Does FBSD support 'software suspend' ?

Fabian Keil freebsd-listen at
Sat Sep 10 05:23:54 PDT 2005

"Pranav Peshwe" <pranavpeshwe at> wrote:

> >AFAIK "software suspend" does not equal to "suspend to RAM".
> >There are two different "suspend to disk" modes. One is "software suspend"
> >the other "BIOS suspend". The second needs help by the BIOS and a special
> >formated slice, the first doesn't.
> >FreeBSD supports "BIOS supend" if the hardware supports it,
> >you can tell by checking hw.acpi.s4bios with sysctl.
> >GNU/Linux supports software suspend for S4 as well, ATM FreeBSD doesn't.

> So, what i surmise is that : the 'suspend to disk' feature in BSD is
> currently  h/w dependent i.e  BSD does not have a 'software suspend'
> feature like in linux provided by suspend2 (

Whereas "hardware" means BIOS. I wasn't that clear above.

> How useful is this feature(s/w suspend) , if implemented ? I am planning to
> take up its development as my final year project.I have not decided for
> final to take it up;any suggestions/remarks regarding its use and feasiblity
> would be very very valuable in helping me to take the right decision.

How useful software suspend to disk would be
depends on the usage of the system.

If the system is powered up and down often,
one would profit from the fastened starting process.

S4 is nice to have for laptops and desktops
but rather useless for servers.

Many newer laptops don't support S4BIOS,
software suspend is the only way to use S4.

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