Version 0.82.1ubuntu2.1 breaks unattended upgrades on unprivileged Docker containers

[Foo]

Since update of the unattended-upgrades package to version 0.82.1ubuntu2.1, unprivileged Docker containers cannot properly perform unattended upgrades anymore. They fail with the following error message:

=================================================
Traceback (most recent call last):
  File "/usr/bin/unattended-upgrade", line 1186, in <module>
    main(options)
  File "/usr/bin/unattended-upgrade", line 993, in main
    os.nice(-19)
PermissionError: [Errno 1] Operation not permitted
=================================================

This is due to the fact that the script tries to set a negative nice value, which is by default not allowed on unprivileged Docker containers. In previous package versions, the script was trying to set a nice value of 0, which was allowed.

To solve this issue, two solutions could be considered:
- The unattended-upgrades package should remain using a nice value of 0
- The containers should be started with the "--cap-add=CAP_SYS_NICE" option. Unfortunately, it is not possible to add this capability to running containers.

More information:

# lsb_release -rd
Description: Ubuntu 14.04.1 LTS
Release: 14.04

# apt-cache policy unattended-upgrades
unattended-upgrades:
  Installed: 0.82.1ubuntu2.1
  Candidate: 0.82.1ubuntu2.1
  Version table:
 *** 0.82.1ubuntu2.1 0
        500 http://ubunturepo/ trusty-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     0.82.1ubuntu2 0
        500 http://ubunturepo/ trusty/main amd64 Packages

[Rolf Wojtech (rolf-g)]

Should be fixed with 0.82.8ubuntu0.2
https://bugs.launchpad.net/ubuntu/+source/unattended-upgrades/+bug/1422345