The current workaround requires deinstalling Tailscale and removing the apt repository, then reinstalling after the Mint upgrade.
Replication Steps
I did a fresh install of Mint 20.3 Cinnamon in a VirtualBox VM. For good measure I ran apt update/upgrade to catch up on packages, and rebooted.
I installed the Tailscale software using (as directed by the Tailscale web site): curl -fsSL https://tailscale.com/install.sh | sh It doesn't matter if Tailscale is actually configured or running, or even actually installed. The problem has to do with the Tailscale repository.
I installed mintupgrade version 2024.01.12 and ran it with sudo. After going through the process for a while, I eventually got the noted error.
Diagnosis
I was able to track down the problem to /usr/lib/linuxmint/mintupgrade/checks.py. In the APTRepoCheck class, method do_run(), section "Check the base repos can handle destination codename", it's checking that a particular URL exists by calling the get_url_last_modified() method and verifying that a timestamp was returned. The Python libraries in use take the timestamp from the Last-Modified: HTTP header.
But it turns out that the repos on tailscale.com don't serve the Last-Modified: header, so even though the URL that the script is trying to locate does exist, it gets a false negative because of the missing timestamp.
This is a refile of https://github.com/linuxmint/linuxmint/issues/666
This is still an issue with the upgrade to Mint 22.0.
Original text follows:
When trying to do a major Mint upgrade using mintupgrade, if Tailscale is installed, it fails with the error:
I also found this forum post from July 2023 describing the same symptoms: https://forums.linuxmint.com/viewtopic.php?t=400691
The current workaround requires deinstalling Tailscale and removing the apt repository, then reinstalling after the Mint upgrade.
Replication Steps
I did a fresh install of Mint 20.3 Cinnamon in a VirtualBox VM. For good measure I ran apt update/upgrade to catch up on packages, and rebooted.
I installed the Tailscale software using (as directed by the Tailscale web site):
curl -fsSL https://tailscale.com/install.sh | shIt doesn't matter if Tailscale is actually configured or running, or even actually installed. The problem has to do with the Tailscale repository.I installed mintupgrade version 2024.01.12 and ran it with sudo. After going through the process for a while, I eventually got the noted error.
Diagnosis
I was able to track down the problem to /usr/lib/linuxmint/mintupgrade/checks.py. In the APTRepoCheck class, method do_run(), section "Check the base repos can handle destination codename", it's checking that a particular URL exists by calling the get_url_last_modified() method and verifying that a timestamp was returned. The Python libraries in use take the timestamp from the Last-Modified: HTTP header.
But it turns out that the repos on tailscale.com don't serve the Last-Modified: header, so even though the URL that the script is trying to locate does exist, it gets a false negative because of the missing timestamp.
This is confirmed with either F12 tools in Firefox or using the last-modified.com site to check https://pkgs.tailscale.com/stable/ubuntu/dists/jammy/Release
This is technically a violation of RFC 2616, section 14.29:
However, it does specify no-cache so the freshness shouldn't ever matter with this URL.
But in this case, the freshness is irrelevant: The code seems to be using this method only as a lazy shortcut to check for existence.