So we have a bunch of random aging servers doing various tasks. One of them needed to mount to a NAS unit with samba, but smbmount was not installed. Tried ‘apt-get install smbfs’ but got a bunch of errors about ‘Failed to fetch’ and ‘404 Not Found [IP: 91.189.88.40 80]’. Found the answer here.
Edit “/etc/apt/sources.list” (with root permissions) substituting all the links: “http://archive.ubuntu.com/…” (in my case us.archive) for “http://old-releases.ubuntu.com/.
Then ‘apt-get install smbfs’ worked perfectly and I was able to mount and move on with my work.