UNIX mtime vs. ctime

Sometimes I get questions from people about stuff that I’ve long since taken for granted. One is “what’s the difference between mtime and ctime?”

The answer is simple, but I wanted to post it here in case it can help anyone. In UNIX:

mtime is “modification time”, and it is the time at which the last modification *TO THE CONTENT* of the file was made.

ctime is “change time”, and it is the time at which the last modification *TO THE PROPERTIES* of the file was made. By “properties” I mean things like ownership and permissions.  You can think of this as “chtime” – the last time a “ch*” command like chown, chmod, or chgrp was performed on the file.