedClone1.vmx $ ls $dst LinkedClone1-000001-delta.vmdk LinkedClone1-000001.vmdk LinkedClone1.vmx
Great ! Now we need to edit
LinkedClone1.vmx file to made some changes:
ethernet0.generatedAddressline (if generated mac address)
extendedConfigFileline if present
Then, edit the following lines:
displayNameaccording to the name you whant to display in ESXi list of VMs
scsi0:0.fileNamewith vmdk new name
ethernet0.addressif not a generated address
Last changes to made are in on the
Extent description, adapt the file name according to the delta file name of you linked clone.
parentFileNameHintwith absolute path of the source vmdk file: ex:
Last step is to register and start our VM:
$ vim-cmd solo/registervm $dst/LinkedClone1.vmx $ vim-cmd vmsvc/getallvms Vmid Name File Guest OS Version 3 CentosTest [LocalDatastore_001] CentosTest/CentosTest.vmx otherLinuxGuest vmx-10 6 CentosTest [LocalDatastore_001] LinkedClone1/LinkedClone1.vmx otherLinuxGuest vmx-10 $ vim-cmd vmsvc/power.on 6 && echo "Powered ON" Powering on VM: Powered ON
You can now check the benefits of a linked clone by looking at the size of the vdisk of this new VM:
$ ls -lh delta.vmdk -rw------- 1 root root 16.0M Feb 24 22:19 LinkedClone1-000001-delta.vmdk
And if we modify or create some file in the linkedClone VM, the vdisk usage increase:
$ ls -lh delta.vmdk -rw------- 1 root root 32.0M Feb 24 22:24 LinkedClone1-000001-delta.vmdk
Very useful to have tiny VM for specific usage !
Convert a linked clone to a full clone
If you need to convert your LinkedClone VM to a virtual machine without link to the reference VM, you can use the vmkfstool:
$ vmkfstools -d thin -i /vmfs/volumes/LocalDatastore_001/LinkedClone1/LinkedClone1-000001.vmdk /vmfs/volumes/LocalDatastore_001/LinkedClone1/LinkedClone1_full.vmdk Destination disk format: VMFS thin-provisioned Cloning disk '/vmfs/volumes/LocalDatastore_001/LinkedClone1/LinkedClone1-000001.vmdk'... Clone: 100% done.
Then you can compare the
linked-cloned and the
$ ls -lh *.vmdk -rw------- 1 root root 32.0M Feb 25 01:23 LinkedClone1-000001-delta.vmdk -rw------- 1 root root 369 Feb 24 22:17 LinkedClone1-000001.vmdk -rw------- 1 root root 8.0G Feb 25 18:34 LinkedClone1_full-flat.vmdk -rw------- 1 root root 528 Feb 25 18:34 LinkedClone1_full.vmdk
Finally you can (with powered-off VM) change vmdk path on the vmx file to use the newly created vmdk, and reload the vmx by using:
$ vim-cmd vmsvc/reload 6
End ! Enjoy with VM snapshots and linked clones !
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