Rpi-monitor https://github.com/XavierBerger/RPi-Monitor is a very nice app for monitoring sbc (single board computers/ actually bigger computers as well) like RPi on a web. it give you a quick look at various system metrics cpu load, uptime, temperatures etc and more on a nice web page. and on top, makes nice time series graphs for the same, practically a dashboard.
Rpi-monitor is normally not found in the common Apt repositories and actually the binary is a little old. I tried installing it based on the 'formal' docs but hit some invalid public keys errors, possibly expired certs. https://xavierberger.github.io/RPi-Monitor-docs/11_installation.html
so here is a 'workaround'
you can find the packages in this repository (note that this may not be permanant and may change) https://github.com/XavierBerger/RPi-Monitor-deb use the rpimonitor_latest.deb file https://github.com/XavierBerger/RPi-Monitor-deb/tree/develop/packages
use apt to install rpimonitor_latest.deb as it has varous package dependencies. e.g. download it to a folder and from there run
sudo apt install ./rpimonitor_latest.deb
the prior step should install rpimonitor, and check that the service is running by going to http://your_sbc_ip_address:8888
rpi-monitor is run as a systemd (unit) service
if it is not running you can try
systemctl status rpimonitor.service
or
journalctl -u rpimonitor.service
to check what went wrong.
to start / stop rpi-monitor it is as per basic systemd services
e.g. systemctl start rpimonitor.service etc
apparently, it is affected by this issue: XavierBerger/RPi-Monitor#374
accordingly the fix/'workaround' is edit /etc/rpimonitor/template/temperature.conf replace
#dynamic.1.postprocess=sprintf("%.2f", $1/1000)
dynamic.1.postprocess=$1/1000
for the rest, the Rpi-monitor docs
https://xavierberger.github.io/RPi-Monitor-docs/
and repo
https://github.com/XavierBerger/RPi-Monitor
are the original source of info and relevant