Hi Brad Babai,
Yes, the doc sequence there is a bit confusing. The Openacs tarball needs to be downloaded[1] to the /tmp dir and uncompressed; then try that 'cp' command.
From the shell, do something like this to download the openacs tarball:
[root src]# cd /tmp
[root src]# wget https://openacs.org/projects/openacs/download/download/openacs-5.1.1.tar.gz
if your computer doesn't recognize wget,
use your browser to save it to /tmp directory.
[root src]# tar xvzf openacs-5.1.1.tar.gz
then, according to directions:
[root src]# cp /tmp/openacs-5.1.1/packages/acs-core-docs/www/files/postgresql.txt /etc/init.d/postgresql
hope this helps
1. https://openacs.org/doc/openacs-5-1/individual-programs.html#openacs-download