Great starting question @jasonnet.
I would say for emonbase/emonpi/emonSD users:
1) If inputs are updating but feeds are not: check that feedwriter is running. This can be done by looking at the emoncms > writer line on the emoncms Administration page. It should say “Daemon is running” and the number of feed points pending write should reset at the interval displayed on the line below e.g 60s.
or check status with SSH:
$ sudo service feedwriter status
Should show that the service is running and active.
2) If neither inputs nor feeds are updating: check emonhub.
The status of emonhub can be checked in Setup > EmonHub > View Log. If the log is updating with new data then this would indicate that emonhub is running. The following clip from the log view is a typical example of new data being read from the emonpi board and passed to the local emoncms via MQTT:
2018-12-01 15:46:55,989 DEBUG RFM2Pi 28954 NEW FRAME : OK 5 125 0 13 0 138 0 139 88 0 0 0 0 0 0 0 0 0 0 0 0 92 239 0 0 (-0)
2018-12-01 15:46:55,993 DEBUG RFM2Pi 28954 Timestamp : 1543679215.99
2018-12-01 15:46:55,994 DEBUG RFM2Pi 28954 From Node : 5
2018-12-01 15:46:55,995 DEBUG RFM2Pi 28954 Values : [125, 13, 138, 226.67000000000002, 0, 0, 0, 0, 0, 0, 61276]
2018-12-01 15:46:55,996 DEBUG RFM2Pi 28954 Sent to channel(start)' : ToEmonCMS
2018-12-01 15:46:55,997 DEBUG RFM2Pi 28954 Sent to channel(end)' : ToEmonCMS
2018-12-01 15:46:56,184 DEBUG MQTT Publishing: emon/emonpi/power1 125
2018-12-01 15:46:56,186 DEBUG MQTT Publishing: emon/emonpi/power2 13
2018-12-01 15:46:56,188 DEBUG MQTT Publishing: emon/emonpi/power1pluspower2 138
2018-12-01 15:46:56,190 DEBUG MQTT Publishing: emon/emonpi/vrms 226.67
2018-12-01 15:46:56,192 DEBUG MQTT Publishing: emon/emonpi/t1 0
2018-12-01 15:46:56,193 DEBUG MQTT Publishing: emon/emonpi/t2 0
2018-12-01 15:46:56,195 DEBUG MQTT Publishing: emon/emonpi/t3 0
2018-12-01 15:46:56,197 DEBUG MQTT Publishing: emon/emonpi/t4 0
2018-12-01 15:46:56,198 DEBUG MQTT Publishing: emon/emonpi/t5 0
2018-12-01 15:46:56,200 DEBUG MQTT Publishing: emon/emonpi/t6 0
2018-12-01 15:46:56,202 DEBUG MQTT Publishing: emon/emonpi/pulsecount 61276
or check status with SSH:
$ sudo service emonhub status
3) If neither inputs nor feeds are updating & emonhub is running: Check mqtt_input:
The status of the mqtt_input service is more complicated to access. This needs improving.
Check status with SSH:
$ sudo service mqtt_input status
Next to add how to fix steps…