Introduction to Blivet

Blivet is a python module for system storage configuration.

The main thing that blivet offers is the ability to model a series of changes without necessarily commiting any of the changes to disk. You can schedule an arbitrarily large series of changes (called ‘actions’), seeing the effects of each (within the DeviceTree instance) as it is scheduled. Nothing is written to disk, however, until you execute the actions.

Building Blocks

Individual block devices are represented by the various subclasses of StorageDevice, while the formatting of the data they contain is represented by the various subclasses of DeviceFormat. The hierarchy of devices is represented by DeviceTree.

DiskDevice, PartitionDevice, LVMLogicalVolumeDevice, and MDRaidArrayDevice are some of the most important examples of StorageDevice subclasses.

Some examples of DeviceFormat subclasses include SwapSpace, DiskLabel, and subclasses of FS such as Ext4FS and XFS.

Every StorageDevice instance has a format that contains an instance of some DeviceFormat subclass – even if it is “blank” or “unformatted” (in which case it is an instance of DeviceFormat itself).

Every DeviceFormat has a device attribute that is a string representing the path to the device node for the block device containing the formatting. StorageDevice and DeviceFormat can represent either existent or non-existent devices and formatting.

StorageDevice and DeviceFormat share a similar API, which consists of methods to control existing devices/formats (setup(), teardown()), methods to create or modify devices/formats (create(), destroy(), resize()) , and attributes to store critical data (status, exists) . Some useful attributes of StorageDevice that are not found in DeviceFormat include parents, isleaf, ancestors, and disks.

DeviceTree provides devices which is a list of StorageDevice instances representing the current state of the system as configured within blivet. It also provides some methods for looking up devices (get_device_by_name()) and for listing devices that build upon a device (get_dependent_devices()).

Getting Started

First Steps

First, create an instance of the Blivet class:

import blivet
b = blivet.Blivet()

Next, scan the system’s storage configuration and store it in the tree:


Now, you can do some simple things like listing the devices:

for device in b.devices:

To make changes to the configuration you’ll schedule actions, but Blivet provides some convenience methods to hide the details. Here’s an example of removing partition ‘/dev/sda3’:

sda3 = b.devicetree.get_device_by_name("sda3")
b.destroy_device(sda3)   # schedules actions to destroy format and device

At this point, the StorageDevice representing sda3 is no longer in the tree. That means you could allocate a new partition from the newly free space if you wanted to (via blivet, that is, since there is not actually any free space on the physical disk yet – you haven’t commited the changes). If you now ran the following line:

sda3 = b.devicetree.get_device_by_name("sda3")

sda3 would be None since that device has been removed from the tree.

When you are ready to commit your changes to disk, here’s how:


That’s it. Now you have actually removed /dev/sda3 from the disk.

Here’s an alternative approach that uses the lower-level DeviceTree class directly:

import blivet
dt = blivet.devicetree.DeviceTree()
sda3 = dt.get_device_by_name("sda3")
action1 = ActionDestroyFormat(sda3)
action2 = ActionDestroyDevice(sda3)

Here’s the Blivet approach again for comparison:

import blivet
b = blivet.Blivet() # contains a DeviceTree instance
b.reset()   # calls DeviceTree.populate()
sda3 = b.devicetree.get_device_by_name("sda3")
b.destroy_device(sda3)   # schedules actions to destroy format and device
b.do_it()    # calls DeviceTree.actions.process()

Scheduling a Series of Actions

Start out as before:

import blivet
from blivet.size import Size
b = blivet.Blivet()
sda3 = b.devicetree.get_device_by_name("sda3")

Now we’re going to wipe the existing formatting from sda3:


Now let’s assume sda3 is larger than 10GiB and resize it to that size:

b.resize_device(sda3, Size("10 GiB"))

And then let’s create a new ext4 filesystem there:

new_fmt = blivet.formats.get_format("ext4", device=sda3.path)
b.format_device(sda3, new_fmt)

If you want to commit the whole set of changes in one shot, it’s easy:


Now you can mount the new filesystem at the directory “/mnt/test”:


Once you’re finished, unmount it as follows:


Disk Partitions

Disk partitions are a little bit tricky in that they require an extra step to actually allocate the partitions from free space on the disk(s). What that means is deciding exactly which sectors on which disk the new partition will occupy. Blivet offers some powerful means for deciding for you where to place the partitions, but it also allows you to specify an exact start and end sector on a specific disk if that’s how you want to do it. Here’s an example of letting Blivet handle the details of creating a partition of minimum size 10GiB on either sdb or sdc that is also growable to a maximum size of 20GiB:

sdb = b.devicetree.get_device_by_name("sdb")
sdc = b.devicetree.get_device_by_name("sdc")
new_part = b.new_partition(size=Size("10 GiB"), grow=True,
                           maxsize=Size("20 GiB"),
                           parents=[sdb, sdc])

Now you could see where it ended up:

print("partition %s of size %s on disk %s" % (,

From here, everything is the same as it was in the first examples. All that’s left is to execute the scheduled action:

b.do_it()    # or b.devicetree.process_actions()

Backing up, let’s see how it looks if you want to specify the start and end sectors. If you specify a start sector you have to also specify a single disk from which to allocate the partition:

new_part = b.new_partition(start=2048, end=204802048, parents=[sdb])

All the rest is the same as the previous partitioning example.