The generated line in /var/lib/dpkg/info/libvirt-daemon-system.postinst for the example of /etc/default/libvirt-bin is:
dpkg-maintscript-helper mv_conffile /etc/default/libvirt-bin /etc/default/libvirtd 1.3.3-2 libvirt-bin -- "$@"
But executed on the target as-is it works:
DPKG_MAINTSCRIPT_NAME=postinst dpkg-maintscript-helper mv_conffile /etc/default/libvirt-bin /etc/default/libvirtd 1.3.3-2 libvirt-bin -- configure 1.3.1-1ubuntu10.10
The generated line in /var/lib/ dpkg/info/ libvirt- daemon- system. postinst for the example of /etc/default/ libvirt- bin is: t-helper mv_conffile /etc/default/ libvirt- bin /etc/default/ libvirtd 1.3.3-2 libvirt-bin -- "$@"
dpkg-maintscrip
But executed on the target as-is it works: T_NAME= postinst dpkg-maintscrip t-helper mv_conffile /etc/default/ libvirt- bin /etc/default/ libvirtd 1.3.3-2 libvirt-bin -- configure 1.3.1-1ubuntu10.10
DPKG_MAINTSCRIP
Continue debugging ...