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Metro is the build system for Funtoo Linux and Gentoo Linux stages. It automates the bootstrapping process.

This tutorial will take you through installing, setting up and running Metro.


How Metro Works

You may be wondering how Metro creates its first stage tarball. As you may have guessed, Metro cannot create a stage tarball out of thin air. To build a new stage tarball, Metro must use an existing, older stage tarball called a "seed" stage. This "seed" stage typically is used as the build environment for creating the stage we want.

Metro can use two kinds of seed stages. Traditionally, Metro has used a stage3 as a seed stage. This stage3 is then used to build a new stage1, which in turn is used to build a new stage2, and then a new stage3. This is generally the most reliable way to build Gentoo Linux or Funtoo Linux, so it's the recommended approach.


After switching metro builds to Funtoo profile, Gentoo stages are no longer provided!

Seeds and Build Isolation

Another important concept to mention here is something called build isolation. Because Metro creates an isolated build environment, and the build environment is explicitly defined using existing, tangible entities -- a seed stage and a portage snapshot -- you will get consistent, repeatable results. In other words, the same seed stage, portage snapshot and build instructions will generate an essentially identical result, even if you perform the build a month later on someone else's workstation.

Local Build

Say you wanted to build a new pentium4 stage3 tarball. The recommended method of doing this would be to grab an existing pentium4 stage3 tarball to use as your seed stage. Metro will be told to use this existing pentium4 stage3 to build a new stage1 for the same pentium4. For this process, the generic pentium4 stage3 would provide the build environment for creating our new stage1. Then, the new stage1 would serve as the build environment for creating the new pentium4 stage2. And the new pentium4 stage2 would serve as the build environment for creating the new pentium4 stage3.

In the Metro terminology this is called a local build, which means a stage3 of a given architecture is used to seed a brand new build of the same architecture. Incidentally this will be the first exercise we are going to perform in this tutorial.

A week later, you may want to build a brand new pentium4 stage3 tarball. Rather than starting from the original pentium4 stage3 again, you'd probably configure Metro to use the most-recently-built pentium4 stage3 as the seed. Metro has built-in functionality to make this easy, allowing it to easily find and track the most recent stage3 seed available.

Remote Build

Metro can also perform remote build, where a stage3 of a different, but binary compatible, architecture is used as a seed to build a different architecture stage3. Consequentiality the second exercise we are going to perform in this tutorial will be to build a core2 32bit stage3 tarball from the pentium4 stage3 tarball we have just built.

TODO: add caveats about what archs can be seeded and what can be not (maybe a table?)

Tailored Build

Last, it's also worthy noting that both in local and remote builds, Metro can be configured to add and/or remove individual packages to the final tarball. Let's say you can't live without app-misc/screen, at the end of this tutorial, we will show how to have your tailored stage3 to include it.

Installing Metro

recommended and supported method is to use the Git repository of Metro. First ensure you remove the dev-util/metro package if you had installed it:

root # emerge -aC dev-util/metro

Then ensure that dev-vcs/git and dev-python/boto installed on your system:

root # emerge dev-vcs/git
root # emerge dev-python/boto

Next, clone the master git repository as follows:

root # install -d /root/git
root # cd /root/git
root # git clone git://
root # ln -s /root/git/metro /usr/lib/metro
root # ln -s /root/git/metro/metro /usr/bin/metro

You will now have a directory called /root/git/metro that contains all the Metro source code. Installation complete!

Configuring Metro

Daniel Robbins maintains Metro, so it comes pre-configured to successfully build both Gentoo Linux and Funtoo Linux releases. Before reading farther, you might want to customize some basic settings like the number of concurrent jobs to fit your hardware's capabilities or the directory to use for produced stage archives. This is accomplished by editing /root/git/metro/etc/metro.conf which is the Metro's master configuration file. The [path/mirror] section defines where Metro will look for things it needs and also dump things it creates. As initially configured, Metro is set up to build Funtoo Linux and Gentoo Linux stage tarballs and place them in the /home/mirror/linux directory:

# Mirror Paths - where to find required files and where to put created files

[section path/mirror]

: /home/mirror/linux

If you want to change the location of your mirror on disk, then edit the /home/mirror/linux line (which defines the path/mirror variable) to point to another directory.

For the purpose of the following steps, set an environment variable:

(~) # export METRO_MIRROR=/home/mirror/linux

Of course, set the environment variable to whatever location you used in the configuration file.

Arch and Subarch

In the following example we are creating a pentium4 stage 3 compiled for x86-32bit binary compatibility. Pentium4 is a subarch of the x86-32bit architecture. Once you have metro installed you may find a full list of each subarch in your /usr/lib/metro/subarch directory each subarch will have the file extension .spec Example:

# ls /usr/lib/metro/subarch/
amd64-k10.spec         athlon-tbird.spec  generic_32.spec       native_32.spec   pentium-mmx.spec
amd64-k8_32.spec       athlon-xp.spec     generic_64.spec       native_64.spec   pentium-m.spec
amd64-k8.spec          atom_32.spec       generic_sparcv9.spec  niagara2.spec    pentiumpro.spec
amd64-k8+sse3_32.spec  atom_64.spec       geode.spec            niagara.spec     pentium.spec
amd64-k8+sse3.spec     btver1_64.spec     i486.spec             nocona.spec      prescott.spec
armv7a.spec            btver1.spec        i686.spec             opteron_64.spec  ultrasparc3.spec
athlon-4.spec          core2_32.spec      k6-2.spec             pentium2.spec    ultrasparc.spec
athlon-mp.spec         core2_64.spec      k6-3.spec             pentium3.spec    xen-pentium4+sse3_64.spec
athlon.spec            corei7.spec        k6.spec               pentium4.spec    xen-pentium4+sse3.spec

For an example list of Architectures, take a look at the directory listing on the Funtoo-Current Mirror.

First stages build (local build)

To get this all started, we need to bootstrap the process by downloading an initial seed stage3 to use for building and place it in its proper location in /home/mirror/linux, so that Metro can find it. We will also need to create some special "control" files in /home/mirror/linux, which will allow Metro to understand how it is supposed to proceed.

Step 0: Optional Quick Copy of Portage Tree

There is a quick step you can perform to avoid having Metro re-clone the entire Portage tree. Perform this as root:

# cd /usr/portage; git checkout origin/master
# install -d /var/tmp/metro/cache/cloned-repositories
# cat /root/git/metro/etc/builds/funtoo-current/build.conf  | grep name
name: portage-mini-2011
# cp -a /usr/portage /var/tmp/metro/cache/cloned-repositories/ports-2012
# cd /usr/portage; git checkout

Step 1: Set up pentium4 repository (local build)

Assuming we're following the basic steps outlined in the previous section, and building an unstable funtoo (funtoo-current) build for the pentium4, using a generic pentium4 stage3 as a seed stage, then here the first set of steps we'd perform:

(~) # install -d "${METRO_MIRROR}/funtoo-current/x86-32bit/pentium4"
(~) # cd "${METRO_MIRROR}/funtoo-current/x86-32bit/pentium4"
(/home/mirror/linux/funtoo-current/x86-32bit/pentium4) # install -d 2011-12-13
(/home/mirror/linux/funtoo-current/x86-32bit/pentium4) # cd 2011-12-13
(/home/mirror/linux/funtoo-current/x86-32bit/pentium4/2011-12-13) # wget -c
(/home/mirror/linux/funtoo-current/x86-32bit/pentium4/2011-12-13) # cd ..
(/home/mirror/linux/funtoo-current/x86-32bit/pentium4) # install -d .control/version
(/home/mirror/linux/funtoo-current/x86-32bit/pentium4) # echo "2011-12-13" > .control/version/stage3
(/home/mirror/linux/funtoo-current/x86-32bit/pentium4) # install -d .control/strategy
(/home/mirror/linux/funtoo-current/x86-32bit/pentium4) # echo "local" > .control/strategy/build
(/home/mirror/linux/funtoo-current/x86-32bit/pentium4) # echo "stage3" > .control/strategy/seed

OK, let's review the steps above. First, we create the directory "${METRO_MIRROR}/funtoo-current/x86-32bit/pentium4", which is where Metro will expect to find unstable funtoo-current pentium4 builds -- it is configured to look here by default. Then we create a specially-named directory to house our seed x86 stage3. Again, by default, Metro expects the directory to be named this way. We enter this directory, and download our seed x86 stage3 from Note that the 2010-12-24 version stamp matches. Make sure that your directory name matches the stage3 name too. Everything has been set up to match Metro's default filesystem layout.

Next, we go back to the "${METRO_MIRROR}/funtoo-current/x86-32bit/pentium4" directory, and inside it, we create a .control directory. This directory and its subdirectories contain special files that Metro references to determine certain aspects of its behavior. The .control/version/stage3 file is used by Metro to track the most recently-built stage3 for this particular build and subarch. Metro will automatically update this file with a new version stamp after it successfully builds a new stage3. But because Metro didn't actually build this stage3, we need to set up the .control/version/stage3 file manually. This will allow Metro to find our downloaded stage3 when we set up our pentium4 build to use it as a seed. Also note that Metro will create a similar .control/version/stage1 file after it successfully builds an pentium4 funtoo-current stage1.

We also set up .control/strategy/build and .control/strategy/seed files with values of local and stage3 respectively. These files define the building strategy Metro will use when we build pentium4 funtoo-current stages. With a build strategy of local, Metro will source its seed stage from funtoo-current pentium4, the current directory. And with a seed strategy of stage3, Metro will use a stage3 as a seed, and use this seed to build a new stage1, stage2 and stage3.

Step 2: Building the pentium4 stages

Incidentally, if all you wanted to do at this point was to build a new pentium4 funtoo-current stage1/2/3 (plus openvz and vserver templates). You would begin the process by typing:

root # cd /root/git/metro
root # scripts/ funtoo-current pentium4

If you have a slow machine, it could take several hours to be completed because several "heavy" components like gcc or glibc have to be recompiled in each stage. Once a stage has been successfully completed, it is placed in the "${METRO_MIRROR}/funtoo-current/x32-bit/pentium4/YYYY-MM-DD" subdirectory, where YYYY-MM-DD is today's date at the time the script was started or the date you put on the command line.

Step 3: The next build

At this point, you now have a new pentium4 stage3. If you'd like, you can reconfigure Metro to use the most recently-built pentium4 stage3 as a seed for any pentium4 builds. To do this, simply type:

(~) # echo "local" > /home/mirror/linux/funtoo-current/x86-32bit/pentium4/.control/strategy/build

Now, Metro will use the most recentpentium4 stage3 as a seed. The .control/remote files you created will be ignored by Metro, since it's no longer going to perform a remote build.

Building for another binary compatible architecture (remote build)

As written above, Metro is able to perform remote build building different architecture stage3 from a binary compatible seeding stage3 (e.g. using a pentium4 stage3 to seed a Intel Core2 32bits stage3).

In the Metro terminology this is called a remote build (a stage 3 of a different, but binary compatible, architecture is used as a seed). What's not compatible? You can't use a Sparc architecture to generate an x86 or ARM based stage and vice-versa. If you use a 32bit stage then you don't want to seed a 64bit build from it. Be sure that you are using a stage from the same architecture that you are trying to seed. Check Funtoo-current FTP Mirror for a stage that is from the same Architecture that you will be building.

Step 1: Set up Core_2 32bit repository

In this example, we're going to use this pentium4 funtoo-current stage3 to seed a new Core_2 32bit funtoo-current build. To get that done, we need to set up the pentium4 build directory as follows:

root #  cd "${METRO_MIRROR}/funtoo-current/x86-32bit"
root # install -d core2_32
root # cd core2_32
root # install -d .control/strategy
root # echo "remote" > .control/strategy/build
root # echo "stage3" > .control/strategy/seed
root # install -d .control/remote
root # echo "funtoo-current" > .control/remote/build
root # echo "pentium4" > .control/remote/subarch

The steps we follow are similar to those we performed for a local build to set up our pentium4 directory for local build. However, note the differences. We didn't download a stage, because we are going to use the pentium4 stage to build a new Core_2 32bit stage. We also didn't create the .control/version/stage{1,3} files because Metro will create them for us after it successfully builds a new stage1 and stage3. We are still using a stage3 seed strategy, but we've set the build strategy to remote, which means that we're going to use a seed stage that's not from this particular subdirectory. Where are we going to get it from? The .control/remote directory contains this information, and lets Metro know that it should look for its seed stage3 in the "${METRO_MIRROR}/home/mirror/linux/funtoo-current/x86-32bit/pentium4" directory. Which one will it grab? You guessed it -- the most recently built stage3 (since our seed strategy was set to stage3) that has the version stamp of 2010-12-24, as recorded in "${METRO_MIRROR}/funtoo-current/x86-32bit/pentium4/.control/version/stage3". Now you can see how all those control files come together to direct Metro to do the right thing.

Step 2: Building the Core_2 32bit stages

Now, you could start building your new Core_2 32bit stage1/2/3 (plus openvz and vserver templates) by typing the following:

(~) # /root/git/metro/scripts/ funtoo-current core2_32

In that case, the produced stages are placed in the "${METRO_MIRROR}/funtoo-current/x32-bit/core2_32/YYYY-MM-DD" subdirectory.

Step 3: The Next Build

At this point, you now have a new Core_2 32bit stage3. If you'd like, you can reconfigure Metro to use the most recently-built Core_2 32bit stage3 as a seed for any new Core_2 32bit builds.

In the Metro terminology this is called a local build (a stage 3 of a a given architecture is used to seed a brand new build of the same architecture).

To do this, simply type:

(~) # echo "local" > /home/mirror/linux/funtoo-current/x86-32bit/core2_32/.control/strategy/build

Now, Metro will use the most recent Core_2 32bit stage3 as a seed. The .control/remote files you created will be ignored by Metro, since it's no longer going to perform a remote build.

Build your own tailored stage3

Metro can be easily configured for building custom stage3 by including additional packages. Notice that including packages with heavy dependencies such as gnome, kde, xorg-server is not recommended (not tested so far). Well tested packages are app-misc/mc, app-misc/screen, sys-process/htop, sys-apps/dstat. An example for funtoo-current stage. Edit the following configuration file /root/git/metro/etc/builds/funtoo-current/build.conf:

[collect ../../fslayouts/funtoo/layout.conf]

[section local]

author: Daniel Robbins <>

[section target]

build: funtoo-current
compression: xz

[section portage]

stable: ~
FEATURES: mini-manifest
SYNC: $[snapshot/source/remote]
profile: default/linux/$[target/arch:zap]/2008.0

[section emerge]

options: --jobs=4 --load-average=3 --keep-going=n
packages: [

[section snapshot]

As you can see MAKEOPTS and emerge default options are additional strings to tweak, --keep-going=n is recommended, if something breaking during the stage building process, you can quickly diagnose the problem.

Distfiles location can be specified in /root/git/metro/etc/metro.conf

# Main metro configuration file
# Path configuration:

[collect ../targets/$[metro/target]/$[target:zap].spec]
[collect ./builds/$[metro/build]/build.conf]
[collect ../subarch/$[target/subarch:zap].spec]

# General Paths

[section path]
tmp: /var/tmp/metro
distfiles: /var/portage/distfiles
work: $[path/tmp]/work/$[metro/build]/$[target/name]

[section path/cache]

Building Gentoo stages