All of the HAL D-Bus interfaces are introspectable using the standard D-Bus introspection methods (e.g. they all implement the org.freedesktop.DBus.Introspectable interface). For example, a command like $ dbus-send --system --print-reply --dest=org.freedesktop.Hal \ /org/freedesktop/Hal/devices/computer \ org.freedesktop.DBus.Introspectable.Introspect will print out the introspection XML for what interfaces (ie. methods and signals) the given hal device object supports. For brevity, the org.freedesktop.Hal prefix have been stripped from the exceptions listed in the following sections. Also note that other exceptions than the ones listed may be thrown; for example the org.freedesktop.Hal.Device.InterfaceLocked exception may be thrown regardless of how the interface is implemented (depending on if some other process is holding a lock on the device cf. ); if PolicyKit support is enabled, the org.freedesktop.Hal.Device.PermissionDeniedByPolicy exception may be thrown (the two first words in the exception detail is resp. a) the privilege the caller didn't have; b) the textual result code from PolicyKit specifying if the caller can obtain the privilege) if the caller is not privileged and so on. Every hal device object (e.g. objects where the object path is prefixed with /org/freedesktop/Hal/devices/) implements this interface. It provides generic functionality. The following methods are available: Method Returns Parameters Throws Description GetProperty Variant String key NoSuchProperty Get property. GetPropertyString String String key NoSuchProperty, TypeMismatch Get property. GetPropertyStringList String[] String key NoSuchProperty, TypeMismatch Get property. GetPropertyInteger Int String key NoSuchProperty, TypeMismatch Get property. GetPropertyUInt64 UInt64 String key NoSuchProperty, TypeMismatch Get property. GetPropertyBoolean Bool String key NoSuchProperty, TypeMismatch Get property. GetPropertyDouble Double String key NoSuchProperty, TypeMismatch Get property. SetProperty Variant String key PermissionDenied Set property. SetPropertyString String String key PermissionDenied, TypeMismatch Set property. SetPropertyStringList String[] String key PermissionDenied, TypeMismatch Set property. SetPropertyInteger Int String key PermissionDenied, TypeMismatch Set property. SetPropertyUInt64 UInt64 String key PermissionDenied, TypeMismatch Set property. SetPropertyBoolean Bool String key PermissionDenied, TypeMismatch Set property. SetPropertyDouble Double String key PermissionDenied, TypeMismatch Set property. RemoveProperty String key NoSuchProperty, PermissionDenied Remove a property. GetPropertyType Int String key NoSuchProperty Get the type of a property. Returns the D-Bus type as an integer. PropertyExists Bool String key Determine if a property exists. AddCapability String capability PermissionDenied Adds a capability to a device. QueryCapability Bool String capability Determine if a device have a capability. Lock Bool String reason DeviceAlreadyLocked Acquires an advisory lock on the device. Returns TRUE if the lock was acquired. Unlock Bool DeviceNotLocked Releases an advisory lock on the device. Returns TRUE if the lock was released. AcquireInterfaceLock String interface_name, Bool exclusive PermissionDenied, Device.InterfaceAlreadyLocked Acquires a lock on an interface for a specific device. See for details. ReleaseInterfaceLock String interface_name PermissionDenied, Device.InterfaceNotLocked Releases a lock on an interface for a specific device. See for details. IsCallerLockedOut Bool String interface_name, String caller_unique_name PermissionDenied Determines whether a given process on the system message bus is locked out from an interface on a specific device. Only HAL helpers are privileged to use this method. See for details. IsCallerPrivileged String String privilege, String caller_unique_name PermissionDenied, Error Determines whether a given process on the system message bus is authorized according to PolicyKit on a specific device for a specific PolicyKit privilege. Unprivileged callers (e.g. with a non-zero uid) can only ask about caller_unique_name that matches their own uid; if this is violated PermissionDenied will be thrown. This can be used ahead of time to see if a given call will succeed or if it requires privilege elevation (TODO: clarify this once PolicyKit can auth over D-Bus). Returns the textual representation of a PolKitResult value on success. If HAL is not built with PolicyKit support, this method always throws the org.freedesktop.Hal.Device.Error exception. IsLockedByOthers Bool String interface_name Determines whether a determines other processes than the caller holds a lock on the given device. See for details. StringListAppend String key, String value PermissionDenied, TypeMismatch Appends an item to a string list. StringListPrepend String key, String value PermissionDenied, TypeMismatch Prepends an item to a string list. StringListRemove String key, String value PermissionDenied, TypeMismatch Removes an item from a string list. EmitCondition Bool String name, String details PermissionDenied Emit a condition on a device object. Rescan Bool PermissionDenied Force an updates of the properties of a device object by rereading data that is not monitored for changes. Reprobe Bool PermissionDenied Cause a synthetic remove and subsequent add of the given device object including all children beneath it. Will generate at least one pair of DeviceRemoved() and DeviceAdded() signals on the Manager interface. ClaimInterface Bool String name, String introspection_xml PermissionDenied An addon can use this method for making the HAL daemon route all D-Bus calls on the given interface to the addon via the peer to peer D-Bus connection between the addon and the HAL daemon. AddonIsReady Bool PermissionDenied An addon needs to call this method when it's ready for the device to be announced on D-Bus. The rationale for this method is to allow an addon to modify the device object and claim interfaces before the device is announced on D-Bus. The following signals are emitted: Signal Parameters Description PropertyModified Int num_changes, Array of struct {String property_name, Bool removed, Bool added} One or more properties on the device object have changed. Condition String name, String details A generic mechanism used to specify a device condition that cannot be expressed in device properties. (NOTE: newly written code should use dedicated signals on a dedicated interface.). InterfaceLockAcquired String lock_name, String lock_owner, Int num_holders Sent when a process acquires an interface lock on the device. InterfaceLockReleased String lock_name, String lock_owner, Int num_holders Sent when a process releases an interface lock on the device. This interface provides a mechanism for discovering when an ACL is added or removed for a device file. The following signals are available: Method Parameters Description ACLAdded UInt unix_user_id Emitted when an ACL have been added for a UNIX user on a device object with the access_control capability. ACLRemoved UInt unix_user_id Emitted when an ACL have been removed for a UNIX user on a device object with the access_control capability. This interface does not export any methods. This interface provides a mechanism to configure CPU frequency scaling. The following methods are available: Method Returns Parameters Throws Description GetCPUFreqAvailableGovernors String[] Retrieves a list of available CPU scaling governors. GetCPUFreqGovernor String Get currently selected CPU Frequency governor. SetCPUFreqGovernor Void String governor CPUFreq.UnknownGovernor Selects a CPU frequency scaling governor for all CPUFreq interfaces the kernel provides. If the userspace governor is set, this interface also contains a proper scaling mechanism. SetCPUFreqPerformance Void Int (1 to 100) CPUFreq.NoSuitableGovernor Sets the performance of the dynamic scaling mechanism. This method summarizes and abstracts all the different settings which can be taken for dynamic frequency adjustments, like at which load to switch up frequency or how many steps the mechanism should traverse until reaching the maximum frequency. The higher the value, the more performance you get. Respectively, the higher the value, the sooner and the more often the frequency is switched up. GetCPUFreqPerformance Int CPUFreq.NoSuitableGovernor Get the tuning value for the governor. SetCPUFreqConsiderNice Void Bool consider_niced_processes CPUFreq.NoSuitableGovernor Whether or not niced processes should be considered on CPU load calculation. If niced processes are considered, they can cause a frequency increment although their absolute load percentage wouldn't trigger the scaling mechanism to switch up the frequency. The default setting is 'false'. GetCPUFreqConsiderNice Bool CPUFreq.NoSuitableGovernor Whether nice'ed processes are considered by the governor. This interface does not emit any signals. This interface provides a mechanism to deal with dock stations. Method Returns Parameters Throws Description Undock Int Void DockStation.NotDocked Undock the system from a dock station This interface does not emit any signals. This interface provides a mechanism to get/set the brightness of the keyboard backlight. The following methods are available: Method Returns Parameters Throws Description GetBrightness Int Get the current brightness. SetBrightness Int brightness Set the current brightness. This interface does not emit any signals. This interface provides a mechanism for both querying whether a radio is on as well as turning it on and off. The following methods are available: Method Returns Parameters Throws Description GetPower Int Returns 1 if, and only if, the power is on. SetPower Bool Set the power of the radio. This interface does not emit any signals. This interface provides a mechanism to get/set the brightness of a LED (light-emitting diode). The following methods are available: Method Returns Parameters Throws Description GetBrightness Int Get the current brightness of the LED. SetBrightness Int brightness Set the current brightness of the LED. The value 0 deactivate normally the LED, any higher value active the LED again. This interface does not emit any signals. This interface provides a mechanism to get/set the brightness of a laptop panel. The following methods are available: Method Returns Parameters Throws Description GetBrightness Int Get the current brightness. SetBrightness Int brightness Set the current brightness. This interface does not emit any signals. This interface provides a mechanism to get information from a light sensor. The following methods are available: Method Returns Parameters Throws Description GetBrightness Int[] The current brightness as measured by the light sensor. This interface does not emit any signals. This interface provides a mechanism to interact with a storage device. The following methods are available: Method Returns Parameters Throws Description Eject Int String[] options Volume.PermissionDenied, Volume.NotMounted, Volume.NotMountedByHal, Volume.Busy, Volume.InvalidEjectOption Unmounts all volumes and possibly ejects the media. Note that this method is not only restricted to optical drives. CloseTray Int String[] options Storage.InvalidCloseTrayOption Attempts to close the tray. Only really makes sense for (optical) drives that uses a tray loading mechanism. This interface does not emit any signals. This interface provides a mechanism to interact with a storage device that uses removable media. The following methods are available: Method Returns Parameters Throws Description CheckForMedia Bool Polls a storage device for media. This interface does not emit any signals. This interface provides a mechanism to affect system-wide power management. Normally only the root computer device object (/org/freedesktop/Hal/devices/computer) implements this interface. The following methods are available: Method Returns Parameters Throws Description Suspend Int Int num_secs_to_wakeup SystemPowerManagement.NotSupported, SystemPowerManagement.AlarmNotSupported Puts the system in a suspended state (typically ACPI S3) for num_secs_to_wakeup seconds. If the given time is zero, the system is put in the suspended state indefinitely. If wake-up isn't supported the the AlarmNotSupported exception is thrown. Latency for the system to return to an operational state is in the order of magnitude of 5 seconds. Hibernate Int SystemPowerManagement.NotSupported Save system state to persistent storage and power off the system (typically ACPI S4). Latency for the system to return to an operational state is in the order of magnitude of one minute. SuspendHybrid Int Int num_secs_to_wakeup SystemPowerManagement.NotSupported, SystemPowerManagement.AlarmNotSupported Puts the system in a suspended state (typically ACPI S3) for num_secs_to_wakeup seconds but also write the system state to persistent storage so the system can resume even if power is removed. Like with Suspend(), if the given time is zero, the system is put in the suspended state indefinitely. If wake-up isn't supported the the AlarmNotSupported exception is thrown. Shutdown Int SystemPowerManagement.NotSupported Shut down the system. Reboot Int SystemPowerManagement.NotSupported Reboot the system. SetPowerSave Int Bool should_save_power SystemPowerManagement.NotSupported If the boolean passed is TRUE, the system will be configured to save as much power as possible by e.g. enabling laptop mode to avoid spinning up disks. Typically, power management daemons will call this method when it determines that the system is running on battery power. This interface does not emit any signals. Implementors of power management daemons should make sure that their software respects the locking guidelines described in . This interface provides a mechanism to interact with a volume that has a mountable file system. The following methods are available: Method Returns Parameters Throws Description Mount Int String mount_point, String fstype, String[] options Volume.PermissionDenied, Volume.AlreadyMounted, Volume.InvalidMountOption, Volume.UnknownFilesystemType, Volume.InvalidMountPoint, Volume.MountPointNotAvailable, Volume.CannotRemount Mounts a volume. Unmount Int String[] options Volume.PermissionDenied, Volume.NotMounted, Volume.NotMountedByHal, Volume.Busy, Volume.InvalidUnmountOption Unmount a volume. Eject Int String[] options Volume.PermissionDenied, Volume.NotMounted, Volume.NotMountedByHal, Volume.Busy, Volume.InvalidEjectOption Unmounts all volumes from the originating drive and possibly ejects the media. Note that this method is not only restricted to optical drives. This interface does not emit any signals. If a volume originates from a storage device (and all volumes do), it also is checked whether the caller is locked out of the org.freedesktop.Hal.Device.Storage interface of the originating storage device. As a corollary, it is sufficient to just either a) lock the storage device; or b) globally lock the org.freedesktop.Hal.Device.Storage interface if one wants to lock out callers from mounting volumes from either a specific drive or all drives. This interface provides a mechanism to interact with a volume that is encrypted at the block layer. The following methods are available: Method Returns Parameters Throws Description Setup Int String passphrase Volume.Crypto.CryptSetupMissing, Volume.Crypto.SetupError, Volume.Crypto.SetupPasswordError Unlocks an encrypted file system. If successful, a cleartext volume will appear. Teardown Int Volume.Crypto.TeardownError Teardown the cleartext volume. This interface does not emit any signals. For objects implementing this interface, it will also be checked if the caller is locked out of the Volume interface on the device (and per this includes checking whether the caller is locked out of the org.freedesktop.Hal.Device.Storage interface for the storage device that the volume originates from). This interface provides a mechanism to configure Wake On LAN capabilities. The following methods are available: Method Returns Parameters Throws Description GetSupported Bool WakeOnLan.NoEthtool Get if device supports Wake On LAN GetEnabled Bool WakeOnLan.NoEthtool Get if Wake On LAN is enabled SetEnabled Void Bool WakeOnLan.NoEthtool Enable or disable Wake On LAN This interface does not emit any signals. Only the /org/freedesktop/Hal/Manager object implements this interface. It's primarily used to discover devices. The following methods are available: Method Returns Parameters Throws Description GetAllDevices Objref[] Get all UDI's in the database. DeviceExists Bool Determines if a given object exists. FindDeviceStringMatch Objref[] String key, String value Find devices for which the given string property assumes the given value. FindDeviceByCapability Objref[] String capability Finds devices of the given capability. NewDevice Objref PermissionDenied Creates a new device object in the temporary device list (TDL) and return the UDI. Caller must be uid 0. Remove Objref tmp_udi NoSuchDevice, PermissionDenied Removes a device object that was created in the TDL. Caller must be uid 0. CommitToGdl Objref tmp_udi, Objref udi NoSuchDevice, PermissionDenied Moves a device from the temporary device list (TDL) to the global device list (GDL). Caller must be uid 0. AcquireGlobalInterfaceLock String interface_name, Bool exclusive Device.InterfaceAlreadyLocked Acquires a global lock on an interface. See for details. ReleaseGlobalInterfaceLock String interface_name Device.InterfaceNotLocked Releases a global lock on an interface. See for details. SingletonAddonIsReady String command_line PermissionDenied, SyntaxError Called by singleton addons to signal that they are ready to handle devices. A singleton addon should implement the org.freedesktop.Hal.Singleton interface. The following signals are emitted: Signal Parameters Description DeviceAdded Objref obj A device was added to the global device list (GDL). DeviceRemoved Objref obj A device was removed from the global device list (GDL). NewCapability Objref obj, String cap A device gained a new capability. GlobalInterfaceLockAcquired String lock_name, String lock_owner, Int num_holders Sent when a process acquires a global interface lock. GlobalInterfaceLockReleased String lock_name, String lock_owner, Int num_holders Sent when a process releases a global interface lock. This interface is provided by singleton addons to allow the Manager to request handling of new devices and removal of old ones. This differs from other HAL interface definitions in that it is provided by addon processes, rather than the HAL daemon itself. It should be exported on the path /org/freedesktop/Hal/Manager. Method Returns Parameters Throws Description DeviceAdded String udi Dict(String,Variant) property_set Called by the HAL Manager when a device is added that has this singleton listed in info.addons.singleton An addon implementing this function should start handling the device before returning, and keep track that is is handling this udi. DeviceRemoved String udi Dict(String,Variant) property_set Called by the HAL Manager when a device is added that has this singleton listed in info.addons.singleton The implementer of this function should keep track of which devices it is still handling and exit when no longer handling any devices. This interface does not export any methods.