Here in Gentoo land, the concept of upgrade is quite different with respect to the rest of the linux world. Probably you already know that we never got in touch with the "classic" way to upgrade software in our distribution to the latest version: waiting for a new release, downloading it, burning, putting it in the cdrom drive and then following the upgrade instructions.

You know (you chose Gentoo, after all) that this process is extremely frustrating for power users that want to live on the bleeding edge. Even power users from other distributions must share the same feelings, given the popularity and spread among them of tools like apt or apt-rpm, which make it possible to have quick and frequent updates. However, no distibution is more suited than Gentoo to satisfy these kind of demanding users, because Gentoo was shaped from the beginning around the concept of fast, incremental updates.

Ideally, you install once and then do not bother anymore about releases: just follow the instructions in Portage and Software in the Gentoo Handbook that explain how to keep your system up to date. While that's the way things go usually, it can happen sometimes that developers push out, together with a new release, an update that touches the basics of the systems. We will consider these cases below, when talking about profiles.

A recurring question about the Gentoo release process is: "Why roll out new releases frequently, if they are not intended to let users update software?". There are various reasons:

• A new release means enhanced and more feature-rich LiveCDs.
• A new release provides an updated set of GRP packages, so that users that choose "the fast way" to install, stage3 + precompiled packages, end up with a system that is not outdated.
• Finally, a new release may (not frequently) implement some features that are incompatible with previous releases.

When a release provides new incompatible features, or provides a set of core packages and settings that deeply modify the behavior of the system, or simply when it makes tricky changes to some default parameters, we say that it provides a new profile.

A profile is a set of configuration files, stored in a subdirectory of /usr/portage/profiles/, that describe things such as the ebuilds that are considered system packages, the default USE flags, the default mapping for virtual packages.

The profile in use is determined by the symbolic link /etc/make.profile, which points to the subdirectory of /usr/portage/profiles which holds the profile files, for instance /usr/portage/profiles/default-x86-2004.2 (old-style location) or /usr/portage/profiles/default-linux/x86/2004.2 (new-style location). With respect to new-style profile directories, note that also the files in parent directories are part of the profile (and are therefore shared by different profiles).

Profiles obsoleted by new ones are kept in /usr/portage/profiles as the current ones, but they are marked as deprecated. When that happens a file named deprecated is put in the profile directory. The content of this file is the name of the profile that should substitute it; portage uses this information to automatically warn you about the new profile.

There are various reasons that justify the creation of a new profile: the release of new versions of core packages (such as baselayout, gcc or glibc) that are incompatible with previous versions, a change in the default USE flags, or in the virtual mappings, or maybe a change in system-wide settings (such as defining udev to be the default manager for /dev instead of devfs).

If a new Gentoo release is announced that does not include a new profile (such as the 2004.1 release for x86), then you can safely pretend that it never happened.

If you update your installed packages as explained in the Gentoo Handbook, then your system will be exactly the same as one that has been installed using the new release.

If a release introduces a new profile, you have the choice to migrate to the new profile.

Naturally, you are not forced to do so, you can continue to use the old profile and just update your packages as explained in the Gentoo Handbook (or you may want to not update your system at all).

However, Gentoo strongly recommends a migration if your profile becomes deprecated and is no more supported by Gentoo developers, that is to say that your profile is not listed anymore in the table below.

If you decide to migrate to the new profile, then you will have to manually perform some actions. Those actions may vary a lot from release to release, it depends on how deep the modifications introduced in the new profile are.

In the simplest case you only have to change the /etc/make.profile link, in the worst case you may have to recompile your system from scratch while doing some voodoo stuff. In every case we will publish the instructions for the migration as part of the release. You can find these instructions also at the end of this guide.

The following profiles are officially supported by Gentoo developers:

To switch to the 2004.2 profile, point the /etc/make.profile link to the new location:

substitute <arch> with your arch
# rm /etc/make.profile
# ln -s ../usr/portage/profiles/default-<arch>-2004.2 /etc/make.profile

x86 - This profile changes the default X11 implementation from x11-base/xfree to x11-base/xorg-x11. This change only touches the default value, and is only relevant for those who have not installed an X server yet. If you already have one installed, then it will not affect you at all, you are free to switch from one X server to the other exactly as before.

amd64 - There are no fundamental changes from previous profiles, no specific action needs to be performed.

To switch to the 2004.0 profile, point the /etc/make.profile link to the new location:

substitute <arch> with your arch
# rm /etc/make.profile
# ln -s ../usr/portage/profiles/default-<arch>-2004.0 /etc/make.profile

All archs - There are no fundamental changes from previous profiles, no specific action needs to be performed.

The instructions for this upgrade are quite complex, you can find them here.