apt-cacher-ng在回复Ubuntu客户端的"sudo apt更新“时遇到了一些问题。

Question

它对Ubuntu 18.04起了作用，但在Ubuntu 20.04上，apt-cacher的问题是这样的，

$ sudo apt update 
Get:1 http://archive.ubuntu.com/ubuntu focal InRelease [265 kB]
Hit:2 http://security.ubuntu.com/ubuntu focal-security InRelease
Hit:3 http://archive.ubuntu.com/ubuntu focal-updates InRelease                                                                                                                                                                                                                 
Hit:4 http://archive.ubuntu.com/ubuntu focal-backports InRelease                                                                                                                                                                                                               
Ign:5 http://archive.ubuntu.com/ubuntu focal/main amd64 c-n-f Metadata                                                                                                                                                                                                         
Ign:6 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages
Ign:7 http://archive.ubuntu.com/ubuntu focal/universe i386 Packages
Ign:8 http://archive.ubuntu.com/ubuntu focal/universe Translation-en
Ign:9 http://archive.ubuntu.com/ubuntu focal/universe amd64 c-n-f Metadata
Ign:10 http://archive.ubuntu.com/ubuntu focal/multiverse amd64 c-n-f Metadata
Ign:5 http://archive.ubuntu.com/ubuntu focal/main amd64 c-n-f Metadata
Get:6 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages [8,600 kB]
Get:7 http://archive.ubuntu.com/ubuntu focal/universe i386 Packages [4,624 kB]                                                                                                                                                                                                 
Get:8 http://archive.ubuntu.com/ubuntu focal/universe Translation-en [5,131 kB]                                                                                                                                                                                                
Get:8 http://archive.ubuntu.com/ubuntu focal/universe Translation-en [5,131 kB]                                                                                                                                                                                                
Ign:9 http://archive.ubuntu.com/ubuntu focal/universe amd64 c-n-f Metadata                                                                                                                                                                                                     
Ign:10 http://archive.ubuntu.com/ubuntu focal/multiverse amd64 c-n-f Metadata                                                                                                                                                                                                  
Ign:5 http://archive.ubuntu.com/ubuntu focal/main amd64 c-n-f Metadata                                                                                                                                                                                                         
Ign:9 http://archive.ubuntu.com/ubuntu focal/universe amd64 c-n-f Metadata                                                                                                                                                                                                     
Ign:10 http://archive.ubuntu.com/ubuntu focal/multiverse amd64 c-n-f Metadata                                                                                                                                                                                                  
Err:5 http://archive.ubuntu.com/ubuntu focal/main amd64 c-n-f Metadata                                                                                                                                                                                                         
  403  Forbidden file type or location [IP: 192.168.17.34 3142]
Ign:9 http://archive.ubuntu.com/ubuntu focal/universe amd64 c-n-f Metadata                                                                                                                                                                                                     
Ign:10 http://archive.ubuntu.com/ubuntu focal/multiverse amd64 c-n-f Metadata                                                                                                                                                                                                  
Fetched 15.2 MB in 1min 15s (203 kB/s)                                                                                                                                                                                                                                         
Reading package lists... Done
E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal/main/cnf/Commands-amd64  403 Forbidden file type or location [IP: 192.168.17.34 3142]
E: Some index files failed to download. They have been ignored, or old ones used instead.

但是没有代理，sudo apt update就像

$ sudo apt update
Hit:1 http://security.ubuntu.com/ubuntu focal-security InRelease         
Hit:2 http://archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:3 http://archive.ubuntu.com/ubuntu focal-backports InRelease
Get:4 http://archive.ubuntu.com/ubuntu focal InRelease [265 kB]
Get:5 http://archive.ubuntu.com/ubuntu focal/main amd64 c-n-f Metadata [29.2 kB]
Get:6 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages [8,600 kB]                                                                                                                                                                                                
Get:7 http://archive.ubuntu.com/ubuntu focal/universe i386 Packages [4,624 kB]                                                                                                                                                                                                 
Get:8 http://archive.ubuntu.com/ubuntu focal/universe Translation-en [5,131 kB]                                                                                                                                                                                                
Get:9 http://archive.ubuntu.com/ubuntu focal/universe amd64 c-n-f Metadata [264 kB]                                                                                                                                                                                            
Get:10 http://archive.ubuntu.com/ubuntu focal/multiverse amd64 c-n-f Metadata [9,164 B]                                                                                                                                                                                        
Fetched 567 kB in 31s (18.4 kB/s)                                                                                                                                                                                                                                              
Reading package lists... Done
Building dependency tree       
Reading state information... Done
All packages are up to date.

我在/etc/apt-cacher-ng/acng.conf上支持的文件类型模式是

PfilePattern = .(.d?deb|.db|.rpm|.drpm|.dsc|.tar(.gz|.bz2|.lzma|.xz|.zst)(.gpg)?|.diff(.gz|.bz2|.lzma|.zst|.xz)|.jigdo|.template|changelog|copyright|.udeb|.debdelta|.diff/..gz|(Devel)?ReleaseAnnouncement(\?.)?|[a-f0-9]+-(susedata|updateinfo|primary|deltainfo).xml.gz|fonts/(final/)?[a-z]+32.exe(\?download.)?|/dists/./installer-[^/]+/[0-9][^/]+/images/.)$

这是/etc/apt/sources.list

# deb cdrom:[Ubuntu-MATE 20.04 LTS _Focal Fossa_ - Beta amd64 (20200402)]/ focal main multiverse restricted universe

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://archive.ubuntu.com/ubuntu focal main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://archive.ubuntu.com/ubuntu focal-updates main restricted
# deb-src http://bd.archive.ubuntu.com/ubuntu/ bionic-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://archive.ubuntu.com/ubuntu focal universe
deb http://archive.ubuntu.com/ubuntu focal-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://archive.ubuntu.com/ubuntu focal multiverse
deb http://archive.ubuntu.com/ubuntu focal-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb-src http://bd.archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu focal partner

deb http://archive.ubuntu.com/ubuntu focal-security main restricted
# deb-src http://security.ubuntu.com/ubuntu bionic-security main restricted
deb http://archive.ubuntu.com/ubuntu focal-security universe
deb http://archive.ubuntu.com/ubuntu focal-security multiverse
deb http://archive.ubuntu.com/ubuntu focal-backports multiverse restricted main universe
#deb http://archive.ubuntu.com/ubuntu focal-proposed multiverse restricted main universe #Not for humans during development stage of release focal

而且问题是只有20.04，因为我没有遇到18.04 (对于真正的机器和VM也是一样的)。问题只存在于sudo apt update，如果我直接更新repo，然后使用apt-chacher作为代理下载包，没有问题。那么到底是哪里出了问题呢？

Answer 1

通过apt-cacher在20.04上看到这个apt update错误，尽管apt upgrade似乎仍然有效。注意到服务器上的文件具有.xz扩展名，如果这是线索的话。

http://archive.ubuntu.com/ubuntu/dists/focal-security/main/cnf/

Index of /ubuntu/dists/focal-security/main/cnf

[ICO]   Name    Last modified   Size
[PARENTDIR] Parent Directory        -
[   ]   Commands-amd64.xz   2020-06-03 12:29    2.6K
[   ]   Commands-i386.xz    2020-06-03 12:29    1.7K
[DIR]   by-hash/    2019-10-25 05:33    -

我还没找到解决办法..。尝试将其添加到acng.cnf (将其标记为“易失性”)，但不确定它是否解决了问题，因为在我注释掉apt代理并执行了apt update之后，这个问题就消失了。

#PfilePatternEx: .*(\.xz)
VfilePatternEx: .*(\.xz)$
SVfilePatternEx: .*(\.xz)$