What does "adjusting candidate version" mean?

Question

When running unattended-upgrades manually, there are no updates detected but some packages report "adjusting candidate version" (see below). They do this every time I run sudo unattended-upgrades -d, not just once.

What does this message mean?

$ sudo unattended-upgrades -d                                                                                                             
Initial blacklisted packages: 
Initial whitelisted packages: 
Starting unattended upgrades script
Allowed origins are: ['origin=*']
adjusting candidate version: 'linux-image-4.12.0-1-amd64=4.12.6-1'
adjusting candidate version: 'linux-image-4.12.0-2-amd64=4.12.13-1'
adjusting candidate version: 'linux-image-4.13.0-1-amd64=4.13.13-1'
adjusting candidate version: 'tracker-gui=1.12.1-1'
pkgs that look like they should be upgraded: 
Fetched 0 B in 0s (0 B/s)                                                                                                                                                    
fetch.run() result: 0
blacklist: []
whitelist: []
No packages found that can be upgraded unattended and no pending auto-removals

Answer 1

unattended-upgrades tracks packages which are upgrade candidates (i.e. available in the allowed origins) by name. When multiple repositories are allowed, you can end up with multiple versions of the same package (keyed by name). When unattended-upgrades encounters a version of a package which it is already tracking, it checks to see whether the new version is allowed and greater than the one it already knows about, and if so, tracks the new version. When this happens, it logs the “adjusting candidate version” message.

Basically, what this means is that multiple versions of linux-image-4.12.0-1-amd64, linux-image-4.12.0-2-amd64, linux-image-4.13.0-1-amd64 and tracker-gui are available in the repositories you’ve configured. There’s nothing to be concerned about here.

You won’t see these messages if you drop the -d option, which you shouldn’t usually need. (It enables debug logging.)