Initrd Dynamic [LWN.net]

Initrd Dynamic

Posted Nov 8, 2002 22:09 UTC (Fri) by Peter (guest, #1127)
In reply to: Initrd Dynamic by pflugstad
Parent article: Initramfs arrives

(note: I like tar better than cpio as well).

You probably mean you like the /usr/bin/tar interface better than the /usr/bin/cpio interface. Hey, who doesn't? `tar' is quite confusing when you first try to figure out the command line, but we've all long since learned the important options. But there's a reason Red Hat picked cpio as the basis for the RPM package format. As people have said on linux-kernel, tar is a mess of a format, compatibility-wise - the original version had some annoying filename length limitations and stored only numeric uid/gids, and there are two or three derivative formats that remove these limitations but as kludges so as not to completely confuse old `tar' programs. I understand cpio is a much saner format, from an implementor's point of view. That's why Al Viro and co. went with it for initramfs.

(Interestingly, although RPM is based on cpio, Debian's .deb format is based on tar.gz or, recently, tar.bz2.)

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Initrd Dynamic

Posted Nov 12, 2002 14:25 UTC (Tue) by IkeTo (subscriber, #2122) [Link] (1 responses)

Debian format isn't based on tar (or tar.gz, or tar.bz2) at all! See deb(5). It is based on ar. Of course, in source package, you need to patch the original of some package, and that original can be of any form, be it tar.gz, or tar.bz2, or even rpm. But the deb format is not based on them.

Initrd Dynamic

Posted Jan 15, 2006 15:17 UTC (Sun) by pkern (subscriber, #32883) [Link]

Old threads die hard...

`ar' is indeed the outer container for a Debian package, but all files and control data inside of it is stored in tar.{gz,bz2}.

Tar vs. cpio

Posted Nov 15, 2002 0:43 UTC (Fri) by EricBackus (guest, #2816) [Link]

Actually, the cpio command-line interface appears cleaner to me than tar's. But that's not enough reason to use cpio.

Both tar and cpio provide similar capabilities and store similar information about the files they contain. However, tar is *far* more commonly used than cpio, which means that tar extraction programs are also far more available than cpio. Furthermore, in spite of the older variations on the tar format, there has for some years been a standard for it.

I'm not convinced that cpio is really "saner" than the standard tar format, but even if that's true, we have known-good code for dealing with tar archives (GNU tar, and probably half a dozen independent implementations).

Tar is the de facto standard, and "standard is better than better".