I tar’d files up on a FreeBSD host and transferred them to a linux host. When extracting the tarball, I was presented with the following warnings:

It seems that FreeBSD‘s tar binary utilizes additional headers that GNU tar does not recognize. There are many blog posts about this. The problem appears to affect tarballs created on various operating systems that employ varying versions of tar and extracting those tarballs with GNU tar.

Generally speaking, these warning can be ignored. On the command line, the files contained within the tarball will still extract (or at least they have every time I’ve encountered this). This does, however, present a problem if one is programmatically encountering this. One can resolve this by addressing the issue within their code or by using the same version of tar on each platform to create and extract the tarballs in question.