OS X tarballs: a saga of extended attributes

Are you a Mac user? Creating a tarball? Beware!

Today I ran into a problem where a tar file that I created had a bunch of ._ files:

$ tar tvf ../bokeh-0.2.tgz
drwxr-xr-x 0 pwang staff 0 Oct 23 15:12 bokeh-0.2/
-rw-r--r-- 0 pwang staff 226 Oct 23 15:04 bokeh-0.2/._.gitattributes
-rw-r--r-- 0 pwang staff 31 Oct 23 15:04 bokeh-0.2/.gitattributes
-rw-r--r-- 0 pwang staff 226 Oct 23 15:04 bokeh-0.2/._.gitignore
-rw-r--r-- 0 pwang staff 1047 Oct 23 15:04 bokeh-0.2/.gitignore
-rwxr-xr-x 0 pwang staff 226 Oct 23 15:04 bokeh-0.2/._bokeh
drwxr-xr-x 0 pwang staff 0 Oct 23 15:04 bokeh-0.2/bokeh/
-rwxr-xr-x 0 pwang staff 226 Oct 23 15:04 bokeh-0.2/._bokeh-server
-rwxr-xr-x 0 pwang staff 1681 Oct 23 15:04 bokeh-0.2/bokeh-server
-rw-r--r-- 0 pwang staff 226 Oct 23 15:04 bokeh-0.2/._CHANGELOG
-rw-r--r-- 0 pwang staff 1388 Oct 23 15:04 bokeh-0.2/CHANGELOG
...

When I looked in the source directory which I was tarring up, I see no such files. What gives?

It turns out that OS X’s version of tar will automatically create these ._ versions for each file that has extended properties and attributes, because it does not want that information lost. Extended attributes are an aspect of the HFS+ filesystem which OS X uses. If you ever do an “ls -l” and see an “@” symbol near the permissions on your files, that indicates that it has extended attributes:

$ ls -l
total 128
-rw-r--r--@ 1 pwang staff 1388 Oct 23 15:04 CHANGELOG
-rw-r--r--@ 1 pwang staff 2587 Oct 23 15:04 QUICKSTART.md

To list these attributes, you do “ls -@”:

$ ls -@l
total 128
-rw-r--r--@ 1 pwang staff 1388 Oct 23 15:04 CHANGELOG
com.apple.quarantine 71
-rw-r--r--@ 1 pwang staff 2587 Oct 23 15:04 QUICKSTART.md
com.apple.quarantine 71

To strip these off, you use the xattr command:

$ xattr -d com.apple.quarantine CHANGELOG

To strip the attributes off of all files in a directory tree, use find:

$ find . -xattr -exec xattr -d com.apple.quarantine {} \;

Now you can create a tarball that won’t be offensive to your friends!