====== fsck (Mac)======
|(hold) command-s|start up in single user mode|
|df  |display disk free space, along with disk names (most useful when you are not in single user mode, so you can see the full drive list) |
|/sbin/fsck -fy  |run a filesystem consistency check and interactive repair, assuming yes to all questions (the -f means check a disk even if it is clean)|
|/sbin/fsck -fn  |run a filesystem consistency check and interactive repair, assuming no to all questions, and do not open the disk for writing|
|reboot          |reboot system from the terminal|
|exit            |startup without rebooting|
|diskutil verifyVolume /|Verify the disk structure of a volume.  Ownership of the affected disk is required.|

===== BAD SUPERBLOCK / MAGIC NUMBER WRONG =====
If you are trying to run fsck on a disk other than the main boot disk, you may see this error:
<code>
BAD SUPER BLOCK: MAGIC NUMBER WRONG
</code>

...so run this instead:
<code>
/sbin/fsck_hfs -fy /dev/rdisk0s3
</code>

Other Operating System references talk about using newfs -N /dev/diskname to get a list of super-block backups, any of which can be used with the -b flag of fsck to make things work.  This is not the case with Mac / HFS, so use fsck_hfs instead.


===== External Links =====
  * [[http://docs.info.apple.com/article.html?artnum=106214|Resolve startup issues and perform disk maintenance with Disk Utility and fsck]]
  * [[http://www.osxfaq.com/Tutorials/fsck/index.ws|How To Run fsck To Examine A Non-boot Volume In Mac OS X]]