What is the purpose of HAL?

pk peterk2 at coolmail.se
Tue Dec 2 13:16:11 PST 2008

Thomas Ilnseher wrote:

> I'm no expert in these things, but afaik udev is used to dynamically
> create device nodes (which is important if linux switches to dynamic
> major / minor allocation). udev is Linux specific. (udev can take some
> extra actions when devices are hotplugged / coldplugged)

I think most OS's have an udev equivalent. FreeBSD has devfs for instance.

> hal is a daemon that informs other clients (listening to hal) when
> devices are cold / hotplugged. it can do other stuff like mounting /
> unmounting upon client request. (the client doesn't need to be root
> therefore). 

Afaict HAL cannot do much on it's own except communicating (with
whatever apps listens).

> Now you could implement the mounting part with udev only, (automatically
> mount partitions / disks when disk is hotplugged), but then:
> * unomunting (w/o) root would not be (easily) possible
> * you have to check the partition type / fs-type before mounting. This
> means you end up hacking some fat bash script.
> * with hal, you can set permissions (eg. for FAT fs) so that the user
> working on the desktop has r/w access to the mountpoint.

You can do this with udev too.

>> Is this really the right mailing list to ask? Not mentioning that the
>> answer is available on the HAL homepage (which you apparently did not
>> check).

I would say so, since Xorg is bringing in HAL as an optional dependency.
No, I didn't check HALs homepage. I checked HAL @ wikipedia. Not that it
was totally unfamiliar for me before, I've run several distros that
comes with it (no choice)... The question was not about HAL in specific
but about building in dependency for HAL in Xorg... Although I follow
the thread "[rant] keeping policy in HAL" with interest. Yes, this is
basically also a rant, so perhaps redundant.

Basically what I want to say is that I think that HAL is doing things
that could be better done by utilising/extending funcionality in
existing resources.

This sums things up somewhat nicely:

Thanks for your input!

Best regards / MfG

Peter K

More information about the xorg mailing list