So I ended up with the Fedora 21 alpha release and I wanted to know which exact package version of systemd is used in the initrd.

As no yum/rpm is available in the initrd, let’s use the build id to find out:

$ objdump -s systemd 

systemd:     file format elf64-x86-64

Contents of section
 02ac 04000000 14000000 03000000 474e5500  ............GNU.
 02bc 7771e45d 58fc3276 70bee168 01a7cab5  wq.]X.2vp..h....
 02cc 23688382                             #h.. 

So the build id of the /usr/lib/systemd/systemd executable is 0x77 0x71 0xe4 0x5d etc.

With this id we can manually search all debuginfo files in the koji:

Sadly we cannot search directly for the build id in koji, so we must go into each relvant debuginfo file and check if it contains our build id.

And after a while I found that build-id belongs to this package systemd-debuginfo-215-11.fc21.x86_64.rpm