Because Alpine Linux is designed to run from RAM, package management involves two phases:

Installing / Upgrading / Deleting packages on a running system
Restoring a system to a previously configured state (e.g. after reboot), including all previously installed packages and locally modified configuration files. (RAM-Based Installs Only)

apk is the tool used to install, upgrade, or delete software on a running sytem.
lbu is the tool used to capture the data necessary to restore a system to a previously configured state.

This page documents the apk tool - See the Alpine Local Backup page for the lbu tool.

Overview

The apk tool has the following applets:

add	Add new packages to the running system
del	Delete packages from the running system
fix	Attempt to repair or upgrade an installed package
update	Update the index of available packages
info	Prints information about installed or available packages
search	Search for packages or descriptions with wildcard patterns
upgrade	Upgrade the currently installed packages
cache	Maintenance operations for locally cached package repository
version	Compare version differences between installed and available packages
index	create a repository index from a list of packages
fetch	download (but not install) packages
audit	List changes to the file system from pristine package install state
verify	Verify a package signature

Packages and Repositories

Software packages for Alpine Linux are digitally signed tar.gz archives containing the programs, configuration files, and dependency metadata. They have the extension "*.apk", and are often called "a-packs"

The packages are stored in one or more repositories. A repository is simply a directory with a collection of *.apk files. The directory must include a special index file, named APKINDEX.tar.gz to be considered a repository.

The apk utility can install packages from multiple repositories. The list of repositories to check is stored in /etc/apk/repositories, one repository per line. If you booted from USB stick (/media/sda1) or CD-ROM (/media/cdrom), your repository file probably looks like this:

/media/sda1/apks/

In addition to local repositories, the apk utility uses busybox wget to fetch packages using http:, https: or ftp: protocols. The following is a valid repository file:

/media/sda1/apks
http://dl-3.alpinelinux.org/alpine/v2.1/main
https://dl-3.alpinelinux.org/alpine/v2.1/main
ftp://dl-3.alpinelinux.org/alpine/v2.1/main

Note: Currently there are no public https or ftp repositories. The protocols are available for local repositories

Update the Package list

Remote repositories change as packages are added and upgraded. To get the latest list of available packages, use the update command. The command downloads the APKINDEX.tar.gz from each repository and stores it in the local cache, typically /var/lib/apk or /etc/apk/cache.

apk update

fetch http://dl-3.alpinelinux.org/alpine/v2.1/main/APKINDEX.tar.gz

Tip: If using remote repositories, it is a good idea to do an update just before doing an add or upgrade command. That way you know you are using the latest software available

Add a Package

Use add to install packages from a repository. Any necessary dependencies are also installed. If you have multiple repositories, the add command installs the newest package.

apk add openssh apk add openssh openntp vim

If you only have the main repository enabled in your configuration, apk will not include packages from the other repositories. To install a package from the edge/testing repository without changing your repository configuration file, use the command below. This will tell apk to use that particular repository.

apk add cherokee -U -X http://dl-3.alpinelinux.org/alpine/edge/testing/ --allow-untrusted

Note: Be careful when using third-party or the testing repository. Your system can go down.

Remove a Package

Use del to remove a package (and dependencies that are no longer needed.)

apk del openssh apk del openssh openntp vim

Upgrade a Running System

To upgrade all the packages of a running system, use upgrade

apk update apk upgrade

To upgrade only a few packages, use the add command with the -u parameter:

apk update apk add -u busybox

Note: Remember that when you reboot your machine, the remote repository will not be available until after networking is started. This means packages newer than your local boot media will likely not be installed after a reboot. To make an "upgrade" persist over a reboot, use a local cache.

Search for Packages

The search command searches the repository Index files for installable packages.

Examples:

To list all packages available, along with their descriptions:
apk search -v
To list all packages are part of the ACF system:
apk search -v 'acf*'
To list all packages that list NTP as part of their description:
apk search -v -d 'NTP'

Info on Packages

The info command provides information on the contents of packages, their dependencies, and which files belong to a package.

For a given package, each element can be chosen (for example, -w to show just the webpage information); or all information is displayed with the -a command.

Example:

apk info -a zlib

zlib-1.2.5-r1 description:
A compression/decompression Library

zlib-1.2.5-r1 webpage:
http://zlib.net

zlib-1.2.5-r1 installed size:
94208

zlib-1.2.5-r1 depends on:
libc0.9.32

zlib-1.2.5-r1 is required by:
libcrypto1.0-1.0.0-r0
apk-tools-2.0.2-r4
openssh-client-5.4_p1-r2
openssh-5.4_p1-r2
libssl1.0-1.0.0-r0
freeswitch-1.0.6-r6
atop-1.25-r0 

zlib-1.2.5-r1 contains:
lib/libz.so.1.2.5
lib/libz.so.1
lib/libz.so 

zlib-1.2.5-r1 triggers:

As shown in the example you can determine

The description of the package
The webpage where the application is hosted
The size the package will require once installed (in bytes)
What packages are required to use this one (depends)
What packages require this one to be installed (required by)
The contents of the package
Any triggers this package sets. Listed here are directories that are watched; if a change happens to the directory, then the trigger script is run at the end of the apk add/delete. For example, doing a depmod once after installing all packages that add kernel modules.

Tip: The info command is also useful to determine which package a file belongs to. For example:

apk info --who-owns /sbin/lbu

will display

/sbin/lbu is owned by alpine-conf-x.x-rx

Additional apk Commands

In progress...

Local 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.

Advanced APK Usage

Holding a specific package back

In certain cases, you may want to upgrade a system, but keep a specific package at a back level. It is possible to add "sticky" or versioned dependencies. For instance, to hold the asterisk package to the 1.6.2 level or lower:

apk add asterisk=1.6.0.21-r0

or

apk add 'asterisk<1.6.1'

after which a

apk upgrade

will upgrade the entire system, keeping the asterisk package at the 1.6.0 or lower level

To later upgrade to the current version,

apk add 'asterisk>1.6.1'