Steven D'Aprano wrote:

> On Fri, Jun 24, 2016 at 12:22:18AM -0400, Gene Heskett wrote:
> 
>> But why should a powerdown as unceremonious as pulling the plug, have
>> deleted /usr/bin/X?  It doesn't grok at this site.
> 
> File system corruption?
> 
> What file system do you have? If it is something with a journal (ext4,
> for example) I would be surprised. If it is something experimental or
> less reliable (btfs, reiserfs?) then I wouldn't be surprised.
> 
> All file systems can lose data if you interrupt them while updating the
> file system, but some are more resiliant than others. I tend to prefer
> the good old ext3 or ext4 standby over flashier, faster but less
> resiliant newer file systems, and older, unjournaled file systems like
> ext2.
> 
> Have a look inside /lost+found (assuming /usr/bin is in the / partition)
> and see if there's anything there. You may find all your X files, and
> more, given generic names. Or you may find nothing at all.
> 
> 

Or unsynced RAID cache - I had it once.