hal-disable-polling - disable polling on drives with removable media
hal-disable-polling can be used to to disable and enable media
detection on drives with removable storage. For more information about
both the big picture and specific HAL properties, refer to the HAL spec
which can be found in /usr/share/doc/hal-doc/spec/hal-spec.html
depending on the distribution.
The following options are supported:
--udi The UDI (Unique Device Identifier) of the device object.
The device file of the drive.
Enable polling instead of disabling it.
--help Print out usage.
Print the version.
This program requires super user privileges.
If the requested operation was successful, this program will exit with
exit code 0.
Polling a storage drive is a necessary evil to detect when the user
inserts or removes media. Human computer interaction studies have shown
that a broad class of users expect their system to react within a few
seconds of this. Thus, the hald daemon polls through the hald-addon-
storage addon (one instance for each drive with removable media).
The purpose of the hald-addon-storage addon is simply to open the
special device file at a regular interval (either every 2 or every 16
seconds) to check for new media. This program tries to open the device
file using the O_EXCL option which means that programs like cdrecord(1)
that uses O_EXCL automatically prevents the hald-addon-storage for
interferring by continously opening the device file. In addition, if
the drive is locked using HAL (see hal-lock(1)) the addon also stops
Unfortunately, polling a storage drive can have adverse side effects if
the hardware and/or device driver for the hardware is malfunctioning.
Additionally, the operating system kernel itself may offer multiple
interfaces for the same device (e.g. /dev/sg0 and /dev/scd0) so even
O_EXCL won’t work. Also, polling a drive may decrease throughput in
certain (odd and/or broken) configurations; for example, if two IDE
drives shares the same host (master/slave), bus traffic and contention
caused by polling e.g. the optical drive (slave) can reduce throughput
to the hard disk (master) and/or interfere with CD burning on another
optical drive (master). Finally, polling a drive incurs an overhead
both in the host system (processes get woken up often, preventing the
CPU to stay in a deep power saving states) and it may prevent the
actual drive from reaching deep power states as well. As a result, more
power is consumed and this affects battery life for laptops.
Despite the existence of support for asynchronous media change
notification in recent MMC (Multi-Media Commands) specifications,
virtually no optical drives are compliant with the specification.
Fortunately newer SATA ATAPI hardware seems to support Asynchronous
Notification (AN) and at this time of writing (March 2007) work is
underway to make both the Linux operating system kernel and HAL take
advantage of this.
It is the position of the HAL team that polling should be avoided at
all costs as long as it doesn’t heavily impact the user experience in a
negative way. This tool is provided as a stop-gap measure to use if a
system is rendered useless due to bugs in drivers and/or hardware that
is provoked by HAL polling the drive. If such a bug is encountered it
should be reported (see the BUGS section below) so it can be fixed -
historically hald have triggered a number of bugs in Linux storage
drivers and related subsystems (such as USB) that have later been
Please send bug reports to either the distribution or the HAL mailing
list, see http://lists.freedesktop.org/mailman/listinfo/hal on how to
hald(8), lshal(1), hal-lock(1), open(2), http://www.t10.org/scsi-3.htm,
Written by David Zeuthen <email@example.com> with a lot of help from many