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13 Oct 2010

Removing Dot-Underscore Files

This is just a quick note, mostly for my own reference, of a few ways to easily delete the dot-underscore (._foo, ._bar, etc.) files created by (badly-behaved) Mac OS X systems on non-AFP server volumes.

First of all, if you’re in a mixed-platform environment, you probably want to run this command on your Mac:

defaults write DSDontWriteNetworkStores true

This doesn’t stop the creation of dot-underscore (resource fork) files, but it does at least cut down on the creation of their equally-obnoxious cousin, the “.DS_Store” file. I’m not aware of a way to automatically and persistently suppress the creation of resource fork files on platforms that don’t deal with resource forks, though.

For the record, it’s not that I’m against the idea of resource forks or filesystem metadata … I think metadata is great and I wish filesystems supported more of it! But hacky solutions like .DS_Store and dot-underscore resource forks are not going to convince anyone who’s on the fence, and give the Mac OS a reputation for crapping all over shared network resources.

To get rid of the dot-underscore files, the most efficient way is using find from the Unix side of things:

find . -name '._*' -exec ls {} \;

Once you’ve verified that you’re only looking at files you want to delete, kill them with:

find . -name '._*' -exec rm -v {} \;

And if you have .DS_Store files around that you need to zap as well, then you’d just do:

find . -name '.DS_Store' -exec rm -v {} \;

The -v switch on rm isn’t strictly necessary, of course, but I like it just so I can see what’s going on. If you’re hardcore, you can omit it. Note that the single-quotes around the search string being passed to find are crucial; if you use double-quotes, your shell will (more than likely, depending on the shell) expand the string before it gets to find. Not good.

A certain amount of caution is advised when running this – although the files are basically useless on any non-Mac platform, they do contain Finder comments and HFS+ EAs, which are significant on OS X and could be important to some users. This is not something you’d want to run globally on a shared system, for instance, unless it was as part of a script that checked to see whether the dot-underscore file was an orphan, or something with similar safeguards.

Unfortunately I don’t see the need for this going away, unless Apple finds some more elegant solution for dealing with Mac-specific metadata in mixed environments. It would be great if copying files from a Mac to a Linux-backed SMB share automatically preserved all the HFS+ metadata and turned it into ext4 extended attributes, obviating the need for the dot-underscore files… I am not going to hold my breath for that, though.

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