On: How modern Linux systems boot

[jschwartzi]

Yes. I have a systemd-based embedded system that uses initramfs so that I can execute some things out of RAM when I need to erase the root filesystem. The old mechanism was initrd which was an ext2 filesystem that was baked into the kernel. The new system, initramfs uses a CPIO archive instead. But it's basically the same idea.

[voltagex_ → jschwartzi]

Does anyone know why CPIO is used in particular? The commands for dealing with those archives are particularly arcane.

[JdeBP → voltagex_]

For dealing with cpio archives, just use pax.

* http://netbsd.gw.com/cgi-bin/man-cgi?pax

* https://manpages.debian.org/unstable/pax/pax.1.en.html

* http://pubs.opengroup.org/onlinepubs/9699919799/

The answer to Why? is given in the kernel doco itself, in Documentation/filesystems/ramfs-rootfs-initramfs.txt .

[vetinari → voltagex_]

Because it is simple, much simpler than tar, and has an universally agreed serialization format, without variants, unlike tar.