[ << ] [ < ] [ Home ] [ > ] [ >> ]

3. Portage Features

• Portage Features
• Distributed Compiling
• Caching Compilation
• Binary Package Support
• Fetching Files
• Pulling Validated Portage Tree Snapshots

3.a. Portage Features

Portage has several additional features that makes your Gentoo experience even better. Many of these features rely on certain software tools that improve performance, reliability, security, ...

To enable or disable certain Portage features you need to edit /etc/portage/make.conf's FEATURES variable which contains the various feature keywords, separated by white space. In several cases you will also need to install the additional tool on which the feature relies.

Not all features that Portage supports are listed here. For a full overview, please consult the make.conf man page:

$ man make.conf

To find out what FEATURES are default set, run emerge --info and search for the FEATURES variable or grep it out:

$ emerge --info | grep FEATURES

3.b. Distributed Compiling

Using distcc

distcc is a program to distribute compilations across several, not necessarily identical, machines on a network. The distcc client sends all necessary information to the available distcc servers (running distccd) so they can compile pieces of source code for the client. The net result is a faster compilation time.

You can find more information about distcc (and how to have it work with Gentoo) in our Gentoo Distcc Documentation.

Installing distcc

Distcc ships with a graphical monitor to monitor tasks that your computer is sending away for compilation. If you use Gnome then put 'gnome' in your USE variable. However, if you don't use Gnome and would still like to have the monitor then you should put 'gtk' in your USE variable.

# emerge distcc

Activating Portage Support

Add distcc to the FEATURES variable inside /etc/portage/make.conf. Next, edit the MAKEOPTS variable to your liking. A known guideline is to fill in "-jX" with X the number of CPUs that run distccd (including the current host) plus one, but you might have better results with other numbers.

Now run distcc-config and enter the list of available distcc servers. For a simple example we assume that the available DistCC servers are 192.168.1.102 (the current host), 192.168.1.103 and 192.168.1.104 (two "remote" hosts):

# distcc-config --set-hosts "192.168.1.102 192.168.1.103 192.168.1.104"

Don't forget to run the distccd daemon as well:

# rc-update add distccd default
# /etc/init.d/distccd start

3.c. Caching Compilation

About ccache

ccache is a fast compiler cache. When you compile a program, it will cache intermediate results so that, whenever you recompile the same program, the compilation time is greatly reduced. The first time you run ccache, it will be much slower than a normal compilation. Subsequent recompiles should be faster. ccache is only helpful if you will be recompiling the same application many times; thus it's mostly only useful for software developers.

If you are interested in the ins and outs of ccache, please visit the ccache homepage.

Installing ccache

To install ccache, run emerge ccache:

# emerge ccache

Activating Portage Support

Open /etc/portage/make.conf and add ccache to the FEATURES variable. Next, add a new variable called CCACHE_SIZE and set it to "2G":

CCACHE_SIZE="2G"

To check if ccache functions, ask ccache to provide you with its statistics. Because Portage uses a different ccache home directory, you need to set the CCACHE_DIR variable as well:

# CCACHE_DIR="/var/tmp/ccache" ccache -s

The /var/tmp/ccache location is Portage' default ccache home directory; if you want to alter this setting you can set the CCACHE_DIR variable in /etc/portage/make.conf.

However, if you would run ccache, it would use the default location of ${HOME}/.ccache, which is why you needed to set the CCACHE_DIR variable when asking for the (Portage) ccache statistics.

Using ccache for non-Portage C Compiling

If you would like to use ccache for non-Portage compilations, add /usr/lib/ccache/bin to the beginning of your PATH variable (before /usr/bin). This can be accomplished by editing .bash_profile in your user's home directory. Using .bash_profile is one way to define PATH variables.

PATH="/usr/lib/ccache/bin:/opt/bin:${PATH}"

3.d. Binary Package Support

Creating Prebuilt Packages

Portage supports the installation of prebuilt packages. Even though Gentoo does not provide prebuilt packages by itself (except for the GRP snapshots) Portage can be made fully aware of prebuilt packages.

To create a prebuilt package you can use quickpkg if the package is already installed on your system, or emerge with the --buildpkg or --buildpkgonly options.

If you want Portage to create prebuilt packages of every single package you install, add buildpkg to the FEATURES variable.

More extended support for creating prebuilt package sets can be obtained with catalyst. For more information on catalyst please read the Catalyst Frequently Asked Questions.

Installing Prebuilt Packages

Although Gentoo doesn't provide one, you can create a central repository where you store prebuilt packages. If you want to use this repository, you need to make Portage aware of it by having the PORTAGE_BINHOST variable point to it. For instance, if the prebuilt packages are on ftp://buildhost/gentoo:

PORTAGE_BINHOST="ftp://buildhost/gentoo"

When you want to install a prebuilt package, add the --getbinpkg option to the emerge command alongside of the --usepkg option. The former tells emerge to download the prebuilt package from the previously defined server while the latter asks emerge to try to install the prebuilt package first before fetching the sources and compiling it.

For instance, to install gnumeric with prebuilt packages:

# emerge --usepkg --getbinpkg gnumeric

More information about emerge's prebuilt package options can be found in the emerge man page:

$ man emerge

3.e. Fetching Files

Parallel fetch

When you are emerging a series of packages, Portage can fetch the source files for the next package in the list even while it is compiling another package, thus shortening compile times. To make use of this capability, add "parallel-fetch" to your FEATURES. Note that this is on by default, so you shouldn't need to specifically enable it.

Userfetch

When Portage is run as root, FEATURES="userfetch" will allow Portage to drop root privileges while fetching package sources. This is a small security improvement.

3.f. Pulling Validated Portage Tree Snapshots

As an administrator, you can opt to only update your local Portage tree with a cryptographically validated Portage tree snapshot as released by the Gentoo infrastructure. This ensures that no rogue rsync mirror is adding unwanted code or packages in the tree you are downloading.

To configure Portage, first create a truststore in which you download and accept the keys of the Gentoo Infrastructure responsible for signing the Portage tree snapshots. Of course, if you want to, you can validate this GPG key as per the proper guidelines (like checking the key fingerprint). You can find the list of GPG keys used by the release engineering team on their project page.

# mkdir -p /etc/portage/gpg
# chmod 0700 /etc/portage/gpg
(... Substitute the keys with those mentioned on the release engineering site ...)
# gpg --homedir /etc/portage/gpg --keyserver subkeys.pgp.net --recv-keys 0x239C75C4 0x96D8BF6D
# gpg --homedir /etc/portage/gpg --edit-key 0x239C75C4 trust
# gpg --homedir /etc/portage/gpg --edit-key 0x96D8BF6D trust

Next, edit /etc/portage/make.conf and enable support for validating the signed Portage tree snapshots (using FEATURES="webrsync-gpg") and disabling updating the Portage tree using the regular emerge --sync method.

FEATURES="webrsync-gpg"
PORTAGE_GPG_DIR="/etc/portage/gpg"
SYNC=""

That's it. Next time you run emerge-webrsync, only the snapshots with a valid signature will be expanded on your file system.

[ << ] [ < ] [ Home ] [ > ] [ >> ]

The contents of this document, unless otherwise expressly stated, are licensed under the CC-BY-SA-2.5 license. The Gentoo Name and Logo Usage Guidelines apply.