Apt-Cacher NG works well on Linux Mint, but their Update Manger (mintupdate) complains that the mirror is unreachable. Even though it will still let you download packages through ACNG, mintupdate is checking the Last-Modified time of <mirror url>/db/version against that of packages.linuxmint.com to determine the age of the mirror. If it can't reach that file, it assumes the entire mirror is unreachable and puts up that message.
ACNG whitelists paths for proxying based on a few regular expressions. We can add this path to the whitelist in the config file, like so:
# Fix for Linux Mint Update Manager (mintupdate) thinking the cache is unreachable because it can't reach the version file # https://mckinley.cc/notes/20241120-mintupdate-apt-cacher-ng.xhtml # https://github.com/linuxmint/mintupdate/blob/da504a6e0d5f49a41568db0053ae9143f625d306/usr/lib/linuxmint/mintUpdate/mintUpdate.py#L1978 VFilePatternEx: ^/db/version$
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