step 2, it says you should already have the OpenACS tar-ball in /tmp. This is thanks to the step "Unpack the OpenACS tarball" on this document
I see the point that this tarball includes the postgresql.txt file, which is the used in step 8 "Set PostgreSQL to start on boot" on this page:
But still, it's a bit confusing and easy to miss the first step on the linux-installation page. Maybe a link back directly to the section that tells you to download the tarball in the first place would help?
I updated the .LRN installation doc a bit to make it slightly more clear.