A little bit more info Using the debug method: sh -c "sync && echo 1 > /sys/power/pm_trace && pm-suspend" The magic number returned is: [ 2.941809] Magic number: 0:278:890 [ 2.961872] hash matches ../drivers/base/power/main.c:736 however this does match any pci device so using: cat /sys/power/pm_trace_dev_match The resulting output is: bsg scsi_device scsi_disk sd pci Thanks