I upgrade my packages using aptitude, specifying the apt options --force-confdef and --force-confold.This generally works, but the package libpam-systemd (204-5ubuntu20.8, on Ubuntu 14.04) still asks if I want to replace the (modified) configuration files.I can see the following processes when the dialog is open:/usr/bin/dpkg --force-confdef --status-fd 113 --configure libpam-systemd:amd64/bin/sh /var/lib/dpkg/info/libpam-systemd:amd64.postinst configure 204-5ubuntu20.7whiptail --backtitle Package configuration --title PAM configuration --output-fd 11 --defaultno --yesno -- One or more of the files /etc/pam.d/common-{auth,account,password,session} have been locally modified.  Please indicate whether these local changes should be overridden using the system-provided  configuration.  If you decline this option, you will need to manage your system's authentication configuration by hand.  Override local changes to /etc/pam.d/common-*? 10 200What can I do in order to run the upgrade non-interactively?
Why libpam-systemd run interactively on apt upgrade, even when specified force-confdef/force-confold
ubuntu;apt;upgrade;pam
As it turned out, such configuration files are handled via a different system:The whiptail prompts are done through debconf, which means that aDEBIAN_FRONTEND=none setting will give you the desired results for anon-interactive upgrade.so in order to upgrade non-interactively, one muse use DEBIAN_FRONTEND=none.