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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.