So I run a NAS media server thing running on Ubuntu server, and I was wondering if anyone knows any software that can be terminal based for monitoring temps, HDD activity, NAS monitoring of some sort, or something like that that can be run on the terminal.
I don't know anything which is an all-in-one type deal but you can use top to look at CPU and memory usage, iotop to look at disk usage, iftop to look at network usage and sensors to look at temperature, voltage and fan speeds.
It doesn't exactly run in the terminal on the machine itself, but Pulseway is a really good monitoring software that does all of that and can run in a browser or app.
This is probably a little over and above your needs, but I use Zabbix here at home for monitoring servers. It's a bit of a chore to set up, but allows a LOT of customizable things to be done.