I am trying to check an entire USB external disk that is not erased. For that reason I have typed

fsck_hfs -fy -l -S -d /dev/disk1s2

This the result

enter image description here

Several messages I found strange here

  1. NO WRITE - how can that be? If I am trying to fix it how can it be no write?
  2. ok, it found a bad block at 137228189184 but at end it says the disk is OK
  3. what is block 26023808 NO MATCH?
  4. at end it says fsmodified = 0??? No modification performed?

I don't understand this. Have fsck_hfs fixed my disk? I by fixed I mean mark the block as unusable or reformatted it or whatever?


1 Answer 1


The command you have given includes the "-l" option, which means to perform a "test-only check" and that "no repairs can be made". Essentially this means that it won't write to the file system, which explains your questions 1 and 4.

Regarding questions 2 and 3: The disk as such might be "OK" (i.e. usable) from the point of view of the filesystem even though a single bad block has been detected. As you have specified the "-S" option, fsck_hfs will attempt to match the bad block to a file name - it found not match. This could indicate that the bad block does not affect any of your files.

Consider replacing the drive when you start having bad blocks.


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