The documentation in Documentation/power/swsusp.txt reads:
,----
| Sleep states summary
| ====================
| | There are three different interfaces you can use, /proc/acpi should
| work like this:
| | In a really perfect world:
| echo 1 > /proc/acpi/sleep # for standby
| echo 2 > /proc/acpi/sleep # for suspend to ram
| echo 3 > /proc/acpi/sleep # for suspend to ram, but with more
| power conservative
| echo 4 > /proc/acpi/sleep # for suspend to disk
| echo 5 > /proc/acpi/sleep # for shutdown unfriendly the system
| | and perhaps
| echo 4b > /proc/acpi/sleep # for suspend to disk via s4bios
`----
I do get:
root@hermes:~# echo 2 > /proc/acpi/sleep
bash: /proc/acpi/sleep: No such file or directory