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257 lines
10 KiB
Markdown
257 lines
10 KiB
Markdown
---
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lang: en
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layout: doc
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permalink: /doc/how-to-use-block-storage-devices/
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redirect_from:
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- /doc/block-devices/
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- /doc/stick-mounting/
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- /en/doc/stick-mounting/
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- /doc/StickMounting/
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- /wiki/StickMounting/
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ref: 193
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title: How to use block storage devices
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---
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*This page is part of [device handling in qubes](/doc/how-to-use-devices/).*
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If you don't know what a "block device" is, just think of it as a fancy way to say "something that stores data".
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## Using the Devices Widget to Attach a Drive
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(**Note:** In the present context, the term "USB drive" denotes any [USB mass storage device](https://en.wikipedia.org/wiki/USB_mass_storage_device_class).
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In addition to smaller flash memory sticks, this includes things like USB external hard drives.)
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Qubes OS supports the ability to attach a USB drive (or just its partitions) to any qube easily, no matter which qube handles the USB controller.
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Attaching USB drives is integrated into the Devices Widget: 
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Simply insert your USB drive and click on the widget.
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You will see multiple entries for your USB drive; typically, `sys-usb:sda`, `sys-usb:sda1`, and `sys-usb:2-1` for example.
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Entries starting with a number (e.g. here `2-1`) are the [whole usb-device](/doc/how-to-use-usb-devices/).
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Entries without a number (e.g. here `sda`) are the whole block-device.
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Other entries are partitions of that block-device (e.r. here `sda1`).
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The simplest option is to attach the entire block drive.
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In our example, this is `sys-usb:sda`, so hover over it.
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This will pop up a submenu showing running VMs to which the USB drive can be connected.
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Click on one and your USB drive will be attached!
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**Note:** attaching individual partitions (e.g. `sys-usb:sda1`) can be slightly more secure because it doesn't force the target app qube to parse the partition table.
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However, it often means the app qube won't detect the new partition and you will need to manually mount it inside the app qube.
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See below for more detailed steps.
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## Block Devices in VMs
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If not specified otherwise, block devices will show up as `/dev/xvdi*` in a linux VM, where `*` may be the partition-number.
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If a block device isn't automatically mounted after attaching, open a terminal in the VM and execute:
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```
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cd ~
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mkdir mnt
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sudo mount /dev/xvdi2 mnt
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```
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where `xvdi2` needs to be replaced with the partition you want to mount.
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This will make your drive content accessible under `~/mnt`.
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Beware that when you attach a whole block device, partitions can be identified by their trailing integer (i.e. `/dev/xvdi2` for the second partition, `/dev/xvdi` for the whole device), whereas if you attach a single partition, the partition has *no trailing integer*.
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If several different block-devices are attached to a single VM, the last letter of the device node name is advanced through the alphabet, so after `xvdi` the next device will be named `xvdj`, the next `xvdk`, and so on.
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To specify this device node name, you need to use the command line tool and its [`frontend-dev`-option](#frontend-dev).
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## Command Line Tool Guide
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The command-line tool you may use to mount whole USB drives or their partitions is `qvm-block`, a shortcut for `qvm-device block`.
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`qvm-block` won't recognise your device by any given name, but rather the device-node the sourceVM assigns.
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So make sure you have the drive available in the sourceVM, then list the available block devices (step 1.) to find the corresponding device-node.
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In case of a USB-drive, make sure it's attached to your computer.
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If you don't see anything that looks like your drive, run `sudo udevadm trigger --action=change` in your USB-qube (typically `sys-usb`)
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1. In a dom0 console (running as a normal user), list all available block devices:
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```
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qvm-block
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```
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This will list all available block devices in your system across all VMs.
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The name of the qube hosting the block device is displayed before the colon in the device ID.
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The string after the colon is the ID of the device used within the qube, like so:
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```
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sourceVM:sdb Cruzer () 4GiB
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sourceVM:sdb1 Disk () 2GiB
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```
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2. Assuming your block device is attached to `sys-usb` and its device node is `sdb`, we attach the device to a qube with the name `work` like so:
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```
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qvm-block attach work sys-usb:sdb
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```
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This will attach the device to the qube as `/dev/xvdi` if that name is not already taken by another attached device, or `/dev/xvdj`, etc.
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You may also mount one partition at a time by using the same command with the partition number, e.g. `sdb1`.
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3. The block device is now attached to the qube.
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If using a default qube, you may open the Nautilus file manager in the qube, and your drive should be visible in the **Devices** panel on the left.
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If you've attached a single partition (e.g. `sdb2` instead of `sdb` in our example), you may need to manually mount before it becomes visible:
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```
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cd ~
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mkdir mnt
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sudo mount /dev/xvdi mnt
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```
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4. When you finish using the block device, click the eject button or right-click and select **Unmount**.
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If you've manually mounted a single partition in the above step, use:
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```
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sudo umount mnt
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```
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5. In a dom0 console, detach the device
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```
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qvm-block detach work sys-usb:sdb
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```
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6. You may now remove the device or attach it to another qube.
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## Recovering From Premature Device Destruction
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If the you fail to detach the device before it's destroyed in the sourceVM (e.g. by physically detaching the thumbdrive), [there will be problems](https://github.com/QubesOS/qubes-issues/issues/1082).
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To recover from this error state, in dom0 run
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```
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virsh detach-disk targetVM xvdi
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```
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(where `targetVM` is to be replaced with the VM name you attached the device to and `xvdi` is to be replaced with the used [frontend device node](#frontend-dev).)
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However, if the block device originated in dom0, you will have to refer to the next section.
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### What if I removed the device before detaching it from the VM?
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Currently (until issue [1082](https://github.com/QubesOS/qubes-issues/issues/1082) gets implemented), if you remove the device before detaching it from the qube, Qubes OS (more precisely, `libvirtd`) will think that the device is still attached to the qube and will not allow attaching further devices under the same name.
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The easiest way to recover from such a situation is to reboot the qube to which the device was attached.
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If this isn't an option, you can manually recover from the situation by following these steps:
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1. Physically connect the device back.
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You can use any device as long as it will be detected under the same name (for example, `sdb`).
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2. Attach the device manually to the same VM using the `xl block-attach` command.
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It is important to use the same "frontend" device name (by default, `xvdi`).
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You can get it from the `qvm-block` listing:
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```shell_session
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[user@dom0 ~]$ qvm-block
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sys-usb:sda DataTraveler_2.0 () 246 MiB (attached to 'testvm' as 'xvdi')
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[user@dom0 ~]$ sudo xl block-attach testvm phy:/dev/sda backend=sys-usb xvdi
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```
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In above example, all `xl block-attach` parameters can be deduced from the output of `qvm-block`.
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In order:
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* `testvm` - name of target qube to which device was attached - listed in brackets by `qvm-block` command
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* `phy:/dev/sda` - physical path at which device appears in source qube (just after source qube name in `qvm-block` output)
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* `backend=sys-usb` - name of source qube, can be omitted in the case of dom0
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* `xvdi` - "frontend" device name (listed at the end of line in `qvm-block` output)
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3. Now properly detach the device, either using Qubes VM Manager or the `qvm-block -d` command.
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## Attaching a File
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To attach a file as block device to another qube, first turn it into a loopback device inside the sourceVM.
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1. In the linux sourceVM run
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```
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sudo losetup -f --show /path/to/file
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```
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[This command](https://linux.die.net/man/8/losetup) will create the device node `/dev/loop0` or, if that is already in use, increase the trailing integer until that name is still available.
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Afterwards it prints the device-node-name it found.
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2. If you want to use the GUI, you're done.
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Click the Device Manager  and select the `loop0`-device to attach it to another qube.
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If you rather use the command line, continue:
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In dom0, run `qvm-block` to display known block devices.
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The newly created loop device should show up:
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```shell_session
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~]$ qvm-block
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BACKEND:DEVID DESCRIPTION USED BY
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sourceVM:loop0 /path/to/file
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```
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3. Attach the `loop0`-device using qvm-block as usual:
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```
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qvm-block a targetVM sourceVM:loop0
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```
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4. After detaching, destroy the loop-device inside the sourceVM as follows:
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```
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sudo losetup -d /dev/loop0
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```
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## Additional Attach Options
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Attaching a block device through the command line offers additional customisation options, specifiable via the `--option`/`-o` option.
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(Yes, confusing wording, there's an [issue for that](https://github.com/QubesOS/qubes-issues/issues/4530).)
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### frontend-dev
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This option allows you to specify the name of the device node made available in the targetVM.
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This defaults to `xvdi` or, if already occupied, the first available device node name in alphabetical order.
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(The next one tried will be `xvdj`, then `xvdk`, and so on ...)
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usage example:
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```
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qvm-block a work sys-usb:sda1 -o frontend-dev=xvdz
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```
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This command will attach the partition `sda1` to `work` as `/dev/xvdz`.
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### read-only
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Attach device in read-only mode.
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Protects the block device in case you don't trust the targetVM.
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If the device is a read-only device, this option is forced true.
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usage example:
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```
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qvm-block a work sys-usb:sda1 -o read-only=true
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```
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There exists a shortcut to set read-only `true`, `--ro`:
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```
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qvm-block a work sys-usb:sda1 --ro
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```
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The two commands are equivalent.
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### devtype
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Usually, a block device is attached as disk.
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In case you need to attach a block device as cdrom, this option allows that.
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usage example:
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```
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qvm-block a work sys-usb:sda1 -o devtype=cdrom
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```
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This option accepts `cdrom` and `disk`, default is `disk`.
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