How do I detect when the system suspends?

I need to be able to log the times that an Ubuntu 10.04 Desktop system is suspended and resumed.

I can detect when the system is resumed via a DBus signal (org.freedesktop.UPower.Resuming()) but the corresponding "org.freedesktop.UPower.Sleeping()" signal is never fired. Ideally, I'd like to use DBus, but given the lack of success I'm having, I'd be happy with any solution providing it can be called from the command line.

I've discovered one way to do it:

tail -f /var/log/pm-suspend.log | grep "performing suspend"

This simply listens on one of the pm logs for the suspend logging. Although this works, it's probably rather brittle. I've found relying on log parsing to be rather problematic in the past due to changes in the log statements.

Ideally I'd like a more robust mechanism. The service that invokes this will be ran as root.

From ubuntu Paul Robinson

• You can drop a script in /etc/apm/suspend.d. It should be executed every time the machine suspends.

  You can also use /etc/apm/resume.d in a similar fashion to run a script when it wakes up.

  Paul Robinson : Thanks for the answer, It seems like I don't have apm support in my kernel. I see "No APM support in kernel" when i run the command "apm". I know that I can enable this in the kernel for my machine. However, I need to run my program on other machines on which I won't be able to make this change so I don't think APM is going to work :-(
  From Javier Rivera

• Try putting the following in /etc/pm/sleep.d. This should be independent of whether your machine uses APM or ACPI.

  #!/bin/sh
  
  LOGFILE="/var/log/sleep.log"
  
  case "$1" in
          resume)
                  echo "Resumed from suspend at `date`" >> "$LOGFILE"
                  ;;
          thaw)
                  echo "Resumed from hibernation at `date`" >> "$LOGFILE"
                  ;;
          suspend)
                  echo "Suspended to ram at `date`" >> "$LOGFILE"
                  ;;
          hibernate)
                  echo "Hibernated to disk at `date`" >> "$LOGFILE"
                  ;;
  esac
  

  From Ryan Thompson