Re: [gentoo-user] virtualbox in headless configuration broken after update: delayed echo [ RESOLVED, kinda ]

[Michael <confabulate@kintzios.com>]

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On Thursday, 18 June 2020 00:09:45 BST William Kenworthy wrote:
> On 18/6/20 3:55 am, J. Roeleveld wrote:
> > On 17 June 2020 21:32:19 CEST, Michael <confabulate@kintzios.com> wrote:
> >> On Wednesday, 17 June 2020 18:31:42 BST J. Roeleveld wrote:
> >>> On 17 June 2020 19:01:54 CEST, Michael <confabulate@kintzios.com>
> > 
> > This brings another problem I have with KVM/QEMU: all howtos and documents
> > I find show long commandline options to just start the VM. I have not
> > found one where I can provide all the config in a single file and use
> > that. Allowing me to duplicate settings by simply copying the file and
> > changing a few lines.
> > 
> > KVM/Qemu seems to be written to be used together with virt-manager which,
> > for me, lacks important features to make it usable in production.
> > 
> > --
> > Joost
> 
> Until a few months ago I was using Qemu/KVM/VirtManager with snapshots
> for linux and Windows VM's running network services - the trick is
> redundancy and suspend.
> 
> Using libvirt, suspend the VM which copies ram to disk, then snapshot
> ((I used btrfs) both the ram and storage and restart the VM - takes
> seconds (so redundancy may be needed) - at this point I backup'ed the
> snapshot and deleted it.

Ahh!  Yes!

I had seen the Virsh command which involves pausing a live image and then 
taking a snapshot of it.  William's pointer makes sense.

However, there is also the option to define a memory file as an object

 '-object memory-backend-file,size=1M,share,mem-path=/dev/shm/blah...'

and this can be attached/detached/migrated/snapshoted/etc between hosts as 
desired.

More details here (search for "Generic object creation"):

https://qemu.readthedocs.io/en/latest/system/invocation.html

> When using snapshots of live systems, I had problems restoring some of
> the more active VM's which this avoids.
> 
> 
> BillK

Perhaps the technique with busy systems, other than pausing > snapshot, could 
involve using a migration of the image to a new location?  As I understand it 
the newly migrated image will take over and start running in place of the old 
image, the moment the migration is completed.

Scratching around I found the way to move an image from a qcow2 file on the 
host fs, to a raw format on a disk/partition.  It is simpler than I thought 
(even with no libvirt):

qemu-img convert -O raw image.qcow2 /dev/sda5

Or, 

the output can be 'image.raw' then keep a backup copy of it as a file and then 
dd it to a partition.disk.

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