I tested with your single-file approach and that also fails. Note that bionic now has systemd 237, so maybe something is missing (or regressed) ?
$ apt-cache policy systemd systemd: Installed: 237-3ubuntu10.26 Candidate: 237-3ubuntu10.26 Version table: *** 237-3ubuntu10.26 500 500 http://nova.clouds.archive.ubuntu.com/ubuntu bionic-proposed/main amd64 Packages 100 /var/lib/dpkg/status 237-3ubuntu10.25 500 500 http://nova.clouds.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages 237-3ubuntu10.19 500 500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages 237-3ubuntu10 500 500 http://nova.clouds.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
I tested with your single-file approach and that also fails. Note that bionic now has systemd 237, so maybe something is missing (or regressed) ?
$ apt-cache policy systemd nova.clouds. archive. ubuntu. com/ubuntu bionic- proposed/ main amd64 Packages dpkg/status 3ubuntu10. 25 500 nova.clouds. archive. ubuntu. com/ubuntu bionic-updates/main amd64 Packages 3ubuntu10. 19 500 security. ubuntu. com/ubuntu bionic- security/ main amd64 Packages nova.clouds. archive. ubuntu. com/ubuntu bionic/main amd64 Packages
systemd:
Installed: 237-3ubuntu10.26
Candidate: 237-3ubuntu10.26
Version table:
*** 237-3ubuntu10.26 500
500 http://
100 /var/lib/
237-
500 http://
237-
500 http://
237-3ubuntu10 500
500 http://