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Bad Block Scan for HD

Sometimes you might want to check a disk for damage. There is no simple way to do this from built-in utilities, but you can do it from the terminal. Note that this is most useful for spinning hard disks and probably shouldn't be used for solid state drives (SSDs).

First, run the "Terminal" app from the "Utilities" folder (inside the "Applications" folder).
Identify the disk you want to work on entering this command: "diskutil list".
Note the Unix name of the disk to be scanned (something like "disk0s1" in the "IDENTIFIER" column).
Enter this command: "sudo dd if=/dev/DISK of=/dev/null bs=1m status=progress".
Where DISK is the name of the disk you noted above.
You will be asked to enter an admin password. This is usually the login password for your computer.
Every block on the disk will be read (nothing will be changed).
There will be a status display showing progress of the scan.
Any errors will be listed (there should be none).

Alternatively enter "sudo fsck_hfs -S /dev/DISK" for older HFS formatted disks.
Note: you can check the format in the "TYPE NAME" column from the diskutil command.

Important Note

I have tested that this tip works, but there are many possible ways it might cause problems because you have a different version of the system, a bad internet connection, and many other things. So I can take no responsibility if it causes problems. I'm sorry if it does, but that risk is yours!