The following seems to work
$ sudo piuparts /tmp/isdnutils-base_3.9.20060704+dfsg.2-8_i386.deb --keyring=/usr/share/keyrings/ubuntu-archive-keyring.gpg
The following seems to work
$ sudo piuparts /tmp/isdnutils- base_3. 9.20060704+ dfsg.2- 8_i386. deb --keyring= /usr/share/ keyrings/ ubuntu- archive- keyring. gpg