There is some error reported when I run Disk Utility and verify the root volume on my OS X MacBook. So I boot and CMD-S into the shell mode and run /sbin/fsck -fy. Errors are like: ** Checking catalog file. Missing thread record (id = ...) In correct number of thread records ** Checking catalog hierarchy. Invalid volume file count (It should be ... instead of ...) ** Repairing Volume Missing directory record (id = ...) I'd like to know what is the cause of the above errors? Hopefully I will be more careful in the future to prevent them from happening again. p.s. I am using a SSD and so I assume mechanical hard disk error is less likely. Thanks!