postinst is in ubuntu-extras-keyring 2010.09.27.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 | #!/bin/sh
set -e
TRUSTEDFILE="/etc/apt/trusted.gpg"
ARCHIVE_KEYRING="/usr/share/keyrings/ubuntu-extras-keyring.gpg"
REMOVED_KEYS="/usr/share/keyrings/ubuntu-extras-keyring-removed-keys.gpg"
GPG_CMD="gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /etc/apt/secring.gpg --trustdb-name /etc/apt/trustdb.gpg"
GPG="$GPG_CMD  --keyring $TRUSTEDFILE --primary-keyring $TRUSTEDFILE"
process_remove_keyring() {
    REMOVED_KEYS="$1"
    if [ -r "$REMOVED_KEYS" ]; then
	# remove no-longer supported/used keys
	keys=`$GPG_CMD --keyring $REMOVED_KEYS --with-colons --list-keys | grep ^pub | cut -d: -f5`
	for key in $keys; do
	    if $GPG --list-keys --with-colons | grep ^pub | cut -d: -f5 | grep -q $key; then
		$GPG  --batch --delete-key --yes ${key}
	    fi
	done
    fi
}
case "$1" in
    configure)
	if [ -x /usr/bin/apt-key ]; then
            echo "Importing extras.ubuntu.com keyring"
	    apt-key add "$ARCHIVE_KEYRING"
        fi
        if [ -x /usr/bin/gpg ]; then
            echo "Processing extras.ubuntu.com removal keyring"
            process_remove_keyring  "$REMOVED_KEYS"
            echo "OK"
	fi
    ;;
    abort-upgrade|abort-remove|abort-deconfigure)
    ;;
    *)
        echo "postinst called with unknown argument \`$1'" >&2
        exit 1
    ;;
esac
exit 0
 |