/usr/share/live/build/data/debian-cd/squeeze/exclude-udebs-s390 is in open-infrastructure-system-build 20161101-lts2-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | # S/390 does not support loading udebs off the CD image,
# so we can exclude all udebs from it
*
|