interruption of dist-upgrade can leave you next release in sources.list

[udippel]

[Impact]
Calling update() or installing packages from apt clients resets their SIGINT and SIGQUIT handlers to SIG_DFL, overriding any signal handlers they might have set for them.

In case of ubuntu-release-upgrader, this results in the release upgrader being unable to handle interrupts after it did the initial update - the default libc handler will run and the program exits.

[Test plan]

[[apt]]
As a standalone test for apt, we can test the following script:

import apt
import time

apt.Cache().update()
print("WAITING")
try:
    time.sleep(10000)
except BaseException as e:
    print("Seen", repr(e))
print("END")

Pressing Ctrl+C while WAITING is printed should print Seen KeyboardInterrupt, and importantly, also the END line.

[[ubuntu-release-upgrader]]
1) On an Ubuntu 18.04 system run do-release-upgrade in a terminal.
2) At the "Do you want to start the upgrade?" question say Y.
3) When you see the "Lock screen disabled" message you will also see "Inhibiting until Ctrl+C is pressed".
4) Press "Ctrl+C"

Your /etc/apt/sources.list file will now have focal in it instead of bionic although the upgrade has quit. With the version of ubuntu-release-upgrader in -proposed you will not see the "Ctrl+C" message. For your sources.list file to be restored you'll need the version of apt from bionic-proposed installed before starting the upgrade.

[Where problems could occur]
apt: This specific change removes the two lines that SIG_DFL the signal handlers after running scripts. AFAWCT those lines are unnecessary - the code that calls it temporarily sets the handlers to SIG_IGN but restores previous handlers at the end; it was wrongly refactored decades ago. A regression could occur in that those signals will now continue to be ignored if we missed a spot.

ubuntu-release-upgrader: The change is wrapping a bunch of code in a try: except: block so if the indentation was off the pyflakes / pycodestyle tests would fail but autopkgtest will catch that.

[Original bug report]
As a long-time-user of ?ubuntu, with apt-get as tool of choice for updates/upgrades I wrote a daily script for updates, with 'dist-upgrade'.
In all earlier years, it wouldn't actually do an upgrade of a ?ubuntu version; just all packages including new ones. Version updates had to be initiated manually, and I was always asked if I really wanted the new ?ubuntu version. Sounds appropriate.

Last night when it (dist-upgrade), it just gave me 20.04. No questions asked. I for one consider this kind of intrusive, though.
It *might* have to make with me trying 'sudo do-release-upgrade -m desktop' a number of times earlier; just to *check* if the upgrade was on offer; but this is only a guess.

In *any* case, a pop-up asking "Are you sure? Are you connected through an adequate pipe? Are you sitting with full batteries; better a power supply?" would be convenient; since I am using my PC for urgent duties, and didn't want to fiddle with unexpected upgrade bugs.

ProblemType: BugDistroRelease: Ubuntu 20.04
Package: ubuntu-release-upgrader-core 1:20.04.25
ProcVersionSignature: Ubuntu 5.4.0-48.52-generic 5.4.60
Uname: Linux 5.4.0-48-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.9
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
CurrentDesktop: KDE
Date: Thu Oct 1 11:48:39 2020
InstallationDate: Installed on 2019-03-14 (566 days ago)
InstallationMedia: Kubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
PackageArchitecture: allSourcePackage: ubuntu-release-upgrader
Symptom: ubuntu-release-upgrader
UpgradeStatus: Upgraded to focal on 2020-09-29 (1 days ago)
VarLogDistupgradeAptlog:
 Log time: 2020-09-29 19:44:28.696289
 Log time: 2020-09-29 19:44:33.573481

[Brian Murray (brian-murray)]

The release upgrade process is interactive and should ask you questions during the upgrade process. Do you have any other log files in /var/log/dist-upgrade? There may be an apt-term.log and / or a screenlog.0 file. Both of those may help sorting out what happened.

[udippel (udippel)]

$ ls -l
total 832
-rw------- 1 root root 834466 Sep 29 19:44 apt-clone_system_state.tar.gz
-rw-r--r-- 1 root root 74 Sep 29 19:44 apt.log
-rw-r--r-- 1 root root 1381 Sep 29 19:44 lspci.txt
-rw-r--r-- 1 root root 7283 Sep 29 19:44 main.log

Would any of these help?

[udippel (udippel)]

https://ubuntuforums.org/showthread.php?t=2451286&p=13989918#post13989918

has come up with an answer that sounds possible to me; though I had it written in here in my OP.
In any case, if the poster was correct, the whole thing would still be a tad off expectations as far as I am concerned: a job cancelled continues on its own later?

[Launchpad Janitor (janitor)]

[Expired for ubuntu-release-upgrader (Ubuntu) because there has been no activity for 60 days.]

[Brian Murray (brian-murray)]

Thinking about this more I suspect what happened was that the release upgrade process (running 'sudo do-release-upgrade -m desktop') was interrupted at a point after it had modified your /etc/apt/sources.list file to focal. Then when 'dist-upgrade' was run because your sources.list file now containted focal all the packages from focal were installed. The release upgrade process should do a better job of restoring your sources.list file in the event that it is interrupted (Ctrl-C).

Also for what its worth do-release-upgrade has a '-c' switch which specifically only checks if a new distribution release is available.

[Balint Reczey (rbalint)]

I've also experienced this in 18.04 -> 20.04 upgrade when running do-release-upgrade without any option.

[Brian Murray (brian-murray)]

While a KeyboardInterrupt handler has been introduced to ubuntu-release-upgrader apt is actually sending the SIGINT back to the distribution upgrade process. This can be fixed in apt by removing the following:

--- apt-2.1.10ubuntu0.2/apt-pkg/contrib/fileutl.cc 2021-01-14 03:29:25.000000000 -0800
+++ apt-2.1.10ubuntu0.3~ppa1/apt-pkg/contrib/fileutl.cc 2021-02-26 09:13:10.000000000 -0800
@@ -140,10 +140,6 @@
       return _error->Errno("waitpid","Couldn't wait for subprocess");
    }

- // Restore sig int/quit
- signal(SIGQUIT,SIG_DFL);
- signal(SIGINT,SIG_DFL);
-
    // Check for an error code.
    if (WIFEXITED(Status) == 0 || WEXITSTATUS(Status) != 0)
    {

[Launchpad Janitor (janitor)]

This bug was fixed in the package apt - 2.2.1

---------------
apt (2.2.1) unstable; urgency=medium

  [ Julian Andres Klode ]
  * Do not require force-loopbreak on Protected packages (Closes: #983014)
  * Branch of as 2.2.y for bullseye
  * configuration: Add missing #include <array>
  * Remove .travis.yml, we are using GitLab CI these days
  * RunScripts: Do not reset SIGQUIT and SIGINT to SIG_DFL (LP: #1898026)
  * regression fix: do require force-loopbreak for Conflicts

  [ Алексей Шилин ]
  * Russian translation update (Closes: #983348)

 -- Julian Andres Klode <email address hidden> Mon, 01 Mar 2021 22:27:55 +0100

[Launchpad Janitor (janitor)]

This bug was fixed in the package ubuntu-release-upgrader - 1:21.04.5

---------------
ubuntu-release-upgrader (1:21.04.5) hirsute; urgency=medium

  [ William 'jawn-smith' Wilson ]
  * Add quirk to block upgrade if docker containers are configured to use the
    aufs storage-driver (LP: #1907713)

  [ Brian Murray ]
  * DistUpgrade/DistUpgradeController.py: where possible restore sources.list
    if a KeyboardInterrupt event is received. (LP: #1898026)
  * DistUpgrade/DistUpgradeController.py: redirect the output of
    gnome-session-inhibit to devnull so a message regarding Ctrl-C is not
    displayed.

 -- Brian Murray <email address hidden> Fri, 26 Feb 2021 11:27:39 -0800

[Julian Andres Klode (juliank)]

For the record, we are going to roll the apt change out in groovy shortly, but delay the LTS updates to give it some more real world testing.

[Brian Murray (brian-murray)]

Hello udippel, or anyone else affected,

Accepted apt into groovy-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/apt/2.1.10ubuntu0.3 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-groovy to verification-done-groovy. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-groovy. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Ubuntu SRU Bot (ubuntu-sru-bot)]

All autopkgtests for the newly accepted apt (2.1.10ubuntu0.3) for groovy have finished running.
The following regressions have been reported in tests triggered by the package:

reprotest/0.7.15 (arm64, s390x)
livecd-rootfs/2.694.3 (amd64, s390x)
dgit/9.11ubuntu1 (arm64)

Please visit the excuses page listed below and investigate the failures, proceeding afterwards as per the StableReleaseUpdates policy regarding autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-migration/groovy/update_excuses.html#apt

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!

[Julian Andres Klode (juliank)]

I checked do-release-upgrade -d before upgrading apt, and pressing Ctrl+C at the prompt for conforming changes left hirsute in sources.list.

I upgraded to apt 2.1.10ubuntu0.3 from proposed, ran it again, and Ctrl+C now caused the restore code to run:

 Continue [yN] Details [d]^C
Restoring original system state

Aborting
Reading package lists... Done
Building dependency tree
Reading state information... Done
=== Command detached from window (Tue Mar 30 15:04:31 2021) ===

[Julian Andres Klode (juliank)]

The small simple script also worked with the proposed version:

# python3 a.py
WAITING
^CSeen KeyboardInterrupt()
END

[udippel (udippel)]

With respect to #12, I am not sufficiently well versed in rolling back to 18_04 in order to try once again, as much as I would love to do so and help by repeating my earlier steps that lead to the upgrade.
Though, it looks like others have been able to simulate the steps.

Thanks a lot for all the efforts!

Uwe

[Launchpad Janitor (janitor)]

This bug was fixed in the package apt - 2.1.10ubuntu0.3

---------------
apt (2.1.10ubuntu0.3) groovy; urgency=medium

  [ David Kalnischkies ]
  * Fix incorrect base64 encoding due to int promotion (LP: #1916050)
  * Harden test for no new acquires after transaction abort (Closes: #984966)
    (LP: #1918920)

  [ Julian Andres Klode ]
  * Implement update --error-on=any (Closes: #594813) (LP: #1693900)
  * Include all translations when building the cache (LP: #1907850)
  * Do not require force-loopbreak on Protected packages (Closes: #983014)
    (LP: #1916725)
  * RunScripts: Do not reset SIGQUIT and SIGINT to SIG_DFL (LP: #1898026)
  * Protect currently running kernel at run-time (LP: #1615381)
  * Make ADDARG{,C}() macros expand to single statements

 -- Julian Andres Klode <email address hidden> Fri, 12 Mar 2021 09:22:11 +0100

[Brian Murray (brian-murray)]

The verification of the Stable Release Update for apt has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

[Steve Langasek (vorlon)]

Hello udippel, or anyone else affected,

Accepted ubuntu-release-upgrader into focal-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/ubuntu-release-upgrader/1:20.04.33 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-focal to verification-done-focal. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-focal. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Brian Murray (brian-murray)]

I tested and upgrade from a Bionic system to Focal using do-release-upgrade -p and as you can see in the attached screenshot the "Inhibiting until Ctrl+C is pressed" message no longer appears. So I'm setting this to verification-done.

[Łukasz Zemczak (sil2100)]

Hello udippel, or anyone else affected,

Accepted ubuntu-release-upgrader into groovy-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/ubuntu-release-upgrader/1:20.10.16 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-groovy to verification-done-groovy. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-groovy. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Launchpad Janitor (janitor)]

This bug was fixed in the package ubuntu-release-upgrader - 1:20.04.33

---------------
ubuntu-release-upgrader (1:20.04.33) focal; urgency=medium

  * DistUpgrade/DistUpgradeController.py: restore sources.list where possible
    if a KeyboardInterrupt event is received and redirect the output of
    gnome-session-inhibit to devnull so a message regarding Ctrl-C is not
    displayed. (LP: #1898026)
  * DistUpgrade/DistUpgradeQuirks.py: Restore code which ensured the python
    package was maked for removal. (LP: #1928397)
  * Update mirrors and translations.

 -- Brian Murray <email address hidden> Thu, 13 May 2021 16:38:41 -0700

[dragonhahney (dragonhahney)]

On Mon, May 24, 2021, 8:20 AM Launchpad Bug Tracker <
<email address hidden>> wrote:

> This bug was fixed in the package ubuntu-release-upgrader - 1:20.04.33
>
> ---------------
> ubuntu-release-upgrader (1:20.04.33) focal; urgency=medium
>
> * DistUpgrade/DistUpgradeController.py: restore sources.list where
> possible
> if a KeyboardInterrupt event is received and redirect the output of
> gnome-session-inhibit to devnull so a message regarding Ctrl-C is not
> displayed. (LP: #1898026)
> * DistUpgrade/DistUpgradeQuirks.py: Restore code which ensured the python
> package was maked for removal. (LP: #1928397)
> * Update mirrors and translations.
>
> -- Brian Murray <email address hidden> Thu, 13 May 2021 16:38:41 -0700
>
> ** Changed in: ubuntu-release-upgrader (Ubuntu Focal)
> Status: Fix Committed => Fix Released
>
> --
> You received this bug notification because you are subscribed to apt in
> Ubuntu.
> Matching subscriptions: dragonhahney
> https://bugs.launchpad.net/bugs/1898026
>
> Title:
> interruption of dist-upgrade can leave you next release in
> sources.list
>
> Status in apt package in Ubuntu:
> Fix Released
> Status in ubuntu-release-upgrader package in Ubuntu:
> Fix Released
> Status in apt source package in Bionic:
> New
> Status in ubuntu-release-upgrader source package in Bionic:
> New
> Status in apt source package in Focal:
> New
> Status in ubuntu-release-upgrader source package in Focal:
> Fix Released
> Status in apt source package in Groovy:
> Fix Released
> Status in ubuntu-release-upgrader source package in Groovy:
> Fix Committed
> Status in apt source package in Hirsute:
> Fix Released
> Status in ubuntu-release-upgrader source package in Hirsute:
> Fix Released
>
> Bug description:
> [Impact]
> Calling update() or installing packages from apt clients resets their
> SIGINT and SIGQUIT handlers to SIG_DFL, overriding any signal handlers they
> might have set for them.
>
> In case of ubuntu-release-upgrader, this results in the release
> upgrader being unable to handle interrupts after it did the initial
> update - the default libc handler will run and the program exits.
>
> [Test plan]
>
> [[apt]]
> As a standalone test for apt, we can test the following script:
>
> import apt
> import time
>
> apt.Cache().update()
> print("WAITING")
> try:
> time.sleep(10000)
> except BaseException as e:
> print("Seen", repr(e))
> print("END")
>
> Pressing Ctrl+C while WAITING is printed should print Seen
> KeyboardInterrupt, and importantly, also the END line.
>
> [[ubuntu-release-upgrader]]
> 1) On an Ubuntu 18.04 system run do-release-upgrade in a terminal.
> 2) At the "Do you want to start the upgrade?" question say Y.
> 3) When you see the "Lock screen disabled" message you will also see
> "Inhibiting until Ctrl+C is pressed".
> 4) Press "Ctrl+C"
>
> Your /etc/apt/sources.list file will now have focal in it instead of
> bionic although the upgrade has quit. With the version of ubuntu-
> release-upgrader in -proposed you will not see the "Ctrl+C" message.
> For your sources.list file to be restored you'll need th...

[Brian Murray (brian-murray)]

I tested and upgrade from a Focal system to Groovy using do-release-upgrade -p and as you can see in the attached screenshot the "Inhibiting until Ctrl+C is pressed" message no longer appears. So I'm setting this to verification-done for ubuntu-release-upgrader.

[Launchpad Janitor (janitor)]

This bug was fixed in the package ubuntu-release-upgrader - 1:20.10.16

---------------
ubuntu-release-upgrader (1:20.10.16) groovy; urgency=medium

  * DistUpgrade/DistUpgradeController.py: restore sources.list where possible
    if a KeyboardInterrupt event is received and redirect the output of
    gnome-session-inhibit to devnull so a message regarding Ctrl-C is not
    displayed. (LP: #1898026)
  * Update mirrors, demotions, and translations.

 -- Brian Murray <email address hidden> Fri, 14 May 2021 10:27:44 -0700

[Brian Murray (brian-murray)]

Hello udippel, or anyone else affected,

Accepted apt into focal-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/apt/2.0.6 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-focal to verification-done-focal. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-focal. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Brian Murray (brian-murray)]

Hello udippel, or anyone else affected,

Accepted apt into bionic-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/apt/1.6.14 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-bionic to verification-done-bionic. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-bionic. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Ubuntu SRU Bot (ubuntu-sru-bot)]

All autopkgtests for the newly accepted apt (1.6.14) for bionic have finished running.
The following regressions have been reported in tests triggered by the package:

apport/2.20.9-0ubuntu7.24 (amd64)

Please visit the excuses page listed below and investigate the failures, proceeding afterwards as per the StableReleaseUpdates policy regarding autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-migration/bionic/update_excuses.html#apt

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!

[Ubuntu SRU Bot (ubuntu-sru-bot)]

All autopkgtests for the newly accepted apt (2.0.6) for focal have finished running.
The following regressions have been reported in tests triggered by the package:

reprotest/0.7.14 (ppc64el)
apport/2.20.11-0ubuntu27.18 (amd64)

Please visit the excuses page listed below and investigate the failures, proceeding afterwards as per the StableReleaseUpdates policy regarding autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-migration/focal/update_excuses.html#apt

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!

[Julian Andres Klode (juliank)]

focal/2.0.6: The standalone test certainly worked, and the keyboard interrupts were delivered to do-release-upgrade

[Julian Andres Klode (juliank)]

bionic, 1.6.14 is good too.

root@b:~# python3 a.py
WAITING
^C
root@b:~# apt install libapt-pkg5.0
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.
The following additional packages will be installed:
  apt apt-utils
Suggested packages:
  apt-doc aptitude | synaptic | wajig dpkg-dev
The following packages will be upgraded:
  apt apt-utils libapt-pkg5.0
3 upgraded, 0 newly installed, 0 to remove and 29 not upgraded.
Need to get 2224 kB of archives.
After this operation, 16.4 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:1 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 libapt-pkg5.0 amd64 1.6.14 [809 kB]
Get:2 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 apt amd64 1.6.14 [1207 kB]
Get:3 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 apt-utils amd64 1.6.14 [209 kB]
Fetched 2224 kB in 0s (7775 kB/s)
(Reading database ... 28937 files and directories currently installed.)
Preparing to unpack .../libapt-pkg5.0_1.6.14_amd64.deb ...
Unpacking libapt-pkg5.0:amd64 (1.6.14) over (1.6.13) ...
Setting up libapt-pkg5.0:amd64 (1.6.14) ...
(Reading database ... 28937 files and directories currently installed.)
Preparing to unpack .../archives/apt_1.6.14_amd64.deb ...
Unpacking apt (1.6.14) over (1.6.13) ...
Setting up apt (1.6.14) ...
(Reading database ... 28937 files and directories currently installed.)
Preparing to unpack .../apt-utils_1.6.14_amd64.deb ...
Unpacking apt-utils (1.6.14) over (1.6.13) ...
Setting up apt-utils (1.6.14) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
Processing triggers for libc-bin (2.27-3ubuntu1.4) ...
root@b:~# python3 a.py
WAITING
^CSeen KeyboardInterrupt()
END

do-release-upgrade was fine too:
Upgrading
Fetched 0 B in 0s (0 B/s)

Restoring original system state

Note that if you Ctrl+C while it's downloading the upgrades, it gets the keyboardinterrupt in the wrong spot - inside the progress handler and does not restore the correct state, probably should be a different bug, though.

[Launchpad Janitor (janitor)]

This bug was fixed in the package apt - 2.0.6

---------------
apt (2.0.6) focal; urgency=medium

  * RunScripts: Do not reset SIGQUIT and SIGINT to SIG_DFL (LP: #1898026)
  * test suite fix: Check for and discard expected warning from MaybeAddAuth
  * Fix downloads of unsized files that are largest in pipeline (LP: #1921626),
    and warn about packages without size (option Acquire::AllowUnsizedPackages)
  * JSON hooks 0.2 and assorted JSON bugfixes (LP: #1926150)
    - encoder fixes:
      + json: Escape strings using \u escape sequences, add test
      + json: Actually pop states
      + json: Encode NULL strings as null
    - json: Flush standard file descriptors before calling hooks
      (this avoids output from hooks in middle of apt output)
    - non-code changes:
      + test/json: Make the test hook more reliable
      + Fix a typo in json-hooks-protocol.md (thanks to Brian Murray)
    - semantic changes (new fields, hooks, and protocol 0.2):
      + json: Add origins fields to version
      + upgrade: Add JSON hook support (AptCli::Hooks::Upgrade)
      + json: Add `package-list` and `statistics` install hooks
      + json: Hook protocol 0.2 (added upgrade,downgrade,reinstall modes)
    + Fix a typo in json-hooks-protocol.md (thanks to Brian Murray)
  * Avoid infinite loop on EOF on media change prompt (LP: #1928687)

 -- Julian Andres Klode <email address hidden> Tue, 15 Jun 2021 13:05:46 +0200

[Launchpad Janitor (janitor)]

This bug was fixed in the package apt - 1.6.14

---------------
apt (1.6.14) bionic; urgency=medium

  * RunScripts: Do not reset SIGQUIT and SIGINT to SIG_DFL (LP: #1898026)
  * Fix downloads of unsized files that are largest in pipeline (LP: #1921626),
    and warn about packages without size (option Acquire::AllowUnsizedPackages)
  * JSON hooks 0.2 and assorted JSON bugfixes (LP: #1926150)
    - encoder fixes:
      + json: Escape strings using \u escape sequences, add test
      + json: Actually pop states
      + json: Encode NULL strings as null
    - json: Flush standard file descriptors before calling hooks
      (this avoids output from hooks in middle of apt output)
    - Minor fixes to include and C++ namespaces
    - non-code changes:
      + test/json: Make the test hook more reliable
      + Fix a typo in json-hooks-protocol.md (thanks to Brian Murray)
    - semantic changes (new fields, hooks, and protocol 0.2):
      + json: Add origins fields to version
      + upgrade: Add JSON hook support (AptCli::Hooks::Upgrade)
      + json: Add `package-list` and `statistics` install hooks
      + json: Hook protocol 0.2 (added upgrade,downgrade,reinstall modes)
    + Fix a typo in json-hooks-protocol.md (thanks to Brian Murray)
  * Avoid infinite loop on EOF on media change prompt (LP: #1928687)

 -- Julian Andres Klode <email address hidden> Tue, 15 Jun 2021 16:12:38 +0200