Comment 3 for bug 1671922

OK, I dug into this a bit. I added the line

print("apt-listchanges arguments: ", str(sys.argv))

as the first line of main in apt-listchanges. Next time apticron was called, it produced this:

---
apticron report [Tue, 27 Jun 2017 23:14:42 -0400]
========================================================================

apticron has detected that some packages need upgrading on:

 morannon.ln.benshome.net
 [ 172.17.113.244 ]

The following packages are currently pending an upgrade:

 bsdutils 1:2.29-1ubuntu2.1
 grub-legacy-ec2 0.7.9-153-g16a7302f-0ubuntu1~17.04.1
 libblkid1 2.29-1ubuntu2.1
 libfdisk1 2.29-1ubuntu2.1
 libmount1 2.29-1ubuntu2.1
 libnss-resolve 232-21ubuntu5
 libpam-systemd 232-21ubuntu5
 libsmartcols1 2.29-1ubuntu2.1
 libsystemd0 232-21ubuntu5
 libudev1 232-21ubuntu5
 libuuid1 2.29-1ubuntu2.1
 mount 2.29-1ubuntu2.1
 nplan 0.23~17.04.1
 systemd 232-21ubuntu5
 systemd-sysv 232-21ubuntu5
 udev 232-21ubuntu5
 util-linux 2.29-1ubuntu2.1
 uuid-runtime 2.29-1ubuntu2.1

========================================================================

Package Details:

Usage: apt-listchanges [options] {--apt | filename.deb ...}
apt-listchanges arguments: ['/usr/bin/apt-listchanges', '--which=both', '--headers', '-f', 'text']
---

The problem appears to be that there are no .deb files provided (as all of the other arguments look valid). The execution of apt-listchanges is in line 225 of /usr/sbin/aptcron (on 17.10):

/usr/bin/apt-listchanges --which=both --headers -f text $DEBS

It would appear that $DEBS at this point is empty, rather than containing pathnames for the .debs to be listed. This would seem to point to a problem in lines 194 - 213, where DEBS is set.