How to Use APK Command Like a Pro in Alpine Linux

Alpine Linux is a small security-focused Linux Distribution. The base installation of Alpine is only a few MB in size. It is more suitable for container environments such as Docker and Kubernetes, and cloud environments.

In this guide, we learn how to use apk command in Alpine Linux.

Introduction to apk Package Manager

apk is the default package management tool in Alpine Linux. It is very similar to other package managers such as apt for Debian and Ubuntu systems. The apk command is commonly used to install, upgrade and remove packages.

The apk package manager retrieves packages and related details from the online repositories. It uses GPG signatures to verify the authenticity of packages.

All software packages kept in a repository are tar.gz archives with digital signatures. These are sometimes called "a-packs" and have the ".apk" extension.

There are three types of repositories in Alpine Linux:

• Main
• Community
• edge
• Testing

The main repository comprises the packages formally supported by the Alpine Linux core team after extensive testing. The community repository houses the packages that the community supports (through approval from the testing or edge repository).

The edge repository contains the latest builds of all the Linux packages until they become stable. The packages in this repository get frequent updates. You need to take extra care while using a package from this repository.

The most recent, flawed, or out-of-date packages are typically found in the testing repository. The packages in this repository receive no support. The packages get clean if they stay longer than six months in this repository without fulfilling the requirements.

These repositories are stored in a configuration file /etc/apk/repositories. You can view the contents of that file using the following command:

cat /etc/apk/repositories

Example:

http://dl-cdn.alpinelinux.org/alpine/v3.17/main
#http://dl-cdn.alpinelinux.org/alpine/v3.17/community
#http://dl-cdn.alpinelinux.org/alpine/edge/main
#http://dl-cdn.alpinelinux.org/alpine/edge/community
#http://dl-cdn.alpinelinux.org/alpine/edge/testing
#https://dl-cdn.alpinelinux.org/alpine/latest-stable/main
#https://dl-cdn.alpinelinux.org/alpine/latest-stable/community

In the above output, each line in the file corresponds to a repository. You can disable any repositories by adding a "#" sign at the start of the line. Later, you can enable it again by removing the sign.

Apk Command with Examples

Here are a few examples of apk command usage:

1. Updating Package Index

Before adding any new package, it is the best practice to run the update command. This will download an updated package index from the repositories.

apk update

Running apt update makes sure you always get the latest package when you run the upgrade or add command. This commands works by downloading APKINDEX.tar.gz from each repository and store in /var/cache/apk

The system by default ran apk update every 4 hours when the cache is invalidated.

2. Upgrade All Packages

To upgrade all the installed packages on a running Alpine system, use upgrade command. This makes sure your package gets the latest security and bug fixes patched.

apk update
apk upgrade

These two commands can be combined in a single command like this:

apk -U upgrade

3. Installing Packages

To install or add a new package in Alpine Linux, you can use add option. The add option install (or upgrades) if the package is not present in the system including all dependencies.

Syntax:

apk add PackageName

Replace <package-name> with the name of the package you need to install. For example, to install the zlib package, you can use the following command:

apk add zlib

In case apk finds any dependencies problem, it tries to stick back to the old version of the package.

Interactively install packages

If you want prompts for permission before installing any package use the -i option:

apk -i add PackageName

Example:

apk -i add nettle

This help to discard installation in case you don't want to continue.

Simulate Installation

apk command allows performing a dry installation (or upgrade) using -s option. This actually runs a simulation that shows which versions of packages will get installed or upgraded. Basically won't make any changes to the system.

Syntax:

apk -s add PackageName

Example:

apk -s add tzdata

This comes more useful when you perform the system upgrade (ie apk -s upgrade).

4. Upgrade specific package

Instead of upgrading all the packages using the upgrade command, you can also upgrade a specific package using the -u option. The syntax is as follows:

apk add -u PackageName

Example:

apk add -u nettle

The figure shows updating the nettle package in Alpine Linux.

5. List installed packages

To get the list of all installed packages use apk command with info option.

apk info

apk info command can have a few options that can give specific information about installed packages.

To display only the description of an installed package, add the -d option like this:

apk info -d PackageName

For example to display the description of Zlib package, type:

apk info -d zlib

To show detailed information of the installed packages, you can use the -a option.

apk info -a PackageName

Example:

apk info -a zlib

This shows the package description, webpage, installed size of the package, package dependencies, contains, and more.

6. Verify package installed status

You can verify a package installed status using the apk info command with -e option.

apk -e info PackageName

If your Alpine Linux system has the specific package installed, the output contains the package name. Otherway, if the package is not installed, it will show no output.

Example:

apk -e info zlib
apk -e info tzdata

Please note the that zlib command has an active installation on the given Alpine Linux server, so the name of the package is being displayed as an output. On the other hand, tzdata is not installed and hence, no output is there.

7. Remove a Package

You can use the apk del command to remove a package. This will also remove all dependency packages that are no longer required.

The syntax will be as follows:

apk del PackageName

Example:

apk del nettle

The output shows the nettle package and its dependencies getting purged.

8. Search packages

The Alpine Linux repositories consist of more than 12,000 packages. You may use the Alpine web interface to search for available packages for installation.

You may use apk search command to search for what package to install. It's powerful enough to search everything from package index including binaries and libraries.

For example to list down all available packages from the index

apk search -v

You may perform specific package search:

apk search -v zlib

apk search mechanism can also perform pattern matching. For example to search all packages which have the term 'lib':

apk search -v 'lib*'

9. Hold Specific Package from Upgrade

You might occasionally need to prevent a software package from being upgraded. There are several justifications for doing this. For instance, new package version conflicts with your app or the new package itself have a bug, in those situations you can stick to the old version while upgrading.

Syntax:

apk add PackageName=version

Example:

apk add zlib=1.2.13-r0

This makes sure zlib package stay at version 1.2.13-ro when performing upgrading even if a new version is available.

10. List files in apk Package

To list the files included in a package, use apk info command with -L option. Syntax:

apk info -L PackageName

For example to list files included in zlib package, type:

apk info -L zlib

11. Display Installed package size

To get the installed package size, use apk info command with -s option. Syntax:

apk info -s PackageName

For example to print zlib package installed size:

apk info -s zlib

12. Install .apk local file

To install locally stored .apk files, use apk add with --allow-untrusted flag.

apk add --allow-untrusted packagefile.apk

All dependencies packages should be specified on the same line one after another.

apk add --allow-untrusted /path/to/packagefile.apk /path/to/dependency-packagefile.apk

13. Find package belong to a file

You know a file and would like to know which package that file belongs to ? apk info command has --who-owns flag to find that.

apk info --who-owns /path/to/filename

Example:

apk info --who-own /lib/libz.so.1

Here you can see the file is owned by zlib-1.2.13-r0 package.

14. List Dependencies of package

To list dependencies of a package use apk info command with -R option. Syntax:

apk -R info PackageName

Example:

apk -R info zlib

15. Clear apk package cache

Its good to perform cache maintenance by cleaning the cache. Basically it deletes all old versions of the packages, which is technically not required as newer packages are added.

apk cache clean

Conclusion

For more information about the apk command and its usage, you can refer to the Alpine Linux documentation or run apk --help to see a list of available options and commands.