Local APK cache

Overview

APK can keep a cache of installed packages on a local disk.

In diskless installations, since these packages are available during boot, packages can then be automatically (re-)installed from local media into RAM when booting, without requiring, and even before there is a network connection. The cache can be stored on any writable media, or at the same location as the .apkovl file from the local backup utility lbu.

HDD or sys mode installs don't need an apk cache to maintain their state, it still allows to serve packages over the network, though, e.g. to get installed by other local machines.

Enabling Local Cache

Execute the script setup-apkcache will assist in enabling a local cache. The script creates a symlink named /etc/apk/cache that points to the cache directory.

setup-apkcache

Cache can also be manually enabled by creating a cache dir and then symlink it to /etc/apk/cache:

mkdir -p /var/cache/apk ln -s /var/cache/apk /etc/apk/cache

On a diskless installation, to make the disk where the cache directory is present be automatically mounted at boot create an empty file .boot_repository inside the cache directory.

Cache maintenance

Removing older packages

When newer packages are added to the cache over time, the older versions of the packages default to remain in the cache directory.

The older versions of packages can be removed with the clean command.

apk cache clean

Or to see what is deleted include the verbose switch:

apk -v cache clean

Download missing packages

If you accidentally delete packages from the cache directory, you can make sure they are there with the download command,

apk cache download

Delete and download in one step

You can combine the two steps into one with the sync command - this cleans out old packages and downloads missing packages.

apk cache -v sync

Automatically Cleaning Cache on Reboot

To automatically attempt to validate your cache on reboot, you can add the above command to a /etc/local.d/*.stop file:

Contents of /etc/local.d/cache.stop

#!/bin/sh # verify the local cache on shutdown apk cache -v sync # We should always return 0 return 0

Tip: Usually the only time you need to reboot is when things have gone horribly wrong; so this is a "best effort" to cover forgetting to sync the cache; It is much better to run sync immediately after adding or upgrading packages.

Local Cache on tmpfs volumes

In some circumstances it might be useful to have the cache reside on tmpfs, for example if you only wish for it to last as long as the system is up.

NOTE: apk is coded to ignore tmpfs caches, and this is correct behaviour in most instances. Using tmpfs as a package cache can consume large amounts of system memory if you install a lot of packages, possibly resulting in a crashed system. You can limit this by restricting the size of your cache to a small number (128M in the example below).

To do it, you need to create an image inside which your cache can live. We do this by creating an image file, formatting it with ext2, and mounting it at /etc/apk/cache.

apk add e2fsprogs dd if=/dev/zero of=/apkcache.img bs=1M count=128 mkfs.ext2 -F /apkcache.img mkdir -p /etc/apk/cache mount -t ext2 /apkcache.img /etc/apk/cache apk update

As usual, if you want to download currently installed packages into the cache, use apk cache sync.