How to find Synology NAS HDD temperature

There are several ways to read the temperature on Synolog NAS HDD. All of them use smartclt that is actual reading the S.M.A.R.T features of the storage device.

First, list the storage devices installed in your Synology NAS

smartctl --scan

For us, it shows:
/dev/hda -d ata # /dev/hda, ATA device
/dev/sda -d scsi # /dev/sda, SCSI device
/dev/sdc -d scsi # /dev/sdc, SCSI device

Use scttempsts to read the real value:

sudo smartctl -l scttempsts /dev/hda | grep Temp
Current Temperature: 33 Celsius
Power Cycle Min/Max Temperature: 25/41 Celsius
Lifetime Min/Max Temperature: 20/44 Celsius
Under/Over Temperature Limit Count: 0/0

Use -A to read all the temperatures and the Celsius temperature can be filtered using grep:

sudo smartctl -A /dev/hda | grep ATT
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE

sudo smartctl -A /dev/hda | grep Temp
194 Temperature_Celsius 0x0022 110 099 000 Old_age Always - 33