# Ubuntu – How does the computer suspend

acpisuspend

Trying to understand how suspend works in 10.10.

I use an alias suspend='sudo /etc/acpi/sleep.sh && sudo alsactl init 0

The alsactl bit is to re-init my sound card which sometimes does not come out of suspend correctly.

And then:

/etc/acpi/sleep.sh -> /usr/sbin/pm-suspend -> /usr/lib/pm-utils/bin/pm-action -> /usr/lib/pm-utils/pm-functions

Irony is /usr/lib/pm-utils/bin/pm-action claims to be "Simple suspend script".

Still don't know how it works. I think I directly used s2ram before.

• The gnome-power-manager tool listens for suspend button events, and spawns pm-suspend. Extensive detail about how pm-suspend operates can be found in the man pm-suspend command output. The quick version:

1. /etc/pm/config.d is scanned for files that define environment variables.
2. Each of the scripts in /etc/pm/sleep.d and /usr/lib/pm-utils/sleep.d are called in order with the "suspend" argument.
3. The system is put to sleep via the defined interface module. By default, this is the kernel suspend interface: echo -n "mem" >/sys/power/state. See /usr/lib/pm-utils/pm-functions where do_suspend is defined.
4. The system wakes up.
5. Each of the scripts in /etc/pm/sleep.d and /usr/lib/pm-utils/sleep.d are called in reverse order with the "resume" argument.

If you need to add a script to the stack, I would suggest adding it to /etc/pm/sleep.d and name it something that does not conflict with other scripts, and make sure it processes the "suspend"/"resume" argument.

For debugging, see /var/log/pm-suspend.log as well as the man page which has more information on how to do testing.