[Bug 2147155] Re: Upgrade from 24.04.4 to 26.04 failed: An unresolvable problem occurred while calculating the upgrade.

[George]

Not a bug of ubuntu-release-upgrader, but a package dependency problem
(see tail of apt.log bellow). Uninstalling lintian package allows the
upgrade to proceed.

```
...
Investigating (19) libyaml-libyaml-perl:amd64 < 0.89+ds-1ubuntu0.24.04.1 -> 0.904.0+ds-1 @ii umU Ib >
Broken libyaml-libyaml-perl:amd64 Breaks on lintian:amd64 < 2.117.0ubuntu1.4 | 2.129.0ubuntu1 @ii umH > (< 2.119.0~)
  Considering lintian:amd64 -1 as a solution to libyaml-libyaml-perl:amd64 1
  Upgrading lintian:amd64 due to Breaks field in libyaml-libyaml-perl:amd64
Investigating (19) lintian:amd64 < 2.117.0ubuntu1.4 -> 2.129.0ubuntu1 @ii umU Ib >
Broken lintian:amd64 Depends on dpkg:amd64 < 1.22.6ubuntu6.5 | 1.23.7ubuntu1 @ii umH > (>= 1.23.4)
  Considering dpkg:amd64 5394 as a solution to lintian:amd64 -1
  MarkKeep lintian:amd64 < 2.117.0ubuntu1.4 -> 2.129.0ubuntu1 @ii umU Ib > FU=0
  Holding Back lintian:amd64 rather than change dpkg:amd64
Done
```

** Changed in: ubuntu-release-upgrader (Ubuntu)
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/2147155

Title:
  Upgrade from 24.04.4 to 26.04 failed: An unresolvable problem occurred
  while calculating the upgrade.

Status in ubuntu-release-upgrader package in Ubuntu:
  Invalid

Bug description:
  $sudo do-release-upgrade -d
  Get:1 Upgrade tool signature [833 B]                                                                                                                      
  Get:2 Upgrade tool [948 kB]                                                                                                                               
  Fetched 949 kB in 0s (0 B/s)                                                                                                                              
  /usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeFetcherCore.py:237: Warning: W:Download is performed unsandboxed as root as file 'resolute.tar.gz.gpg' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
    result = fetcher.run()
  authenticate 'resolute.tar.gz' against 'resolute.tar.gz.gpg' 
  extracting 'resolute.tar.gz'

  Reading cache

  Checking package manager
  Reading package lists... Done
  Building dependency tree... Done
  Reading state information... Done
  Hit http://nl.archive.ubuntu.com/ubuntu noble InRelease      
  ...
  Reading package lists... Done    
  Building dependency tree... Done 
  Reading state information... Done

  Checking for installed snaps

  Calculating snap size requirements

  Updating repository information
  Get:1 http://nl.archive.ubuntu.com/ubuntu resolute InRelease [124 kB]                                                                                     
  ...
  Fetched 189 MB in 6s (2,208 kB/s)                                                                                                                         

  Checking package manager
  Reading package lists... Done    
  Building dependency tree... Done 
  Reading state information... Done

  Calculating the changes

  Calculating the changes

  Could not calculate the upgrade

  An unresolvable problem occurred while calculating the upgrade.

  If none of this applies, then please report this bug using the 
  command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. If 
  you want to investigate this yourself the log files in 
  '/var/log/dist-upgrade' will contain details about the upgrade. 
  Specifically, look at 'main.log' and 'apt.log'. 

  
  Restoring original system state

  Aborting
  Reading package lists... Done    
  Building dependency tree... Done 
  Reading state information... Done

  ProblemType: Bug
  DistroRelease: Ubuntu 24.04
  Package: ubuntu-release-upgrader-core 1:24.04.28
  ProcVersionSignature: Ubuntu 6.8.0-107.107-generic 6.8.12
  Uname: Linux 6.8.0-107-generic x86_64
  ApportVersion: 2.28.1-0ubuntu3.8
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CrashDB: ubuntu
  CurrentDesktop: ubuntu
  Date: Fri Apr  3 00:03:06 2026
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to noble on 2026-04-02 (0 days ago)

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