Comment # 29 on bug 1228929 from Martin Wilck

I'm not seeing any trace messages from regenerate-initrd-posttrans. Are you
sure you have installed the file provided in the correct path
(/usr/lib/module-init-tools/regenerate-initrd-posttrans)?

Please run this tool manually.

# test 1

mkdir /run/regenerate-initrd
touch /run/regenerate-initrd/6.6.50-1-longterm
/usr/lib/module-init-tools/regenerate-initrd-posttrans


# test 2

mkdir /run/regenerate-initrd
touch /run/regenerate-initrd/all
touch /run/regenerate-initrd/6.6.50-1-longterm
/usr/lib/module-init-tools/regenerate-initrd-posttrans

The initrd should be rebuilt in both cases.