Fwd: Question on apt-get update
kavitha R
kavitha.r0573 at gmail.com
Wed Sep 25 00:22:32 UTC 2019
I am curious to know about the apt code so that I can contribute to this
project and learn from it.
I have a question on "apt-get update" implementation. I did go through the
code for a couple of days but couldn't get full clarity so need your help.
/var/lib/apt/lists - This contains two kinds of files. One set of files (*
_Packages) that has the full package information with the short
description. Another set of files (* _i18n_Translation-en) has just the
full description for all the packages.
/var/cache/apt/ - This directory has two different caches (pkgcache.bin,
srcpkgcache.bin). These are constructed from the information stored in the
/var/lib/apt/lists directory.
*Here are my questions,*
1. How does apt-cache create and updates the local package cache? Is it
periodic or manual? As far as my investigation, it is manual (apt-get
update).
fyi, I am using Linux 4.4.0-18362-Microsoft. "apt-config dump" command
output doesn't show "APT::Cache::Generate".
1. When we run "apt-get update", does it download all the packages
information that will be stored in /var/lib/apt/lists/* _Packages file? Is
there a advanced logic, where client sends current state information (like
all packageNames and their versions)? This is a puzzle as the code is very
cryptic to understand.
I modified
/var/lib/apt/lists/security.ubuntu.com_ubuntu_dists_xenial-security_restricted_binary-amd64_Packages
(changed the version for one of the package) and ran "apt-get update" but
it didn't revert my change. Why?
This confirms, apt-get is looking at someother file to make the decision to
update the /var/lib/apt/lists/* _Packages file. When does the
/var/lib/apt/lists/* _Packages file gets updated?
Can you explain whether it's expected behavior or not.
I did notice that the /var/cache/apt/pkgcache.bin (and srcpkgcache.bin) are
updated everytime I run "apt-get update".
1.
What goes into pkgcache.bin and srcpkgcache.bin? I couldn't find any
useful information in the internet.
2.
Why do we store the package full description in a different file? Is it
because we want make cache faster that has only the short package
description?
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