Comment 4 for bug 1789637

Tested with 1.1ubuntu1.18.04.6:

root@uu-frontend-lock:~# strace unattended-upgrade --verbose --dry-run 2>&1 | grep lock
openat(AT_FDCWD, "/var/run/unattended-upgrades.lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 4
openat(AT_FDCWD, "/var/lib/dpkg/lock-frontend", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 5
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
openat(AT_FDCWD, "/var/lib/dpkg/lock-frontend", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 5
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
openat(AT_FDCWD, "/var/cache/apt/archives/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 37
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
openat(AT_FDCWD, "/var/lib/dpkg/lock-frontend", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 5
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
root@uu-frontend-lock:~# apt-get install una
unaccent unace-nonfree unagi unagi-dev unar
unace unadf unagi-dbg unalz unattended-upgrades
root@uu-frontend-lock:~# apt-get install unattended-upgrades
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following package was automatically installed and is no longer required:
  libfreetype6
Use 'apt autoremove' to remove it.
Suggested packages:
  bsd-mailx default-mta | mail-transport-agent needrestart
The following packages will be upgraded:
  unattended-upgrades
1 upgraded, 0 newly installed, 0 to remove and 23 not upgraded.
Need to get 37.7 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 unattended-upgrades all 1.1ubuntu1.18.04.6 [37.7 kB]
Fetched 37.7 kB in 0s (186 kB/s)
Preconfiguring packages ...
(Reading database ... 28996 files and directories currently installed.)
Preparing to unpack .../unattended-upgrades_1.1ubuntu1.18.04.6_all.deb ...
Unpacking unattended-upgrades (1.1ubuntu1.18.04.6) over (1.1ubuntu1.18.04.5) ...
Processing triggers for ureadahead (0.100.0-20) ...
Processing triggers for systemd (237-3ubuntu10.3) ...
Setting up unattended-upgrades (1.1ubuntu1.18.04.6) ...
Processing triggers for man-db (2.8.3-2) ...
root@uu-frontend-lock:~# strace unattended-upgrade --verbose --dry-run 2>&1 | grep lock
openat(AT_FDCWD, "/var/run/unattended-upgrades.lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 4
openat(AT_FDCWD, "/var/lib/dpkg/lock-frontend", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 5
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
openat(AT_FDCWD, "/var/cache/apt/archives/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 37
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
root@uu-frontend-lock:~#