What are .#foo files?

Question

I have placed my autosave and backup files in a single directory .emacs-saves.

Backup files appear as ~foo

Autosave files appear as #foo#

But Emacs seems to also generate .#foo in the current directory whenever a change is made in a buffer.

What's the purpose of these files and is there a way to specify their default directory?

Answer 1

These are lock files. See Save lock-files to a directory instead of disabling them

If you are accessing files remotely (think tramp or nfs) then it is a lot simpler to have the lock files in the same directory as the file being edited.