Description of problem:
"man systemd-sleep" says:
> All executables in this directory are executed in parallel, and execution
> of the action is not continued until all executables have finished.

It makes sense to wait for all scripts to finish during system suspend, yes. But do they have to be blocking even during system resume? I have several use cases in which I'd love to have non-blocking resume scripts:

1. I have some short-running resume scripts, for example a script that uses hdparm to set sane power-management settings to my HDD (because the vendor defaults are really bad). It is executed in a second, very quick. But I don't need this to be a blocking call, I'd be very happy to have this running in parallel with the system resume procedures and not wait for it. If I were able to make it non-blocking, I'd have my wifi reconnected a second earlier (currently network initialization waits for the systemd-sleep scripts to finish). Systemd is based on the "proper design" principle, which makes the system behave quick. It seems to me that this is exactly the proper design - let's not delay my network just because I need HDD power management settings adjusted.

2. I have some long-running resume scripts (ten seconds or more). One of them was a workaround for bug 866212 (which should be hopefully resolved now) - a long standing kernel problem that killed my battery life on resume if undetected. I used the script to collect powertop data over several seconds, and alert me if the kernel bug was triggered. Again, I don't need to block the resume procedures with this. I certainly don't want to wait 15 more seconds for my wifi to connect every time I resume my laptop. But I need to run this script on every resume, otherwise my battery will get depleted very quickly without me noticing it.

I tried to work around systemd constraints by spawning background tasks inside the resume scripts. Unfortunately, it seems that systemd kills all child processes once the parent script has finished.

I know that I can write a dbus listener that will run the whole time and wait for system resume signal and then run the task I need, but this is firstly much more complicated, and secondly it wastes some resources - the script needs to run (and listen) the whole time, instead of just running once per resume.

Please, give us some way (any way) to run non-blocking scripts during system resume.

Could you please consider following ideas?

a) Allow a particular script to be non-blocking during resume, by marking it in same way as such.

-or-

b) Allow all scripts to be non-blocking during resume (but blocking during suspend, of course).

-or-

c) Consider all scripts to be blocking during both suspend and resume, but allow scripts to spawn background tasks during resume (i.e. don't kill their children processes once the scripts finish).

What do you think?


Version-Release number of selected component (if applicable):
systemd-204-9.fc19.x86_64

How reproducible:
always

Steps to Reproduce:
1. put this script into /usr/lib/systemd/system-sleep/foo.sh
#!/bin/sh
case $1/$2 in
  post/*)
    sleep 15
    ;;
esac
2. see that your network reconnects no sooner than after 15 seconds after resume
-or-
1. put this script into /usr/lib/systemd/system-sleep/bar.sh
#!/bin/sh
case $1/$2 in
  post/*)
    for i in {1..100}; do touch /tmp/bar$i; sleep 0.1; done &
    sleep 3
    ;;
esac
2. see that there is /tmp/bar30 after resume, but no /tmp/bar40, meaning that the background process was killed