Instruction how to recover from prematurely detached device

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Marek Marczykowski-Górecki 2015-07-31 17:42:32 +02:00
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@ -62,3 +62,36 @@ This will attach the device as "/dev/xvdi", if not already taken by another atta
**Warning: Do not remove the device before detatching it from the VM!** Otherwise you
will not be able to attach it anywhere later. See [this
ticket](https://github.com/QubesOS/qubes-issues/issues/1082) for details.
What if I removed the device before detaching it from the VM?
------------------------------------------------------------
Currently (until [this
ticket](https://github.com/QubesOS/qubes-issues/issues/1082) got implemented),
if you remove the device before detaching it from the VM, Qubes (more precisely
- libvirtd) will think that the device is still attached to the VM and will not
allow attaching further devices under the same name. The easiest way to recover
from such situation is to reboot the VM to which device was attached. But if
this isn't an option, you can manually recover from the situation by following
this steps:
1. Physically connect the device back. You can use any device as long as it
will be detected under the same name (for example `sdb`).
2. Attach the device manually to the same VM using `xl block-attach` command.
It is important to use the same "frontend" device name (by default `xvdi`) -
you can get it from `qvm-block` listing:
[user@dom0 ~]$ qvm-block
sys-usb:sda DataTraveler_2.0 () 246 MiB (attached to 'testvm' as 'xvdi')
[user@dom0 ~]$ xl block-attach testvm phy:/dev/sda backend=sys-usb xvdi
In above example all `xl block-attach` parameters can be deducted from
`qvm-block` output. In order:
* `testvm` - name of target VM to which device was attached - listed in brackets by `qvm-block` command
* `phy:/dev/sda` - physical path at which device appears in source VM (just after source VM name in `qvm-block` output)
* `backend=sys-usb` - name of source VM, can be omitted in case of dom0
* `xvdi` - "frontend" device name (listed at the end of line in `qvm-block` output
3. Now properly detach the device, either using Qubes Manager, or `qvm-block -d` command.