> The message itself comes (or at least should) in response to > Dir::Cache::pkgcache and Dir::Cache::srcpkgcache being empty and if > the cache is forbidden to be build entirely in memory – which is the > case for apt running as root for, well, reasons. I guess we should > drop this, even through keeping everything in memory can be very slow…
I'm not opposed to changing/removing that config (or adding more config as appropriate), but I would note that this is documented in apt.conf(5): | Generation of caches can be turned off by setting pkgcache or | srcpkgcache to "". This will slow down startup but save disk space. It | is probably preferable to turn off the pkgcache rather than the | srcpkgcache. The goal in the Docker case is that we can have a "layer" in an image whose filesystem changes consist only of the files from the packages we've installed, and the metadata updates noting which packages were indeed installed. The configuration we've got now actually gets us reasonably close to that via incantations like the following: | RUN apt-get update && apt-get install -y some-packages && rm -rf /var/lib/apt/lists/* Relevant list for a simple package like "busybox-static": | A /bin/busybox | A /usr/share/man/man1/busybox.1.gz | A /usr/share/doc/busybox-static/changelog.Debian.gz | ... | A /usr/share/doc/busybox-static/syslog.conf.txt | A /usr/share/initramfs-tools/hooks/zz-busybox | C /var/lib/dpkg/status-old | C /var/lib/dpkg/triggers | C /var/lib/dpkg/triggers/Lock | C /var/lib/dpkg/info | A /var/lib/dpkg/info/busybox-static.list | A /var/lib/dpkg/info/busybox-static.md5sums | C /var/lib/dpkg/status | C /var/lib/dpkg/lock | A /var/lib/apt/extended_states | A /var/lib/apt/lists/httpredir.debian.org_debian_dists_sid_InRelease | A /var/lib/apt/lists/httpredir.debian.org_debian_dists_sid_main_binary-amd64_Packages.gz | A /var/lib/apt/lists/lock | A /var/log/apt/history.log | A /var/log/apt/term.log | C /var/log/dpkg.log If there's a better way to accomplish this, I'm very interested, because I'm not particularly happy about hard-coding so much APT internal knowledge (especially since the "/var/lib/apt/lists" bit there gets encoded in actual "end-user" Dockerfiles, not just baked into the base image). The full source of all configuration modifications is in the script that builds the images: https://github.com/docker/docker/blob/5fd15da7daad56c07842ecda082e9c5d0e6ff620/contrib/mkimage/debootstrap#L36-L152 ♥, - Tianon 4096R / B42F 6819 007F 00F8 8E36 4FD4 036A 9C25 BF35 7DD4
