As you know, Unix filesystems store a number of timestamps for each file. This means that you can use these timestamps to find out when any file or directory was last accessed (read from or written to), changed (file access permissions were changed) or modified (written to).
File and directory timestamps in Unix
Three times tracked for each file in Unix are these:
- access time – atime
- change time – ctime
- modify time – mtime
INTERESTING: there's no file creation timestamp kept in most filesystems – meaning you can't run a command like "show me all files created on certain date". This said, it's usually possible to deduce the same from ctime and mtime (if they match – this probably means that's when the file was created).