Binary package guide

Next to the usual support for ebuilds, Portage supports building and installing binary packages. This guide explains how to create them, install them, and how to setup a binary package server.

Introduction
There are many reasons why some system administrators like using binary packages for software installations on Gentoo:


 * It allows administrators to save time when keeping similar systems updated. Having to compile everything from source can become time consuming. Maintaining several similar systems, possibly some of them with older hardware, can be much easier if only one system has to compile everything from source and the other systems use the binary packages.
 * Do safe updates. For mission-critical systems in production it is important to stay usable as much as possible. This can be done by a staging server that performs all updates first to itself. Once the staging server is in a good state the updates can then be applied to the critical systems. A variant of this approach is to do the updates in a chroot on the same system and use the binaries created there on the real system.
 * As a backup. Often binary packages are the only way of recovering a broken system (i.e. broken compiler). Having pre-compiled binaries around either on a binary package server or locally can be of great help in case of a broken toolchain.
 * It aids in updating very old systems. The task of updating very old systems can be greatly eased using binary packages. It is usually helpful to install binary packages on old systems because they do not require build time dependencies to be installed/updated. Binaries packages also avoid failures in build processes since they are pre-compiled.

This guide will focus on the following topics:


 * Creating binary packages.
 * Distributing the packages to clients.
 * Implementing binary packages.
 * Maintaining the binary packages.

Near the end a few more advanced topics on dealing with binary packages will be covered.

Creating binary packages
There are three main methods for creating binary packages:


 * 1) After a regular installation, using the  application.
 * 2) Explicitly during an  operation by using the    option.
 * 3) Automatically through the use of the   (build binary packages for all packages) or   (build binary packages only for the system set) values in Portage's FEATURES variable.

All three methods will create a binary package in the directory pointed to by the PKGDIR variable (which defaults to ).

Using quickpkg
The application (included in Portage) takes one or more dependency atoms (or package sets) and creates binary packages for all installed packages that match that atom.

For instance, to create binary packages of all installed GCC versions:

To create binary packages for the system set:

To create binary packages of all installed packages on the system, use the  glob:

There is a caveat with this method: it relies on the installed files, which can be a problem in case of configuration files. Administrators often change configuration files after installing software. Because this could leak out important (perhaps even confidential) data into the packages, by default does not include configuration files that are protected through the CONFIG_PROTECT method. To force inclusion of configuration files, use the  or   options.

Using --buildpkg as an emerge option
When installing software using, Portage can be asked to create binary packages by using   option:

It is also possible to ask Portage to only create a binary package but not to install the software on the live system. For this, the   option can be used:

The latter approach however requires all build time dependencies to be previously installed.

Implementing buildpkg as a Portage feature
The most common way to automatically create binary packages whenever a package is installed by Portage is to use the  feature, which can be set in  like so:

With this feature enabled, every time Portage installs software it will create a binary package as well.

Excluding creation of some packages
It is possible to tell Portage not to create binary packages for a select few packages or categories. This is done by passing the  option to emerge:

This could be used for packages that have little to no benefit in having a binary package available. Examples would be the Linux kernel source packages or upstream binary packages (those ending with -bin like ).

Setting up a binary package host
Portage supports a number of protocols for downloading binary packages: FTP, FTPS, HTTP, HTTPS, and SSH/SFTP. This leaves room for many possible binary package host implementations.

There is, however, no "out-of-the-box" method provided by Portage for distributing binary packages. Depending on the desired setup additional software will need to be installed.

Web based binary package host
A common approach for distributing binary packages is to create a web-based binary package host.

Use a web server such as lighttpd and configure it to provide read access to 's PKGDIR location.

Then, on the client systems, configure the PORTAGE_BINHOST variable accordingly:

SSH binary package host
To provide an authenticated approach for binary package mirrors, Portage can be configured to use the SSH protocol to access binary packages.

When using SSH, it is possible to use the root Linux user's SSH key (without passphrase as the installations need to happen in the background) to connect to a remote binary package host.

To accomplish this, make sure that the root user's SSH key is allowed on the server. This will need to happen for each machine that will connect to the SSH capable binary host:

The PORTAGE_BINHOST variable could then look like so:

NFS exported
When using binary packages on an internal network, it might be easier to export the packages through NFS and mount it on the clients.

The file could look like so:

On the clients, the location can then be mounted. An example entry would look like so:

Using binary packages
For binary packages to be usable on other systems they must fulfill some requirements:


 * The client and server architecture and CHOST must match.
 * The CFLAGS and CXXFLAGS variables used to build the binary packages must be compatible with all clients.
 * USE flags for processor specific instruction set features (like MMX, SSE, etc.) have to be carefully selected; all clients need to support them.

The utility can be used to find a subset of CFLAGS that is supported by both the server and client(s). For example, the host might return:

While the client might return:

In this example CFLAGS could be set to  since   is a full subset of. and  are not included as these are not supported but the client. However,  is included as the client does not support. To find which 's are subsets of others, check the [//gcc.gnu.org/onlinedocs/gcc/x86-Options.html gcc manual], if there is no suitable subset set e.g..

Optionally, it is also possible to set  or   to tell gcc to tune code to a specific arch. In contrast to, the   argument does not prevent code from being executed on other processors. For example, to compile code which is compatible with ivybridge and up but is tuned to run best on skylake set CFLAGS to. When  is not set it defaults to whatever   is set to.

When changing  to a lower subset for using binary packages on a client, a full recompilation is required to make sure that all binaries are compatible with the client's processor, to save time packages that are not compiled with e.g. gcc/clang can be excluded:

Similarly, can be used to find a suitable subset of processor specific instruction set USE flags. For example, the host might return:

While the client might return:

In this example CPU_FLAGS_X86 can be set to  in  because these flags are supported by both the client and the host

Next to these, Portage will check if the binary package is built using the same USE flags as expected on the client. If a package is built with a different USE flag combination, Portage will either ignore the binary package (and use source-based build) or fail, depending on the options passed to the command upon invocation (see Installing binary packages).

On clients, a few configuration changes are needed in order for the binary packages to be used.

Installing binary packages
There are a few options that can be passed on to the command that inform Portage about using binary packages:

In order to automatically use binary package installations, the appropriate option can be added to the EMERGE_DEFAULT_OPTS variable:

There is a Portage feature that automatically implements the equivalent of   without the need for updating the EMERGE_DEFAULT_OPTS variable with the   value:

Pulling packages from a binary package host
When using a binary package host, clients need to have the PORTAGE_BINHOST variable set in or the sync-uri variable in. Otherwise, the client will not know where the binary packages are stored which results in Portage being unable to retrieve them.

The PORTAGE_BINHOST variable uses a space-separated list of URIs. This allows administrators to use several binary package servers simultaneously. The URI must always point to the directory in which the file resides.

Reinstalling modified binary packages
Passing the  option to  will reinstall every binary that has been rebuilt since the package was installed. This is useful in case rebuilding tools like are run on the binary package server.

A related option is. It causes emerge not to consider binary packages for a re-install if those binary packages have been built before the given time stamp. This is useful to avoid re-installing all packages, if the binary package server had to be rebuild from scratch but  is used otherwise.

Additional client settings
Next to the  feature, Portage also listens to the   feature. This one controls if log files for successful binary package installations should be kept. It is only relevant if the PORT_LOGDIR variable has been set and is enabled by default.

Similar to excluding binary packages for a certain set of packages or categories, clients can be configured to exclude binary package installations for a certain set of packages or categories.

To accomplish this, use the  option:

To enable such additional settings for each emerge command, add the options to the EMERGE_DEFAULT_OPTS variable in the file:

Maintaining binary packages
Exporting and distributing the binary packages will lead to useless storage consumption if the binary package list is not actively maintained.

Removing outdated binary packages
In the package an application called  is provided. It allows for maintaining Portage-related variable files, such as downloaded source code files, but also binary packages.

The following command will remove all binary packages that have no corresponding ebuild in the installed ebuild repositories:

For more details please read the Eclean article.

Another tool that can be used is the tool from the  package. However, this tool is a bit less configurable.

To clean up unused binary packages (in the sense of used by the server on which the binary packages are stored):

Maintaining the Packages file
Inside the packages directory exists a manifest file called. This file acts as a cache for the metadata of all binary packages in the packages directory. The file is updated whenever Portage adds a binary package to the directory. Similarly, updates it when it removes binary packages.

If for some reason binary packages are simply deleted or copied into the packages directory, or the file gets corrupted or deleted, then it must be recreated. This is done using command:

Creating snapshots of the packages directory
When deploying binary packages for a large number of client systems it might become worthwhile to create snapshots of the packages directory. The client systems then do not use the packages directory directly but use binary packages from the snapshot.

Snapshots can be created using the or  tool. It takes four arguments:


 * 1) A source directory (the path to the packages directory).
 * 2) A target directory (that must not exist).
 * 3) A URI.
 * 4) A binary package server directory.

The files from the package directory are copied to the target directory. A file is then created inside the binary package server directory (fourth argument) with the provided URI.

Client systems need to use an URI that points to the binary package server directory. From there they will be redirected to the URI that was given to. This URI has to refer to the target directory.

Understanding the binary package format
Binary packages created by Portage have the file name ending with. These files consist of two parts:


 * 1) A  archive containing the files that will be installed on the system.
 * 2) A  archive containing package metadata, the ebuild, and the environment file.

See for a description of the format.

In some tools exists that are able to split or create  and  files.

The following command will split the into a  and an  file:

The file can be examined using the  utility.

To list the contents:

The next command will extract a file called which contains the enabled USE flags for this package:

The PKGDIR layout
The currently used format version 2 has the following layout:

The file is the major improvement (and also the trigger for Portage to know that the binary package directory uses version 2) over the first binary package directory layout (version 1). In version 1, all binary packages were also hosted inside a single directory (called ) and the category directories only had symbolic links to the binary packages inside the directory.

Unpacking with quickunpkg
Zoobab wrote a simple shell tool named quickunpkg to quickly unpack files.