"Creating snapshot failed" error

Description

In some cases, VM operations may fail with errors such as "Unhandled exception: Error message: Creating snapshot fail. Command exited with message error: unsupported flags (0x200) in function qemuDomainSnapshotCreateXML".

Such errors may occur in the following scenarios:

• after updating the OS or qemu and libvirt software on a cluster node. The error occurs because the OS continues to run older versions of qemu and libvirt services;
• when attempting to create a VM backup via the interface. The error appears if a VM snapshot already exists.

To view details:

1. In the Virtual Machines section, select the VM.
2. Enter Parameters → Information → Last 10 events.
3. Click on the Failed status in the Event column. This displays the Task Information tab with the detailed error text:

Unhandled exception: Error message: Creating snapshot fail
Command exited with message error: unsupported configuration: nothing selected for snapshot 

Solution

Error after updating the OS or qemu and libvirt software on a cluster node

To resolve the issue, restart the libvirt service:

1. Connect to the cluster node via SSH. For more information about connecting via SSH, see Workstation setup.
2. Execute the command:
   

   systemctl restart libvirtd

Error when attempting to create a VM backup via the interface

To resolve the issue:

1. Connect to the cluster node via SSH. For more information about connecting via SSH, see Workstation setup.
2. Determine the internal name of the problematic VM:
   

   sudo virsh list --all | grep <VM_name>

3. Get a list of virtual disks:

   virsh domblklist <internal_VM_name>

   Comment

   <internal_VM_name> — the name obtained in step 2. In most cases, it follows the format <VM ID>_<VM name>. For example: 2698_test-alma8
   Example output

   # virsh domblklist 2698_test-alma8
   Target Source
   ------------------------------------------------
   vda /vm2/2711_test-alma8.2698_test-alma8_snapshot

   The output shows that the VM already has a snapshot.

4. Compare the modification dates of the virtual disk master file and the snapshot. Determine which file was modified later:

   stat <virtual_disk_file>
   stat <snapshot_file>

   Example output for the virtual disk master file. See Modify parameter:

   # stat /vm2/2711_test-alma8
    File: /vm2/2711_test-alma8
    Size: 2419458048 Blocks: 4725400 IO Block: 4096 regular file
   Device: 902h/2306d Inode: 23330831 Links: 1
   Access: (0644/-rw-r--r--) Uid: ( 107/ qemu) Gid: ( 107/ qemu)
   Access: 2023-11-20 12:04:25.826960539 +0200
   Modify: 2023-11-20 12:06:15.420142110 +0200
   Change: 2023-11-20 12:06:15.420142110 +0200
    Birth: 2023-10-26 08:38:45.574566975 +0300

5. The next steps depend on which file was modified later and is relevant:
   

   • if the disk file is more relevant, delete the snapshot:

     rm <snapshot_file>

   • If the more relevant file is the snapshot file:

     1. Merge the file data:

        virsh blockcommit <internal_VM_name> vda --active --verbose --pivot

        Comment

        <internal_VM_name> — the name obtained in step 2. In most cases, it follows the format <VM ID>_<VM name>. For example: 2698_test-alma8
        Example reply for a successful merge

        # virsh blockcommit 2698_test-alma8 vda --active --verbose --pivot
        Block commit: [100 %]
        Successfully pivoted

     2. Delete the snapshot:

        rm <snapshot_file>

6. Repeat the backup.