Verified on a fresh container (with the conf then removed to show the difference):


root@needrestart-nrconf:~# dpkg -l needrestart | tail -n 1
ii  needrestart    3.6-7ubuntu4.1 all          check which daemons need to be restarted after library upgrades
root@needrestart-nrconf:~# e^C
root@needrestart-nrconf:~# echo '$nrconf{restart} = "l";' > /etc/needrestart/conf.d/listmode.conf
root@needrestart-nrconf:~# apt reinstall libc6
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 0 not upgraded.
Need to get 3263 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu noble-updates/main amd64 libc6 amd64 2.39-0ubuntu8.2 [3263 kB]
Fetched 3263 kB in 0s (20.3 MB/s)
Preconfiguring packages ...
(Reading database ... 34412 files and directories currently installed.)
Preparing to unpack .../libc6_2.39-0ubuntu8.2_amd64.deb ...
Unpacking libc6:amd64 (2.39-0ubuntu8.2) over (2.39-0ubuntu8.2) ...
Setting up libc6:amd64 (2.39-0ubuntu8.2) ...
Processing triggers for libc-bin (2.39-0ubuntu8.2) ...
Disabling Ubuntu mode, explicit restart mode configuredScanning processes... [                                                                                            Scanning processes...
Scanning candidates...

Services to be restarted:
 systemctl restart console-getty.service
 systemctl restart cron.service
 systemctl restart packagekit.service
 systemctl restart polkit.service
 systemctl restart rsyslog.service
 systemctl restart systemd-journald.service
 systemctl restart systemd-networkd.service
 systemctl restart systemd-resolved.service
 systemctl restart systemd-udevd.service
 systemctl restart udisks2.service

Service restarts being deferred:
 /etc/needrestart/restart.d/dbus.service
 systemctl restart systemd-logind.service
 systemctl restart unattended-upgrades.service

No containers need to be restarted.

No user sessions are running outdated binaries.

No VM guests are running outdated hypervisor (qemu) binaries on this host.
root@needrestart-nrconf:~# rm /etc/needrestart/conf.d/listmode.conf
root@needrestart-nrconf:~# apt reinstall libc6
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 0 not upgraded.
Need to get 3263 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu noble-updates/main amd64 libc6 amd64 2.39-0ubuntu8.2 [3263 kB]
Fetched 3263 kB in 0s (17.3 MB/s)
Preconfiguring packages ...
(Reading database ... 34412 files and directories currently installed.)
Preparing to unpack .../libc6_2.39-0ubuntu8.2_amd64.deb ...
Unpacking libc6:amd64 (2.39-0ubuntu8.2) over (2.39-0ubuntu8.2) ...
Setting up libc6:amd64 (2.39-0ubuntu8.2) ...
Processing triggers for libc-bin (2.39-0ubuntu8.2) ...
Scanning processes...
Scanning candidates...

Restarting services...
 systemctl restart console-getty.service cron.service packagekit.service polkit.service rsyslog.service systemd-journald.service systemd-networkd.service systemd-resolved.service systemd-udevd.service udisks2.service

Service restarts being deferred:
 /etc/needrestart/restart.d/dbus.service
 systemctl restart systemd-logind.service
 systemctl restart unattended-upgrades.service

No containers need to be restarted.

No user sessions are running outdated binaries.

No VM guests are running outdated hypervisor (qemu) binaries on this host.
root@needrestart-nrconf:~#