I'm ahving a Dell Inspiron 1525.
I installed there a stock Ubuntu 10. However I can see no "hibernate" item in the shutdown menu.
ACPI supported on
1525? If it is, how can I make hibernate work there?
Solved: my bad, swap wasn't on.
Yes, ACPI should be supported on the Inspiron 1525 and hibernate should be available as an option on the shutdown menu. I don't own a 1525, but do own a variety of other similar Dells (1420, 1425, 1505) all of which have functioning (albeit sometimes buggy) hibernate.
It is possible the hibernate feature was disabled for the particular model due to bugs. That's really the only reason I could imagine it to be missing. For instance, it might be you have a proprietary driver loaded that can't do it.
If you're curious if ACPI is present at all, look in /proc/acpi.
If you want to check if hibernate works manually, the kernel command to enable it is:
echo -n 4 | sudo tee /proc/acpi/sleep
If that doesn't work then it's likely hibernate is either disabled or not supported. Check the ubuntu kernel bug reports for your card.