Comment by LatencyKills
4 days ago
Ex-Apple engineer here. This is, for better or worse, just the way Apple approaches this type of problem. From Apple's perspective, this is the way to preserve Finder / Gatekeeper / metadata semantics. It avoids silent data loss when round-tripping archives between Macs. This behavior also maintains consistency with copyfile(3) (as well as the Archive Utility behavior).
Apple treats tar less like “portable Unix interchange” and more like “archive this filesystem object faithfully.” That is very Apple, and very libarchive. ;-)
This is probably going to get worse (as Apple continues to add macOS-specific metadata), so your workaround is very helpful.
I haven't tested it in a while, but at one point, setting the COPYFILE_DISABLE=1 env variable would disable the inclusion of macOS-specific metadata.
Arguably, principle of least surprise is very Apple.
If I point "tape archive" at a file system, I want that file system archived to tape. And so, tar does.
If I don't, well, that's a fine option, and there's a fine option for that.
So it's less of a "workaround" or something that "gets worse", than, "No, I don't really want a tape archive of this filesystem, only of some of it." And that's supported.
That said, never seeing another .DS_Store should be a system-wide option!
> Arguably, principle of least surprise is very Apple.
Principle of least surprise is good engineering practice. The question is always whose surprise. Someone who expects tar to behave like other UNIX systems is going to be surprised by this. Someone who expects tar on Apple to have perfect fidelity would be surprised by not-this.
I increasingly feel like build systems should never be relying on any "native" utilities from the host system, and should instead be bringing them in via dependencies. You can't have this problem if your packaging system pulls in a specific portable `tar` library.
What should be really surprising for the users of UNIX-like operating systems is when they lose data because traditional UNIX utilities like cp, tar or cpio do not make complete copies of files, as one would expect from their description.
What is worse is that these utilities do not give any warnings when they do not make complete copies. For cp, the root cause is that it has bad default options, while for tar and cpio the standard file formats cannot store the metadata of modern file systems.
The various tar programs have their own different file format extensions to deal with modern file systems, which are guaranteed to work only when using the same tar program for both creation and extraction. The better tar programs implement both their own file format extensions and the file format extensions used by other popular tar programs.
The author of the TFA has used some obsolete tar program, which is the cause for the surprising behavior that was seen.
To avoid loss of data on Linux, I always use the PAX file format instead of tar or cpio, with the extensions implemented by "bsdtar --create --format=pax" from libarchive, and I always alias cp to '/bin/cp --no-dereference --recursive --one-file-system --preserve=all --strip-trailing-slashes --verbose --interactive', where cp has been built with extended attributes support.
> The question is always whose surprise.
I think that the surprise of more data than expected is more desirable than the surprise of data loss. So in this case, it seems like the safe choice.
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> Someone who expects tar to behave like other UNIX systems is going to be surprised by this
They shouldn’t. The GNU tar manual already shows this behavior. https://www.gnu.org/software/tar/manual/html_node/What-tar-D...:
Because the archive created by tar is capable of preserving file information and directory structure, tar is commonly used for performing full and incremental backups of disks”
And yes, that same page also says:
“You can create an archive on one system, transfer it to another system, and extract the contents there. This allows you to transport a group of files from one system to another.”
> You can't have this problem if your packaging system pulls in a specific portable `tar` library.
You can’t pull in specific portable stuff all the way down (not even when running in Docker or a VM), so that will decrease the risk, but it cannot completely remove it. As an example, I think GNU tar will happily include .DS_Store files in archives.
Apple is always surprised that non-Apple devices exist.
See: the permanent undismissable red icon to "finish setting up your Apple TV with your iPhone"
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> I increasingly feel like build systems should never be relying on any "native" utilities from the host system, and should instead be bringing them in via dependencies.
Well, you see, while this, frankly, applies not just to build systems but to most of software, the consensus in the community of distro-maintainers is that it's actually wrong: you should use your system's package manager, and tools it can install, and let it fiddle with the ambient environment and give you that delicious "path dependency". And if your distro's packaging environment doesn't allow to do the things you need (e.g. being able to install both mongodb 3.8 and mongodb 5.0, ideally at the same time, but okay, I can keep running apt remove/install over and over, but I do need to check if my app correctly handled the wire protocol changes), well, that's your problem for desiring strange things.
Nixos has a pretty solid solution to this issue: key your dependencies with checksums of the content. That way you get the best of both worlds: you always get the exact version you want, and you can share a copy of that exact version with other software that wants to use that exact version too!
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> I want that file system archived to tape. And so, tar does.
The traditional UNIX tar and cpio utilities cannot archive the modern Linux file systems without loss of metadata.
Most modern tar programs implement various file format extensions as a workaround for this, but the extensions may be incompatible between distinct tar programs and frequently they are very poorly documented.
Some years in the past, libarchive was the only archiver available on Linux that guaranteed lossless backups for the Linux file systems, e.g. xfs or ext4 (and also lossless file transfers between Linux file systems and FreeBSD file systems). Therefore that is what I have been using on Linux since then.
Presumably since then GNU tar and other tar programs should have caught up with it, but I have not verified this.
Whichever tar program was used in TFA, it was an obsolete tar program, and that was the real problem, not that the archives had been created on an Apple computer.
If you think that most people who run the tar command are assuming it will work like a tape archive, you'll probably be the one surprised
> That said, never seeing another .DS_Store should be a system-wide option!
Yes please.
.DS_Store, .fseventsd, .Spotlight-V100, .Trashes, and ._this and ._that
These can all die in a fire too, as far as I am concerned. macOS loves to treat the user's filesystem as its own personal garbage dump.
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Yes, I completely disagree with TFA.
The problem described in TFA is not specific to Apple, but the same problem appears when archiving any decent filesystem that has been designed during the last 3 decades and not a half of century ago, including all Linux file systems.
The problem described in TFA is not caused by Apple, but by the author using an obsolete tar program and not being aware of this.
The traditional tar file format cannot store a lot of the metadata that is contained in modern file systems (e.g. high resolution timestamps, access control lists, extended file attributes), so it is useless for such file systems.
Most modern "tar" implementations have added extensions to the tar file format, to make it usable with modern file systems, such as Linux XFS or Linux EXT4. But many of these extensions are incompatible between themselves, so certain tar files can be fully extracted only with the same tar program that has created them.
I strongly recommend against using the old tar or cpio file formats. Even with various extensions it is not guaranteed that they always work correctly.
I always use only the pax file format, which has also required extensions in order to work with the modern file systems, but the pax extensions are cleaner than those for tar, because the file format is better designed.
Libarchive, which was mentioned in TFA, is available in most Linux distributions or it can be built from source on any Linux computer. It provides an executable that is preferable to tar (better invoked as "bsdtar --format=pax") for the backup or transfer of any Linux files.
I have not checked recently GNU tar or other tar programs available on Linux, and I hope that meanwhile they have been upgraded to be able to archive losslessly the Linux file systems, but some years ago that was not true, so using tar or cpio on Linux could easily corrupt the archived files.
It's a good attitude to have, in my opinion. Portability is overrated. Linux developers should be doing a lot more of this. We should be making everything work better for us without caring how it's going to impact other irrelevant platforms. Let the people who actually care about those platforms worry about such things.
It would at least be nice if there was a way to keep apple users from shitting all over the filesystem with remote mounts and ds_store files. Perhaps by automatically unmounting if one is detected.
At least with Samba you can use the "veto files" and "delete veto files" global directives to deal with those, I personally use the following for veto files:
I understand that I may loose resource forks, but that isn't a problem for the use case of my server.
defaults write com.apple.desktopservices DSDontWriteNetworkStores true
At least if you're using ZFS as the backing store and Samba, you can set vfs objects = catia fruit streams_xattr and similar config options to use extended attributes.
Portability of tar archives at least. We should have some like .zip which are standardised and allow some like tar to be faithful replicas of exactly how the OS stores data.
Except that zip does not preserve permissions.
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> Linux developers should be doing a lot more of this. We should be making everything work better for us without caring how it's going to impact other irrelevant platforms
Linux developers already do. Using a BSD can already be a pain in the arse, thanks to (often poorly thought out) Linux-isms cropping up everywhere.
Many have a tendency to mix GNU/Linux with UNIX, unfortunely.
Which is why I enjoy at least on embedded we are having plenty of choice between FreeRTOS, NuttX, and plenty others.
Funnily enough, I got the error message and asked Claude Code, and it replied;
then just edited the code as
To me, the big question is why Apple needs all these file attribute ? If the files are extracted OK, just ignore the errors :)
Apple has had multiple streams per file since the very beginning, and it can store useful and necessary information (the latter is quite rare now, as most things have sane defaults, but losing the extended attributes can lose things that can be annoying).