Comment 13 for bug 1803749

Tested with 1.1ubuntu1.18.04.7~16.04.1:

$ sudo chroot x-test-1803749/
root@MacBookAir-test:/# apt install unattended-upgrades zsh
Reading package lists... Done
Building dependency tree... Done
The following additional packages will be installed:
  iso-codes python-apt-common python3-apt xz-utils zsh-common
Suggested packages:
  isoquery python3-apt-dbg python-apt-doc bsd-mailx mail-transport-agent zsh-doc
The following NEW packages will be installed:
  iso-codes python-apt-common python3-apt unattended-upgrades xz-utils zsh zsh-common
0 upgraded, 7 newly installed, 0 to remove and 0 not upgraded.
Need to get 6354 kB of archives.
After this operation, 32.2 MB of additional disk space will be used.
Do you want to continue? [Y/n]
Get:1 http://archive.ubuntu.com/ubuntu xenial/main amd64 zsh-common all 5.1.1-1ubuntu2 [3170 kB]
Get:2 http://archive.ubuntu.com/ubuntu xenial/main amd64 zsh amd64 5.1.1-1ubuntu2 [651 kB]
Get:3 http://archive.ubuntu.com/ubuntu xenial/main amd64 iso-codes all 3.65-1 [2268 kB]
Get:4 http://archive.ubuntu.com/ubuntu xenial/main amd64 python-apt-common all 1.1.0~beta1build1 [17.3 kB]
Get:5 http://archive.ubuntu.com/ubuntu xenial/main amd64 python3-apt amd64 1.1.0~beta1build1 [137 kB]
Get:6 http://archive.ubuntu.com/ubuntu xenial/main amd64 xz-utils amd64 5.1.1alpha+20120614-2ubuntu2 [78.8 kB]
Get:7 http://archive.ubuntu.com/ubuntu xenial/main amd64 unattended-upgrades all 0.90 [31.6 kB]
Fetched 6354 kB in 6s (1024 kB/s)
Preconfiguring packages ...
E: Can not write log (Is /dev/pts mounted?) - posix_openpt (19: No such device)
Selecting previously unselected package zsh-common.
(Reading database ... 10444 files and directories currently installed.)
Preparing to unpack .../zsh-common_5.1.1-1ubuntu2_all.deb ...
Unpacking zsh-common (5.1.1-1ubuntu2) ...
Selecting previously unselected package zsh.
Preparing to unpack .../zsh_5.1.1-1ubuntu2_amd64.deb ...
Unpacking zsh (5.1.1-1ubuntu2) ...
Selecting previously unselected package iso-codes.
Preparing to unpack .../iso-codes_3.65-1_all.deb ...
Unpacking iso-codes (3.65-1) ...
Selecting previously unselected package python-apt-common.
Preparing to unpack .../python-apt-common_1.1.0~beta1build1_all.deb ...
Unpacking python-apt-common (1.1.0~beta1build1) ...
Selecting previously unselected package python3-apt.
Preparing to unpack .../python3-apt_1.1.0~beta1build1_amd64.deb ...
Unpacking python3-apt (1.1.0~beta1build1) ...
Selecting previously unselected package xz-utils.
Preparing to unpack .../xz-utils_5.1.1alpha+20120614-2ubuntu2_amd64.deb ...
Unpacking xz-utils (5.1.1alpha+20120614-2ubuntu2) ...
Selecting previously unselected package unattended-upgrades.
Preparing to unpack .../unattended-upgrades_0.90_all.deb ...
Unpacking unattended-upgrades (0.90) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for systemd (229-4ubuntu4) ...
Setting up zsh-common (5.1.1-1ubuntu2) ...
Setting up zsh (5.1.1-1ubuntu2) ...
update-alternatives: using /bin/zsh5 to provide /bin/zsh (zsh) in auto mode
update-alternatives: using /bin/zsh5 to provide /bin/rzsh (rzsh) in auto mode
Setting up iso-codes (3.65-1) ...
Setting up python-apt-common (1.1.0~beta1build1) ...
Setting up python3-apt (1.1.0~beta1build1) ...
Setting up xz-utils (5.1.1alpha+20120614-2ubuntu2) ...
update-alternatives: using /usr/bin/xz to provide /usr/bin/lzma (lzma) in auto mode
Setting up unattended-upgrades (0.90) ...

Creating config file /etc/apt/apt.conf.d/20auto-upgrades with new version

Creating config file /etc/apt/apt.conf.d/50unattended-upgrades with new version
update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for systemd (229-4ubuntu4) ...
root@MacBookAir-test:/# apt-mark auto zsh
zsh set to automatically installed.
root@MacBookAir-test:/# echo "Unattended-Upgrade::Package-Blacklist {"libs";}" > /etc/apt/apt.conf.d/51unattended-upgrades
root@MacBookAir-test:/# echo "deb http://archive.ubuntu.com/ubuntu xenial-security main" >> /etc/apt/sources.list
root@MacBookAir-test:/# echo "deb http://archive.ubuntu.com/ubuntu xenial-updates main" >> /etc/apt/sources.list
root@MacBookAir-test:/# apt update -qq
105 packages can be upgraded. Run 'apt list --upgradable' to see them.
root@MacBookAir-test:/# unattended-upgrades --dry-run --verbose --debug
Initial blacklisted packages: libs
Initial whitelisted packages:
Starting unattended upgrades script
...
adjusting candidate version: 'libkmod2=22-1ubuntu5'
adjusting candidate version: 'libstdc++6=5.4.0-6ubuntu1~16.04.10'
adjusting candidate version: 'sudo=1.8.16-0ubuntu1.4'
marking zsh-common for remove
marking zsh for remove
Packages that are auto removed: 'zsh zsh-common'
E: Can not write log (Is /dev/pts mounted?) - posix_openpt (19: No such device)
/usr/bin/dpkg --status-fd 197 --force-depends --force-remove-essential --remove zsh:amd64 zsh-common:all
/usr/bin/dpkg --status-fd 199 --configure --pending
Packages were successfully auto-removed
InstCount=0 DelCount=2 BrokenCount=0
root@MacBookAir-test:/# echo "deb http://archive.ubuntu.com/ubuntu xenial-proposed main" >> /etc/apt/sources.list
root@MacBookAir-test:/# apt update -qq

105 packages can be upgraded. Run 'apt list --upgradable' to see them.
root@MacBookAir-test:/#
root@MacBookAir-test:/# apt install unattended-upgrades
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  dbus gir1.2-glib-2.0 libcap-ng0 libdbus-1-3 libdbus-glib-1-2 libgirepository-1.0-1 libglib2.0-0 libglib2.0-data
  libicu55 libxml2 powermgmt-base python3-dbus python3-gi sgml-base shared-mime-info xdg-user-dirs xml-core
Suggested packages:
  dbus-user-session | dbus-x11 python-dbus-doc python3-dbus-dbg sgml-base-doc bsd-mailx default-mta
  | mail-transport-agent needrestart debhelper
The following NEW packages will be installed:
  dbus gir1.2-glib-2.0 libcap-ng0 libdbus-1-3 libdbus-glib-1-2 libgirepository-1.0-1 libglib2.0-0 libglib2.0-data
  libicu55 libxml2 powermgmt-base python3-dbus python3-gi sgml-base shared-mime-info xdg-user-dirs xml-core
The following packages will be upgraded:
  unattended-upgrades
1 upgraded, 17 newly installed, 0 to remove and 104 not upgraded.
Need to get 11.0 MB of archives.
After this operation, 43.5 MB of additional disk space will be used.
Do you want to continue? [Y/n]
Get:1 http://archive.ubuntu.com/ubuntu xenial-security/main amd64 libglib2.0-0 amd64 2.48.2-0ubuntu4.1 [1120 kB]
Get:2 http://archive.ubuntu.com/ubuntu xenial/main amd64 sgml-base all 1.26+nmu4ubuntu1 [12.5 kB]
Get:3 http://archive.ubuntu.com/ubuntu xenial/main amd64 libcap-ng0 amd64 0.7.7-1 [10.9 kB]
Get:4 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 libdbus-1-3 amd64 1.10.6-1ubuntu3.3 [161 kB]
Get:5 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 dbus amd64 1.10.6-1ubuntu3.3 [142 kB]
Get:6 http://archive.ubuntu.com/ubuntu xenial/main amd64 libgirepository-1.0-1 amd64 1.46.0-3ubuntu1 [88.3 kB]
Get:7 http://archive.ubuntu.com/ubuntu xenial/main amd64 gir1.2-glib-2.0 amd64 1.46.0-3ubuntu1 [127 kB]
Get:8 http://archive.ubuntu.com/ubuntu xenial/main amd64 libdbus-glib-1-2 amd64 0.106-1 [67.1 kB]
Get:9 http://archive.ubuntu.com/ubuntu xenial-security/main amd64 libglib2.0-data all 2.48.2-0ubuntu4.1 [132 kB]
Get:10 http://archive.ubuntu.com/ubuntu xenial-security/main amd64 libicu55 amd64 55.1-7ubuntu0.4 [7646 kB]
Get:11 http://archive.ubuntu.com/ubuntu xenial-security/main amd64 libxml2 amd64 2.9.3+dfsg1-1ubuntu0.6 [697 kB]
Get:12 http://archive.ubuntu.com/ubuntu xenial/main amd64 powermgmt-base all 1.31+nmu1 [7178 B]
Get:13 http://archive.ubuntu.com/ubuntu xenial/main amd64 python3-dbus amd64 1.2.0-3 [83.1 kB]
Get:14 http://archive.ubuntu.com/ubuntu xenial/main amd64 python3-gi amd64 3.20.0-0ubuntu1 [153 kB]
Get:15 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 shared-mime-info amd64 1.5-2ubuntu0.2 [405 kB]
Get:16 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 xdg-user-dirs amd64 0.15-2ubuntu6.16.04.1 [61.8 kB]
Get:17 http://archive.ubuntu.com/ubuntu xenial/main amd64 xml-core all 0.13+nmu2 [23.3 kB]
Get:18 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 unattended-upgrades all 1.1ubuntu1.18.04.7~16.04.1 [40.2 kB]
Fetched 11.0 MB in 6s (1827 kB/s)
...
Processing triggers for sgml-base (1.26+nmu4ubuntu1) ...
root@MacBookAir-test:/# unattended-upgrades --dry-run --verbose --debug
Initial blacklisted packages: libs
...
applying set ['python3.5', 'python3.5-minimal', 'libpython3.5-stdlib', 'libpython3.5-minimal']
apt_pkg.pkgsystem_unlock() failed due to not holding the lock but trying to continue
E: Can not write log (Is /dev/pts mounted?) - posix_openpt (19: No such device)
/usr/bin/dpkg --status-fd 139 --unpack --auto-deconfigure /var/cache/apt/archives/python3.5_3.5.2-2ubuntu0~16.04.5_amd64.deb /var/cache/apt/archives/libpython3.5-stdlib_3.5.2-2ubuntu0~16.04.5_amd64.deb /var/cache/apt/archives/python3.5-minimal_3.5.2-2ubuntu0~16.04.5_amd64.deb /var/cache/apt/archives/libpython3.5-minimal_3.5.2-2ubuntu0~16.04.5_amd64.deb
/usr/bin/dpkg --status-fd 141 --configure libpython3.5-minimal:amd64 python3.5-minimal:amd64 libpython3.5-stdlib:amd64 python3.5:amd64
/usr/bin/dpkg --status-fd 143 --configure --pending
left to upgrade set()
All upgrades installed
InstCount=0 DelCount=0 BrokenCount=0
root@MacBookAir-test:/#