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5. Installing the Gentoo Installation Files

• Installing a Stage Tarball
• Using a Stage from the Internet
• Configuring the Compile Options

5.a. Installing a Stage Tarball

Setting the Date/Time Right

Before you continue you need to check your date/time and update it. A misconfigured clock may lead to strange results in the future!

To verify the current date/time, run date:

# date
Fri Mar 29 16:21:18 UTC 2005

If the date/time displayed is wrong, update it using the date MMDDhhmmYYYY syntax (Month, Day, hour, minute and Year). At this stage, you should use UTC time. You will be able to define your timezone later on. For instance, to set the date to March 29th, 16:21 in the year 2005:

# date 032916212005

Making your Choice

The next step you need to perform is to install the stage3 tarball onto your system. The command uname -m can be used to help you decide which stage file to download as it provides information on the architecture of your system.

5.b. Using a Stage from the Internet

Downloading the Stage Tarball

Go to the Gentoo mountpoint at which you mounted your filesystems (most likely /mnt/gentoo):

# cd /mnt/gentoo

Depending on your installation medium, you have a couple of tools available to download a stage. If you have links available, then you can immediately surf to the Gentoo mirrorlist and choose a mirror close to you: type links http://www.gentoo.org/main/en/mirrors.xml and press enter.

If you don't have links available you should have lynx at your disposal. If you need to go through a proxy, export the http_proxy and ftp_proxy variables:

# export http_proxy="http://proxy.server.com:port"
# export ftp_proxy="http://proxy.server.com:port"

We will now assume that you have links at your disposal.

Select a mirror closeby. Usually HTTP mirrors suffice, but other protocols are available as well. Move to the releases/arm/autobuilds/ directory. There you should see all available stage files for your architecture (they might be stored within subdirectories named after the individual subarchitectures). Select one and press D to download. When you're finished, press Q to quit the browser.

# links http://www.gentoo.org/main/en/mirrors.xml

(If you need proxy support with links:)
# links -http-proxy proxy.server.com:8080 http://www.gentoo.org/main/en/mirrors.xml

Make sure you download a stage3 tarball - installations using a stage1 or stage2 tarball are not supported anymore (and in most cases, you will not find stage1 or stage2 tarballs on our regular download mirrors anyway).

If you want to check the integrity of the downloaded stage tarball, use openssl and compare the output with the checksums provided on the mirror. The digests files provide several checksums, each taken with a different algorithm. The recommended ones are SHA512 and Whirlpool.

## Calculating the SHA512 checksum
# openssl dgst -r -sha512 stage3-armv<version>-<release>.tar.bz2
or
# sha512sum stage3-armv<version>-<release>.tar.bz2

## Calculating the Whirlpool checksum
# openssl dgst -r -whirlpool stage3-armv<version>-<release>.tar.bz2

Then compare the output of these commands with the value registered in the .DIGESTS files that can be found on the mirrors as well. The values need to match, otherwise the downloaded file might be corrupt (or the digests file is).

Unpacking the Stage Tarball

Now unpack your downloaded stage onto your system. We use tar to proceed as it is the easiest method:

# tar xvjpf stage3-*.tar.bz2

Make sure that you use the same options (xvjpf). The x stands for Extract, the v for Verbose to see what happens during the extraction process (optional), the j for Decompress with bzip2, the p for Preserve permissions and the f to denote that we want to extract a file, not standard input.

Now that the stage is installed, continue with Configuring the Compile Options.

5.c. Configuring the Compile Options

Introduction

To optimize Gentoo, you can set a couple of variables which impact Portage behaviour. All those variables can be set as environment variables (using export) but that isn't permanent. To keep your settings, Portage provides you with /etc/portage/make.conf, a configuration file for Portage. It is this file we will edit now.

Fire up your favorite editor (in this guide we use nano) so we can alter the optimization variables we will discuss hereafter.

# nano -w /mnt/gentoo/etc/portage/make.conf

As you probably noticed, the make.conf.example file is structured in a generic way: commented lines start with "#", other lines define variables using the VARIABLE="content" syntax. The make.conf file uses the same syntax. Several of those variables are discussed next.

CFLAGS and CXXFLAGS

The CFLAGS and CXXFLAGS variables define the optimization flags for the gcc C and C++ compiler respectively. Although we define those generally here, you will only have maximum performance if you optimize these flags for each program separately. The reason for this is because every program is different.

In make.conf you should define the optimization flags you think will make your system the most responsive generally. Don't place experimental settings in this variable; too much optimization can make programs behave bad (crash, or even worse, malfunction).

We will not explain all possible optimization options. If you want to know them all, read the GNU Online Manual(s) or the gcc info page (info gcc -- only works on a working Linux system). The make.conf.example file itself also contains lots of examples and information; don't forget to read it too.

A first setting is the -march= or -mcpu= flag, which specifies the name of the target architecture. Possible options are described in the make.conf.example file (as comments). A commonly used value is native as that tells the compiler to select the target architecture of the current system (the one you are installing on).

A second one is the -O flag (that is a capital O, not a zero), which specifies the gcc optimization class flag. Possible classes are s (for size-optimized), 0 (zero - for no optimizations), 1, 2 or even 3 for more speed-optimization flags (every class has the same flags as the one before, plus some extras). -O2 is the recommended default. -O3 is known to cause problems when used system-wide, so we recommend that you stick to -O2.

Another popular optimization flag is -pipe (use pipes rather than temporary files for communication between the various stages of compilation). It has no impact on the generated code, but uses more memory. On systems with low memory, gcc might get killed. In that case, do not use this flag.

Using -fomit-frame-pointer (which doesn't keep the frame pointer in a register for functions that don't need one) might have serious repercussions on the debugging of applications.

When you define the CFLAGS and CXXFLAGS, you should combine several optimization flags. The default values contained in the stage3 archive you unpacked should be good enough. The following example is just an example:

CFLAGS="-Os -march=armv7-a -mfloat-abi=softfp -mfpu=vfp -pipe   # Be sure to change -march to match your CPU type
# Use the same settings for both variables
CXXFLAGS="${CFLAGS}"

MAKEOPTS

With MAKEOPTS you define how many parallel compilations should occur when you install a package. A good choice is the number of CPUs (or CPU cores) in your system plus one, but this guideline isn't always perfect.

MAKEOPTS="-j2"

Ready, Set, Go!

Update your /mnt/gentoo/etc/portage/make.conf to your own preference and save (nano users would hit Ctrl-X). You are now ready to continue with Installing the Gentoo Base System.

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