udisks — Disk Manager
udisks provides interfaces to enumerate and perform operations
on disks and storage devices. Any application (including
unprivileged ones) can access the
daemon via the name org.freedesktop.UDisks2
on the system message bus.
In addition to the D-Bus API, a
libudisks2 is also provided. This
library can be used from C/C++ and any high-level language with
udisks is only indirectly involved in what devices and objects
are shown in the user interface. See these
for what is shown in GNOME 3.
By default, logged-in users in active log-in sessions are
permitted to perform operations (for example, mounting,
unlocking or modifying) on devices attached to the seat their
session is on. Access-control is fine-grained and based on
see the “Authorization
Checks” chapter in the udisks documentation for
Note that the
x-udisks-auth option can be
used in the
/etc/crypttab files to specify that
additional authorization is required to mount resp. unlock the
device (typically requiring the user to authenticate as an
At start-up and when a drive is connected,
will apply configuration stored in the file
where IDENTIFIER is the value of the
property for the drive. If the file changes on disk its new
contents will also be applied to the drive.
Typically, users or administrators will never need to edit drive
configuration files as they are effectively managed through
graphical applications such as
Manually editing configuration files is however supported — the file
format is a simple .ini-like format
Desktop Entry Specification
for the exact syntax). New groups and keys may
be added in the future.
ATA group is for settings that apply to
drives using the ATA command-set. The following keys are
The standby timeout. A value of zero means "timeouts
are disabled": the device will not automatically enter
standby mode. Values from 1 to 240 specify multiples of
5 seconds, yielding timeouts from 5 seconds to 20
minutes. Values from 241 to 251 specify from 1 to 11
units of 30 minutes, yielding timeouts from 30 minutes
to 5.5 hours. A value of 252 signifies a timeout of 21
minutes. A value of 253 sets a vendor-defined timeout
period between 8 and 12 hours, and the value 254 is
reserved. 255 is interpreted as 21 minutes plus 15
seconds. Note that some older drives may have very
different interpretations of these values.
This is similar to the
The Advanced Power Management level. A low value means
aggressive power management and a high value means
better performance. Possible settings range from values
1 through 127 (which permit spin-down), and values 128
through 254 (which do not permit spin-down). The
highest degree of power management is attained with a
setting of 1, and the highest I/O performance with a
setting of 254. A value of 255 can be used to disable
Advanced Power Management altogether on the drive (not
all drives support disabling it, but most do).
This is similar to the
The Automatic Acoustic Management level. Most modern
harddisk drives have the ability to speed down the head
movements to reduce their noise output. The possible
values are between 0 and 254. 128 is the most quiet (and
therefore slowest) setting and 254 the fastest (and
loudest). Some drives have only two levels (quiet /
fast), while others may have different levels between
128 and 254. At the moment, most drives only support 3
options, off, quiet, and fast. These have been assigned
the values 0, 128, and 254 at present, respectively, but
integer space has been incorporated for future
expansion, should this change.
This is similar to the
A boolean specifying whether to enable or disable the
Write Cache. Valid values for this key are
“true” and “false”. This is
similar to the
udisks relies on recent versions of udev(7) and the Linux kernel. Influential device properties in the udev database include:
If set, this overrides the value of the HintSystem property.
If set, this overrides the value of the HintIgnore property.
If set, this overrides the value of the HintAuto property.
If set, this overrides the value of the CanPowerOff property.
The name to use for the device when presenting it in an user interface. This corresponds to the HintName property.
The icon to use for the device when presenting it in an user interface using a symbolic icon. If set, the name must adhere to the freedesktop.org icon theme specification. This corresponds to the HintSymbolicIconName property.
If set to 1, the filesystem on the device will be mounted in a shared directory (e.g.
The physical seat the device is attached to. If unset or set to the empty string, “seat0” (the first seat) is assumed.
udisks guarantees a stable D-Bus API within the same major
version and this guarantee also extends to the client-side
libudisks2. Additionally, several
major versions of udisks can be installed and operate at the
same time although interoperability may be limited - for
example, a device mounted using the udisks N.x API may require
additional authorization if attempting to unmount it through the
the (N-1).x API.
The udisks developers do not anticipate breaking API but does reserve the right to do so and if it happens, promises to bump the major version and ensure the new major version of udisks is parallel-installable with any older major version. However, note that programs, man pages and other artifacts may change name (for example, adopt a “2” suffix) to make room for the next major version. Therefore, applications can not rely on tools like e.g. udisksctl(1) to be available. Additionally, there is no guarantee that the options, command-line switches etc. of command-line tools or similar will remain stable.
Instead, applications should only use the D-Bus API, the
libudisks2 library or tools such as
to interact with
The intended audience of udisks include operating system developers working on the higher-level parts of the operating system, for example the desktop shell (such as GNOME) and disk management applications (e.g. GNOME's Disks application). Software on this level typically depend on a specific (major) version of udisks and may even have support for previous versions of udisks or alternative interfaces performing the same role as udisks.
While udisks indeed provides a stable API and a clear upgrade path, it may not be an appropriate dependency for third party applications. For example, if the operating system switches to udisks version N.x and an application is still using the udisks (N-1).x API, the application will not work unless udisks (N-1).x is installed. While this situation is still workable (since both udisks N.x and udisks (N-1).x can be installed) it may not be desirable to ask the user to install the old version - in fact, the operating system vendor may not even provide a packaged version of the old version. Hence, if an application does not want to tie itself to a specific version of the operating system, it should not use udisks.
Viable alternatives to udisks are APIs that are guaranteed to be around for longer time-frames, including:
In particular, for desktop applications it is a much better idea to use something like GVolumeMonitor since it will make the application show the same devices as the desktop shell (e.g. file manager, file chooser and so on) is showing.
Written by David Zeuthen
<firstname.lastname@example.org> with a lot of help
from many others.
Please send bug reports to either the distribution bug tracker or the upstream bug tracker at http://bugs.freedesktop.org/enter_bug.cgi?product=udisks.