Below is a list of smartctl commands I frequently use to quickly verify disk health and status, specially when you have smartd logging errors to messages log file.
Print all SMART (Self-Monitoring, Analysis and Reporting Technology) information for drive /dev/sda (Primary Master).
smartctl -a /dev/sda
Enable SMART on device.
smartctl --smart=on /dev/sda
Get info about the device:
smartctl -i /dev/sda
Show the capabilities of drive. Also provides status when tests are being carried out.
smartctl -c /dev/sda
Basic health status:
smartctl -H /dev/sda
Display attributes. The attributes to look out for failing disk is Reallocated_Sector_Ct, Reallocated_Event_Count, Current_Pending_Sector and Offline_Uncorrectable. Their RAW_VALUE should normally be "0".
smartctl -A /dev/sda
Immediate offline test which updates attributes value. Good to run after a badblocks fsck check before checking on the attributes values.
smartctl -t offline /dev/sda
Run a thorough long test if you see suspect attributes with -A option as mentioned above.
smartctl -t long /dev/sda
Examine self-test log. Shows if tests failed or passed.
smartctl -l selftest /dev/sda
Display most recent error log.
smartctl -l error /dev/sda
There are more examples in man smartctl.